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Edward I Solomon - One of the best experts on this subject based on the ideXlab platform.
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description of the ground state covalencies of the bis dithiolato transition metal complexes from x ray absorption spectroscopy and time dependent density functional calculations
Chemistry: A European Journal, 2007Co-Authors: Serena Debeer George, Edward I Solomon, Karl Wieghardt, Frank NeeseAbstract:: The electronic structures of [M(L(Bu))(2)](-) (L(Bu)=3,5-di-tert-butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(-) forms. The extent of electron transfer strongly depends on the Effective Nuclear Charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(L(Bu))(2)](-) (M=Ni, Pd, Pt) and [Au(L(Bu))(2)] are best described as delocalized class III mixed-valence ligand radicals bound to low-spin d(8) central metal ions while [M(L(Bu))(2)](-) (M=Cu, Au) and [M(L(Bu))(2)](2-) (M=Ni, Pd, Pt) contain completely reduced dithiolato(2-) ligands. The case of [Co(L(Bu))(2)](-) remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S(1s)-->valence-pi versus S(1s)-->valence-sigma transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal-sulfur bonds from ligand K-edge absorption spectroscopy.
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spectroscopic investigation of stellacyanin mutants axial ligand interactions at the blue copper site
Journal of the American Chemical Society, 2003Co-Authors: Serena Debeer George, Britt Hedman, Keith O Hodgson, Lipika Basumallick, Robert K Szilagyi, David W Randall, Michael G Hill, A M Nersissian, Joan Selverstone Valentine, Edward I SolomonAbstract:Detailed electronic and geometric structural descriptions of the blue copper sites in wild-type (WT) stellacyanin and its Q99M and Q99L axial mutants have been obtained using a combination of XAS, resonance Raman, MCD, EPR, and DFT calculations. The results show that the origin of the short Cu−S(Cys) bond in blue copper proteins is the weakened axial interaction, which leads to a shorter (based on EXAFS results) and more covalent (based on S K-edge XAS) Cu−S bond. XAS pre-edge energies show that the Effective Nuclear Charge on the copper increases going from O(Gln) to S(Met) to no axial (Leu) ligand, indicating that the weakened axial ligand is not fully compensated for by the increased donation from the thiolate. This is further supported by EPR results. MCD data show that the decreased axial interaction leads to an increase in the equatorial ligand field, indicating that the site acquires a more trigonally distorted tetrahedral structure. These geometric and electronic structural changes, which result f...
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s k edge x ray absorption studies of tetraNuclear iron sulfur clusters mu sulfide bonding and its contribution to electron delocalization
Journal of the American Chemical Society, 2001Co-Authors: Thorsten Glaser, Britt Hedman, Keith O Hodgson, Kendra Rose, Susan E Shadle, Edward I SolomonAbstract:X-ray absorption spectroscopy (XAS) at the sulfur ( approximately 2470 eV) and chlorine ( approximately 2822 eV) K-edges has been applied to a series of 4Fe-4S model complexes. These are compared to 2Fe-2S model complexes to obtain insight into the localized ground state in the mixed-valence dimer versus the delocalized ground state in the mixed-valence tetramer. The preedges of hypothetical delocalized mixed-valence dimers [Fe(2)S(2)](+) are estimated using trends from experimental data and density functional calculations, for comparison to the delocalized mixed-valence tetramer [Fe(4)S(4)](2+). The differences between these two mixed-valence sites are due to the change of the sulfide-bridging mode from micro(2) to micro(3). The terminal chloride and thiolate ligands are used as spectator ligands for the electron density of the iron center. From the intensity of the preedge, the covalency of the terminal ligands is found to increase in the tetramer as compared to the dimer. This is associated with a higher Effective Nuclear Charge on the iron in the tetramer (derived from the energies of the preedge). The micro(3)-bridging sulfide in the tetramer has a reduced covalency per bond (39%) as compared to the micro(2)-bridging sulfide in the dimer (51%). A simple perturbation model is used to derive a quadratic dependence of the superexchange coupling constant J on the covalency of the metal ions with the bridging ligands. This relationship is used to estimate the superexchange contribution in the tetramer (J = -156 cm(-)(1)) as compared to the mixed-valence dimer (J = -360 cm(-)(1)). These results, combined with estimates for the double exchange and the vibronic coupling contributions of the dimer sub-site of the tetramer, lead to a delocalized S(t) = (9)/(2) spin ground state for the mixed-valence dimer in the tetramer. Thus, the decrease in the covalency, hence the superexchange pathway associated with changing the bridging mode of the sulfides from micro(2) to micro(3) on going from the dimer to the tetramer, significantly contributes to the delocalization of the excess electron over the dimer sub-site in the tetramer.
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investigation of the electronic structure of 2fe 2s model complexes and the rieske protein using ligand k edge x ray absorption spectroscopy
Journal of the American Chemical Society, 1999Co-Authors: Kendra Rose, Britt Hedman, Keith O Hodgson, Thorsten Glaser, Susan E Shadle, S De Vries, Alexey V Cherepanov, Gerard W Canters, Edward I SolomonAbstract:X-ray absorption spectroscopy at the sulfur K-edge (∼2470 eV) has been applied to a series of 2Fe−2S model complexes to obtain insight into their electronic structures. Since these 2Fe−2S complexes contain both terminal thiolates and bridging sulfides, contributions to covalency from both sets of ligands can be evaluated. Importantly, the pre-edge feature of sulfide can be resolved from that of thiolate due to differences in Effective Nuclear Charge. In our previous studies, the covalency of the metal−thiolate bond in [Fe(SR)4]- was determined. In this study, sulfide covalency is quantified for the first time on the basis of an analysis of previous X-ray photoelectron and X-ray absorption spectroscopic studies of [FeCl4]- which are then applied to the bis-μ2-sulfide compound KFeS2. With references for both sulfide and thiolate covalencies thus established for open d-shell systems, comparisons are made between thiolate and sulfide bonding. Sulfide−Fe covalency in the [Fe2S2(SR)4]2- complexes is higher than...
Kwong T Chung - One of the best experts on this subject based on the ideXlab platform.
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energy and fine structure of 1s2np states n 2 3 4 and 5 for the lithium isoelectronic sequence
Physica Scripta, 1993Co-Authors: Z W Wang, X W Zhu, Kwong T ChungAbstract:The non-relativistic energies of 1s2np (n = 2, 3, 4 and 5) states for the lithium isoelectronic sequence from Li I to Ne VIII are calculated using the full-core plus correlation method. Relativistic and mass polarization effects on the energy are evaluated using first order perturbation theory. The fine structures are determined from the expectation values of the spin-orbit and spin-other-orbit interaction operators in the Pauli-Breit approximation. The higher order relativistic effects are estimated using the hydrogenic solution to the Dirac equation with an Effective Nuclear Charge. The QED correction is also included. Our results are compared with the experimental and theoretical data in the literature. The fine structure results agree well with experiment. For 1s2np energies with n ≥ 3, it appears that our results are quite accurate for all Z investigated. However, for the 1s22p systems, the discrepancy with experiment grows monotonically from 0.5 cm−1 for Li I to 29 cm−1 for Ne VIII. This is very different from all the other 1s2nl systems we have investigated using the same method. What separates 1s22p apart from the others is the unusually large orbit-orbit interaction and mass polarization effects. For Z > 6, the expectation values of these perturbation operators are opposite in sign to those of the 1s2 core. This energy increases quickly with Z.
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energy of 1s2ns n 3 4 and 5 states for the lithium isoelectronic sequence
Physical Review A, 1992Co-Authors: Zhao Wang, X W Zhu, Kwong T ChungAbstract:The nonrelativistic energies of the lithiumlike ls 2 ns (n=3, 4, and 5) states for Z=3 to 10 are calculated by using a full-core-plus-correlation method with multiconfiguration-interaction wave functions. Relativistic and mass-polarization effects on the energy are evaluated as the first-order perturbation corrections. The quantum-electrodynamic (QED) correction to the energy is included using Effective Nuclear Charge. Our results are compared with the experimental data in the literature. For Z<8 systems, the discrepancies are about 1 cm -1 or less in most cases
Britt Hedman - One of the best experts on this subject based on the ideXlab platform.
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spectroscopic investigation of stellacyanin mutants axial ligand interactions at the blue copper site
Journal of the American Chemical Society, 2003Co-Authors: Serena Debeer George, Britt Hedman, Keith O Hodgson, Lipika Basumallick, Robert K Szilagyi, David W Randall, Michael G Hill, A M Nersissian, Joan Selverstone Valentine, Edward I SolomonAbstract:Detailed electronic and geometric structural descriptions of the blue copper sites in wild-type (WT) stellacyanin and its Q99M and Q99L axial mutants have been obtained using a combination of XAS, resonance Raman, MCD, EPR, and DFT calculations. The results show that the origin of the short Cu−S(Cys) bond in blue copper proteins is the weakened axial interaction, which leads to a shorter (based on EXAFS results) and more covalent (based on S K-edge XAS) Cu−S bond. XAS pre-edge energies show that the Effective Nuclear Charge on the copper increases going from O(Gln) to S(Met) to no axial (Leu) ligand, indicating that the weakened axial ligand is not fully compensated for by the increased donation from the thiolate. This is further supported by EPR results. MCD data show that the decreased axial interaction leads to an increase in the equatorial ligand field, indicating that the site acquires a more trigonally distorted tetrahedral structure. These geometric and electronic structural changes, which result f...
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s k edge x ray absorption studies of tetraNuclear iron sulfur clusters mu sulfide bonding and its contribution to electron delocalization
Journal of the American Chemical Society, 2001Co-Authors: Thorsten Glaser, Britt Hedman, Keith O Hodgson, Kendra Rose, Susan E Shadle, Edward I SolomonAbstract:X-ray absorption spectroscopy (XAS) at the sulfur ( approximately 2470 eV) and chlorine ( approximately 2822 eV) K-edges has been applied to a series of 4Fe-4S model complexes. These are compared to 2Fe-2S model complexes to obtain insight into the localized ground state in the mixed-valence dimer versus the delocalized ground state in the mixed-valence tetramer. The preedges of hypothetical delocalized mixed-valence dimers [Fe(2)S(2)](+) are estimated using trends from experimental data and density functional calculations, for comparison to the delocalized mixed-valence tetramer [Fe(4)S(4)](2+). The differences between these two mixed-valence sites are due to the change of the sulfide-bridging mode from micro(2) to micro(3). The terminal chloride and thiolate ligands are used as spectator ligands for the electron density of the iron center. From the intensity of the preedge, the covalency of the terminal ligands is found to increase in the tetramer as compared to the dimer. This is associated with a higher Effective Nuclear Charge on the iron in the tetramer (derived from the energies of the preedge). The micro(3)-bridging sulfide in the tetramer has a reduced covalency per bond (39%) as compared to the micro(2)-bridging sulfide in the dimer (51%). A simple perturbation model is used to derive a quadratic dependence of the superexchange coupling constant J on the covalency of the metal ions with the bridging ligands. This relationship is used to estimate the superexchange contribution in the tetramer (J = -156 cm(-)(1)) as compared to the mixed-valence dimer (J = -360 cm(-)(1)). These results, combined with estimates for the double exchange and the vibronic coupling contributions of the dimer sub-site of the tetramer, lead to a delocalized S(t) = (9)/(2) spin ground state for the mixed-valence dimer in the tetramer. Thus, the decrease in the covalency, hence the superexchange pathway associated with changing the bridging mode of the sulfides from micro(2) to micro(3) on going from the dimer to the tetramer, significantly contributes to the delocalization of the excess electron over the dimer sub-site in the tetramer.
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investigation of the electronic structure of 2fe 2s model complexes and the rieske protein using ligand k edge x ray absorption spectroscopy
Journal of the American Chemical Society, 1999Co-Authors: Kendra Rose, Britt Hedman, Keith O Hodgson, Thorsten Glaser, Susan E Shadle, S De Vries, Alexey V Cherepanov, Gerard W Canters, Edward I SolomonAbstract:X-ray absorption spectroscopy at the sulfur K-edge (∼2470 eV) has been applied to a series of 2Fe−2S model complexes to obtain insight into their electronic structures. Since these 2Fe−2S complexes contain both terminal thiolates and bridging sulfides, contributions to covalency from both sets of ligands can be evaluated. Importantly, the pre-edge feature of sulfide can be resolved from that of thiolate due to differences in Effective Nuclear Charge. In our previous studies, the covalency of the metal−thiolate bond in [Fe(SR)4]- was determined. In this study, sulfide covalency is quantified for the first time on the basis of an analysis of previous X-ray photoelectron and X-ray absorption spectroscopic studies of [FeCl4]- which are then applied to the bis-μ2-sulfide compound KFeS2. With references for both sulfide and thiolate covalencies thus established for open d-shell systems, comparisons are made between thiolate and sulfide bonding. Sulfide−Fe covalency in the [Fe2S2(SR)4]2- complexes is higher than...
Keith O Hodgson - One of the best experts on this subject based on the ideXlab platform.
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spectroscopic investigation of stellacyanin mutants axial ligand interactions at the blue copper site
Journal of the American Chemical Society, 2003Co-Authors: Serena Debeer George, Britt Hedman, Keith O Hodgson, Lipika Basumallick, Robert K Szilagyi, David W Randall, Michael G Hill, A M Nersissian, Joan Selverstone Valentine, Edward I SolomonAbstract:Detailed electronic and geometric structural descriptions of the blue copper sites in wild-type (WT) stellacyanin and its Q99M and Q99L axial mutants have been obtained using a combination of XAS, resonance Raman, MCD, EPR, and DFT calculations. The results show that the origin of the short Cu−S(Cys) bond in blue copper proteins is the weakened axial interaction, which leads to a shorter (based on EXAFS results) and more covalent (based on S K-edge XAS) Cu−S bond. XAS pre-edge energies show that the Effective Nuclear Charge on the copper increases going from O(Gln) to S(Met) to no axial (Leu) ligand, indicating that the weakened axial ligand is not fully compensated for by the increased donation from the thiolate. This is further supported by EPR results. MCD data show that the decreased axial interaction leads to an increase in the equatorial ligand field, indicating that the site acquires a more trigonally distorted tetrahedral structure. These geometric and electronic structural changes, which result f...
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s k edge x ray absorption studies of tetraNuclear iron sulfur clusters mu sulfide bonding and its contribution to electron delocalization
Journal of the American Chemical Society, 2001Co-Authors: Thorsten Glaser, Britt Hedman, Keith O Hodgson, Kendra Rose, Susan E Shadle, Edward I SolomonAbstract:X-ray absorption spectroscopy (XAS) at the sulfur ( approximately 2470 eV) and chlorine ( approximately 2822 eV) K-edges has been applied to a series of 4Fe-4S model complexes. These are compared to 2Fe-2S model complexes to obtain insight into the localized ground state in the mixed-valence dimer versus the delocalized ground state in the mixed-valence tetramer. The preedges of hypothetical delocalized mixed-valence dimers [Fe(2)S(2)](+) are estimated using trends from experimental data and density functional calculations, for comparison to the delocalized mixed-valence tetramer [Fe(4)S(4)](2+). The differences between these two mixed-valence sites are due to the change of the sulfide-bridging mode from micro(2) to micro(3). The terminal chloride and thiolate ligands are used as spectator ligands for the electron density of the iron center. From the intensity of the preedge, the covalency of the terminal ligands is found to increase in the tetramer as compared to the dimer. This is associated with a higher Effective Nuclear Charge on the iron in the tetramer (derived from the energies of the preedge). The micro(3)-bridging sulfide in the tetramer has a reduced covalency per bond (39%) as compared to the micro(2)-bridging sulfide in the dimer (51%). A simple perturbation model is used to derive a quadratic dependence of the superexchange coupling constant J on the covalency of the metal ions with the bridging ligands. This relationship is used to estimate the superexchange contribution in the tetramer (J = -156 cm(-)(1)) as compared to the mixed-valence dimer (J = -360 cm(-)(1)). These results, combined with estimates for the double exchange and the vibronic coupling contributions of the dimer sub-site of the tetramer, lead to a delocalized S(t) = (9)/(2) spin ground state for the mixed-valence dimer in the tetramer. Thus, the decrease in the covalency, hence the superexchange pathway associated with changing the bridging mode of the sulfides from micro(2) to micro(3) on going from the dimer to the tetramer, significantly contributes to the delocalization of the excess electron over the dimer sub-site in the tetramer.
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investigation of the electronic structure of 2fe 2s model complexes and the rieske protein using ligand k edge x ray absorption spectroscopy
Journal of the American Chemical Society, 1999Co-Authors: Kendra Rose, Britt Hedman, Keith O Hodgson, Thorsten Glaser, Susan E Shadle, S De Vries, Alexey V Cherepanov, Gerard W Canters, Edward I SolomonAbstract:X-ray absorption spectroscopy at the sulfur K-edge (∼2470 eV) has been applied to a series of 2Fe−2S model complexes to obtain insight into their electronic structures. Since these 2Fe−2S complexes contain both terminal thiolates and bridging sulfides, contributions to covalency from both sets of ligands can be evaluated. Importantly, the pre-edge feature of sulfide can be resolved from that of thiolate due to differences in Effective Nuclear Charge. In our previous studies, the covalency of the metal−thiolate bond in [Fe(SR)4]- was determined. In this study, sulfide covalency is quantified for the first time on the basis of an analysis of previous X-ray photoelectron and X-ray absorption spectroscopic studies of [FeCl4]- which are then applied to the bis-μ2-sulfide compound KFeS2. With references for both sulfide and thiolate covalencies thus established for open d-shell systems, comparisons are made between thiolate and sulfide bonding. Sulfide−Fe covalency in the [Fe2S2(SR)4]2- complexes is higher than...
Thorsten Glaser - One of the best experts on this subject based on the ideXlab platform.
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s k edge x ray absorption studies of tetraNuclear iron sulfur clusters mu sulfide bonding and its contribution to electron delocalization
Journal of the American Chemical Society, 2001Co-Authors: Thorsten Glaser, Britt Hedman, Keith O Hodgson, Kendra Rose, Susan E Shadle, Edward I SolomonAbstract:X-ray absorption spectroscopy (XAS) at the sulfur ( approximately 2470 eV) and chlorine ( approximately 2822 eV) K-edges has been applied to a series of 4Fe-4S model complexes. These are compared to 2Fe-2S model complexes to obtain insight into the localized ground state in the mixed-valence dimer versus the delocalized ground state in the mixed-valence tetramer. The preedges of hypothetical delocalized mixed-valence dimers [Fe(2)S(2)](+) are estimated using trends from experimental data and density functional calculations, for comparison to the delocalized mixed-valence tetramer [Fe(4)S(4)](2+). The differences between these two mixed-valence sites are due to the change of the sulfide-bridging mode from micro(2) to micro(3). The terminal chloride and thiolate ligands are used as spectator ligands for the electron density of the iron center. From the intensity of the preedge, the covalency of the terminal ligands is found to increase in the tetramer as compared to the dimer. This is associated with a higher Effective Nuclear Charge on the iron in the tetramer (derived from the energies of the preedge). The micro(3)-bridging sulfide in the tetramer has a reduced covalency per bond (39%) as compared to the micro(2)-bridging sulfide in the dimer (51%). A simple perturbation model is used to derive a quadratic dependence of the superexchange coupling constant J on the covalency of the metal ions with the bridging ligands. This relationship is used to estimate the superexchange contribution in the tetramer (J = -156 cm(-)(1)) as compared to the mixed-valence dimer (J = -360 cm(-)(1)). These results, combined with estimates for the double exchange and the vibronic coupling contributions of the dimer sub-site of the tetramer, lead to a delocalized S(t) = (9)/(2) spin ground state for the mixed-valence dimer in the tetramer. Thus, the decrease in the covalency, hence the superexchange pathway associated with changing the bridging mode of the sulfides from micro(2) to micro(3) on going from the dimer to the tetramer, significantly contributes to the delocalization of the excess electron over the dimer sub-site in the tetramer.
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investigation of the electronic structure of 2fe 2s model complexes and the rieske protein using ligand k edge x ray absorption spectroscopy
Journal of the American Chemical Society, 1999Co-Authors: Kendra Rose, Britt Hedman, Keith O Hodgson, Thorsten Glaser, Susan E Shadle, S De Vries, Alexey V Cherepanov, Gerard W Canters, Edward I SolomonAbstract:X-ray absorption spectroscopy at the sulfur K-edge (∼2470 eV) has been applied to a series of 2Fe−2S model complexes to obtain insight into their electronic structures. Since these 2Fe−2S complexes contain both terminal thiolates and bridging sulfides, contributions to covalency from both sets of ligands can be evaluated. Importantly, the pre-edge feature of sulfide can be resolved from that of thiolate due to differences in Effective Nuclear Charge. In our previous studies, the covalency of the metal−thiolate bond in [Fe(SR)4]- was determined. In this study, sulfide covalency is quantified for the first time on the basis of an analysis of previous X-ray photoelectron and X-ray absorption spectroscopic studies of [FeCl4]- which are then applied to the bis-μ2-sulfide compound KFeS2. With references for both sulfide and thiolate covalencies thus established for open d-shell systems, comparisons are made between thiolate and sulfide bonding. Sulfide−Fe covalency in the [Fe2S2(SR)4]2- complexes is higher than...
