Co-reporter:Sarah M. Lauinger, Brandon D. Piercy, Wei Li, Qiushi Yin, Daniel L. Collins-Wildman, Elliot N. Glass, Mark D. Losego, Dunwei Wang, Yurii V. Geletii, and Craig L. Hill
ACS Applied Materials & Interfaces October 11, 2017 Volume 9(Issue 40) pp:35048-35048
Publication Date(Web):September 20, 2017
DOI:10.1021/acsami.7b12168
Fast and earth-abundant-element polyoxometalates (POMs) have been heavily studied recently as water oxidation catalysts (WOCs) in homogeneous solution. However, POM WOCs can be quite unstable when supported on electrode or photoelectrode surfaces under applied potential. This article reports for the first time that a nanoscale oxide coating (Al2O3) applied by the atomic layer deposition (ALD) aids immobilization and greatly stabilizes this now large family of molecular WOCs when on electrode surfaces. In this study, [{RuIV4(OH)2(H2O)4}(γ-SiW10O34)2]10– (Ru4Si2) is supported on hematite photoelectrodes and then protected by ALD Al2O3; this ternary system was characterized before and after photoelectrocatalytic water oxidation by Fourier transform infrared, X-ray photoelectron spectroscopy, energy-dispersive X-ray, and voltammetry. All these studies indicate that Ru4Si2 remains intact with Al2O3 ALD protection, but not without. The thickness of the Al2O3 layer significantly affects the catalytic performance of the system: a 4 nm thick Al2O3 layer provides optimal performance with nearly 100% faradaic efficiency for oxygen generation under visible-light illumination. Al2O3 layers thicker than 6.5 nm appear to completely bury the Ru4Si2 catalyst, removing all of the catalytic activity, whereas thinner layers are insufficient to maintain a long-term attachment of the catalytic POM.Keywords: atomic layer deposition; hematite; immobilization; polyoxometalates; water oxidation;
Co-reporter:Kevin P. Sullivan;Wade A. Neiwert;Huadong Zeng;Anil K. Mehta;Qiushi Yin;Daniel A. Hillesheim;Skanda Vivek;Panchao Yin;Daniel L. Collins-Wildman;Eric R. Weeks;Tianbo Liu
Chemical Communications 2017 vol. 53(Issue 83) pp:11480-11483
Publication Date(Web):2017/10/17
DOI:10.1039/C7CC05657E
We report the synthesis and characterization of a new class of organic/inorganic hybrid polymers composed of covalently-bound 1,3,5-benzenetricarboxamide linkers and anionic polyoxovanadate clusters with varying counter-cations. These materials form gels within seconds upon contact with polar aprotic organic liquids and catalyze the degradation of odorants and toxic molecules under mild conditions including aerobic oxidation of thiols, hydrogen peroxide-catalyzed oxidation of sulfides, and hydrolysis of organophosphate chemical warfare agent analogues.
Co-reporter:Weiwei Guo, Hongjin Lv, Zheyuan Chen, Kevin P. Sullivan, Sarah M. Lauinger, Yingnan Chi, Jordan M. Sumliner, Tianquan Lian and Craig L. Hill
Journal of Materials Chemistry A 2016 vol. 4(Issue 16) pp:5952-5957
Publication Date(Web):08 Mar 2016
DOI:10.1039/C6TA00011H
A polyoxometalate (POM), Pt nanoparticles (NPs) and a metal–organic framework (MOF, NH2-MIL-53) self-assemble into a hybrid material, PNPMOF, that displays synergistic activity for visible-light-driven catalytic hydrogen evolution (the PNPMOF is far more active than any of the three functional components alone). The POM has four targeted functions in this hybrid material: it reduces H2PtCl6 to Pt NPs, stabilizes the Pt NPs, induces a strong electrostatic association of the negatively charged Pt NPs with the protonated NH2-MIL-53 sites on the particle surfaces, and facilitates the catalytic reduction reaction itself. The NH2-MIL-53 in this work protects the light sensitive 2-aminoterephthalate groups in the pores from oxidation by the POMs, while the surface protonated NH2 units on the MOF particle surfaces strongly bind the negatively charged POM-stabilized Pt NPs.
Co-reporter:Elliot N. Glass, John Fielden, Zhuangqun Huang, Xu Xiang, Djamaladdin G. Musaev, Tianquan Lian, and Craig L. Hill
Inorganic Chemistry 2016 Volume 55(Issue 9) pp:4308-4319
Publication Date(Web):April 15, 2016
DOI:10.1021/acs.inorgchem.6b00060
A series of hetero-bimetallic transition metal-substituted polyoxometalates (TMSPs) were synthesized based on the CoII-centered ligand [CoIIW11O39]10–. The eight complex series, [CoII(MxOHy)W11O39](12–x−y)– (MxOHy = VIVO, CrIII(OH2), MnII(OH2), FeIII(OH2), CoII(OH2), NiII(OH2), CuII(OH2), ZnII(OH2)), of which six are reported for the first time, was synthesized starting from [CoIIIW11O39]9– and studied using spectroscopic, electrochemical, and computational techniques to evaluate the influence of substituted transition metals on the photodynamics of the metal-to-polyoxometalate charge transfer (MPCT) transition. The bimetallic complexes all show higher visible light absorption than the plenary [CoIIW12O40]6– and demonstrate the same MPCT transition as the plenary complex, but they have shorter excited-state lifetimes (sub-300 ps in aqueous media). The decreased lifetimes are rationalized on the basis of nonradiative relaxation due to coordinating aqua ligands, increased interaction with cations due to increased negative charge, and the energy gap law, with the strongest single factor appearing to be the charge on the anion. The most promising results are from the Cr- and Fe-substituted systems, which retain excited-state lifetimes at least 50% of that of [CoIIW12O40]6– while more than tripling the absorbance at 400 nm.
Co-reporter:Hongjin Lv, Yuanzhe Gao, Weiwei Guo, Sarah M. Lauinger, Yingnan Chi, John Bacsa, Kevin P. Sullivan, Marika Wieliczko, Djamaladdin G. Musaev, and Craig L. Hill
Inorganic Chemistry 2016 Volume 55(Issue 13) pp:6750
Publication Date(Web):June 20, 2016
DOI:10.1021/acs.inorgchem.6b01032
Copper-based complexes have been largely neglected as potential water reduction catalysts. This article reports the synthesis and characterization of a tetra-copper-containing polyoxotungstate, Na3K7[Cu4(H2O)2(B-α-PW9O34)2]·30H2O (Na3K7-Cu4P2). Cu4P2 is a water-compatible catalyst for efficient visible-light-driven hydrogen evolution when coupled to (4,4′-di-tert-butyl-2,2′-dipyridyl)-bis(2-phenylpyridine(1H))-iridium(III) hexafluorophosphate ([Ir(ppy)2(dtbbpy)][PF6]) as a light absorber and triethanolamine (TEOA) as sacrificial electron donor. Under minimally optimized conditions, a turnover number (TON) of ∼1270 per Cu4P2 catalyst is obtained after 5 h of irradiation (light-emitting diode; λ = 455 nm; 20 mW); a photochemical quantum efficiency of as high as 15.9% is achieved. Both oxidative and reductive quenching pathways are observed by measuring the luminescence intensity of excited state [Ir(ppy)2(dtbbpy)]+* in the presence of Cu4P2 or TEOA, respectively. Many stability studies (e.g., UV–vis absorption, FT-IR, dynamic light scattering, transmission electron microscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy) show that catalyst Cu4P2 undergoes slow decomposition under turnover conditions; however, both the starting Cu4P2 as well as its molecular decomposition products are the dominant catalytically active species for H2 evolution not Cu or CuOx particles. Considering the high abundance and low cost of copper, the present work provides considerations for the design and synthesis of efficient, molecular, water-compatible Cu-based water reduction catalysts.
Co-reporter:Weiwei Guo; Hongjin Lv; John Bacsa; Yuanzhe Gao; Je Seong Lee
Inorganic Chemistry 2016 Volume 55(Issue 2) pp:461-466
Publication Date(Web):October 19, 2015
DOI:10.1021/acs.inorgchem.5b01935
The syntheses, structural characterization, and catalytic properties of two different nickel-containing polyoxometalates (POMs) are presented. The dinickel-containing sandwich-type POM [Ni2(P2W15O56)2]20– (Ni2) exhibits an unusual αααα geometry. The trinickel-containing Wells–Dawson POM [Ni3(OH)3(H2O)3P2W16O59]9– (Ni3) shows a unique structure where the [α-P2W15O56]12– ligand is capped by a triangular Ni3O13 unit and a WO6 octahedron. Ni3 shows a high catalytic activity for visible-light-driven hydrogen evolution, while the activity for Ni2 is minimal. An analysis of the structures of multinickel-containing POMs and their hydrogen evolution activity is given.
Co-reporter:Weiwei Guo;Dr. Hongjin Lv;Kevin P. Sullivan;Wesley O. Gordon;Alex Balboa;George W. Wagner;Dr. Djamaladdin G. Musaev;Dr. John Bacsa; Craig L. Hill
Angewandte Chemie International Edition 2016 Volume 55( Issue 26) pp:7403-7407
Publication Date(Web):
DOI:10.1002/anie.201601620
Abstract
A wide range of chemical warfare agents and their simulants are catalytically decontaminated by a new one-dimensional polymeric polyniobate (P-PONb), K12[Ti2O2][GeNb12O40]⋅19 H2O (KGeNb) under mild conditions and in the dark. Uniquely, KGeNb facilitates hydrolysis of nerve agents Sarin (GB) and Soman (GD) (and their less reactive simulants, dimethyl methylphosphonate (DMMP)) as well as mustard (HD) in both liquid and gas phases at ambient temperature and in the absence of neutralizing bases or illumination. Three lines of evidence establish that KGeNb removes DMMP, and thus likely GB/GD, by general base catalysis: a) the k(H2O)/k(D2O) solvent isotope effect is 1.4; b) the rate law (hydrolysis at the same pH depends on the amount of P-PONb present); and c) hydroxide is far less active against the above simulants at the same pH than the P-PONbs themselves, a critical control experiment.
Co-reporter:Baofang Zhang, Jie Song, Dong Li, Lang Hu, Craig L. Hill, and Tianbo Liu
Langmuir 2016 Volume 32(Issue 48) pp:12856-12861
Publication Date(Web):November 7, 2016
DOI:10.1021/acs.langmuir.6b02308
Two novel polyoxovanadate (POV)-containing fluorosurfactants, each with two hydrophobic fluorinated “tails” and one nanosized, hydrophilic, rigid POV “head group”, are synthesized for the first time. They self-assemble into spherical, bilayer vesicles in acetonitrile/water mixed solvents, as evidenced by systemic studies using laser light scattering (LLS) and electron microscopy techniques. The vesicle sizes demonstrate dynamic change over different solvent compositions mainly as a result of the solvent swelling of the fluorocarbon chains, although the charge number on the POVs changes over the solvent polarity as well.
Co-reporter:Weiwei Guo;Dr. Hongjin Lv;Kevin P. Sullivan;Wesley O. Gordon;Alex Balboa;George W. Wagner;Dr. Djamaladdin G. Musaev;Dr. John Bacsa; Craig L. Hill
Angewandte Chemie 2016 Volume 128( Issue 26) pp:7529-7533
Publication Date(Web):
DOI:10.1002/ange.201601620
Abstract
A wide range of chemical warfare agents and their simulants are catalytically decontaminated by a new one-dimensional polymeric polyniobate (P-PONb), K12[Ti2O2][GeNb12O40]⋅19 H2O (KGeNb) under mild conditions and in the dark. Uniquely, KGeNb facilitates hydrolysis of nerve agents Sarin (GB) and Soman (GD) (and their less reactive simulants, dimethyl methylphosphonate (DMMP)) as well as mustard (HD) in both liquid and gas phases at ambient temperature and in the absence of neutralizing bases or illumination. Three lines of evidence establish that KGeNb removes DMMP, and thus likely GB/GD, by general base catalysis: a) the k(H2O)/k(D2O) solvent isotope effect is 1.4; b) the rate law (hydrolysis at the same pH depends on the amount of P-PONb present); and c) hydroxide is far less active against the above simulants at the same pH than the P-PONbs themselves, a critical control experiment.
Co-reporter:John Fielden, Jordan M. Sumliner, Nannan Han, Yurii V. Geletii, Xu Xiang, Djamaladdin G. Musaev, Tianquan Lian and Craig L. Hill
Chemical Science 2015 vol. 6(Issue 10) pp:5531-5543
Publication Date(Web):11 Jun 2015
DOI:10.1039/C5SC01439E
Visible light driven water oxidation has been demonstrated at near-neutral pH using photoanodes based on nanoporous films of TiO2, polyoxometalate (POM) water oxidation catalyst [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10− (1), and both known photosensitizer [Ru(bpy)2(H4dpbpy)]2+ (P2) and the novel crown ether functionalized dye [Ru(5-crownphen)2(H2dpbpy)](H22). Both triads, containing catalyst 1, and catalyst-free dyads, produce O2 with high faradaic efficiencies (80 to 94%), but presence of catalyst enhances quantum yield by up to 190% (maximum 0.39%). New sensitizer H22 absorbs light more strongly than P2, and increases O2 quantum yields by up to 270%. TiO2-2 based photoelectrodes are also more stable to desorption of active species than TiO2–P2: losses of catalyst 1 are halved when pH > TiO2 point-of-zero charge (pzc), and losses of sensitizer reduced below the pzc (no catalyst is lost when pH < pzc). For the triads, quantum yields of O2 are higher at pH 5.8 than at pH 7.2, opposing the trend observed for 1 under homogeneous conditions. This is ascribed to lower stability of the dye oxidized states at higher pH, and less efficient electron transfer to TiO2, and is also consistent with the 4th1-to-dye electron transfer limiting performance rather than catalyst TOFmax. Transient absorption reveals that TiO2–2–1 has similar 1st electron transfer dynamics to TiO2–P2–1, with rapid (ps timescale) formation of long-lived TiO2(e−)–2–1(h+) charge separated states, and demonstrates that metallation of the crown ether groups (Na+/Mg2+) has little or no effect on electron transfer from 1 to 2. The most widely relevant findings of this study are therefore: (i) increased dye extinction coefficients and binding stability significantly improve performance in dye-sensitized water splitting systems; (ii) binding of POMs to electrode surfaces can be stabilized through use of recognition groups; (iii) the optimal homogeneous and TiO2-bound operating pHs of a catalyst may not be the same; and (iv) dye-sensitized TiO2 can oxidize water without a catalyst.
Co-reporter:Sarah M. Lauinger, Jordan M. Sumliner, Qiushi Yin, Zihao Xu, Guijie Liang, Elliot N. Glass, Tianquan Lian, and Craig L. Hill
Chemistry of Materials 2015 Volume 27(Issue 17) pp:5886
Publication Date(Web):August 20, 2015
DOI:10.1021/acs.chemmater.5b01248
Solutions to two general limitations in the immobilization of molecular water oxidation catalysts (WOCs) on nanoparticle or photoelectrode surfaces have been investigated: (a) a straightforward electrostatic method to bind charged WOCs more effectively to these surfaces and (b) a method to increase the concentration of the semiconductor- and/or electrode-immobilized WOCs so they can be spectroscopically characterized in this form. Polyoxometalate (POM) WOCs, known to be fast, selective, and oxidatively stable under homogeneous conditions, and their high negative charges are a good test case to assess the viability of electrostatic surface immobilization. The POM WOCs, [RuIV4O5(OH)(H2O)4(γ-PW10O36)2]9– (Ru4P2) and [{RuIV4(OH)2(H2O)4}(γ-SiW10O34)2]10- (Ru4Si2), have been immobilized by silanization on TiO2 nanoparticles and nanoporous electrodes and have been found to retain catalytic water oxidation activity. In photoelectrochemical systems, increased current density of WOC-TiO2/FTO electrodes is consistent with water oxidation occurring on the derivatized, modified semiconductor surface. The simple use of semiconductor nanoparticles (versus conventional larger particles or surfaces) provides sufficient concentrations of immobilized POM WOCs to enable their spectroscopic and electron microscopic characterization after photoelectrocatalytic use. Multiple techniques have been used to observe the effectiveness of silanization for POM WOC immobilization on nanoparticle surfaces as well as TiO2/FTO electrodes before and after photoelectrocatalysis.
Co-reporter:Mooeung Kim, Ira A. Weinstock, Yurii V. Geletii, and Craig L. Hill
ACS Catalysis 2015 Volume 5(Issue 12) pp:7048
Publication Date(Web):October 20, 2015
DOI:10.1021/acscatal.5b01771
The reaction of reduced polyoxometalates (POMs) with dioxygen is centrally important in POM catalysis. We report that this process, as represented by the one-electron-reduced Keggin complexes POMred (α-AlW12O406–, α-SiW12O405–, and α-PW12O404–), is efficiently catalyzed by copper complexes. The Cu-catalyzed pathway is dominant in the presence of as low as ∼0.1 μM of Cu, a copper concentration that is typically lower than the copper ion contamination in aqueous solutions. The reaction kinetics and mechanism have been comprehensively studied in sodium sulfate buffer at pH 2.0. The catalytic pathway includes a reversible reduction of Cu(II) by POMred, followed by a fast reoxidation of Cu(I) by O2 to regenerate Cu(II). The rate constants of the first catalytic steps were determined by three approaches and found to be (1.8 ± 0.3) × 105 and 57 ± 15 M–1 s–1 for SiW12O405– and PW12O404–, respectively. These reactions are thermodynamically more favorable and therefore proceed significantly more quickly than those for the direct outer-sphere electron transfer to O2. The proposed reaction mechanism quantitatively describes the experimental kinetic curves over a wide range of experimental conditions.Keywords: catalytic oxidation; oxidation by dioxygen; reaction mechanism; reduced Keggin polyoxometalates; submicromolar copper catalysis
Co-reporter:Weiwei Guo; John Bacsa; Jan van Leusen; Kevin P. Sullivan; Hongjin Lv; Paul Kögerler
Inorganic Chemistry 2015 Volume 54(Issue 22) pp:10604-10609
Publication Date(Web):October 23, 2015
DOI:10.1021/acs.inorgchem.5b01387
A novel manganese(IV)-containing symmetrical heteropolyvanadate was prepared by the transformation of K7[MnV13O38]·18H2O (K7MnV13) to K4Li2[MnV14O40]·21H2O (1) at pH 4. The heteropolyanion [MnV14O40]6– (MnV14) is composed of a MnO6 octahedron surrounded by 14 edge-sharing VO6 octahedra. The simplified representation of MnV14 has a new topology termed jba1 with a total point symbol of {310}2{314.47}4{318.410}8{344.446.5}. In the crystal lattice of 1, MnV14 packs with potassium ions, forming a 2D layered K2[MnV14O40]4– network (ABABAB...). Four K+ ions cap the four square O4 faces of MnV14, apparently stabilizing the heteropolyanion. Compound 1 catalyzes the t-BuOOH-based oxidation of 2-chloroethyl ethyl sulfide (a mustard gas simulant). The magnetic and catalytic properties of 1 are discussed.
Co-reporter:Yingnan Chi, Wenting Xu, Yan Yang, Zhichao Yang, Hongjin Lv, Song Yang, Zhengguo Lin, Jikun Li, Jingkai Gu, Craig L. Hill, and Changwen Hu
Crystal Growth & Design 2015 Volume 15(Issue 8) pp:3707
Publication Date(Web):June 29, 2015
DOI:10.1021/acs.cgd.5b00297
Three new salts, [H3N(CH2)2NH3][can]·2H2O (1), [H3N(CH2)3NH3][can]·2H2O (2), and [NH4][Hcan] (3), of the minimally soluble antihypertensive drug, Candesartan (H2can), have been prepared by solvent-assisted grinding. Salts 1–3 also have been thoroughly characterized by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, thermogravimetry, and differential scanning calorimetry. In the case of 1 and 2, two protons of carboxyl and tetrazole groups of Candesartan transfer to the diamine, resulting in salts where both hydrogen bonding and electrostatic interactions that link the Candesartan and diamine (diammonium) units into a one-dimensional supramolecular ribbon. However, unlike the case in 1 and 2, only one proton from the carboxyl group of Candesartan transfers to ammonia in 3 and ionic components now assemble into a three-dimensional supramolecular network. Dissolution studies indicate that both the apparent solubility and dissolution rate of salts 2 and 3 in phosphate buffer are dramatically improved compared to those of the original active pharmaceutical ingredient (API). Furthermore, to evaluate the absorption effect of salts 1–3 in vivo, pharmacokinetic studies were performed in rats. It is notable that the oral bioavailability of salts 1–3 is enhanced by 1.3, 2.5, and 3.1 times, respectively, compared to that of the API.
Co-reporter:Hongjin Lv;Dr. Yingnan Chi;Jan vanLeusen; Paul Kögerler;Dr. Zheyuan Chen;Dr. John Bacsa;Dr. Yurii V. Geletii;Weiwei Guo; Tianquan Lian; Craig L. Hill
Chemistry - A European Journal 2015 Volume 21( Issue 48) pp:17363-17370
Publication Date(Web):
DOI:10.1002/chem.201503010
Abstract
A new structural polyoxometalate motif, [{Ni4(OH)3AsO4}4(B-α-PW9O34)4]28−, which contains the highest nuclearity structurally characterized multi-nickel-containing polyanion to date, has been synthesized and characterized by single-crystal X-ray diffraction, temperature-dependent magnetism and several other techniques. The unique central {Ni16(OH)12O4(AsO4)4} core shows dominant ferromagnetic exchange interactions, with maximum χmT of 69.21 cm3 K mol−1 at 3.4 K. Significantly, this structurally unprecedented complex is an efficient, water-compatible, noble-metal-free catalyst for H2 production upon visible light irradiation (photosensitizer=[Ir(ppy)2(dtbbpy)][PF6]; sacrificial electron donor=triethylamine or triethanolamine). The highest turnover number of approximately 580, corresponding to a best quantum yield of approximately 4.07 %, is achieved when using triethylamine as electron donor in the presence of water. The mechanism of this photodriven process has been probed by time-solved luminescence and by static emission quenching.
Co-reporter:Chongchao Zhao ; Elliot N. Glass ; Bryant Chica ; Djamaladdin G. Musaev ; Jordan M. Sumliner ; R. Brian Dyer ; Tianquan Lian
Journal of the American Chemical Society 2014 Volume 136(Issue 34) pp:12085-12091
Publication Date(Web):July 30, 2014
DOI:10.1021/ja5060127
Two MOF-like but all-inorganic polyoxometalate-based networks, [Na7X2W18Sn9Cl5O68·(H2O)m]n (1, X = Si, m = 35; 2, X = Ge, m = 41), and the molecular tetramer Na6[{Na(μ-OH2)(OH2)2}6{Sn6(B-SbW9O33)2}2]·50H2O (3) have been prepared and characterized by X-ray diffraction and spectroscopic methods. All three compounds exhibit unique structural features, and networks 1 and 2 incorporate the highest nuclearity of Sn(II)-containing POMs to date. Tetramer 3 comprises bridging Sn(II) ions with [B-SbW9O33]9– units and exhibits two highly unusual features, a long-range Sb···Sb interaction and an intramolecular charge-transfer transition involving donation of the lone-pair electron density on both Sb(III) and Sn(II) to the POM. The electronic structure and excited-state dynamics have been studied by transient spectroscopy, spectroelectrochemistry, DFT calculations, and resonance Raman spectroscopy. The synergistic effect of two types of stereoactive lone-pairs on Sb(III) and Sn(II) is critical for the charge-transfer absorption feature in the visible.
Co-reporter:Hongjin Lv ; Jie Song ; Yurii V. Geletii ; James W. Vickers ; Jordan M. Sumliner ; Djamaladdin G. Musaev ; Paul Kögerler ; Petro F. Zhuk ; John Bacsa ; Guibo Zhu
Journal of the American Chemical Society 2014 Volume 136(Issue 26) pp:9268-9271
Publication Date(Web):June 17, 2014
DOI:10.1021/ja5045488
An all-inorganic, oxidatively and thermally stable, homogeneous water oxidation catalyst based on redox-active (vanadate(V)-centered) polyoxometalate ligands, Na10[Co4(H2O)2(VW9O34)2]·35H2O (Na101-V2, sodium salt of the polyanion 1-V2), was synthesized, thoroughly characterized and shown to catalyze water oxidation in dark and visible-light-driven conditions. This synthetic catalyst is exceptionally fast under mild conditions (TOF > 1 × 103 s–1). Under light-driven conditions using [Ru(bpy)3]2+ as a photosensitizer and persulfate as a sacrificial electron acceptor, 1-V2 exhibits higher selectivity for water oxidation versus bpy ligand oxidation, the final O2 yield by 1-V2 is twice as high as that of using [Co4(H2O)2(PW9O34)2]10– (1-P2), and the quantum efficiency of O2 formation at 6.0 μM 1-V2 reaches ∼68%. Multiple experimental results (e.g., UV–vis absorption, FT-IR, 51V NMR, dynamic light scattering, tetra-n-heptylammonium nitrate-toluene extraction, effect of pH, buffer, and buffer concentration, etc.) confirm that the polyanion unit (1-V2) itself is the dominant active catalyst and not Co2+(aq) or cobalt oxide.
Co-reporter:Weiwei Guo, Zhen Luo, Hongjin Lv, and Craig L. Hill
ACS Catalysis 2014 Volume 4(Issue 4) pp:1154
Publication Date(Web):March 3, 2014
DOI:10.1021/cs5000763
Three tetra-n-butylammonium (TBA) salts of polyvanadotungstates, [n-Bu4N]6[PW9V3O40] (PW9V3), [n-Bu4N]5H2PW8V4O40 (PW8V4), and [n-Bu4N]4H5PW6V6O40·20H2O (PW6V6), have been synthesized and shown to be effective catalysts for the aerobic oxidation of formaldehyde to formic acid under ambient conditions. These complexes, characterized by elemental analysis, Fourier transform infrared spectroscopy, UV–vis spectroscopy, and thermogravimetric analysis, exhibit a catalytic activity for this reaction comparable to those of other polyoxometalates. Importantly, they are more effective in the presence of water than the metal oxide-supported Pt and/or Au nanoparticles traditionally used as catalysts for formaldehyde oxidation in the gas phase. The polyvanadotungstate-catalyzed oxidation reactions are first-order in formaldehyde, parabolic-order (slow, fast, and slow again) in catalyst, and zero-order in O2. Under optimized conditions, a turnover number of ∼57 has been obtained. These catalysts can be recycled and reused without a significant loss of catalytic activity.Keywords: aerobic catalysis; formaldehyde oxidation; polyvanadotungstates; water-compatible reaction
Co-reporter:Si-Xuan Guo, Chong-Yong Lee, Jie Zhang, Alan M. Bond, Yurii V. Geletii, and Craig L. Hill
Inorganic Chemistry 2014 Volume 53(Issue 14) pp:7561-7570
Publication Date(Web):July 7, 2014
DOI:10.1021/ic500878w
The water insoluble complex Rb4[RuII(bpy)3]5[{RuIII4O4(OH)2(H2O)4}(γ-SiW10O36)2], ([RuIIbpy]5[RuIII4POM]), was synthesized from Rb8K2[{RuIV4O4(OH)2(H2O)4}(γ-SiW10O36)2] and used for electrocatalytic water oxidation under both thin- and thick-film electrode conditions. Results demonstrate that the [RuIIbpy]5[RuIII4POM] modified electrode enables efficient water oxidation to be achieved at neutral pH using thin-film conditions, with [Ru(bpy)3]3+([RuIIIbpy]) acting as the electron transfer mediator and [RuV4POM] as the species releasing O2. The rotating ring disc electrode (RRDE) method was used to quantitatively determine the turnover frequency (TOF) of the catalyst, and a value of 0.35 s–1 was obtained at a low overpotential of 0.49 V (1.10 V vs Ag/AgCl) at pH 7.0. The postulated mechanism for the mediator enhanced catalytic water process in a pH 7 buffer containing 0.1 M LiClO4 as an additional electrolyte includes the following reactions (ion transfer for maintaining charge neutrality is omitted for simplicity): [RuIIbpy]5[RuIII4POM] → [RuIIIbpy]5[RuV4POM] + 13 e– and [RuIIIbpy]5[RuV4POM] + 2H2O → [RuIIIbpy]5[RuIV4POM] + O2 + 4H+. The voltammetry of related water insoluble [RuIIbpy]2[S2M18O62] (M = W and Mo) and [FeIIPhen]x[RuIII4POM] materials has also been studied, and the lack of electrocatalytic water oxidation in these cases supports the hypothesis that [RuIIIbpy] is the electron transfer mediator and [RuV4POM] is the species responsible for oxygen evolution.
Co-reporter:James W. Vickers, Jordan M. Sumliner, Hongjin Lv, Mike Morris, Yurii V. Geletii and Craig L. Hill
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 24) pp:11942-11949
Publication Date(Web):07 Mar 2014
DOI:10.1039/C3CP55406F
As the field of water oxidation catalysis grows, so does the sophistication of the associated experimental apparatuses. However, problems persist in studying some of the most basic aspects of catalytic water oxidation including acquisition of satisfactory early-reaction-time kinetics and rapid quantification of O2 concentration. We seek to remedy these problems and through better experimental design, elucidate mechanistic aspects of catalytic water oxidation with theory backed by experimental data. Two new methods for evaluating homogeneous water oxidation catalysts by reaction with a stoichiometric oxidant are presented which eliminate problems of incomplete fast mixing and O2 measurement response time. These methods generate early-reaction-time kinetics that have previously been unavailable.
Co-reporter:Chongchao Zhao, Elliot N. Glass, Jordan M. Sumliner, John Bacsa, Daniel Taehyun Kim, Weiwei Guo and Craig L. Hill
Dalton Transactions 2014 vol. 43(Issue 10) pp:4040-4047
Publication Date(Web):15 Jan 2014
DOI:10.1039/C3DT53374C
Several polyoxometalate-supported metal carbonyl complexes, K7Na3P2W23O80{Re(CO)3}2·38H2O (1), (C3H10N)8Na2P2W23O80{Re(CO)3}2·10H2O (1a) and (C3H10N)6KNa3P2W23O80{Mn(CO)3}2·7H2O (2), have been prepared from the dimerization of the monovacant Keggin [α-PW11O39]7− with metal carbonyl complexes [M(CO)3]+ (M = Re, Mn) in acidic aqueous solutions. The resulting “twisted-sandwich” architectures are chiral, but their crystalline solids are racemic. A detailed investigation involving syntheses, crystal structures, and electrochemistry is presented.
Co-reporter:Jordan M. Sumliner;Hongjin Lv;John Fielden;Yurii V. Geletii
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 4) pp:635-644
Publication Date(Web):
DOI:10.1002/ejic.201301573
Abstract
The viable production of solar fuels requires a visible-light-absorbing unit, a H2O (or CO2) reduction catalyst (WRC), and a water oxidation catalyst (WOC) that work in tandem to split water or reduce CO2 with H2O rapidly, selectively, and for long periods of time. Most catalysts and photosensitizers developed to date for these triadic systems are oxidatively, thermally, and/or hydrolytically unstable. Polyoxometalates (POMs) constitute a huge class of complexes with extensively tunable properties that are oxidatively, thermally, and (over wide and adjustable pH ranges) hydrolytically stable. POMs are some of the fastest and most stable WOCs to date under optimal conditions. This Microreview updates the very active POM WOC field; it reports the application of POMs as WRCs and initial self-assembling metal oxide semiconductor–photosensitizer–POM catalyst triad photoanodes. The complexities of investigating these POM systems, including but not limited to the study of POM-hydrated metal-ion–metal-oxide speciation processes, are outlined. The achievements and challenges in POM WOC, WRC, and triad research are outlined.
Co-reporter:Elliot N. Glass;Dr. John Fielden;Dr. Alexey L. Kaledin;Dr. Djamaladdin G. Musaev;Dr. Tianquan Lian;Dr. Craig L. Hill
Chemistry - A European Journal 2014 Volume 20( Issue 15) pp:4297-4307
Publication Date(Web):
DOI:10.1002/chem.201304119
Abstract
In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition-metal-substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been used to study the cobalt-containing Keggin POMs, [CoIIW12O40]6− (1 a), [CoIIIW12O40]5− (2 a), [SiCoII(H2O)W11O39]6− (3 a), and [SiCoIII(H2O)W11O39]5− (4 a), finding the longest lived charge transfer excited state so far observed in a POM and elucidating the electronic structures and excited-state dynamics of these compounds at an unprecedented level. All species exhibit a bi-exponential decay in which early dynamic processes with time constants in the fs domain yield longer lived excited states which decay with time constants in the ps to ns domain. The initially formed states of 1 a and 3 a are considered to result from metal-to-polyoxometalate charge transfer (MPCT) from CoII to W, while the longer-lived excited state of 1 a is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion (1 a) is far longer-lived (τ=420 ps in H2O; τ=1700 ps in MeCN) than that of 3 a (τ=1.3 ps), in which the single CoII atom is located in a pseudo-octahedral addendum site. Short-lived states are observed for the two CoIII-containing heteropolyanions 2 a (τ=4.4 ps) and 4 a (τ=6.3 ps) and assigned solely to OCoIII charge transfer. The dramatically extended lifetime for 1 a versus 3 a is ascribed to a structural change permitted by the coordinatively flexible central site, weak orbital overlap of the central Co with the polytungstate framework, and putative transient valence trapping of the excited electron on a single W atom, a phenomenon not noted previously in POMs.
Co-reporter:Si-Xuan Guo, Yuping Liu, Chong-Yong Lee, Alan M. Bond, Jie Zhang, Yurii V. Geletii and Craig L. Hill
Energy & Environmental Science 2013 vol. 6(Issue 9) pp:2654-2663
Publication Date(Web):12 Jun 2013
DOI:10.1039/C3EE41892H
The electrochemistry of the Ru-containing polyoxometalate (POM) water oxidation molecular catalyst, Rb8K2[{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10− (Rb8K2-1), has been studied by cyclic and rotating disk electrode voltammetric methods in aqueous media under acidic and neutral pH conditions using bare glassy carbon (GC) and graphene modified GC electrodes. High concentrations of supporting electrolyte are needed in neutral pH conditions to overcome the electrical double layer effect associated with the highly negatively charged 1. Complex 1 can be confined within the highly porous wet graphene film to form a stable modified electrode, which shows excellent catalytic activity and high stability toward the water oxidation reaction under neutral pH conditions, particularly in the presence of 1.0 M Ca(NO3)2. The catalytic activity of the graphene supported 1electrode is nearly two orders of magnitude higher than that reported with a polymer coated multiwalled carbon nanotube supported 1electrode when both are employed at a moderate overpotential of 0.35 V.
Co-reporter:James W. Vickers ; Hongjin Lv ; Jordan M. Sumliner ; Guibo Zhu ; Zhen Luo ; Djamaladdin G. Musaev ; Yurii V. Geletii
Journal of the American Chemical Society 2013 Volume 135(Issue 38) pp:14110-14118
Publication Date(Web):August 26, 2013
DOI:10.1021/ja4024868
Distinguishing between homogeneous and heterogeneous catalysis is not straightforward. In the case of the water oxidation catalyst (WOC) [Co4(H2O)2(PW9O34)2]10– (Co4POM), initial reports of an efficient, molecular catalyst have been challenged by studies suggesting that formation of cobalt oxide (CoOx) or other byproducts are responsible for the catalytic activity. Thus, we describe a series of experiments for thorough examination of active species under catalytic conditions and apply them to Co4POM. These provide strong evidence that under the conditions initially reported for water oxidation using Co4POM (Yin et al. Science, 2010, 328, 342), this POM anion functions as a molecular catalyst, not a precursor for CoOx. Specifically, we quantify the amount of Co2+(aq) released from Co4POM by two methods (cathodic adsorptive stripping voltammetry and inductively coupled plasma mass spectrometry) and show that this amount of cobalt, whatever speciation state it may exist in, cannot account for the observed water oxidation. We document that catalytic O2 evolution by Co4POM, Co2+(aq), and CoOx have different dependences on buffers, pH, and WOC concentration. Extraction of Co4POM, but not Co2+(aq) or CoOx into toluene from water, and other experiments further confirm that Co4POM is the dominant WOC. Recent studies showing that Co4POM decomposes to a CoOx WOC under electrochemical bias (Stracke and Finke, J. Am. Chem. Soc., 2011, 133, 14872), or displays an increased ability to reduce [Ru(bpy)3]3+ upon aging (Scandola, et al., Chem. Commun., 2012, 48, 8808) help complete the picture of Co4POM behavior under various conditions but do not affect our central conclusions.
Co-reporter:Guibo Zhu, Yurii V. Geletii, Jie Song, Chongchao Zhao, Elliot N. Glass, John Bacsa, and Craig L. Hill
Inorganic Chemistry 2013 Volume 52(Issue 2) pp:1018-1024
Publication Date(Web):December 26, 2012
DOI:10.1021/ic302279m
Di- and tricobalt silicotungstate complexes, K5Na4H4[{Na3(μ-OH2)2Co2(μ-OH)4} (Si2W18O66)]·37H2O (1) and K6Na3[Na(H2O){Co(H2O)3}2{Co(H2O)2}(Si2W18O66)]·22H2O (2), have been synthesized through reaction of cobalt chloride and [A-α-SiW9O34]10– in acidic buffer solution. They have been characterized by X-ray crystallography, elemental analysis, cyclic voltammetry, infrared, and UV–vis spectroscopy. In 1, two cobalt atoms as well as three sodium atoms are incorporated in the central pocket of the [Si2W18O66]16– polyanion. In 2, one cobalt atom and one sodium atom are incorporated in the pocket of [Si2W18O66]16–; two other cobalt atoms in this complex protrude outside the pocket and connect with WO6 units of other [Si2W18O66]16– polyanions to form a one-dimensional polymeric structure. The crucial parameters in the synthesis of these two compounds are discussed, and their stability in different buffer solutions is studied. The decomposition of 1 or 2 in heated potassium acetate buffer (pH 4.8, 1 M) yields K11[{Co2(H2O)8}K(Si2W18O66)]·17H2O (3) based on spectroscopic studies and an X-ray crystal structure.
Co-reporter:Chongchao Zhao ; William Rodríguez-Córdoba ; Alexey L. Kaledin ; Ye Yang ; Yurii V. Geletii ; Tianquan Lian ; Djamaladdin G. Musaev
Inorganic Chemistry 2013 Volume 52(Issue 23) pp:13490-13495
Publication Date(Web):November 15, 2013
DOI:10.1021/ic4018823
A polyoxometalate-supported trirhenium carbonyl cluster, mimicking metal oxide supported interfacial dyadic structures, has been synthesized and characterized. Multiple techniques, including computational and transient absorption spectroscopy, have been applied to characterize the charge-transfer dynamics occurring at the interfaces of this “double cluster”. The stepwise kinetics of charge separation and recombination has been thoroughly investigated.
Co-reporter:Chongchao Zhao, Choon Sung Kambara, Ye Yang, Alexey L. Kaledin, Djamaladdin G. Musaev, Tianquan Lian, and Craig L. Hill
Inorganic Chemistry 2013 Volume 52(Issue 2) pp:671-678
Publication Date(Web):January 3, 2013
DOI:10.1021/ic301766b
A new series of complexes containing two electron donating groups, {M(CO)3}+ ions, M = Re or Mn, on one polytungstate electron acceptor group have been prepared and characterized. These complexes containing two electron donating groups, {M(CO)3}+ ions, M = Re or Mn, on one polytungstate electron acceptor group have been prepared and characterized. These two-component polyoxometalate (POM) compounds have been made by reaction of solvated {M(CO)3}+ ions (M = Re or Mn) with [X2W22O74(OH)2]12– (X = Sb or Bi) POM multidentate ligands in aqueous solution. These syntheses reveal that the fac-{WO(OH)2}2+ groups in the terminal positions of these two POM ligands are easily replaced by the topologically equivalent units fac-{M(CO)3}+. Four compounds, [X2W20O70{M(CO)3}2]12– (1a: X = Sb, M = Re; 1b: X = Bi, M = Re; 2a: X = Sb, M = Mn; 2b: X = Bi, M = Mn) have been isolated and characterized of X-ray crystallography, spectroscopic, and computational methods. The charge transfer dynamics, investigated by femtosecond transient absorption (TA) spectroscopy of 1a and 1b combined with the density functional theory (DFT) calculations indicate that both complexes exhibit metal-to-polyoxometalate charge-transfer (MPCT) from the Re centers to the POM ligands, while MPCT from the Mn centers to the POM ligands in 2a and 2b leads to decomposition of starting compounds. The studies suggest a general synthetic route to a potentially very large class of POM-based hybrid compounds.
Co-reporter:Hongjin Lv;Jie Song;Yurii V. Geletii;Weiwei Guo;John Bacsa
European Journal of Inorganic Chemistry 2013 Volume 2013( Issue 10-11) pp:1720-1725
Publication Date(Web):
DOI:10.1002/ejic.201201130
Abstract
The hexanuclear cobalt-containing tungstovanadate complex, Na17[(Co(OH2)Co2VW9O34)2(VW6O26)]·31H2O (1) has been synthesized through reaction of cobalt nitrate, sodium tungstate, and V2O5 in acetate buffer solution. The title compound has been characterized by X-ray crystallography, elemental analysis, FTIR, UV/Vis, and 51V NMR spectroscopy and by cyclic voltammetry. Complex 1 crystallizes in the monoclinic space group P21/c (a = 15.706(3) Å, b = 21.973(5) Å, c = 35.080(8) Å, α = 90°, β = 97.420(3)°, γ = 90°; V = 12005(5) Å3; Z = 4; based on 192337 independent reflections), which consists of two tri-CoII substituted B-α-[(Co(OH2)Co2VW9O39)] Keggin units bridged by one unique [VW6O16] fragment leading to a banana-shaped structure with idealized C2ν symmetry. Stability studies show that polyoxoanion 1 ultimately transforms into the tetracobalt-containing sandwich-type polyoxoanion, 2, as confirmed by 51V NMR and X-ray crystallographic analyses. Polyoxoanion 1 shows catalytic activity for the H2O2-based epoxidation of 1-hexene and cyclohexene in 1,2-dichloroethane solvent.
Co-reporter:Xu Xiang, John Fielden, William Rodríguez-Córdoba, Zhuangqun Huang, Naifei Zhang, Zhen Luo, Djamaladdin G. Musaev, Tianquan Lian, and Craig L. Hill
The Journal of Physical Chemistry C 2013 Volume 117(Issue 2) pp:918-926
Publication Date(Web):December 18, 2012
DOI:10.1021/jp312092u
Triadic photoanodes have been prepared based on nanoporous films of the metal oxides ZrO2, TiO2, and SnO2, sensitizer [Ru(bpy)2(dpbpy)]2+ (P2), and polyoxometalate water oxidation catalyst [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10– (1) and investigated for their potential utility in water-splitting dye-sensitized photoelectrochemical cells. Transient visible and mid-IR absorption spectroscopic studies were carried out to investigate the charge separation dynamics of these systems, indicating that electron transfer from photoexcited P2 to TiO2 and SnO2 is still the main excited state quenching pathway in the presence of 1. Furthermore, the accelerated recovery of the P2 ground state bleach in the presence of 1 results from ultrafast (nanosecond) electron transfer from catalyst to oxidized dye. Catalyst loading appears to depend largely on the point of zero charge of the supporting oxide and as such is significantly lower on SnO2 than on TiO2: nonetheless, the rate of recovery of the ground state bleach is similar in both TiO2-P2-1 and SnO2-P2-1 films. Spectral evidence for the formation of long-lived charged separated states is provided by the observation of signals persisting beyond 0.5 μs which are attributed to Stark effect induced change of the P2 spectrum and/or formation of oxidized 1. Photoelectrochemical measurements on TiO2-P2 and TiO2-P2-1 photoanodes under visible light irradiation indicate a ca. 100% photocurrent enhancement in the presence of 1, suggesting light-driven water oxidation by the TiO2-P2-1 system with an internal quantum efficiency of ca. 0.2%. The fast formation and long lifetime of the photo-oxidized catalyst suggest that photoanodes of this type may reward further optimization through the introduction of faster catalysts and stabilization of the binding of the dye to the electrode.
Co-reporter:Hongjin Lv, Yurii V. Geletii, Chongchao Zhao, James W. Vickers, Guibo Zhu, Zhen Luo, Jie Song, Tianquan Lian, Djamaladdin G. Musaev and Craig L. Hill
Chemical Society Reviews 2012 vol. 41(Issue 22) pp:7572-7589
Publication Date(Web):12 Sep 2012
DOI:10.1039/C2CS35292C
In the last five years and currently, research on solar fuels has been intense and no sub-area in this field has been more active than the development of water oxidation catalysts (WOCs). In this timeframe, a new class of molecular water oxidation catalysts based on polyoxometalates have been reported that combine the advantages of homogeneous and heterogeneous catalysts. This review addresses central issues in green energy generation, the challenges in water oxidation catalyst development, and the possible uses of polyoxometalates in green energy science.
Co-reporter:Kevin P. O’Halloran, Chongchao Zhao, Nicole S. Ando, Arthur J. Schultz, Thomas F. Koetzle, Paula M. B. Piccoli, Britt Hedman, Keith O. Hodgson, Elena Bobyr, Martin L. Kirk, Sushilla Knottenbelt, Ezra C. Depperman, Benjamin Stein, Travis M. Anderson, Rui Cao, Yurii V. Geletii, Kenneth I. Hardcastle, Djamaladdin G. Musaev, Wade A. Neiwert, Xikui Fang, Keiji Morokuma, Shaoxiong Wu, Paul Kögerler, and Craig L. Hill
Inorganic Chemistry 2012 Volume 51(Issue 13) pp:7025-7031
Publication Date(Web):June 13, 2012
DOI:10.1021/ic2008914
Terminal oxo complexes of the late transition metals Pt, Pd, and Au have been reported by us in Science and Journal of the American Chemical Society. Despite thoroughness in characterizing these complexes (multiple independent structural methods and up to 17 analytical methods in one case), we have continued to study these structures. Initial work on these systems was motivated by structural data from X-ray crystallography and neutron diffraction and 17O and 31P NMR signatures which all indicated differences from all previously published compounds. With significant new data, we now revisit these studies. New X-ray crystal structures of previously reported complexes K14[P2W19O69(OH2)] and “K10Na3[PdIV(O)(OH)WO(OH2)(PW9O34)2]” and a closer examination of these structures are provided. Also presented are the 17O NMR spectrum of an 17O-enriched sample of [PW11O39]7– and a careful combined 31P NMR-titration study of the previously reported “K7H2[Au(O)(OH2)P2W20O70(OH2)2].” These and considerable other data collectively indicate that previously assigned terminal Pt-oxo and Au-oxo complexes are in fact cocrystals of the all-tungsten structural analogues with noble metal cations, while the Pd-oxo complex is a disordered Pd(II)-substituted polyoxometalate. The neutron diffraction data have been re-analyzed, and new refinements are fully consistent with the all-tungsten formulations of the Pt-oxo and Au-oxo polyoxometalate species.
Co-reporter:Guibo Zhu, Yurii V. Geletii, Chongchao Zhao, Djamaladdin G. Musaev, Jie Song and Craig L. Hill
Dalton Transactions 2012 vol. 41(Issue 33) pp:9908-9913
Publication Date(Web):23 Jul 2012
DOI:10.1039/C2DT30733B
A dodecazinc silicotungstate K20Na2[Zn6(OH)7(H2O)(Si2W18O66)]2·34H2O (1) has been synthesized and characterized by X-ray crystallography, elemental analysis, infrared, UV-vis spectroscopy, cyclic voltammetry, acid–base titration, and DFT calculations. The twelve zinc atoms between the two [Si2W18O66]16− frameworks make this complex more stable hydrolytically than the heteropolytungstate ligands, [Si2W18O66]16−, themselves. The structurally unique central Zn12 core is formed by the fusion of two [Zn6(OH)7(H2O)]5+ units through two edge-sharing Zn6 atoms. DFT B3LYP calculations give HOMO–LUMO and (HOMO − 1)–LUMO energy gaps of ∼3.65 and 3.91 eV, respectively, as compared to the band gap in ZnO of 3.35 eV.
Co-reporter:Guibo Zhu, Elliot N. Glass, Chongchao Zhao, Hongjin Lv, James W. Vickers, Yurii V. Geletii, Djamaladdin G. Musaev, Jie Song and Craig L. Hill
Dalton Transactions 2012 vol. 41(Issue 42) pp:13043-13049
Publication Date(Web):17 Jul 2012
DOI:10.1039/C2DT30331K
A new pentanickel silicotungstate complex, K10H2[Ni5(OH)6(OH2)3(Si2W18O66)]·34H2O (KH-1), has been synthesized and characterized by X-ray crystallography and several other methods. Dynamic light scattering, kinetics and other experiments confirm that 1 in the presence of [Ru(bpy)3]2+ (the photosensitizer for light-driven water oxidations) and [Ru(bpy)3]3+ (the oxidant in the dark water oxidations) exists in an equilibrium between solution (soluble) and a [Ru(bpy)3]n+-1 complex (minimally soluble) form. This new pentanickel polyoxometalate catalyzes efficient water oxidation in both the dark and on irradiation with 455 nm LED light with 1.0 mM [Ru(bpy)3]2+ photosensitizer and 5.0 mM Na2S2O8, sacrificial electron acceptor. Four lines of evidence indicate that 1 in this solution ⇌ Ru(bpy)3]n+-1 complex equilibrium remains molecular and does not decompose to nickel hydroxide particles.
Co-reporter:Travis M. Anderson;Wade A. Neiwert;Martin L. Kirk;Paula M. B. Piccoli;Arthur J. Schultz;Thomas F. Koetzle;Djamaladdin G. Musaev;Keiji Morokuma;Rui Cao
Science 2012 Volume 337(Issue 6092) pp:290
Publication Date(Web):20 Jul 2012
DOI:10.1126/science.337.6092.290-a
Co-reporter:Chongchao Zhao ; Zhuangqun Huang ; William Rodríguez-Córdoba ; Choon Sung Kambara ; Kevin P. O’Halloran ; Ken I. Hardcastle ; Djamaladdin G. Musaev ; Tianquan Lian
Journal of the American Chemical Society 2011 Volume 133(Issue 50) pp:20134-20137
Publication Date(Web):November 17, 2011
DOI:10.1021/ja209360x
[P4W35O124{Re(CO)3}2]16– (1), a Wells–Dawson [α2-P2W17O61]10– polyoxometalate (POM)-supported [Re(CO)3]+ complex containing covalent WVI–O–ReI bonds has been synthesized and characterized by several methods, including X-ray crystallography. This complex shows a high visible absorptivity (ε470 nm = 4000 M–1 cm–1 in water) due to the formation of a ReI-to-POM charge transfer (MPCT) band. The complex was investigated by computational modeling and transient absorption measurements in the visible and mid-IR regions. Optical excitation of the MPCT transition results in instantaneous (<50 fs) electron transfer from the ReI center to the POM ligand.
Co-reporter:Jie Song ; Zhen Luo ; David K. Britt ; Hiroyasu Furukawa ; Omar M. Yaghi ; Kenneth I. Hardcastle
Journal of the American Chemical Society 2011 Volume 133(Issue 42) pp:16839-16846
Publication Date(Web):September 13, 2011
DOI:10.1021/ja203695h
A combination of polyanion size and charge allows the Keggin-type polyoxometalate (POM), [CuPW11O39]5–, a catalyst for some air-based organic oxidations, to fit snuggly in the pores of MOF-199 (HKUST-1), a metal–organic framework (MOF) with the POM countercations residing in alternative pores. This close matching of POM diameter and MOF pore size in this POM–MOF material, [Cu3(C9H3O6)2]4[{(CH3)4N}4CuPW11O39H] (1), results in a substantial synergistic stabilization of both the MOF and the POM. In addition, this heretofore undocumented POM–MOF interaction results in a dramatic increase in the catalytic turnover rate of the POM for air-based oxidations. While 1 catalyzes the rapid chemo- and shape-selective oxidation of thiols to disulfides and, more significantly, the rapid and sustained removal of toxic H2S via H2S + 1/2 O2 → 1/8 S8 + H2O (4000 turnovers in <20 h), the POM or the MOF alone is catalytically slow or inactive. Three arguments are consistent with the catalytic reactions taking place inside the pores. POM activation by encapsulation in the MOF likely involves electrostatic interactions between the two components resulting in a higher reduction potential of the POM.
Co-reporter:Dong Li ; Jie Song ; Panchao Yin ; Silas Simotwo ; Andrew J. Bassler ; YuYu Aung ; James E. Roberts ; Kenneth I. Hardcastle ; Craig L. Hill ;Tianbo Liu
Journal of the American Chemical Society 2011 Volume 133(Issue 35) pp:14010-14016
Publication Date(Web):July 27, 2011
DOI:10.1021/ja204034g
Two inorganic–organic hybrid clusters with one or two covalently linked pyrene fluorescent probes, [(n-C4H9)4N]2[V6O13{(OCH2)3C(NH(CO)CH2CH2CH2C16H9)}{(OCH2)3C–(NH2)}] ((TBA+)21) and [(n-C4H9)4N]2[V6O13{(OCH2)3C(NH(CO)CH2CH2CH2C16H9)}2] ((TBA+)22), respectively, are synthesized from Lindqvist type polyoxometalates (POMs). The incorporation of pyrene into POMs results in amphiphilic hybrid molecules and simultaneously offers a great opportunity to study the interaction between hybrid clusters and their counterions. 2D-NOESY NMR and fluorescence techniques have been used to study the role of counterions such as tetrabutyl ammonium (TBA) in the vesicle formation of the hybrid clusters. The TBA+ ions not only screen the electrostatic repulsions between the POM head groups but also are involved in the hydrophobic region of the vesicular structure where they interrupt the formation of pyrene excimers that greatly perturbs the luminescence signal from the vesicle solution. By replacing the TBA+ counterions with protons, the new vesicles demonstrate interesting pH-dependent fluorescence properties.
Co-reporter:Zhuangqun Huang ; Zhen Luo ; Yurii V. Geletii ; James W. Vickers ; Qiushi Yin ; David Wu ; Yu Hou ; Yong Ding ; Jie Song ; Djamaladdin G. Musaev ; Craig L. Hill ;Tianquan Lian
Journal of the American Chemical Society 2011 Volume 133(Issue 7) pp:2068-2071
Publication Date(Web):January 26, 2011
DOI:10.1021/ja109681d
The abundant-metal-based polyoxometalate complex [Co4(H2O)2(PW9O34)2]10− is a hydrolytically and oxidatively stable, homogeneous, and efficient molecular catalyst for the visible-light-driven catalytic oxidation of water. Using a sacrificial electron acceptor and photosensitizer, it exhibits a high (30%) photon-to-O2 yield and a large turnover number (>220, limited solely by depletion of the sacrificial electron acceptor) at pH 8. The photocatalytic performance of this catalyst is superior to that of the previously reported precious-metal-based polyoxometalate water oxidation catalyst [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10−.
Co-reporter:Zhen Luo, Yurii V. Geletii, Daniel A. Hillesheim, Yimin Wang, and Craig L. Hill
ACS Catalysis 2011 Volume 1(Issue 10) pp:1364
Publication Date(Web):August 15, 2011
DOI:10.1021/cs2003643
Many studies have noted that mixtures of nitrogen oxides (or oxyanions; NOx = NO3–, NO2–, NO–, etc.) and halide (particularly bromine) with or without a transition metal salt (most frequently, copper and iron complexes) are fast and highly selective catalysts for aerobic sulfoxidation and decontamination of many oxidizable toxic compounds. However, the lack of extensive and rigorous kinetic information has kept unequivocal mechanistic inferences on these important catalyst systems to a minimum. Through a series of spectroscopic and kinetics studies on NOx/bromine systems in acetonitrile, the following clarifying technical points have been established: (1) bromine is the reactive species in these oxidations; (2) nitrosonium and hypobromite are not kinetically important, (3) tribromide (Br3–) functions as a stable reservoir for Br2; (4) salts of Br3– and nitrate are stable, storable decontamination catalyst precursors; and (5) most importantly, the multiple complex roles of water (required for catalysts yet inhibitory at most concentrations) have been clarified.Keywords: air-based sulfoxidation; bromine; mechanism; nitrate; tribromide;
Co-reporter:Rui Cao, Kevin P. O'Halloran, Daniel A. Hillesheim, Sheri Lense, Kenneth I. Hardcastle and Craig L. Hill
CrystEngComm 2011 vol. 13(Issue 3) pp:738-740
Publication Date(Web):26 Nov 2010
DOI:10.1039/C0CE00828A
The synthesis of an unprecedented vacant polytungstate ligand and its use to obtain a crystallographically characterized {MaMbMc(PW9)2}-type sandwich structure, the first example of the purposeful and controlled metal incorporation into a derivatized POM, are reported.
Co-reporter:Yurii V. Geletii;Qiushi Yin;Yu Hou;Zhuangqun Huang;Huiyuan Ma;Jie Song;Claire Besson;Zhen Luo;Rui Cao;Kevin P. O'Halloran;Guibo Zhu;Chongchao Zhao;James W. Vickers;Yong Ding;Sajjad Mohebbi;Aleksey E. Kuznetsov;Djamaladdin G. Musaev;Tianquan Lian
Israel Journal of Chemistry 2011 Volume 51( Issue 2) pp:238-246
Publication Date(Web):
DOI:10.1002/ijch.201100021
Abstract
Water oxidation catalysts (WOCs) are of core importance in several green energy production technologies, including water splitting and water reduction of CO2 driven by electrochemical potential and/or photons (radiant energy). General challenges in solar fuel generating structures, WOC design concepts, and some success-limiting considerations in WOC development are described. The first class of WOCs are presented that combine the stability benefits of heterogeneous WOCs with the reactivity and other benefits of homogeneous WOCs.
Co-reporter:Qiushi Yin;Jeffrey Miles Tan;Claire Besson;Yurii V. Geletii;Djamaladdin G. Musaev;Aleksey E. Kuznetsov;Zhen Luo;Ken I. Hardcastle
Science 2010 Vol 328(5976) pp:342-345
Publication Date(Web):16 Apr 2010
DOI:10.1126/science.1185372
Co-reporter:Claire Besson, Zhuangqun Huang, Yurii V. Geletii, Sheri Lense, Kenneth I. Hardcastle, Djamaladdin G. Musaev, Tianquan Lian, Anna Proust and Craig L. Hill
Chemical Communications 2010 vol. 46(Issue 16) pp:2784-2786
Publication Date(Web):25 Feb 2010
DOI:10.1039/B926064A
The tetraruthenium-substituted polyoxometalate Cs9[(γ-PW10O36)2Ru4O5(OH)(H2O)4] was synthesized and structurally, spectroscopically and electrochemically characterized; it was shown to be a catalyst for visible-light-induced water oxidation.
Co-reporter:Yu Hou ; Lin Xu ; Morgan J. Cichon ; Sheri Lense ; Kenneth I. Hardcastle
Inorganic Chemistry 2010 Volume 49(Issue 9) pp:4125-4132
Publication Date(Web):April 1, 2010
DOI:10.1021/ic9024712
A new family of sandwich-type polytungstophosphates containing two different types of metals in the central belt, M′2M2(PW9O34)212− (M′ = Na or Li, M = Mn2+, Co2+, Ni2+, and Zn2+), have been synthesized and characterized by infrared spectroscopy, 31P solution NMR spectroscopy, and elemental analysis. Compounds Na2Co2(PW9O34)212− (Na2Co2), Na2Ni2(PW9O34)212− (Na2Ni2), Li2Ni2(PW9O34)212− (Li2Ni2), Na2Mn2(PW9O34)212− (Na2Mn2), and Li2Zn2(PW9O34)212− (Li2Zn2) were characterized by X-ray crystallography. All these compounds have similar structures, in which two transition-metal ions and two alkali metal ions (sodium or lithium) are sandwiched between two [B-α-PW9O34]9− units; the transition and alkali metals reside in the internal and external (solvent exposed) positions of the central belt, respectively. By adding LiCl to aqueous solutions of compounds Na2M2, lithium−sodium exchanges in the external belt positions are observed by 31P solution NMR spectroscopy and X-ray crystallography. Magnetic measurements indicate ferromagnetic exchange interactions between the two Ni2+ ions in Na2Ni2 at 10−300 K and the two Co2+ ions in Na2Co2 at 6−30 K. In contrast, Na2Mn2 exhibits an antiferromagnetic interaction between the Mn2+ ions at 2−50 K.
Co-reporter:Rui Cao, Kevin P. O'Halloran, Daniel A. Hillesheim, Kenneth I. Hardcastle and Craig L. Hill
CrystEngComm 2010 vol. 12(Issue 5) pp:1518-1525
Publication Date(Web):08 Jan 2010
DOI:10.1039/B919934A
Three new phenyltin-substituted polyoxometalates, ((CH3)2NH2)4[Sn(C6H5)PW11O39] (1), K7[Sn(C6H5)P2W17O61] (2), and ((CH3)2NH2)6K[Sn(C6H5)(H2O)P2W20O70(H2O)2] (3), have been synthesized and characterized by single crystal X-ray diffraction, 31P and 1H NMR, and FT-IR spectroscopy. Significantly, the mono-substituted phenyltin group in all three complexes is not positionally disordered. The Sn(C6H5) group is unambiguously determined and refined anisotropically with full occupancy, a result that is very unusual for mono-substituted polyoxometalates, and in particular polytungstates. Three factors account for these disorder-free mono-phenyltin-substituted polyanion structures: the steric bulk and rigidity of the phenyl group, hydrogen bonding and cation–π interactions between the phenyl ring and countercations. These results demonstrate the ability of a phenyl group to remove the crystallographically imposed positional disorder typically seen in mono-substituted polyoxometalates, an attribute that usually renders structural and structure-related reactivity studies of this large class of polyoxometalates quite difficult.
Co-reporter:Jie Song, Zhen Luo, Haiming Zhu, Zhuangqun Huang, Tianquan Lian, Alexey L. Kaledin, Djamaladdin G. Musaev, Sheri Lense, Kenneth I. Hardcastle, Craig L. Hill
Inorganica Chimica Acta 2010 Volume 363(Issue 15) pp:4381-4386
Publication Date(Web):10 December 2010
DOI:10.1016/j.ica.2010.07.022
Two hybrid materials based on the tris(bipyridine)ruthenium(II), [Ru(bpy)3]2+ and Keggin-type polyoxometalates, [PW11O39]7− and [PW12O40]3−, namely, [Ru(bpy)3][K5PW11O39] (1) and [Ru(bpy)3][KPW12O40] (2) were synthesized. X-ray crystallographic study of the red-colored complex, 2, shows that it crystallizes in the orthorhombic space group Pbcn and the polyanions are associated with the [Ru(bpy)3]2+ counterions by Coulombic forces and supramolecular interactions. The molecular complex is further connected and forms a three-dimensional framework through C–H⋯OPOM and other weak interactions. These complexes were further characterized by FT-IR, UV–Vis, 1H and 31P NMR, luminescent spectra and computational studies. Significantly, these combined spectroscopic studies show that these polyoxometalate–dye hybrids have strong electronic interactions between the cationic dye and polyanion units.Two complexes involving a [Ru(bpy)3]2+ photosensitizer and a polyoxometalate (POM), [Ru(bpy)3][K5PW11O39] (1) and [Ru(bpy)3][KPW12O40] (2), have been characterized by X-ray crystallography and several spectroscopic techniques. Significantly, the photosensitizer and POM units exhibit strong inter-unit electronic interactions.
Co-reporter:Yurii V. Geletii ; Zhuangqun Huang ; Yu Hou ; Djamaladdin G. Musaev ; Tianquan Lian
Journal of the American Chemical Society 2009 Volume 131(Issue 22) pp:7522-7523
Publication Date(Web):May 12, 2009
DOI:10.1021/ja901373m
A totally homogeneous, molecular, visible-light-driven water oxidation system is reported. The three system components are (i) a water oxidation catalyst, 1 (a RuIV4O4 cluster stabilized by oxidatively resistant [SiW10O32]8- ligands); (ii) a photosensitizer, [Ru(bpy)3]2+; and (iii) a sacrificial electron acceptor, S2O82−. Dioxygen is formed rapidly with an initial turnover frequency of ∼8 × 10−2 s−1 and an estimated quantum yield (defined as the number of O2 molecules formed per two photons absorbed) of ∼9%.
Co-reporter:Yurii V. Geletii ; Claire Besson ; Yu Hou ; Qiushi Yin ; Djamaladdin G. Musaev ; David Quiñonero ; Rui Cao ; Kenneth I. Hardcastle ; Anna Proust ; Paul Kögerler
Journal of the American Chemical Society 2009 Volume 131(Issue 47) pp:17360-17370
Publication Date(Web):November 6, 2009
DOI:10.1021/ja907277b
Several key properties of the water oxidation catalyst Rb8K2[{RuIV4O4(OH)2(H2O)4}(γ-SiW10O36)2] and its mechanism of water oxidation are given. The one-electron oxidized analogue [{RuVRuIV3O6(OH2)4}(γ-SiW10O36)2]11− has been prepared and thoroughly characterized. The voltammetric rest potentials, X-ray structures, elemental analysis, magnetism, and requirement of an oxidant (O2) indicate these two complexes contain [RuIV4O6] and [RuVRuIV3O6] cores, respectively. Voltammetry and potentiometric titrations establish the potentials of several couples of the catalyst in aqueous solution, and a speciation diagram (versus electrochemical potential) is calculated. The potentials depend on the nature and concentration of counterions. The catalyst exhibits four reversible couples spanning only ca. 0.5 V in the H2O/O2 potential region, keys to efficient water oxidation at low overpotential and consistent with DFT calculations showing very small energy differences between all adjacent frontier orbitals. The voltammetric potentials of the catalyst are evenly spaced (a Coulomb staircase), more consistent with bulk-like properties than molecular ones. Catalysis of water oxidation by [Ru(bpy)3]3+ has been examined in detail. There is a hyperbolic dependence of O2 yield on catalyst concentration in accord with competing water and ligand (bpy) oxidations. O2 yields, turnover numbers, and extensive kinetics data reveal several features and lead to a mechanism involving rapid oxidation of the catalyst in four one-electron steps followed by rate-limiting H2O oxidation/O2 evolution. Six spectroscopic, scattering, and chemical experiments indicate that the catalyst is stable in solution and under catalytic turnover conditions. However, it decomposes slowly in acidic aqueous solutions (pH < 1.5).
Co-reporter:Rui Cao, Huiyuan Ma, Yurii V. Geletii, Kenneth I. Hardcastle and Craig L. Hill
Inorganic Chemistry 2009 Volume 48(Issue 13) pp:5596-5598
Publication Date(Web):May 26, 2009
DOI:10.1021/ic900538g
The first structurally characterized iridium-substituted polyoxometalate, K14[(IrCl4)KP2W20O72]·23H2O [1; orthorhombic Pnnm, with a = 18.6546(7) Å, b = 19.5192(6) Å, c = 14.8670(5) Å, V = 5413.4(3) Å3, and Z = 2, final R = 0.0730], is reported. Elemental analysis, X-ray crystallography, and NMR all indicate one Ir atom in each molecule, while IR and electronic absorption spectroscopy, thermal gravimetric analysis, and electrochemistry all indicate its purity in both solid and solution states. Complex 1 is a molecular model of iridium supported on redox-active metal oxides, and aqueous solutions of 1 catalyze oxidation of water to O2.
Co-reporter:Zhen Luo ; Paul Kögerler ; Rui Cao
Inorganic Chemistry 2009 Volume 48(Issue 16) pp:7812-7817
Publication Date(Web):July 17, 2009
DOI:10.1021/ic9007729
A series of tetrabutylammonium salts of transition-metal substituted Wells−Dawson polyoxometalates has been synthesized by phase-transfer techniques and characterized by infrared spectroscopy, elemental analysis, and variable-temperature magnetic measurements. X-ray-quality crystals were obtained with a diffusion method using different organic solvents. The X-ray crystal structure of [(n-C4H9)4N]11H5[Cu4(P2W15O56)2] (1) (monoclinic, P2(1)/n, Z = 2, a = 19.7269(6) Å, b = 17.6602(5) Å, c = 44.2525(11) Å, β = 91.182(2)°; R1 = 8.35% based on 31 282 independent reflections) reveals the presence of two unusual coordinatively unsaturated Cu(II) centers. In the absence of cocatalysts, 1 does not catalyze the aerobic oxidation of organic substrates in organic solvents.
Co-reporter:Zhen Luo, Paul Kögerler, Rui Cao, Craig L. Hill
Polyhedron 2009 28(2) pp: 215-220
Publication Date(Web):
DOI:10.1016/j.poly.2008.09.031
Co-reporter:Alice Merca, Hartmut Bögge, Marc Schmidtmann, Yunshan Zhou, Erhard T. K. Haupt, M. Khaled Sarker, Craig L. Hill and Achim Müller
Chemical Communications 2008 (Issue 8) pp:948-950
Publication Date(Web):25 Jan 2008
DOI:10.1039/B718260K
The unique molybdenum oxide-based nucleophilic porous capsule/artificial cell [{(MoVI)MoVI5O21(H2O)6}12{MoV2O4(SO4)30}]72−, according to an X-ray crystallographic study, traps [Al(H2O)6]3+ complexes above the pores while interacting with the latter viahydrogen bonds; this is supported by 27Al NMR studies of the interaction of the capsule with hydrated Al3+ cations in aqueous solution.
Co-reporter:Zhen Luo, Paul Kögerler, Rui Cao, Imroz Hakim and Craig L. Hill
Dalton Transactions 2008 (Issue 1) pp:54-58
Publication Date(Web):17 Oct 2007
DOI:10.1039/B711584A
A new structurally distinct dimeric silicotungstate K9Na2Cu0.5[γ-Cu2(H2O)SiW8O31]2·38H2O (1) has been synthesized and characterized by infrared spectroscopy, elemental analysis, and variable-temperature magnetic measurements. Blue needle-like crystals of 1 were obtained by reaction of K8[γ-SiW10O36] with 2 equivalents of Cu(II) in a 0.5 M sodium acetate solution (pH 4.2) and subsequent addition of an equal volume of ethylene glycol. The structure of 1 was determined by single-crystal X-ray diffraction: final R1 = 3.41% based on 9709 independent reflections. The structure consists of two [γ-Cu2(H2O)SiW8O31]6− Keggin-like units with the [Cu2O(H2O)(μ3-O)(μ2-O)] moiety of one unit bonded to the top of a [W2O6] moiety of the other unit. Magnetic susceptibility measurements indicate competing ferro- and antiferromagnetic intramolecular coupling between the four S = 1/2 Cu(II) centers in the cluster anion.
Co-reporter:YuriiV. Geletii Dr.;Bogdan Botar Dr.;Paul Kögerler Dr.;DanielA. Hillesheim;DjamaladdinG. Musaev Dir.Dr.;CraigL. Hill Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 21) pp:3896-3899
Publication Date(Web):
DOI:10.1002/anie.200705652
Co-reporter:Rui Cao Dr.;TravisM. Anderson Dr.;DanielA. Hillesheim;Paul Kögerler Dr.;KennethI. Hardcastle Dr.;CraigL. Hill Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 49) pp:9380-9382
Publication Date(Web):
DOI:10.1002/anie.200800919
Co-reporter:Rui Cao Dr.;TravisM. Anderson Dr.;DanielA. Hillesheim;Paul Kögerler Dr.;KennethI. Hardcastle Dr.;CraigL. Hill Dr.
Angewandte Chemie 2008 Volume 120( Issue 49) pp:9520-9522
Publication Date(Web):
DOI:10.1002/ange.200800919
Co-reporter:Xikui Fang Dr.;Craig L. Hill Dr.
Angewandte Chemie International Edition 2007 Volume 46(Issue 21) pp:
Publication Date(Web):19 APR 2007
DOI:10.1002/anie.200700004
Back and forth: The two complexes [{P2W15O54(H2O)2}2Zr]12− and [{P2W15O54(H2O)2}Zr{P2W17O61}]14− exhibit extensive dynamic structural changes induced by completely reversible multiple protonation behavior, comparable to the flexing of a muscle (see picture). The pH titration of the former complex indicates a two-step dissociation of all eight protons, in agreement with the structural and spectroscopic studies.
Co-reporter:Yu Hou;Xikui Fang;Craig L. Hill Dr.
Chemistry - A European Journal 2007 Volume 13(Issue 34) pp:
Publication Date(Web):23 OCT 2007
DOI:10.1002/chem.200701160
A chiral polyoxometalate [Hf(PW11O39)2]10− (1) has been prepared and structurally characterized. It crystallizes in the chiral space group P21212, as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. The absolute configuration of 1 was determined from the Flack parameter by X-ray crystallography. The structure of 1 comprises two lacunary [PW11O39]7− units, each functioning as a tetra-dentate ligand sandwiching an 8-coordinate HfIV centre in a distorted square antiprismatic geometry. Optically active crystals of both enantiomers were spectroscopically distinguishable by means of solid state circular dichroism spectroscopy. This hafnium-substituted polyoxometalate (POM), 1, shows that spontaneous chiral resolution, a rare phenomenon, can be operable in POM systems.
Co-reporter:Xikui Fang Dr.;Craig L. Hill Dr.
Angewandte Chemie 2007 Volume 119(Issue 21) pp:
Publication Date(Web):19 APR 2007
DOI:10.1002/ange.200700004
Vor und zurück: Ausgeprägte dynamische Strukturänderungen werden in den Komplexen [{P2W15O54(H2O)2}2Zr]12− und [{P2W15O54(H2O)2}Zr{P2W17O61}]14− durch vollständig reversible Mehrfachprotonierungen ausgelöst – vergleichbar mit der Anspannung eines Muskels (siehe Bild). Die pH-Titration des ersten Komplexes spricht für eine zweistufige Dissoziation aller acht Protonen, in Einklang mit den Struktur- und spektroskopischen Untersuchungen.
Co-reporter:Jong Woo Han;Kenneth I. Hardcastle
European Journal of Inorganic Chemistry 2006 Volume 2006(Issue 13) pp:
Publication Date(Web):27 APR 2006
DOI:10.1002/ejic.200600096
The redox-active bis(pyridyl)-capped hexavanadate [V6O13{(OCH2)3C(4-CONHC5H4N)}2]2– (1) reacts with divalent first-row transition-metal cations (MnII, CoII, NiII, or ZnII) to yield crystalline linear zwitterionic coordination polymers (1M). The zwitterionic coordination chains are connected to each other by hydrogen bonds to form a 3D network. Microporous channels are formed along the packing axes of the 2D networks. All four compounds exhibit almost identical cell parameters, space group (P) and crystal morphology. The materials have been characterized by X-ray crystallography, 1H and 51V NMR, IR, UV/Vis, elemental analysis, and TGA. All compounds 1M are reversibly reduced by chemical reductants such as phenylhydrazine and NaBH4 in CCl4 in which the hexavanadates are insoluble. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Co-reporter:Bogdan Botar, Paul Kögerler, Achim Müller, Ricardo Garcia-Serres and Craig L. Hill
Chemical Communications 2005 (Issue 45) pp:5621-5623
Publication Date(Web):20 Oct 2005
DOI:10.1039/B512244A
The self-assembly of molybdate building units in the presence of FeII and VIV produces the first mixed-spin heterometal keplerate-type clusters displaying ferrimagnetic interactions.
Co-reporter:Xikui Fang, Travis M. Anderson, Yu Hou and Craig L. Hill
Chemical Communications 2005 (Issue 40) pp:5044-5046
Publication Date(Web):16 Sep 2005
DOI:10.1039/B508468G
Pure enantiomers of a polytungstate cluster [(α-P2W16O59)Zr2(μ3-O)(mal)]218−
(mal = malate) have been obtained and their conversion to meso diastereomers was observed by 31P NMR.
Co-reporter:Bogdan Botar, Yurii V. Geletii, Paul Kögerler, Djamaladdin G. Musaev, Keiji Morokuma, Ira A. Weinstock and Craig L. Hill
Dalton Transactions 2005 (Issue 11) pp:2017-2021
Publication Date(Web):09 May 2005
DOI:10.1039/B503665H
A new monomeric diiron β-Keggin derivative, [(CH3)2NH2]5[β-SiFe2W10O36(OH)2(H2O)Cl]·7H2O (1) with non-adjacent substituted sites has been obtained in good yield by reaction of Fe(III) cations with [γ-SiW10O36]8− in aqueous solution. The use of hydrogen bonding counter-cations produced a disorder-free polyanion. This situation facilitates unequivocal identification of the terminal ligands on Fe atoms and interpretation of the magnetic properties, which are also addressed by DFT calculations. Electrochemical studies establish that 1 can be step-wise reduced by two electrons and then reversibly oxidized.
Co-reporter:Travis M. Anderson;Rui Cao;Wade A. Neiwert;Kenneth I. Hardcastle;Malika Ammam;Bineta Keita;Louis Nadjo
European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 9) pp:
Publication Date(Web):28 APR 2005
DOI:10.1002/ejic.200401061
A structural and electrochemical investigation of dimerization and Baker–Figgis (rotational) isomerization in the tri-ferric-substituted silicotungstates has been undertaken because these phenomena are important in a large number of polyoxometalates. A single-crystal X-ray diffraction analysis of K4Na7[(β-SiFe3W9(OH)3O34)2(OH)3] (β1) has been carried out [a = 12.9709(7) Å, b = 38.720(2) Å, c = 21.4221(12) Å, orthorhombic, Pbcm, R1 = 8.48 %, based on 13809 independent reflections]. The complex is isostructural with [(α-SiFe3W9(OH)3O34)2(OH)3]11– (α1) except that the edge-shared W3O13 caps in each [SiFe3W9(OH)3O34]4– unit are rotated by 60°. Electrochemical measurements, performed in a pH 5 acetate buffer, indicate a positive shift in the FeIII-based peak potential (and no change for the WVI-based potential) upon going from α1 to its monomeric derivative [(α-Si(FeOH2)3W9(OH)3O34)]4– (α2) (–0.484 ± 0.005 V and –0.474 ± 0.005 V, respectively). In contrast, the peak potentials of the FeIII- and WVI-based redox processes of β1 are both found at more negative values than its rotational isomer α1. The absolute values of the reduction peak potential differences are 0.022 V for FeIII and 0.162 V for WVI. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Co-reporter:Xikui Fang;Travis M. Anderson Dr. Dr.
Angewandte Chemie 2005 Volume 117(Issue 23) pp:
Publication Date(Web):20 MAY 2005
DOI:10.1002/ange.200500415
Kleine Gruppe – große Wirkung: Der Chiralitätstransfer von einer kleinen organischen Gruppe (D- oder L-Tartrat) auf ein großes Metalloxid-Netzwerk führt zu den enantiomerenreinen, nicht racemisierenden Polywolframaten d- und L-1 (siehe Bild, der mittlere Teil ist als Polyedermodell dargestellt; Zr purpurrot, W grau, P blau, C schwarz, O rot). Bei dieser neuen Methode zur Steuerung der Chiralität von Polyoxoanionen schreibt die Tartrat-Gruppe der anorganischen Einheit die absolute Konfiguration vor.
Co-reporter:Xikui Fang;Travis M. Anderson Dr. Dr.
Angewandte Chemie International Edition 2005 Volume 44(Issue 23) pp:
Publication Date(Web):20 MAY 2005
DOI:10.1002/anie.200500415
Small but influential: Chirality transfer from a small chiral organic unit (D- or L-tartrate) to a very large metal–oxide framework is demonstrated by the enantiomerically pure, nonracemizing polytungstates d- or L-1 (see picture, the central part is shown in polyhedral form; purple Zr, gray W, blue P, black C, red O). The tartrate unit determines the absolute configuration of the inorganic moiety, offering a new method to control the chirality of polyoxoanions.
Co-reporter:Xikui Fang;Travis M. Anderson Dr.;Cristiano Benelli
Chemistry - A European Journal 2005 Volume 11(Issue 2) pp:
Publication Date(Web):2 DEC 2004
DOI:10.1002/chem.200400774
Carbonate-assisted hydrolysis of Y or YbIII ions in the presence of the trivacant Wells–Dawson polyoxoanion, α-[P2W15O56]12−, produced two polyoxometalate-supported Y– or YbIII–hydroxo/oxo clusters, which have been characterized by single-crystal X-ray structure determination. The structure of the Y complex consists of a distorted Y4(OH)4 cubane cluster encapsulated by two lacunary α-[P2W15O56]12− units, while the Yb cluster features a hexametallic core centered around a μ6-oxo atom with each triangular face capped by an oxo or a hydroxo group. Magnetization measurements of the ytterbium(III) derivative suggested that intermolecular dipolar exchange is present at low temperatures (below 15 K). Despite its absence in the structures themselves, control experiments show that carbonate not only functions in the hydrolysis, it also influences the structure of the complexes by complexation to yttrium and the f-block elements.
Co-reporter:Travis M. Anderson;Wade A. Neiwert;Martin L. Kirk;Paula M. B. Piccoli;Arthur J. Schultz;Thomas F. Koetzle;Djamaladdin G. Musaev;Keiji Morokuma;Rui Cao
Science 2004 Vol 306(5704) pp:2074-2077
Publication Date(Web):17 Dec 2004
DOI:10.1126/science.1104696
Abstract
Terminal mono-oxo complexes of the late transition metal elements have long been considered too unstable to synthesize because of repulsion between the oxygen electrons and the mostly filled metal d orbitals. A platinum(IV)-oxo compound flanked by two polytungstate ligands, K7Na9[O=Pt(H2O)L2], L = [PW9O349–], has now been prepared and isolated at room temperature as air-stable brown crystals. X-ray and neutron diffraction at 30 kelvin revealed a very short [1.720(18) angstrom] Pt–O bond and no evidence of a hydrogen atom at the terminal oxygen, ruling out a better precedented Pt–OH complex. Density functional theory and spectroscopic data account for the stability of the Pt(IV)-oxo unit by electron withdrawal into delocalized orbitals of the polytungstates.
Co-reporter:Israel Martyr Mbomekalle, Bineta Keita, Louis Nadjo, Kenneth I. Hardcastle, Craig L. Hill and Travis M. Anderson
Dalton Transactions 2004 (Issue 24) pp:4094-4095
Publication Date(Web):15 Nov 2004
DOI:10.1039/B414831B
The tri-tungsten-vacant polyoxometalate, [α-AsW15(OH)4O52]13−, derived from the semi-vacant Wells–Dawson complex [α-AsW18(OH)4O58]7−, reacts with the late-transition metal cations, Cu(II) or Zn(II), to form sandwich-type species; the X-ray crystal structure of [αββα-(CuIIOH2)2(CuII)2(AsW15(OH2)3(OH)O52)2]12−, prepared by the acidification of [αββα-(CuIIOH2)2(CuII)2(AsW15(OH)4O52)2]18−, reveals that the missing heteroatoms are distal to the central Cu4 unit and the vertices of the vacant tetrahedron are occupied by one OH− and three OH2 groups.
Co-reporter:Bineta Keita;Israel Martyr Mbomekalle;Yu Wei Lu;Louis Nadjo;Patrick Berthet;Travis M. Anderson;Craig L. Hill
European Journal of Inorganic Chemistry 2004 Volume 2004(Issue 17) pp:
Publication Date(Web):17 JUN 2004
DOI:10.1002/ejic.200400099
The physicochemical and electrocatalytic behaviors of eight multi-iron Wells−Dawson sandwich-type polyoxometalates were studied with specific emphasis on the FeIII centers. Magnetization measurements were used to identify and quantify the antiferromagnetic interactions between the edge-sharing FeIII units. Electrochemical studies show the stepwise reduction of the FeIII centers, in complete agreement with magnetization conclusions. The location of the potential of each wave depends on the pH of the solution, as well as the concentration and composition of the electrolyte. In addition, ion-pairing studies show there is a positive shift of the FeIII centers with an increase in ion pairing (i.e. K+ > Na+ > Li+). The electrocatalytic reduction of dioxygen and hydrogen peroxide is efficient for all the complexes. However, there is a pronounced increase in efficiency as the number of FeIII centers in the complex increases (i.e. 4 FeIII > 3 FeIII > 2 FeIII). The mixed-metal complexes [αββα-Na14(MnIIOH2)2(FeIII)2(As2W15O56)2 and αββα-Na14(MnIIOH2)2(FeIII)2(P2W15O56)2] are also efficient catalysts for the reduction of NO and HNO2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Co-reporter:Craig L. Hill Dr.
Angewandte Chemie 2004 Volume 116(Issue 4) pp:
Publication Date(Web):14 JAN 2004
DOI:10.1002/ange.200301701
Weniger anfällige Katalysatoren für Oxidationen werden durch Selbstorganisation stabiler Vorstufen unter Katalysebedingungen erhalten. Der beschriebene Polyoxometallat(POM)-Epoxidierungs-Katalysator ist schnell, selektiv und sicher – und das unter umweltfreundlichen Bedingungen. Das selbstorganisierende System ist ein wichtiger Schritt in Richtung grüner Katalyse (siehe Schema).
Co-reporter:Craig L. Hill Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 4) pp:
Publication Date(Web):14 JAN 2004
DOI:10.1002/anie.200301701
Increased stability of oxidation catalysts results from the self-assembly of the catalysts under near-turnover conditions from oxidatively resistant precursors. The described polyoxometalate epoxidation catalyst uses a green oxidant (H2O2), solvent, and separation conditions and is fast, selective, and safe. This self-assembling system is an important step towards truly green catalysis (see scheme).
Co-reporter:Waldemar Adam;Marike Herold;Craig L. Hill;Chantu R. Saha-Möller
European Journal of Organic Chemistry 2002 Volume 2002(Issue 5) pp:
Publication Date(Web):12 FEB 2002
DOI:10.1002/1099-0690(200203)2002:5<941::AID-EJOC941>3.0.CO;2-A
2-Cyclohexenol (1) is oxidized chemoselectively to 2-cyclohexenone (2a) by the α-Keggin chromium-substituted polyoxometalate (POM) Ia as the catalyst and iodosobenzene as the oxygen source. For the chromium(salen) catalyst IIa the same chemoselectivity in favor of allylic CH oxidation is observed. The manganese-substituted POM Ib and the manganese(salen) complex IIb, however, afford appreciable amounts of the epoxy alcohol 2b. For the stereolabeled 5-tert-butyl-2-cyclohexenols 5, the diastereoselectivity of the epoxidation was appreciable (syn:anti 82:18) in the case of the manganese(salen) complex IIb with the cis isomer, while the manganese-substituted POM Ib exhibited no syn versus anti π-facial differentiation for the cis or trans diastereomer of the cyclohexenol 5. The observed syn hydroxy directivity for the manganese(salen) complex IIb is rationalized in terms of optimal hydrogen bonding between the MnV oxo complex IIb and the trans diastereomer of the allylic alcohol substrate 5. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
Co-reporter:Yurii V. Geletti, Alan J. Bailey, Eric A. Boring and Craig L. Hill
Chemical Communications 2001 (Issue 16) pp:1484-1485
Publication Date(Web):26 Jul 2001
DOI:10.1039/B104159M
The simple salt CuCl2·2H2O, and the new Cu-substituted polyoxometalate (POM), Na7[CuCoW11O39]·5H2O 1 are highly efficient catalysts for the oxidation of ascorbic acid by peroxynitrite.
Co-reporter:Ira A. Weinstock,
Elena M.G. Barbuzzi,
Michael W. Wemple,
Jennifer J. Cowan,
Richard S. Reiner,
Dan M. Sonnen,
Robert A. Heintz,
James S. Bond
and
Craig L. Hill
Nature 2001 414(6860) pp:191
Publication Date(Web):
DOI:10.1038/35102545
Although many enzymes can readily and selectively use oxygen in water—the most familiar and attractive of all oxidants and solvents, respectively—the design of synthetic catalysts for selective water-based oxidation processes utilizing molecular oxygen1, 2, 3, 4 remains a daunting task5, 6. Particularly problematic is the fact that oxidation of substrates by O2 involves radical chemistry, which is intrinsically non-selective and difficult to control. In addition, metallo-organic catalysts are inherently susceptible to degradation5 by oxygen-based radicals, while their transition-metal-ion active sites often react with water to give insoluble, and thus inactive, oxides or hydroxides7. Furthermore, pH control is often required to avoid acid or base degradation of organic substrates or products. Unlike metallo-organic catalysts, polyoxometalate anions are oxidatively stable and are reversible oxidants8, 9 for use with O2 (refs 8,9,10). Here we show how thermodynamically controlled self-assembly of an equilibrated ensemble of polyoxometalates, with the heteropolytungstate anion11, 12 [AIVVW11O40]6- as its main component, imparts both stability in water and internal pH-management. Designed to operate at near-neutral pH, this system facilitates a two-step O2-based process for the selective delignification of wood (lignocellulose) fibres. By directly monitoring the central Al atom, we show that equilibration reactions typical of polyoxometalate anions13, 14 keep the pH of the system near 7 during both process steps.
Co-reporter:Huadong Zeng;George R. Newkome Dr.;Craig L. Hill Dr.
Angewandte Chemie 2000 Volume 112(Issue 10) pp:
Publication Date(Web):15 MAY 2000
DOI:10.1002/(SICI)1521-3757(20000515)112:10<1841::AID-ANGE1841>3.0.CO;2-F
Co-reporter:Rhoma P. Johnson
Journal of Applied Toxicology 1999 Volume 19(Issue Supplement 1) pp:S71-S75
Publication Date(Web):21 DEC 1999
DOI:10.1002/(SICI)1099-1263(199912)19:1+3.0.CO;2-#
The aim of this research is to determine if appropriate polyoxometalates (POMs) could be added to perfluoropolyether topical skin protectants (TSPs) currently available or under development to give these TSPs the additional capability of detecting and in some cases catalytically decontaminating sulfur mustard (HD) and perhaps other chemical warfare agents (CWAs) at ambient temperatures. Detection would be based on significant color changes in the POM upon reduction by the CWA whereas catalytic decontamination would be based on the ability of some families of POMs to catalyze O2-based oxidations by more than one mechanism. Five POMs (10–25% by weight) were each suspended in ca. 5 g of the perfluoropolyether (PFPE, CF3O[-CF(CF3)CF2O-]x(-CF2O-)yCF3) ‘barrier’ cream. A stoichiometric amount of HD sulfide simulant was layered on top of each POM–cream mixture. The short reaction times were recorded for each system. Mechanistic studies were conducted using an PFPE oil analog of the barrier cream in a microemulsion with the sulfide simulant, POM, PFPE surfactant and 2,2,2-trifluoroethanol co-surfactant. Copyright © 1999 John Wiley & Sons, Ltd.
Co-reporter:Gyu-Shik Kim;Huadong Zeng;Don VanDerveer;Craig L. Hill
Angewandte Chemie 1999 Volume 111(Issue 21) pp:
Publication Date(Web):26 OCT 1999
DOI:10.1002/(SICI)1521-3757(19991102)111:21<3413::AID-ANGE3413>3.0.CO;2-O
Riesenpolyoxometallate mit katalytischen, magnetischen und antiviralen Eigenschaften, die zumindest teilweise auf ihre Strukturen zurückzuführen sind, sind derzeit von großem Interesse. Hier wird die Synthese und Charakterisierung von 1 beschrieben, einem strukturell neuartigen tetrameren Komplex aus Keggin-Ionen (siehe Bild). Dieser Komplex ist im Magenmilieu (pH 1–2) stabil, was insofern interessant ist, als verwandte Keggin-Anionen zu den am stärksten antiviral wirksamen und dabei am wenigsten toxischen der mehr als 300 bisher biologisch und pharmakologisch untersuchten Polyoxometallate gehören.
Co-reporter:Gyu-Shik Kim;Huadong Zeng;Don VanDerveer
Angewandte Chemie International Edition 1999 Volume 38(Issue 21) pp:
Publication Date(Web):26 OCT 1999
DOI:10.1002/(SICI)1521-3773(19991102)38:21<3205::AID-ANIE3205>3.0.CO;2-U
Giant polyoxometalates with catalytic, magnetic, and antiviral properties, which are in part attributable to their structures, are currently of great interest. Herein is described the synthesis and characterization of 1, a structurally novel tetrameric complex from Keggin ions (see picture). This complex is stable under the physiological conditions of the stomach (pH 1–2), which is interesting since related keggin anions are among the least toxic and yet most potent antiviral agents of the more than 300 polyoxometalates investigated biologically and pharmacologically.
Co-reporter:Hongjin Lv, Jie Song, Haiming Zhu, Yurii V. Geletii, John Bacsa, Chongchao Zhao, Tianquan Lian, Djamaladdin G. Musaev, Craig L. Hill
Journal of Catalysis (November 2013) Volume 307() pp:48-54
Publication Date(Web):1 November 2013
DOI:10.1016/j.jcat.2013.06.028
•A water-compatible, homogeneous polyoxometalate water reduction catalyst is reported.•This POM catalyst can oxidatively quench the excited state [Ru(bpy)3]2+∗.•The reduced form of the catalyst reacts with water to generate hydrogen.•Isotope labeling experiments demonstrate that the hydrogen comes from water.•The stability of the catalyst is assessed using multiple spectroscopic methods.In an effort to address the need to develop hydrolytically more stable, molecular water reduction catalysts (WRCs) amenable to in-depth investigation, we report here one prototype: a tetra-manganese-containing V-centered polyoxotungstate, Na10[Mn4(H2O)2(VW9O34)2] (1). The electronic structure of 1 was elucidated using the DFT approach. Complex 1 is readily prepared by a one-pot procedure in aqueous solution and catalyzes the reduction of water using visible light irradiation (λ = 455 nm) with [Ru(bpy)3]2+ and triethanolamine (TEOA) as a photosensitizer and sacrificial electron donor, respectively. Upon irradiation, the excited state [Ru(bpy)3]2+* is oxidatively quenched by 1, as confirmed by steady-state and time-resolved fluorescence decay studies, to form [Ru(bpy)3]3+ and a reduced form of the catalyst. The [Ru(bpy)3]2+ is rapidly regenerated by reaction with TEOA. The reduced form of the catalyst, 1, reacts with water to generate hydrogen. Isotope labeling experiments demonstrate that the hydrogen comes from water. The stability of the catalyst was assessed using different spectroscopic methods. A mechanism based on experimental results is proposed.Download high-res image (114KB)Download full-size image
Co-reporter:Hongjin Lv ; Weiwei Guo ; Kaifeng Wu ; Zheyuan Chen ; John Bacsa ; Djamaladdin G. Musaev ; Yurii V. Geletii ; Sarah M. Lauinger ; Tianquan Lian
Journal of the American Chemical Society () pp:
Publication Date(Web):September 22, 2014
DOI:10.1021/ja5084078
A tetra-nickel-containing polyoxotungstate, Na6K4[Ni4(H2O)2(PW9O34)2]·32H2O (Na6K4-Ni4P2), has been synthesized in high yield and systematically characterized. The X-ray crystal structure confirms that a tetra-nickel cluster core [Ni4O14] is sandwiched by two trivacant, heptadentate [PW9O34]9– POM ligands. When coupled with (4,4′-di-tert-butyl-2,2′-dipyridyl)-bis(2-phenylpyridine(1H))-iridium(III) hexafluorophosphate [Ir(ppy)2(dtbbpy)][PF6] as photosensitizer and triethanolamine (TEOA) as sacrificial electron donor, the noble-metal-free complex Ni4P2 works as an efficient and robust molecular catalyst for H2 production upon visible light irradiation. Under minimally optimized conditions, Ni4P2 catalyzes H2 production over 1 week and achieves a turnover number (TON) of as high as 6500 with almost no loss in activity. Mechanistic studies (emission quenching, time-resolved fluorescence decay, and transient absorption spectroscopy) confirm that, under visible light irradiation, the excited state [Ir(ppy)2(dtbbpy)]+* can be both oxidatively and reductively quenched by Ni4P2 and TEOA, respectively. Extensive stability studies (e.g., UV–vis absorption, FT-IR, mercury-poison test, dynamic light scattering (DLS) and transmission electron microscopy (TEM)) provide very strong evidence that Ni4P2 catalyst remains homogeneous and intact under turnover conditions.
Co-reporter:Hongjin Lv, Yurii V. Geletii, Chongchao Zhao, James W. Vickers, Guibo Zhu, Zhen Luo, Jie Song, Tianquan Lian, Djamaladdin G. Musaev and Craig L. Hill
Chemical Society Reviews 2012 - vol. 41(Issue 22) pp:NaN7589-7589
Publication Date(Web):2012/09/12
DOI:10.1039/C2CS35292C
In the last five years and currently, research on solar fuels has been intense and no sub-area in this field has been more active than the development of water oxidation catalysts (WOCs). In this timeframe, a new class of molecular water oxidation catalysts based on polyoxometalates have been reported that combine the advantages of homogeneous and heterogeneous catalysts. This review addresses central issues in green energy generation, the challenges in water oxidation catalyst development, and the possible uses of polyoxometalates in green energy science.
Co-reporter:Claire Besson, Zhuangqun Huang, Yurii V. Geletii, Sheri Lense, Kenneth I. Hardcastle, Djamaladdin G. Musaev, Tianquan Lian, Anna Proust and Craig L. Hill
Chemical Communications 2010 - vol. 46(Issue 16) pp:NaN2786-2786
Publication Date(Web):2010/02/25
DOI:10.1039/B926064A
The tetraruthenium-substituted polyoxometalate Cs9[(γ-PW10O36)2Ru4O5(OH)(H2O)4] was synthesized and structurally, spectroscopically and electrochemically characterized; it was shown to be a catalyst for visible-light-induced water oxidation.
Co-reporter:Alice Merca, Hartmut Bögge, Marc Schmidtmann, Yunshan Zhou, Erhard T. K. Haupt, M. Khaled Sarker, Craig L. Hill and Achim Müller
Chemical Communications 2008(Issue 8) pp:NaN950-950
Publication Date(Web):2008/01/25
DOI:10.1039/B718260K
The unique molybdenum oxide-based nucleophilic porous capsule/artificial cell [{(MoVI)MoVI5O21(H2O)6}12{MoV2O4(SO4)30}]72−, according to an X-ray crystallographic study, traps [Al(H2O)6]3+ complexes above the pores while interacting with the latter viahydrogen bonds; this is supported by 27Al NMR studies of the interaction of the capsule with hydrated Al3+ cations in aqueous solution.
Co-reporter:Chongchao Zhao, Elliot N. Glass, Jordan M. Sumliner, John Bacsa, Daniel Taehyun Kim, Weiwei Guo and Craig L. Hill
Dalton Transactions 2014 - vol. 43(Issue 10) pp:NaN4047-4047
Publication Date(Web):2014/01/15
DOI:10.1039/C3DT53374C
Several polyoxometalate-supported metal carbonyl complexes, K7Na3P2W23O80{Re(CO)3}2·38H2O (1), (C3H10N)8Na2P2W23O80{Re(CO)3}2·10H2O (1a) and (C3H10N)6KNa3P2W23O80{Mn(CO)3}2·7H2O (2), have been prepared from the dimerization of the monovacant Keggin [α-PW11O39]7− with metal carbonyl complexes [M(CO)3]+ (M = Re, Mn) in acidic aqueous solutions. The resulting “twisted-sandwich” architectures are chiral, but their crystalline solids are racemic. A detailed investigation involving syntheses, crystal structures, and electrochemistry is presented.
Co-reporter:Guibo Zhu, Elliot N. Glass, Chongchao Zhao, Hongjin Lv, James W. Vickers, Yurii V. Geletii, Djamaladdin G. Musaev, Jie Song and Craig L. Hill
Dalton Transactions 2012 - vol. 41(Issue 42) pp:NaN13049-13049
Publication Date(Web):2012/07/17
DOI:10.1039/C2DT30331K
A new pentanickel silicotungstate complex, K10H2[Ni5(OH)6(OH2)3(Si2W18O66)]·34H2O (KH-1), has been synthesized and characterized by X-ray crystallography and several other methods. Dynamic light scattering, kinetics and other experiments confirm that 1 in the presence of [Ru(bpy)3]2+ (the photosensitizer for light-driven water oxidations) and [Ru(bpy)3]3+ (the oxidant in the dark water oxidations) exists in an equilibrium between solution (soluble) and a [Ru(bpy)3]n+-1 complex (minimally soluble) form. This new pentanickel polyoxometalate catalyzes efficient water oxidation in both the dark and on irradiation with 455 nm LED light with 1.0 mM [Ru(bpy)3]2+ photosensitizer and 5.0 mM Na2S2O8, sacrificial electron acceptor. Four lines of evidence indicate that 1 in this solution ⇌ Ru(bpy)3]n+-1 complex equilibrium remains molecular and does not decompose to nickel hydroxide particles.
Co-reporter:Weiwei Guo, Hongjin Lv, Zheyuan Chen, Kevin P. Sullivan, Sarah M. Lauinger, Yingnan Chi, Jordan M. Sumliner, Tianquan Lian and Craig L. Hill
Journal of Materials Chemistry A 2016 - vol. 4(Issue 16) pp:NaN5957-5957
Publication Date(Web):2016/03/08
DOI:10.1039/C6TA00011H
A polyoxometalate (POM), Pt nanoparticles (NPs) and a metal–organic framework (MOF, NH2-MIL-53) self-assemble into a hybrid material, PNPMOF, that displays synergistic activity for visible-light-driven catalytic hydrogen evolution (the PNPMOF is far more active than any of the three functional components alone). The POM has four targeted functions in this hybrid material: it reduces H2PtCl6 to Pt NPs, stabilizes the Pt NPs, induces a strong electrostatic association of the negatively charged Pt NPs with the protonated NH2-MIL-53 sites on the particle surfaces, and facilitates the catalytic reduction reaction itself. The NH2-MIL-53 in this work protects the light sensitive 2-aminoterephthalate groups in the pores from oxidation by the POMs, while the surface protonated NH2 units on the MOF particle surfaces strongly bind the negatively charged POM-stabilized Pt NPs.
Co-reporter:Zhen Luo, Paul Kögerler, Rui Cao, Imroz Hakim and Craig L. Hill
Dalton Transactions 2008(Issue 1) pp:NaN58-58
Publication Date(Web):2007/10/17
DOI:10.1039/B711584A
A new structurally distinct dimeric silicotungstate K9Na2Cu0.5[γ-Cu2(H2O)SiW8O31]2·38H2O (1) has been synthesized and characterized by infrared spectroscopy, elemental analysis, and variable-temperature magnetic measurements. Blue needle-like crystals of 1 were obtained by reaction of K8[γ-SiW10O36] with 2 equivalents of Cu(II) in a 0.5 M sodium acetate solution (pH 4.2) and subsequent addition of an equal volume of ethylene glycol. The structure of 1 was determined by single-crystal X-ray diffraction: final R1 = 3.41% based on 9709 independent reflections. The structure consists of two [γ-Cu2(H2O)SiW8O31]6− Keggin-like units with the [Cu2O(H2O)(μ3-O)(μ2-O)] moiety of one unit bonded to the top of a [W2O6] moiety of the other unit. Magnetic susceptibility measurements indicate competing ferro- and antiferromagnetic intramolecular coupling between the four S = 1/2 Cu(II) centers in the cluster anion.
Co-reporter:Guibo Zhu, Yurii V. Geletii, Chongchao Zhao, Djamaladdin G. Musaev, Jie Song and Craig L. Hill
Dalton Transactions 2012 - vol. 41(Issue 33) pp:NaN9913-9913
Publication Date(Web):2012/07/23
DOI:10.1039/C2DT30733B
A dodecazinc silicotungstate K20Na2[Zn6(OH)7(H2O)(Si2W18O66)]2·34H2O (1) has been synthesized and characterized by X-ray crystallography, elemental analysis, infrared, UV-vis spectroscopy, cyclic voltammetry, acid–base titration, and DFT calculations. The twelve zinc atoms between the two [Si2W18O66]16− frameworks make this complex more stable hydrolytically than the heteropolytungstate ligands, [Si2W18O66]16−, themselves. The structurally unique central Zn12 core is formed by the fusion of two [Zn6(OH)7(H2O)]5+ units through two edge-sharing Zn6 atoms. DFT B3LYP calculations give HOMO–LUMO and (HOMO − 1)–LUMO energy gaps of ∼3.65 and 3.91 eV, respectively, as compared to the band gap in ZnO of 3.35 eV.
Co-reporter:James W. Vickers, Jordan M. Sumliner, Hongjin Lv, Mike Morris, Yurii V. Geletii and Craig L. Hill
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 24) pp:
Publication Date(Web):
DOI:10.1039/C3CP55406F
Co-reporter:John Fielden, Jordan M. Sumliner, Nannan Han, Yurii V. Geletii, Xu Xiang, Djamaladdin G. Musaev, Tianquan Lian and Craig L. Hill
Chemical Science (2010-Present) 2015 - vol. 6(Issue 10) pp:NaN5543-5543
Publication Date(Web):2015/06/11
DOI:10.1039/C5SC01439E
Visible light driven water oxidation has been demonstrated at near-neutral pH using photoanodes based on nanoporous films of TiO2, polyoxometalate (POM) water oxidation catalyst [{Ru4O4(OH)2(H2O)4}(γ-SiW10O36)2]10− (1), and both known photosensitizer [Ru(bpy)2(H4dpbpy)]2+ (P2) and the novel crown ether functionalized dye [Ru(5-crownphen)2(H2dpbpy)](H22). Both triads, containing catalyst 1, and catalyst-free dyads, produce O2 with high faradaic efficiencies (80 to 94%), but presence of catalyst enhances quantum yield by up to 190% (maximum 0.39%). New sensitizer H22 absorbs light more strongly than P2, and increases O2 quantum yields by up to 270%. TiO2-2 based photoelectrodes are also more stable to desorption of active species than TiO2–P2: losses of catalyst 1 are halved when pH > TiO2 point-of-zero charge (pzc), and losses of sensitizer reduced below the pzc (no catalyst is lost when pH < pzc). For the triads, quantum yields of O2 are higher at pH 5.8 than at pH 7.2, opposing the trend observed for 1 under homogeneous conditions. This is ascribed to lower stability of the dye oxidized states at higher pH, and less efficient electron transfer to TiO2, and is also consistent with the 4th1-to-dye electron transfer limiting performance rather than catalyst TOFmax. Transient absorption reveals that TiO2–2–1 has similar 1st electron transfer dynamics to TiO2–P2–1, with rapid (ps timescale) formation of long-lived TiO2(e−)–2–1(h+) charge separated states, and demonstrates that metallation of the crown ether groups (Na+/Mg2+) has little or no effect on electron transfer from 1 to 2. The most widely relevant findings of this study are therefore: (i) increased dye extinction coefficients and binding stability significantly improve performance in dye-sensitized water splitting systems; (ii) binding of POMs to electrode surfaces can be stabilized through use of recognition groups; (iii) the optimal homogeneous and TiO2-bound operating pHs of a catalyst may not be the same; and (iv) dye-sensitized TiO2 can oxidize water without a catalyst.
![Tungstate(3-),tetracosa-m-oxododecaoxo[m12-[phosphato(3-)-kO:kO:kO:kO':kO':kO':kO'':kO'':kO'':kO''':kO''':kO''']]dodeca-,hydrogen (1:3)](http://img.cochemist.com/ccimg/1400/1343-93-7.png)
![Tungstate(3-),tetracosa-m-oxododecaoxo[m12-[phosphato(3-)-kO:kO:kO:kO':kO':kO':kO'':kO'':kO'':kO''':kO''':kO''']]dodeca-,hydrogen (1:3)](http://img.cochemist.com/ccimg/1400/1343-93-7_b.png)
![[(sulfonatoperoxy)sulfonyl]oxidanide](http://img.cochemist.com/ccimg/15100/15092-81-6.png)
![[(sulfonatoperoxy)sulfonyl]oxidanide](http://img.cochemist.com/ccimg/15100/15092-81-6_b.png)
![Tungstate(10-), [m9-[orthosilicato(4-)-kO:kO:kO:kO':kO':kO'':kO'':kO''':kO''']]pentadeca-m-oxopentadecaoxonona-, sodium (1:10)](http://img.cochemist.com/ccimg/64700/64684-57-7.png)
![Tungstate(10-), [m9-[orthosilicato(4-)-kO:kO:kO:kO':kO':kO'':kO'':kO''':kO''']]pentadeca-m-oxopentadecaoxonona-, sodium (1:10)](http://img.cochemist.com/ccimg/64700/64684-57-7_b.png)
