Geometric and Electronic Structure of the Heme-Peroxo-Copper Complex [(F8TPP)FeIII-(O22)-Cu"(TMPA)](CIO4).

The geometric and electronic structure of the untethered heme–peroxo–copper model complex [(F8TPP)FeIII–(O22-)–CuII(TMPA)](ClO4) (1) has been investigated using Cu and Fe K-edge EXAFS spectroscopy and density functional theory calculations in order to describe its geometric and electronic structure. The Fe and Cu K-edge EXAFS data were fit with a CuߪFe distance of ∼3.72 Å. Spin-unrestricted DFT calculations for the ST = 2 spin state were performed on [(P)FeIII–(O22-)–CuII(TMPA)]+ as a model of 1. The peroxo unit is bound end-on to the copper, and side-on to the high-spin iron, for an overall μ-η¹; η² coordination mode. The calculated CuߪFe distance is ∼0.3 Å longer than that observed experimentally. Fleoptimization of [(P)FeII–(O22-)–CuII(TMPA)]+ with a 3.7 Å CuߪFe constrained distance results in a similar energy and structure that retains the overall μ-η¹η²-peroxo coordination mode. The primary bonding interaction between the copper and the peroxide involves electron donation into the half-occupied Cu dZ² orbital from the peroxide π*σ orbital. In the case of the FeIII––peroxide η² bond, the two major components arise from the donor interactions of the peroxide π*σ and π*v orbitals with the Fe dXZ and dxy orbitals, which give rise to σ and δ bonds, respectively. The π*σ interaction with both the half-occupied dZ² orbital on the copper (η¹) and the dxz orbital on the iron (η²), provides an effective superexchange pathway for strong antiferromagnetic coupling between the metal centers. [ABSTRACT FROM AUTHOR]