Dimeric and Tetrameric Complexes of Copper(O)

Abstract

STABLE compounds of copper(O) appear to be unknown except for the barium salt of the complex acetylide anion [PhC≡C—Cu—Cu—C≡CPh]²⁻ described by Nast et al.¹ and perhaps a phthalocyanine complex². Derivatives of copper(O) if monomeric should be paramagnetic (4s¹ configuration) and, if dimeric, diamagnetic like the isoelectronic mercuric chloride. The dimeric acetylide copper(O) anion is indeed diamagnetic as is, presumably, the Cu₂ molecule, which exists in equilibrium with copper atoms in the gas phase. The Cu₂ molecule has a surprisingly high dissociation energy (45.5±2 kcal/mole), the corresponding value⁵ for Ag₂ and Au₂ being 39 and 51.5 kcal/mole respectively³. Nevertheless, the Cu₂ species is thermodynamically unstable with respect to metallic copper, because for the reaction Cu_2(g)→ 2Cu_(C), ΔH = − 115.5 kcal. The stabilization of the Cu₂ and Cu₄ species has now been achieved using a variety of different ligands.