Ab initio study of structures, energetics, and bonding in formally high-oxidation-state copper organometallics

Geometry-optimized structures, energies, and harmonic vibrational frequencies of closed-shell states of CuL<SUP>+</SUP>, XCu<SUP>I</SUP>L, and XCu<SUP>III</SUP>L fragments (L = CO, C<SUB>2</SUB>H<SUB>4</SUB>, C<SUB>2</SUB>H<SUB>2</SUB>; X = H<SUP>-</SUP>, F<SUP>-</SUP>, OH<SUP>-</SUP>, O<SUP>2-</SUP>, N<SUP>3-</SUP>) have been obtained at the MP2 level using valence-DZP-quality basis sets with effective core potentials. Natural population analyses have been used to interpret the nature of metal-ligand interactions. The computed data for all the Cu(I) species are along expected lines. Interestingly, the formally high-oxidation-state species also have effectively d<SUP>10</SUP> configurations, with the electron deficiency localized in the ligands. As a result, the Cu-X bonds are long and, in a few cases, the ligand L dissociates during geometry optimization. In the computed minima, the Cu-L interaction energies are fairly large, primarily due to electrostatic interactions. The extent of &#960;-back-donation is generally low in "Cu(III)" systems. However, a strong &#960;-donor group enhances the ability of the metal to engage in d&#960;-p&#960; bonding with CO, C<SUB>2</SUB>H<SUB>4</SUB>, or C<SUB>2</SUB>H<SUB>2</SUB>, making it comparable to a typical Cu<SUP>I</SUP>L system in all respects. The trends are virtually identical in all three lowest energy closed-shell states of the ethylene and acetylene complexes