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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 [Cu 2 O 2 ] 2+ species in a closed shell singlet state, namely the side-on μ-η 2 :η 2 -[Cu 2 O 2 ] 2+ with D 2h 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 65 cm −1 and the triplet state at several eV higher. Some ammine complexes of [Cu 2 O 2 ] 2+ , studied by Ross and Solomon previously by the Xα-method, were also examined. Several features emerge: (a) the complex involving trans -[Cu 2 O 2 ] 2+ dissociates into 2[Cu(NH 3 ) 2 ] 2+ +O 2 ,; (b) the bare cis -[Cu 2 O 2 ] 2+ , species, which is unstable with an uncompleted co-ordination sphere, is greatly stabilised by an endogenous bridge such as OH − and 2NH 3 at each Cu centre; (c) the hydroxo bridged cis -[Cu 2 O 2 ] 2+ species shows two minima, one structure with short OO bond (1.2 A as in O 2 ) and another structure with long OO bond (1.4 A as in O 2 2− ); the two minima are separated by a low ( −1 ) barrier, thus hopping between them may occur. These findings cast light on the possible conversion of co-ordinated molecular oxygen to peroxide. |
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