First-principle computation of zero-field splittings: Application to a high valent Fe(IV)-oxo model of nonheme iron proteins

We report the computational implementation of a combined spin-density-functional theory and perturbation theory (SDFT-PT) methodology for the accurate calculation of zero-field splittings (ZFS) in complexes of the most diverse nature including metal centers in proteins. We have applied the SDFT-PT methodology to study the cation of the recently synthesized complex [Fe-IV(O)-(TMC)(NCCH3)](OTf)(2), [J. Rohde , Science 299, 1037 (2003)] which is an important structural and functional analog of high-valent intermediates in catalytic cycles of nonheme iron enzymes. The calculated value (D-Theory=28.67 cm(-1)) is in excellent agreement with the unusually large ZFS reported by experiment (D-Exp=29 +/- 3 cm(-1)). The principal component D-zz of the ZFS tensor is oriented along the Fe-IV=oxo bond indicating that the oxo ligand dominates the electronic structure of the complex.