Accurate Calculation of Electron Paramagnetic Resonance Parameters for Molybdenum Compounds.

Paramagnetic molybdenum compounds are of great interest in inorganic chemistry and metalloenzyme catalysis. Electron paramagnetic resonance (EPR) spectroscopies that determine hyperfine coupling constants (HFCs) and g-tensor values are essential for investigating the electronic structure of these compounds, but require support from accurate quantum chemical approaches. Here, a database of Mo(V) complexes with well-defined structures and EPR parameters is presented, and optimal quantum chemical protocols for ⁹⁵Mo HFCs and g-values are investigated. It is shown that unmodified segmented all- electron relativistically contracted (SARC) all-electron basis sets can produce converged results for HFCs and g-values with the exact-2-component (X2C) Hamiltonian. The dependence of EPR parameters on the functional is studied in detail. Double-hybrid functionals and global hybrids with high exact exchange are top performers for ⁹⁵Mo HFCs, with PBE0-DH achieving the best agreement with experiment. Comparison of density functional theory (DFT)-derived HFCs with values obtained by coupled cluster theory with the domain-based local pair natural orbital approach (DLPNO-CCSD) shows that DFT remains the method of choice for the present set of compounds. Smaller differentiation among functionals is observed for g-tensors, although PBE0-DH is still a top performer and can be recommended as the most reliable approach overall for describing both valence and core properties of Mo compounds.