title: Geometric and electronic structure of the heme-peroxo-copper complex [(F8TPP)FeIII-(O22-)-CuII(TMPA)](ClO4).
abstract: The geometric and electronic structure of the untethered heme-peroxo-copper model complex [(F(8)TPP)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](ClO(4)) (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 Cu...Fe distance of approximately 3.72 A. Spin-unrestricted DFT calculations for the S(T) = 2 spin state were performed on [(P)Fe(III)-(O(2)(2)(-))-Cu(II)(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 mu-eta(1):eta(2) coordination mode. The calculated Cu...Fe distance is approximately 0.3 A longer than that observed experimentally. Reoptimization of [(P)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](+) with a 3.7 A Cu...Fe constrained distance results in a similar energy and structure that retains the overall mu-eta(1):eta(2)-peroxo coordination mode. The primary bonding interaction between the copper and the peroxide involves electron donation into the half-occupied Cu d(z)2 orbital from the peroxide pi(sigma) orbital. In the case of the Fe(III)-peroxide eta(2) bond, the two major components arise from the donor interactions of the peroxide pi*(sigma) and pi*(v) orbitals with the Fe d(xz) and d(xy) orbitals, which give rise to sigma and delta bonds, respectively. The pi*(sigma) interaction with both the half-occupied d(z)2 orbital on the copper (eta(1)) and the d(xz) orbital on the iron (eta(2)), provides an effective superexchange pathway for strong antiferromagnetic coupling between the metal centers.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Del Río
authors.forename: Ritimukta
authors.initials: R
authors.lastname: Sarangi
authors.forename: Eduardo E
authors.initials: EE
authors.lastname: Chufán
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D003300:Copper / Q000737:chemistry; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000378:metabolism; D006418:Heme / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010472:Perchlorates / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D026901:Membrane Transport Proteins; D009942:Organometallic Compounds; D010472:Perchlorates; D010545:Peroxides; D006418:Heme; D003300:Copper; D007501:Iron; D003576:Electron Transport Complex IV; D010100:Oxygen