Spectroscopic and computational studies of an end-on bound superoxo-Cu(II) complex: Geometric and electronic factors that determine the ground state

Abstract

A variety of techniques including absorption, magnetic circular dichroism (MCD), variable-temperature, variable-field MCD (VTVH-MCD), and resonance Raman (rR) spectroscopies are combined with density functional theory (DFT) calculations to elucidate the electronic structure of the end-on (η 1) bound superoxo-Cu(II) complex [TMG 3trenCuO 2] + (where TMG 3tren is 1,1,1-tris[2-[N 2-(1,1,3,3-tetramethylguanidino)]ethyl]amine). The spectral features of [TMG 3-trenCuO 2] + are assigned, including the first definitive assignment of a superoxo intraligand transition in a metalsuperoxo complex, and a detailed description of end-on superoxo-Cu(II) bonding is developed. The lack of overlap between the two magnetic orbitals of [TMG 3trenCuO 2] + eliminates antiferromagnetic coupling between the copper(II) and the superoxide, while the significant superoxo π * δ character of the copper dz 2 orbital leads to its ferromagnetically coupled, triplet, ground state. © 2010 American Chemical Society.