Comparative calculation of EPR spectral parameters in [Mo^VOX₄]⁻, [Mo^VOX₅]²⁻, and [Mo^VOX₄(H₂O)]⁻ complexes

The EPR spectral parameters, i.e.g-tensors and molybdenum hyperfine couplings, for several d¹ systems of the general formula [Mo^VEX₄]ⁿ⁻, [Mo^VOX₅]²⁻, and [Mo^VOX₄(H₂O)]⁻ (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 MoE distance and EMo–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.