Determination of the g-Tensors and Their Orientations for cis,trans-(L-N2S2)MoV
OX (X = Cl, SCH2Ph) by Single-Crystal EPR Spectroscopy and Molecular Orbital 
Calculations

Mader Cosper, Michele; Neese, Frank; Astashkin, Andrei V.; Carducci, Michael D.; Raitsimring, Arnold M.; Enemark, John H.

doi:10.1021/ic0483850

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Determination of the g-Tensors and Their Orientations for cis,trans-(L-N₂S₂)Mo^VOX (X = Cl, SCH₂Ph) by Single-Crystal EPR Spectroscopy and Molecular Orbital Calculations

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Neese, Frank
Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society;

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Mader Cosper, M., Neese, F., Astashkin, A. V., Carducci, M. D., Raitsimring, A. M., & Enemark, J. H. (2005). Determination of the g-Tensors and Their Orientations for cis,trans-(L-N₂S₂)Mo^VOX (X = Cl, SCH₂Ph) by Single-Crystal EPR Spectroscopy and Molecular Orbital Calculations. Inorganic Chemistry, 44(5), 1290-1301. doi:10.1021/ic0483850.

Cite as: https://hdl.handle.net/21.11116/0000-0008-38A6-E

Abstract

A single-crystal study of cis,trans-(L-N₂S₂)Mo^VOCl (1) doped into cis,trans-(N₂S₂)Mo^VIO₂ (3) has enabled the g-tensor of 1 and its orientation with respect to the molecular structure to be determined. The EPR parameters (g₁, 2.004; g₂, 1.960; g₃, 1.946; A₁, 71.7 × 10^-4 cm^-1; A₂, 11.7 × 10^-4 cm^-1; A₃, 32.0 × 10^-4 cm^-1) of cis,trans-(L-N₂S₂)Mo^VOCl [L-N₂S₂H₂ = N,N‘-dimethyl-N,N‘-bis(mercaptophenyl)ethylenediamine] mimic those of the low-pH form of sulfite oxidase and the “very rapid” species of xanthine oxidase. The principal axis that corresponds to g₁ is rotated ∼10° from the Mo⋮O vector, while the principal axis that corresponds to g₃ is located in the equatorial plane and ∼38° from the Mo−Cl vector. Independent theoretical calculations of the g-tensor of 1 were performed using two types of techniques: (1) the spectroscopically parametrized intermediate neglect of differential overlap technique (INDO/S) combined with single-excitation configuration interaction (CIS); (2) a scalar relativistic DFT (BP86 and B3LYP functionals) treatment using the zeroth order regular approximation to relativistic effects (ZORA) in combination with recently developed accurate multicenter mean field spin−orbit operators (RI-SOMF) and the estimation of solvent effects using dielectric continuum theory at the conductor-like screening model (COSMO) level. The excellent agreement between experiment and theory, as well as the high consistency between the INDO/S and BP86/ZORA results, provides a sound basis for analysis of the calculated orientation of the g-tensor for cis,trans-(L-N₂S₂)Mo^VO(SCH₂Ph) (2), for which single-crystal EPR data are not available but which contains three equatorial sulfur donor atoms, as occurs in sulfite oxidase and xanthine oxidase. The implications of these results for the EPR spectra of the Mo(V) centers of enzymes are discussed.