Water-soluble copper(II) complexes of the dianionic tridentate pincer ligand N,N′-2,6-dimethylphenyl-2,6-pyridinedicarboxamidate (L) are catalysts for water oxidation. In [L-CuII-DMF] (1, DMF = dimethylformamide) and [L-CuII-OAc]− (2, OAc = acetate), ligand L binds CuII through three N atoms, which define an equatorial plane. The fourth coordination site of the equatorial plane is occupied by DMF in 1 and by OAc– in 2. These two complexes can electrocatalyze water oxidation to evolve O2 in 0.1 M pH 10 carbonate buffer. Spectroscopic, titration, and crystallographic studies show that both 1 and 2 undergo ligand exchange when they are dissolved in carbonate buffer to give [L-CuII-CO3H]− (3). Complex 3 has a similar structure as those of 1 and 2 except for having a carbonate group at the fourth equatorial position. A catalytic cycle for water oxidation by 3 is proposed based on experimental and theoretical results. The two-electron oxidized form of 3 is the catalytically active species for water oxidation. Importantly, for these two oxidation events, the calculated potential values of Ep,a = 1.01 and 1.59 V vs normal hydrogen electrode (NHE) agree well with the experimental values of Ep,a = 0.93 and 1.51 V vs NHE in pH 10 carbonate buffer. The potential difference between the two oxidation events is 0.58 V for both experimental and calculated results. With computational evidence, this Cu-bound carbonate group may act as a proton shuttle to remove protons for water activation, a key role resembling intramolecular bases as reported previously.

Aligned cobalt metal nanoparticles were prepared from the pyrolysis of cobalt oxalate nanoplate precursors for efficient electrocatalytic water oxidation. The 2D morphology of the precursor guided the 2D alignment of the derived cobalt metal nanoparticles. The as-prepared Co@CoOx electrocatalyst requires an ultra-low overpotential of 289 mV to achieve a current density of 10 mA cm−2 on a simple glassy carbon (GC) electrode in a 1 M KOH aqueous solution. The metallic nature of the bulk of the electrocatalyst and the compact alignment of the nanoparticles can facilitate the inner- and inter-particulate charge transfers.

NiFe film for oxygen evolution reaction (OER): An ultrathin NiFe-hydroxide film is generated by stepwise electrodeposition with a significantly improved catalytic OER activity, as compared to NiFe films obtained by using traditional methods. The turnover frequency of 8.7 s−1 at an overpotential of 329 mV is extraordinary and represents the highest value among heterogeneous OER catalysts.

Cobalt corroles with different acid/base pendants, LBr–Co, LCOOH–Co, LPO(OH)2–Co, and LCH2PO(OH)2–Co (L = 5,15-bis-(pentafluorophenyl)-10-(4-dibenzofuran)corrole), were synthesized and examined as catalysts for oxygen and hydrogen evolution from neutral aqueous solutions. Co corroles with phosphonic acid pendants showed improved activities in both processes, highlighting the importance of the secondary coordination sphere in catalyst design.

A water-soluble binuclear CuII complex, synthesized using a polypyridine–polyamide ligand, was able to catalyze oxygen reduction to water from neutral aqueous solutions. Electrocatalytic results suggested that one CuII center was first reduced by one electron to form a CuIICuI species, which reacted with O2 to give a superoxide radical intermediate.

A series of cobalt complexes of 5,10,15-tris(pentafluorophenyl)-corrole [Co(tpfc)] (1) with various axial ligands were synthesized and examined as single-site catalysts for water oxidation. The used axial ligands include 4-cyanopyridine (py-CN), pyridine (py), 4-(dimethylamino)pyridine (py-NMe2), 4-methoxypyridine (py-OMe), 1-methylimidazole (im-Me), and thiophenolate (thi). Complexes 1–py and 1–py-OMe were structurally characterized. The Co ion in both structures has an almost identical distorted octahedral coordination environment with the four N atoms of tpfc defining the equatorial plane and the two molecules of pyridine (for 1–py) or 4-methoxypyridine (for 1–py-OMe) occupying the axial positions. Electrochemical studies of these Co corroles in acetonitrile showed that they all display two oxidation events and the oxidation waves shift to the cathodic direction with electron-donating axial ligands, a trend that is consistent with increased electron densities on Co ions. All these Co corroles were found to be active for electrocatalytic water oxidation: by using catalyst-coated fluorine-doped tin oxide (FTO) working electrodes, cyclic voltammograms displayed pronounced catalytic waves for water oxidation in 0.1 M pH 7.0 phosphate buffer solutions. The onset overpotentials are in the range of 510 to 580 mV, depending on the electron-donating ability of the trans axial ligands. These results demonstrate that the catalytic activities of Co corroles for water oxidation are considerably affected by the trans axial ligands on Co centers and provide valuable insights into the design of new catalysts for water oxidation.

Globally increasing energy demands and environmental concerns related to the use of fossil fuels have stimulated extensive research to identify new energy systems and economies that are sustainable, clean, low cost, and environmentally benign. Hydrogen generation from solar-driven water splitting is a promising strategy to store solar energy in chemical bonds. The subsequent combustion of hydrogen in fuel cells produces electric energy, and the only exhaust is water. These two reactions compose an ideal process to provide clean and sustainable energy. In such a process, a hydrogen evolution reaction (HER), an oxygen evolution reaction (OER) during water splitting, and an oxygen reduction reaction (ORR) as a fuel cell cathodic reaction are key steps that affect the efficiency of the overall energy conversion. Catalysts play key roles in this process by improving the kinetics of these reactions. Porphyrin-based and corrole-based systems are versatile and can efficiently catalyze the ORR, OER, and HER. Because of the significance of energy-related small molecule activation, this review covers recent progress in hydrogen evolution, oxygen evolution, and oxygen reduction reactions catalyzed by porphyrins and corroles.

The development of new materials/structures for efficient electrocatalytic water oxidation, which is a key reaction in realizing artificial photosynthesis, is an ongoing challenge. Herein, a Co(OH)F material as a new electrocatalyst for the oxygen evolution reaction (OER) is reported. The as-prepared 3D Co(OH)F microspheres are built by 2D nanoflake building blocks, which are further woven by 1D nanorod foundations. Weaving and building the substructures (1D nanorods and 2D nanoflakes) provides high structural void porosity with sufficient interior space in the resulting 3D material. The hierarchical structure of this Co(OH)F material combines the merits of all material dimensions in heterogeneous catalysis. The anisotropic low-dimensional (1D and 2D) substructures possess the advantages of a high surface-to-volume ratio and fast charge transport. The interconnectivity of the nanorods is also beneficial for charge transport. The high-dimensional (3D) architecture results in sufficient active sites per the projected electrode surface area and is favorable for efficient mass diffusion during catalysis. A low overpotential of 313 mV is required to drive an OER current density of 10 mA cm−2 on a simple glassy carbon (GC) working electrode in a 1.0 m KOH aqueous solution.

Water splitting is an attractive way to produce recyclable hydrogen energy resource. The oxygen evolution reaction (OER) is the rate-determine step of water electrolysis. The exploring of low-cost, highly efficient and durable electrocatalysts for OER is thus extremely important. In this work, we developed a facile two-phase protocol to fabricate an α-Co(OH)2 using sodium oleate as the phase-transfer surfactant. The crystallinity and structure of the α-Co(OH)2 was regulated by heat treatments toward enhanced electrocatalytic OER activity. With the calcination of the as-prepared α-Co(OH)2 at 200 °C, a networked and well-dispersed CoO nanoparticles were formed. The CoO sample afforded an OER current density of 10 mA cm−2 under a low overpotential of 312 mV in a 1 mol L−1 KOH aqueous solution. The high activity of the CoO material is believed to be associated with its ultra-small particle size and plentiful open spaces in the material, both of which can provide abundant surface catalytic sites.Download high-res image (184KB)Download full-size image

Hollow metal oxide materials with nanometer-to-micrometer dimensions have attracted tremendous attention because of their potential applications in energy conversion and storage systems. Numerous efforts have been focused on developing versatile methods for the rational synthesis of various hollow structures to act as efficient water oxidation catalysts. In this work, a unique porous and hollow CoO tetragonal prism-like structure has been successfully synthesized via a facile and efficient co-precipitation method with polyvinylpyrrolidone (PVP K30) followed by a heating treatment of the resulted precipitates. The as-prepared porous and hollow CoO microprisms displayed a high activity and stability for water oxidation in 1.0 M KOH solution. To reach a current density of 10 mA/cm2, a low overpotential of 280 mV is required. The remarkable activity can be attributed to the synergistic effect between two different but well-distributed CoO crystalline phases, uniform particle size, ameliorative crystallinity, high surface area and the low mass transfer resistance benefitted from the unique porous structure.PVP-assisted synthesis of porous CoO prisms is reported. The porous CoO microprisms, which are highly uniform and have discrete tetragonal prism-like structure, display enhanced activity for electrocatalytic water oxidation.Download high-res image (120KB)Download full-size image

•A NiSe/NF electrode was conveniently prepared from electrodeposition method.•The uniform and dense coverage of NiSe on NF provided plentiful surface catalytic sites.•The electrode is bifunctional for both electrocatalytic HER and OER in an alkaline electrolyte.•The electrode is extremely efficient for OER.•A two-electrode water electrolyser based on this janus electrode showed efficient and stable water splitting performance under low cell voltages.Water electrolysis is a feasible way for large-scale production of hydrogen gas. If the electricity is provided by a solar cell, we can convert the sustainable solar energy into chemical energy. In this technology, the development of water splitting electrocatalysts contributes significantly to enhance the solar-to-hydrogen efficiency. Herein, an electrodeposited NiSe/NF electrode is reported with superior electrocatalytic activities for both water reduction and oxidation. A water electrolysis cell was fabricated using this cheap, easily-obtained, efficient and robust electrode as both anode and cathode to achieve high water splitting current density of 20 mA cm−2 at cell voltage around 1.50 V.Download high-res image (179KB)Download full-size image

Efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are the determinants of the realization of a hydrogen-based society, as sluggish OER and ORR are the bottlenecks for the production and utilization of H2, respectively. A Co complex of 5,15-bis(pentafluorophenyl)-10-(4)-(1-pyrenyl)phenylcorrole (1) bearing a pyrene substituent was synthesized. When it was immobilized on multiwalled carbon nanotubes (MWCNTs), the 1/MWCNT composite displayed very high electrocatalytic activity and durability for both OER and ORR in aqueous solutions: it catalyzed a direct four-electron reduction of O2 to H2O in 0.5 M H2SO4 with an onset potential of 0.75 V vs normal hydrogen electrode (NHE), and it catalyzed the oxidation of water to O2 in neutral aqueous solution with an onset potential of 1.15 V (vs NHE, η = 330 mV). Control studies using a Co complex of 5,10,15-tris(pentafluorophenyl)corrole (2) demonstrated that the enhanced catalytic performance of 1 was due to the strong noncovalent π–π interactions between its pyrene moiety and MWCNTs, which were considered to facilitate the fast electron transfer from the electrode to 1 and also to increase the adhesion of 1 on carbon supports. The noncovalent immobilization of molecular complexes on carbon supports through strong π–π interactions appears to be a simple and straightforward strategy to prepare highly efficient electrocatalytic materials.Keywords: cobalt corrole; electrocatalysis; noncovalent immobilization; oxygen evolution; oxygen reduction

A homoleptic, all-alkynyl-stabilized [Au8Ag8(ArCC)16] (1, Ar = 3,5-di-tert-butylphenyl) cluster was synthesized and characterized with a single crystal X-ray structure. Reactions of 3,5-di-tert-butyl-phenylacetylene with Ag(I) and Au(I) gave [Ag(ArCC)]n and Au(PPh3)(ArCC), respectively, where both have unusually high solubility in nonpolar organic solvents. In addition to drastically increased solubility, the two bulky tert-butyl substituents on the phenyl ring can confine the metal core to a certain size by preventing infinite aggregation of d10 metals. This feature makes the isolation of an all-alkynyl-stabilized Au–Ag cluster possible. Complex 1 is intensely luminescent with a very high quantum yield of 0.67 in solution at room temperature. Theoretical studies offered valuable insights into the intriguing photophysical properties, and revealed the significant role of metal–alkynyl bond interactions and enhanced molecular rigidity provided by tert-butyl groups.

Several copper corrole complexes were synthesized, and their catalytic activities for hydrogen (H2) evolution were examined. Our results showed that substituents at the meso positions of corrole macrocycles played significant roles in regulating the redox and thus the catalytic properties of copper corrole complexes: strong electron-withdrawing substituents can improve the catalysis for hydrogen evolution, while electron-donating substituents are not favored in this system. The copper complex of 5,15-pentafluorophenyl-10-(4-nitrophenyl)corrole (1) was shown to have the best electrocatalytic performance among copper corroles examined. Complex 1 can electrocatalyze H2 evolution using trifluoroacetic acid (TFA) as the proton source in acetonitrile. In cyclic voltammetry, the value of icat/ip = 303 (icat is the catalytic current, ip is the one-electron peak current of 1 in the absence of acid) at a scan rate of 100 mV s–1 and 20 °C is remarkable. Electrochemical and spectroscopic measurements revealed that 1 has the desired stability in concentrated TFA acid solution and is unchanged by functioning as an electrocatalyst. Stopped-flow, spectroelectrochemistry, and theoretical studies provided valuable insights into the mechanism of hydrogen evolution mediated by 1. Doubly reduced 1 is the catalytic active species that reacts with a proton to give the hydride intermediate for subsequent generation of H2.Keywords: copper corroles; electrocatalysis; hydrogen evolution; reduction; stopped-flow

Correction for ‘Aromatic sulfonate anion-induced pseudorotaxanes: environmentally benign synthesis, selectivity, and structural characterization’ by Han-Yuan Gong et al., Chem. Commun., 2015, DOI: 10.1039/c4cc08284b.

An ultrathin Fe-based film was prepared by electrodeposition from an FeII solution through a fast and simple cyclic voltammetry method. The extremely low Fe loading of 12.3 nmol cm–2 on indium tin oxide electrodes is crucial for high atom efficiency and transparence of the resulted film. This Fe-based film was shown to be a very efficient electrocatalyst for oxygen evolution from neutral aqueous solution with remarkable activity and stability. In a 34 h controlled potential electrolysis at 1.45 V (vs NHE) and pH 7.0, impressive turnover number of 5.2 × 104 and turnover frequency of 1528 h–1 were obtained. To the best of our knowledge, these values represent one of the highest among electrodeposited catalyst films for water oxidation under comparable conditions. The morphology and the composition of the catalyst film was determined by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, and X-ray photoelectron spectroscopy, which all confirmed the deposition of Fe-based materials with FeIII oxidation state on the electrode. This study is significant because of the use of iron, the fast and simple cyclic voltammetry electrodeposition, the extremely low catalyst loading and thus the transparency of the catalyst film, the remarkable activity and stability, and the oxygen evolution in neutral aqueous media.Keywords: electrocatalysis; film preparation; iron; oxygen evolution; water splitting;

Anion-induced molecular threading is an emerging strategy for generating mechanically interlocked molecular architectures. Herein, we report the preparation of two pseudorotaxane structures generated from aromatic sulfonate anions and a tetraimidazolium-containing macrocycle in organic media, as well as under environmentally benign aqueous conditions.

The water-soluble cationic nickel(II) complex of meso-tetrakis(4-N-methylpyridyl)porphyrin (1) can electrocatalyze water oxidation to O2 in neutral aqueous solution (pH 7.0) with the onset of the catalytic wave appearing at ∼1.0 V (vs NHE). The homogeneous catalysis with 1 was verified. Catalyst 1 exhibited water oxidation activity in a pH range 2.0–8.0 and had a strict linear dependence of catalytic current on its concentration. After 10 h of constant potential electrolysis at 1.32 V (vs NHE), a negligible difference of the solution was observed by UV–vis. In addition, inspection of the working electrode by electrochemistry, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX) showed no sign of deposition of NiOx films. These results strongly argued that 1 is a real molecular electrocatalyst for water oxidation. The turnover frequency (TOF) for this process was 0.67 s–1 at 20 °C. On the basis of results from the kinetic isotope effect (KIE) and inhibition experiments, electrochemical studies in various buffer solutions with different anions and pHs, and DFT calculations, a catalytic cycle of 1 for water oxidation via a formally Ni(IV) species was proposed.

Silver acetylide complex [Ag(ArC≡C)]n (Ar = 3,5-di-tert-butylphenyl) with unprecedented high solubility in common organic solvents has been designed and synthesized. The high solubility is due to two bulky tert-butyl substituents on the phenyl ring. This feature is significant to construct and isolate single crystals of all-alkynyl-stabilized silver clusters, which are crucial to investigate the intrinsic binding interaction and coordination modes between Ag(I) and ethynide ligands. Crystallization of [Ag(ArC≡C)]n under various conditions resulted in three high-nuclearity homoleptic silver acetylide clusters, namely, [Ag21(ArC≡C)20](OH) (1), [Ag16(ArC≡C)16] (2), and [Ag15(ArC≡C)15] (3). Complex 1 has a [Ag21] cluster protected by twenty 3,5-di-tert-butyl-phenylethynide ligands. Complexes 2 and 3 have neutral [Ag16] and [Ag15] clusters, respectively. In addition to these homoleptic silver clusters, two new silver acetylides [Ag20(ArC≡C)16(CH3COO)4] (4) and [Ag22(ArC≡C)16(NO3)4(CH3CH2OH)4](OH)2 (5) were synthesized. The acetate and nitrate anions in these structures are more like counterions instead of acting as critical building blocks or templates for cluster assembly. These results illustrated the significance of 3,5-di-tert-butyl-phenylethynide ligands in the construction and stabilization of high-nuclearity silver clusters. Analysis of structures of 1–5 revealed several novel coordination modes between Ag(I) and ethynide ligands, which contributed considerably to our knowledge of Ag(I)–ethynide binding interactions.

This study focused on the aromatic plane effect of the binding modes between ‘Texas-sized’ molecular box and carboxylate anion species. The molecular box, namely cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)-[2](1,4-dimethylenebenzene) (14+; studied as the PF6− salt), easily constructs interpenetrated structures (i.e., pseudorotaxanes) with carboxylate anions via the introduction of aromatic rings. As revealed by 1H NMR titration, two-dimensional nuclear Overhauser effect spectroscopy (NOESY), UV–Vis spectroscopic study, and electrospray ionization mass spectrometry (ESI-MS), the determination effect of aromatic plane in the binding modes between 14+ and carboxylate anions was studied in detail. This research reveals the important role of aromatic plane substitute groups on anions for building anion-induced interpenetrated self-assembly structures.

•Synthesized a positively charged and flexible ligand L.•Constructed eight silver(I) chain structures using ligand L.•All eight compounds were characterized by single crystal X-ray diffraction.•The conformation of these 1-D chains were controlled by various counter anions.•These silver(I) compounds of L displayed interesting anion exchange properties.Eight silver(I) coordination polymers were synthesized and structurally characterized. Direct reaction of various Ag(I) starting materials with a positively charged and flexible ligand, 1,3-di(2-picolyl)imidazolium (L) in different salts, including L-Cl, L-ClO4 and L-PF6, gave compounds [AgL(NO3)2] (1), [AgL(CH3CN)](BF4)2 (2), [Ag2L2(NO3)2](NO3)Cl (3), [AgL(CH3CN)](PF6)2·0.5CH3CN (4), [AgL(NO3)](PF6) (5), [AgL](NO3)(PF6) (6), [AgL(CH3CN)2](ClO4)(PF6)·CH3CN (7), and [AgL](ClO4)2·CH3CN (8). Structural analysis revealed that ligand L has three kinds of conformations in these structures. As benefited by the flexible feature of L, the silver chains in 1–8 are different and are depended on the shape and the size of counter anions. Anion exchange studies showed that crystals of 4, 6 and 8 had anion exchange properties, and the channel size in the corresponding solid state structures played a crucial role. These results highlighted the significance of positively charged and flexible ligand L in the construction of various silver chain structures with different conformations and thus packing diagrams for anion exchange studies.We report syntheses and single crystal structures of eight novel Ag(I) coordination compounds using a positively charged and flexible ligand, 1,3-di(2-picolyl)imidazolium in different salts. The structural diversity of the compound and the conformation of the ligand were examined. In addition, anion exchange properties of several compounds were studied, showing a reversible anion exchange property.

Reversible mechanochromic luminescence in cationic platinum(II) terpyridyl complexes is described. The complexes [Pt(Nttpy)Cl]X2 (Nttpy = 4′-(p-nicotinamide-N-methylphenyl)-2,2′:6′,2″-terpyridine, X = PF6 (1), SbF6 (2), Cl (3), ClO4 (4), OTf (5), BF4 (6)) exhibit different colors under ambient light in the solid state, going from red to orange to yellow. All of these complexes are brightly luminescent at both room temperature and 77 K. Upon gentle grinding, the yellow complexes (4–6) turn orange and exhibit bright red luminescence. The red luminescence can be changed back to yellow by the addition of a few drops of acetonitrile to the sample. Crystallographic studies of the yellow and red forms of complex 5 suggest that the mechanochromic response is likely the result of a change in intermolecular Pt···Pt distances upon grinding.

Six cobalt and manganese corrole complexes were synthesized and examined as single-site catalysts for water splitting. The simple cobalt corrole [Co(tpfc)(py)2] (1, tpfc = 5,10,15-tris(pentafluorophenyl)corrole, py = pyridine) catalyzed both water oxidation and proton reduction efficiently. By coating complex 1 onto indium tin oxide (ITO) electrodes, the turnover frequency for electrocatalytic water oxidation was 0.20 s−1 at 1.4 V (vs. Ag/AgCl, pH = 7), and it was 1010 s−1 for proton reduction at −1.0 V (vs. Ag/AgCl, pH = 0.5). The stability of 1 for catalytic oxygen evolution and hydrogen production was evaluated by electrochemical, UV-vis and mass measurements, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), which confirmed that 1 was the real molecular catalyst. Titration and UV-vis experiments showed that the pyridine group on Co dissociated at the beginning of catalysis, which was critical to subsequent activation of water. A proton-coupled electron transfer process was involved based on the pH dependence of the water oxidation reaction catalyzed by 1. As for manganese corroles 2–6, although their oxidizing powers were comparable to that of 1, they were not as stable as 1 and underwent decomposition at the electrode. Density functional theory (DFT) calculations indicated that water oxidation by 1 was feasible through a proposed catalytic cycle. The formation of an O–O bond was suggested to be the rate-determining step, and the calculated activation barrier of 18.1 kcal mol−1 was in good agreement with that obtained from experiments.

Catalysts play very important roles in artificial photosynthesis for solar energy conversion. In this present study, two water-insoluble cobalt porphyrin complexes, cobalt(II) meso-tetraphenylporphyrin (CoP-1) and cobalt(II) 5,10,15,20-tetrakis-(4-bromophenyl)porphyrin (CoP-2), were synthesized and coated as thin films on the FTO working electrode. The films showed good activities for electrocatalytic water oxidation in aqueous solutions at pH 9.2. The Faradaic efficiencies of both films approached to ∼100%, measured using a fluorescence-based oxygen sensor. The turnover frequencies were close to 0.50 s−1 and 0.40 s−1 for CoP-1 and CoP-2, respectively, under an applied anodic potential of 1.3 V (vs. Ag/AgCl) at pH 9.2. Importantly, no cobalt oxide particles were observed on the working electrode after catalysis. The stability of the catalyst films was further evaluated by UV-vis spectroscopy, inhibition measurements, mass spectrometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The pH dependence of water oxidation on CoP-1 and CoP-2 suggested a proton-coupled electron transfer (PCET) mechanism. The catalyst films could be recycled and showed almost unchanged catalytic activities when they were reused in new electrocatalytic studies of water oxidation.

The vapochromism of the platinum(II) terpyridyl complex [Pt(tpy)Cl](PF6) (1, tpy = 2,2′:6′,2′′-terpyridine) was investigated. Complex 1 was found to exist in two forms. The yellow form of 1 turned to red by exposing the solid to either vapor or solution of acetonitrile, accompanied by changes in luminescence spectroscopy. This process could be reversed upon the loss of acetonitrile. Complex 1 was also demonstrated to show aggregation in a diethyl ether–acetonitrile system through Pt⋯Pt and terpyridyl π–π interactions to afford the red form of 1. Crystals of the red and yellow forms of 1 were analyzed. The red form of 1 crystallizes in the orthorhombic space group Pnma with a co-crystallized acetonitrile solvent molecule and thus is defined as 1-MeCN, while the yellow form is found to have the previously reported non-solvated crystal structure of 1. In 1-MeCN, the square planar [Pt(tpy)Cl]+ monocations stack to give an extended chain-like array of Pt atoms with a short Pt⋯Pt distance of 3.362 Å, while in 1, there are two alternating Pt⋯Pt distances (4.032 and 3.340 Å). Time-dependent density functional theory (TDDFT) calculations demonstrated that Pt⋯Pt and terpyridyl π–π interactions play important roles in electronic absorption features of the [Pt(tpy)Cl]+ system. Compared to dimers, the stack of three molecules of 1 with a short Pt⋯Pt distance considerably lowers the transition energy of metal–metal-to-ligand charge transfer (MMLCT), which causes a dramatic red shift in UV-vis spectroscopy.

O–O bond formation catalyzed by a variety of β-octafluoro hangman corrole metal complexes was investigated using density functional theory methods. Five transition metal elements, Co, Fe, Mn, Ru, and Ir, that are known to lead to water oxidation were examined. Our calculations clearly show that the formal CoV catalyst has a CoIV–corrole•+ character and is the most efficient water oxidant among all eight transition-metal complexes. The O–O bond formation barriers were found to change in the following order: Co(V) ≪ Fe(V) < Mn(V) < Ir(V) < Co(IV) < Ru(V) < Ir(IV) < Mn(IV). The efficiency of water oxidation is discussed by analysis of the O–O bond formation step. Thus, the global trend is determined by the ability of the ligand d-block to accept two electrons from the nascent OH–, as well as by the OH• affinity of the TM(IV)═O species of the corresponding TM(V)═O·H2O complex. Exchange-enhanced reactivity (EER) is responsible for the high catalytic activity of the Co(V) species in its S = 1 state.Keywords: density functional theory; hangman corrole; nucleophilic attack; O−O bond formation; transition metal; water oxidation;

•Synthesized and used a bifunctional (4-ethynylphenyl)diphenyl phosphine ligand.•Constructed four new silver acetylide coordination polymers.•All four complexes were characterized by single crystal X-ray diffraction.•The bifunctional ligand played a key role in assembling these complexes.•These complexes represented unusual high-nuclearity silver cluster building blocks.A bifunctional ligand precursor (4-ethynylphenyl)diphenyl phosphine was synthesized and used for constructing silver acetylide frameworks. Its reaction with Ag(I) in the presence of triethylamine afforded silver acetylide [AgL]n, in which L = Ph2P-C6H4-4-CC− could act as a bifunctional ligand bearing both phenylethynide and phosphine binding sites for Ag(I). Reactions of [AgL]n and AgCF3CO2 under different conditions gave four silver acetylides. They are [Ag18L8(CF3COO)6(HCO3)4(DMF)4]n (1, DMF = dimethylformamide), [Ag20L8(CF3COO)12(DMF)6]n (2), [Ag17L6(CF3COO)9(HCO3)2]n (3), and [Ag17L6(CF3COO)9.58(HCO3)1.42]n (4). Crystallographic studies revealed that complex 1 crystallized in the triclinic space group P1¯ with a = 14.1252(9) Å, b = 18.6012(12) Å, c = 25.2137(17) Å, α = 108.340(2)°, β = 95.386(2)°, γ = 95.535(2)°, V = 6204.6(7) Å3, and Z = 1. Complex 2 crystallized in the monoclinic space group C2/c with a = 48.046(4) Å, b = 14.1860(10) Å, c = 34.943(2) Å, β = 98.315(3)°, V = 23,566(3) Å3, and Z = 4. Complex 3 crystallized in the triclinic space group P1¯ with a = 15.5690(7) Å, b = 16.7707(8) Å, c = 34.0810(16) Å, α = 93.4040(10)°, β = 100.3690(10)°, γ = 94.8250(10)°, V = 8697.1(7) Å3, and Z = 2. Complex 4 crystallized in the triclinic space group P1¯ with a = 15.5396(6) Å, b = 16.7595(7) Å, c = 34.0225(15) Å, α = 93.8140(10)°, β = 100.1000(10)°, γ = 94.9770(10)°, V = 8660.2(6) Å3, and Z = 2. The presence of Ag(I)–ethynide, Ag(I)–P and Ag(I)–Ag(I) bonding interactions makes all four silver acetylides to have two- and three-dimensional framework structures with unusual high-nuclearity silver cluster building blocks.We report the syntheses and single crystal X-ray structures of four novel silver acetylide coordination polymers using a bifunctional (4-ethynylphenyl)diphenyl phosphine ligand. The presence of Ag(I)–ethynide, Ag(I)–P and Ag(I)–Ag(I) bonding interactions makes all four silver acetylides to have two- and three-dimensional framework structures with unusual high-nuclearity silver cluster building blocks.

A homoleptic, all-alkynyl-stabilized [Au8Ag8(ArCC)16] (1, Ar = 3,5-di-tert-butylphenyl) cluster was synthesized and characterized with a single crystal X-ray structure. Reactions of 3,5-di-tert-butyl-phenylacetylene with Ag(I) and Au(I) gave [Ag(ArCC)]n and Au(PPh3)(ArCC), respectively, where both have unusually high solubility in nonpolar organic solvents. In addition to drastically increased solubility, the two bulky tert-butyl substituents on the phenyl ring can confine the metal core to a certain size by preventing infinite aggregation of d10 metals. This feature makes the isolation of an all-alkynyl-stabilized Au–Ag cluster possible. Complex 1 is intensely luminescent with a very high quantum yield of 0.67 in solution at room temperature. Theoretical studies offered valuable insights into the intriguing photophysical properties, and revealed the significant role of metal–alkynyl bond interactions and enhanced molecular rigidity provided by tert-butyl groups.

Correction for ‘Aromatic sulfonate anion-induced pseudorotaxanes: environmentally benign synthesis, selectivity, and structural characterization’ by Han-Yuan Gong et al., Chem. Commun., 2015, DOI: 10.1039/c4cc08284b.

A water-soluble binuclear CuII complex, synthesized using a polypyridine–polyamide ligand, was able to catalyze oxygen reduction to water from neutral aqueous solutions. Electrocatalytic results suggested that one CuII center was first reduced by one electron to form a CuIICuI species, which reacted with O2 to give a superoxide radical intermediate.

Six cobalt and manganese corrole complexes were synthesized and examined as single-site catalysts for water splitting. The simple cobalt corrole [Co(tpfc)(py)2] (1, tpfc = 5,10,15-tris(pentafluorophenyl)corrole, py = pyridine) catalyzed both water oxidation and proton reduction efficiently. By coating complex 1 onto indium tin oxide (ITO) electrodes, the turnover frequency for electrocatalytic water oxidation was 0.20 s−1 at 1.4 V (vs. Ag/AgCl, pH = 7), and it was 1010 s−1 for proton reduction at −1.0 V (vs. Ag/AgCl, pH = 0.5). The stability of 1 for catalytic oxygen evolution and hydrogen production was evaluated by electrochemical, UV-vis and mass measurements, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), which confirmed that 1 was the real molecular catalyst. Titration and UV-vis experiments showed that the pyridine group on Co dissociated at the beginning of catalysis, which was critical to subsequent activation of water. A proton-coupled electron transfer process was involved based on the pH dependence of the water oxidation reaction catalyzed by 1. As for manganese corroles 2–6, although their oxidizing powers were comparable to that of 1, they were not as stable as 1 and underwent decomposition at the electrode. Density functional theory (DFT) calculations indicated that water oxidation by 1 was feasible through a proposed catalytic cycle. The formation of an O–O bond was suggested to be the rate-determining step, and the calculated activation barrier of 18.1 kcal mol−1 was in good agreement with that obtained from experiments.

Cobalt corroles with different acid/base pendants, LBr–Co, LCOOH–Co, LPO(OH)2–Co, and LCH2PO(OH)2–Co (L = 5,15-bis-(pentafluorophenyl)-10-(4-dibenzofuran)corrole), were synthesized and examined as catalysts for oxygen and hydrogen evolution from neutral aqueous solutions. Co corroles with phosphonic acid pendants showed improved activities in both processes, highlighting the importance of the secondary coordination sphere in catalyst design.

Anion-induced molecular threading is an emerging strategy for generating mechanically interlocked molecular architectures. Herein, we report the preparation of two pseudorotaxane structures generated from aromatic sulfonate anions and a tetraimidazolium-containing macrocycle in organic media, as well as under environmentally benign aqueous conditions.

A series of cobalt complexes of 5,10,15-tris(pentafluorophenyl)-corrole [Co(tpfc)] (1) with various axial ligands were synthesized and examined as single-site catalysts for water oxidation. The used axial ligands include 4-cyanopyridine (py-CN), pyridine (py), 4-(dimethylamino)pyridine (py-NMe2), 4-methoxypyridine (py-OMe), 1-methylimidazole (im-Me), and thiophenolate (thi). Complexes 1–py and 1–py-OMe were structurally characterized. The Co ion in both structures has an almost identical distorted octahedral coordination environment with the four N atoms of tpfc defining the equatorial plane and the two molecules of pyridine (for 1–py) or 4-methoxypyridine (for 1–py-OMe) occupying the axial positions. Electrochemical studies of these Co corroles in acetonitrile showed that they all display two oxidation events and the oxidation waves shift to the cathodic direction with electron-donating axial ligands, a trend that is consistent with increased electron densities on Co ions. All these Co corroles were found to be active for electrocatalytic water oxidation: by using catalyst-coated fluorine-doped tin oxide (FTO) working electrodes, cyclic voltammograms displayed pronounced catalytic waves for water oxidation in 0.1 M pH 7.0 phosphate buffer solutions. The onset overpotentials are in the range of 510 to 580 mV, depending on the electron-donating ability of the trans axial ligands. These results demonstrate that the catalytic activities of Co corroles for water oxidation are considerably affected by the trans axial ligands on Co centers and provide valuable insights into the design of new catalysts for water oxidation.