| Sumario: | The geometric and electronic structure of the untethered heme–peroxo–copper model complex [(FTPP)Fe–(O)–Cu(TMPA)](ClO) (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 S = 2 spin state were performed on [(P)Fe–(O)–Cu(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)Fe–(O)–Cu(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 d orbital from the peroxide π* orbital. In the case of the Fe––peroxide η² bond, the two major components arise from the donor interactions of the peroxide π* and π* orbitals with the Fe d and d orbitals, which give rise to σ and δ bonds, respectively. The π* interaction with both the half-occupied d orbital on the copper (η¹) and the d orbital on the iron (η²), provides an effective superexchange pathway for strong antiferromagnetic coupling between the metal centers.
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