Theoretical and experimental potential energy surface (PES) of pentachlorocuprate(II) in two dimensions

Abstract

A new structural index φ is devised to describe the distortions in five-coordinate copper(II) complexes which can be square pyramidal, trigonal bipyramid or in between. It is shown that this single parameter can describe the characteristic energy of penta-chlorocuprate(II) anion which is crystallized in different geometries depending on the nature of the counter cation. The potential energy surface for this copper anion is delineated in terms of φ and the single point energies calculated by DFT at the BP86/6-31+G(2d,p) level and the semiempirical method PM6. The population diagram for some 136 five-coordinate copper(II) complexes, chosen mostly at random, characterized by X-ray crystallography is drawn in terms of φ. It is found that at minimas of the theoretical potential energy surface, maximas of clustering of complexes occur in the population diagram; deeper the minima, more is the grouping. Thus a one-to-one correspondence between the two figures is established. Accordingly, the population diagram is proposed as an experimental potential anergy surface for the cuprate anion.