Impact on ligand-field theory of the real ground state for CuCl2

Abstract

The recent prediction by coupled pair functional Hartree–Fock calculations of a degenerate ²Π_g ground term for linear CuCl₂ has been confirmed by local density funtional (LDF) Slater-type orbital calculations. This has prompted a new cellular ligand field (CLF) analysis. Contrary to previous results on higher-co-ordinate chlorocuprates(II) and other complexes, the relative σ to π Cu–Cl bonding ratios for CuCl₂, as predicted by the CLF e_λ parameters on the one hand and by the LDF overlap populations on the other, do not agree. However, the CLF data do correlate with the computed LDF bonding energies but only when the whole d manifold (i.e. the ²Π_g, ²Σ_g⁺ and ²Δ_g states) is taken into account. The interpretation and implications of these results within the ligand-field formalism are discussed.