Comparative calculation of EPR spectral parameters in [Mo^VOX_4]^-, [Mo^VOX_5]^(2-), and [Mo^VOX_4(H_2O)]^- complexes

Abstract

The EPR spectral parameters, i.e. g-tensors and molybdenum hyperfine couplings, for several d^1 systems of the general formula [Mo^VEX_4]^(n-), [Mo^VOX_5]^(2-), and [Mo^VOX_4(H_2O)]^- (E = O, N; X = F, Cl, Br; n = 1 or 2) were calculated using Density Functional Theory. The influence of basis sets, their contraction scheme, the type of exchange-correlation functional, the amount of Hartree-Fock exchange, molecular geometry, and relativistic effects on the calculated EPR spectra parameters have been discussed. The g-tensors and molybdenum hyperfine coupling parameters were calculated using a relativistic Hamiltonian coupled with several LDA, GGA, and 'hybrid' exchange-correlation functionals and uncontracted full-electron DGauss DZVP basis sets. The calculated EPR parameters are found to be sensitive to the Mo=E distance and E=Mo-Cl angle, and thus the choice of starting molecular geometry should be considered as an important factor in predicting the g-tensors and hyperfine coupling constants in oxo-molybdenum compounds. In the present case, the GGA exchange-correlation functionals provide a better agreement between the theory and the experiment.