Structure and spectra of dicopper(I) dioxygen species and their ammino complexes studied by ab initio calculations

Abstract

Ab initio calculations were carried out on the species resulting from the co-ordination of molecular oxygen to two Cu(I) centres. The calculations were performed at the HF and QCISD(T) levels with different sets of wave functions (a) STO-3G∗∗; (b) 3-21G∗∗ basis; (c) 3-21G∗∗ for Cu and 6-31G∗∗ for O. The highest symmetry structure of [Cu2O2]2+ species in a closed shell singlet state, namely the side-on μ-η2:η2-[Cu2O2]2+ with D2h symmetry, was found to be the lowest energy one (the global minimum) on the six-dimensional hypersurface. The open shell singlet of this species is at about 65cm−1 and the triplet state at several eV higher. Some ammine complexes of [Cu2O2]2+, studied by Ross and Solomon previously by the Xα-method, were also examined. Several features emerge: (a) the complex involving trans-[Cu2O2]2+ dissociates into 2[Cu(NH3)2]2++O2,; (b) the bare cis-[Cu2O2]2+, species, which is unstable with an uncompleted co-ordination sphere, is greatly stabilised by an endogenous bridge such as OH− and 2NH3 at each Cu centre; (c) the hydroxo bridged cis-[Cu2O2]2+ species shows two minima, one structure with short OO bond (1.2Å as in O2) and another structure with long OO bond (1.4Å as in O22−); the two minima are separated by a low (<300cm−1) barrier, thus hopping between them may occur. These findings cast light on the possible conversion of co-ordinated molecular oxygen to peroxide.