Four-Component Relativistic Density Functional Calculations of EPR Parameters for Model Complexes of Tungstoenzymes

For a closer validation
of four-component relativistic DFT methods
within the matrix Dirac–Kohn–Sham (mDKS) framework with
global hybrid functionals for EPR parameter calculations to be applied
in the modeling of tungsten enzymes, we refine a previously suggested
protocol for computations on 5d systems. This is done for a series
of larger, unsymmetrical W­(V) complexes thought to closely resemble
enzyme active sites in this oxidation state. Particular focus is placed
on complexes with thiolate and dithiolene ligands, along with an evaluation
of the influence of different amounts of exact-exchange incorporated
in hybrid PBE0-xHF functionals, an implicit solvent
model, and structural changes on the computed EPR parameters. Compared
to previous work, a slightly modified protocol with different optimal
exact-exchange admixtures for electronic g- and hyperfine A-tensors is found to provide the best agreement with experimental
EPR data. It will provide the basis for our subsequent tungsten enzyme
modeling efforts.