Co-reporter:Juergen Bartelmess, Aaron J. Francis, Karim A. El Roz, Felix N. Castellano, Walter W. Weare, and Roger D. Sommer
Inorganic Chemistry May 5, 2014 Volume 53(Issue 9) pp:
Publication Date(Web):April 11, 2014
DOI:10.1021/ic500218q
Co-reporter:Eric M. Goggins;Travis T. Lekich;Walter W. Weare;Roger D. Sommer;Marcos A. Ribeiro;Carlos B. Pinheiro
European Journal of Inorganic Chemistry 2016 Volume 2016( Issue 7) pp:1054-1059
Publication Date(Web):
DOI:10.1002/ejic.201501325
Abstract
A series of heterodimetallic molecules, centered around an LTi=OM2+L′ (M = Mn, Fe, Co, Ni, Cu, Zn) core, are described. Each of these complexes are structurally similar, with L = tmtaa and L′ = Py5Me2. The Ti=OM linkage is slightly bent, varying from 157° (Mn) to 170° (Zn), with bond lengths typical of a dative bond between the Ti=O group and the M2+ center. The relative strength of the heterodimetallic linkage is correlated with the Lewis acidity of the M2+ precursor, with Mn2+ showing the strongest interaction and Ni2+ the weakest. By varying the metal identity the electrochemical properties of the molecules can be tuned, along with the M3+/2+ redox couple. This series of complexes provide a platform for studying structure/function relationships in heterodimetallic molecules linked through a single atom. For instance, spectroscopic features such as IR stretching frequencies can be roughly correlated with structural features such as bond lengths and angles.
Co-reporter:Xinyuan Wu, Tao Huang, Travis T. Lekich, Roger D. Sommer, and Walter W. Weare
Inorganic Chemistry 2015 Volume 54(Issue 11) pp:5322-5328
Publication Date(Web):May 13, 2015
DOI:10.1021/acs.inorgchem.5b00370
Heterobimetallic complexes composed only of first-row transition metals [(TMTAA)VIV═O→MIIPy5Me2](OTf)2 (TMTAA = 7,16-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine; Py5Me2 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine; M = MnII, FeII, CoII, NiII, CuII; OTf = trifluoromethanesulfonate) have been synthesized through a dative interaction between a terminal oxido and MII metal centers. This is the first series of VIV═O→MII heterobimetallic complexes containing an unsupported oxido bridge. Among these five complexes, only VIV═O→FeII (3b) has a clear new absorption band upon formation of the dinuclear species (502 nm, ε = 1700 M–1 cm–1). This feature is assigned to a metal-to-metal charge transfer (MMCT) transition from VIV to FeII, which forms a VV—O—FeI excited state. This assignment is supported by electrochemical data, electronic absorption profiles, and resonance Raman spectroscopy and represents the first report of visible-light induced MMCT in a heterobimetallic oxido-bridged molecule where the electron originates on a d1 metal center.
Co-reporter:Tao Huang, Xinyuan Wu, Xiao Song, Hao Xu, Tatyana I. Smirnova, Walter W. Weare and Roger D. Sommer
Dalton Transactions 2015 vol. 44(Issue 43) pp:18937-18944
Publication Date(Web):07 Oct 2015
DOI:10.1039/C5DT02719E
Convenient strategies have been developed to synthesize heterobi/trimetallic oxido complexes containing V(IV)–O–Cr(III), V(IV)–O–Cr(III)–O–Ti(IV) and V(IV)–O–Cr(III)–O–V(IV) cores. These compounds can serve as ground state models for probing the magnetic properties of metal-to-metal charge transfer excited states. Each of these complexes represents the first experimental demonstration of ferromagnetic coupling in a d1–d3 oxido bridged compound, which confirms a long standing theoretical prediction for such a linkage. Structural characterization reveals a similar structure for each of the bi/trimetallic complexes with identical VO bond lengths (∼1.644 Å) and a linear V–O–Cr geometry. The Cr–O distances (1.943–1.964 Å) are significantly influenced by the ligands in the trans axial positions. Ferromagnetic coupling between the V(IV) and Cr(III) of V–O–Cr is measured by temperature-dependent magnetic susceptibility, showing J = +42.5 to +50.7 cm−1 (H = −2JŜVŜCr). This is further supported by variable temperature X-band EPR. The values of J are found to be consistent with the function J = Aeβr (A = 9.221 × 108 and β = 8.607 Å−1), where r is the Cr–O bond distance. We propose a model that links either ferromagnetic or antiferromagentic exchange coupling with long excited state lifetimes in metal-to-metal charge transfer (MMCT) chromophores.
Co-reporter:A. J. Falzone, J. Nguyen, W. W. Weare, R. D. Sommer and P. D. Boyle
Chemical Communications 2014 vol. 50(Issue 17) pp:2139-2141
Publication Date(Web):24 Dec 2013
DOI:10.1039/C3CC49066A
A terminal and unsupported chromium(III) hydroxide is reported. The terminal hydroxide is used to synthesize the first example of a heterobimetallic Ti–O–Cr compound containing an unsupported μ-oxo bridge. The heterobimetallic complex exhibits a new absorbance at 288 nm (4.32 eV), which is assigned to a metal-to-metal charge transfer (MMCT) transition.
Co-reporter:Tao Huang;Xinyuan Wu;Walter W. Weare;Roger D. Sommer
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 33) pp:5662-5674
Publication Date(Web):
DOI:10.1002/ejic.201402800
Abstract
A series of oxido-bridged heterobi- and heterotrimetallic complexes, [(tmtaa)Ti=OCr(Por)Cl] and [(tmtaa)Ti=OCr(Por)O=Ti(tmtaa)]+ (tmtaa = 7,16-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine; Por = 5,10,15,20-tetraarylporphyrin), have been synthesized. To the best of our knowledge, these complexes are the first structurally characterized examples to contain a Ti=OCr or Ti=OCrO=Ti structural motif. Crystal structures of representative heterobimetallic compounds, including the Ti=OCr binuclear complex 2 and two separate trimers, [Ti=OCrO=Ti]SbF6 (10) and [Ti=OCrO=Ti]Cl (12), are reported. The bi- and trimetallic molecules have similar structural parameters, including Ti–O, Cr–O, and Ti–O–Cr bond lengths and angles with a linear Ti=OCr geometry. Magnetic studies showed that a high-spin CrIII (S = 3/2) center is present in both the bi- and trinuclear molecules. The redox potentials for CrIV/III (ΔE = 320 mV) and Por/Por·– (ΔE = 260 mV) can be tuned by modifying the porphyrin ligand. By determining the thermodynamics and kinetics of the formation of these complexes by titration experiments and electrochemistry, it was found that the bi- and trimetallic species undergo isomerization in solution, allowing easy substitution of the apical chlorido ligand.
Co-reporter:Juergen Bartelmess, Walter W. Weare and Roger D. Sommer
Dalton Transactions 2013 vol. 42(Issue 41) pp:14883-14891
Publication Date(Web):30 Aug 2013
DOI:10.1039/C3DT51849C
We report the synthesis of four boron–dipyrromethene (BODIPY) sensitized cobaloxime complexes as structural models of light-driven proton reduction catalysts. The BODIPY chromophore is covalently linked to the cobaloxime via a pyridine molecule in the meso-position of the BODIPY. Electron withdrawing or donating substituents on the pyridine (e.g. chloro- or methyl-groups) allow a comparison of the influence of these substituents on cobaloxime–BODIPY interactions. This includes altering the overall stability of the complexes and tuning the catalytically relevant CoII/III redox couple over a range of 220 mV, which will assist in the design of future cobaloxime–chromophore complexes. All complexes were characterized using electrochemistry, electronic absorption and fluorescence spectroscopy. Additionally, we present crystal structures of the four new BODIPY–cobaloxime complexes and elucidate the influence of the structural modifications. We found that these compounds produce sub-stoichiometric quantities of hydrogen under standard photon-driven hydrogen evolving conditions.
Co-reporter:Juergen Bartelmess, Walter W. Weare, Narah Latortue, Christina Duong and Daniel S. Jones
New Journal of Chemistry 2013 vol. 37(Issue 9) pp:2663-2668
Publication Date(Web):17 Jun 2013
DOI:10.1039/C3NJ00426K
A series of meso-pyridyl substituted BODIPY molecules has been synthesized, characterized and their optical and electrochemical properties compared. By utilizing ethanol and dichloromethane during the initial condensation reactions, there is a significant increase in the isolated yields compared to standard protocols. The properties of the highly fluorescent BODIPYs could be tuned by modifying the substituents of the pyridine, leading to pyridyl BODIPY as prospective ligands for future metal complexes. Furthermore, the presented BODIPY derivatives are shown to be applicable for fluorescence pH sensing over selective pH ranges.
Co-reporter:A. J. Falzone, J. Nguyen, W. W. Weare, R. D. Sommer and P. D. Boyle
Chemical Communications 2014 - vol. 50(Issue 17) pp:NaN2141-2141
Publication Date(Web):2013/12/24
DOI:10.1039/C3CC49066A
A terminal and unsupported chromium(III) hydroxide is reported. The terminal hydroxide is used to synthesize the first example of a heterobimetallic Ti–O–Cr compound containing an unsupported μ-oxo bridge. The heterobimetallic complex exhibits a new absorbance at 288 nm (4.32 eV), which is assigned to a metal-to-metal charge transfer (MMCT) transition.
Co-reporter:Juergen Bartelmess, Walter W. Weare and Roger D. Sommer
Dalton Transactions 2013 - vol. 42(Issue 41) pp:NaN14891-14891
Publication Date(Web):2013/08/30
DOI:10.1039/C3DT51849C
We report the synthesis of four boron–dipyrromethene (BODIPY) sensitized cobaloxime complexes as structural models of light-driven proton reduction catalysts. The BODIPY chromophore is covalently linked to the cobaloxime via a pyridine molecule in the meso-position of the BODIPY. Electron withdrawing or donating substituents on the pyridine (e.g. chloro- or methyl-groups) allow a comparison of the influence of these substituents on cobaloxime–BODIPY interactions. This includes altering the overall stability of the complexes and tuning the catalytically relevant CoII/III redox couple over a range of 220 mV, which will assist in the design of future cobaloxime–chromophore complexes. All complexes were characterized using electrochemistry, electronic absorption and fluorescence spectroscopy. Additionally, we present crystal structures of the four new BODIPY–cobaloxime complexes and elucidate the influence of the structural modifications. We found that these compounds produce sub-stoichiometric quantities of hydrogen under standard photon-driven hydrogen evolving conditions.
Co-reporter:Tao Huang, Xinyuan Wu, Xiao Song, Hao Xu, Tatyana I. Smirnova, Walter W. Weare and Roger D. Sommer
Dalton Transactions 2015 - vol. 44(Issue 43) pp:NaN18944-18944
Publication Date(Web):2015/10/07
DOI:10.1039/C5DT02719E
Convenient strategies have been developed to synthesize heterobi/trimetallic oxido complexes containing V(IV)–O–Cr(III), V(IV)–O–Cr(III)–O–Ti(IV) and V(IV)–O–Cr(III)–O–V(IV) cores. These compounds can serve as ground state models for probing the magnetic properties of metal-to-metal charge transfer excited states. Each of these complexes represents the first experimental demonstration of ferromagnetic coupling in a d1–d3 oxido bridged compound, which confirms a long standing theoretical prediction for such a linkage. Structural characterization reveals a similar structure for each of the bi/trimetallic complexes with identical VO bond lengths (∼1.644 Å) and a linear V–O–Cr geometry. The Cr–O distances (1.943–1.964 Å) are significantly influenced by the ligands in the trans axial positions. Ferromagnetic coupling between the V(IV) and Cr(III) of V–O–Cr is measured by temperature-dependent magnetic susceptibility, showing J = +42.5 to +50.7 cm−1 (H = −2JŜVŜCr). This is further supported by variable temperature X-band EPR. The values of J are found to be consistent with the function J = Aeβr (A = 9.221 × 108 and β = 8.607 Å−1), where r is the Cr–O bond distance. We propose a model that links either ferromagnetic or antiferromagentic exchange coupling with long excited state lifetimes in metal-to-metal charge transfer (MMCT) chromophores.
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