g- and a-tensor calculations in the zero-order approximation for relativistic effects of Ni complexes Ni(mnt)2- and Ni(CO)3H as model complexes for the active center of [NiFe]-hydrogenase

Fully relativistic calculations in the zero-order regular approximation (ZORA) for relativistic effects were performed for the inorganic complexes bis(maleonitriledithiolato)nickelate(III) (Ni(mnt)(2)(-)) and nickeltricarbonylhydride (Ni(CO)(3)H). They have some similarities with the active center of the [NiFe] hydrogenase. The influence of scalar-relativistic (SR) effects on the structural parameters are discussed. For both complexes, magnetic resonance parameters (g-, hyperfine, and quadrupole tensors) are obtained. The deviation of the calculated g-tensor values from the experimental data is proportional to the deviation from the free electron value. The agreement between calculated and experimental hyperfine tensors for transition metals is very good when scalar-relativistic (SR) effects and spin-orbit (SO) coupling are considered. The isotropic hyperfine interaction is taken from SR unrestricted calculations and the anisotropic part from SR and SO spin-restricted calculations. The relativistic effects are not so large for the lighter ligand atoms.