On the electronic structures and spectra of NiCl2 and CuCl2

Abstract

The geometry and ground state of NiCl₂ have been studied using local density-functional (LDF) calculations within the linear combination of Gaussian-type orbitals (LCGTO) framework. The molecule is found to be linear with a ³Σ_g^– ground state in agreement with recent experimental results but contrary to previous theoretical studies. The calculated bond length and vibrational frequencies are in excellent agreement with experiment. A cellular ligand-field (CLF) analysis of the spectrum has been performed. The LDF and CLF calculations provide a consistent description of the bonding and suggest that the chloride ions are acting as good σ and π donors in this molecule with both roles enhanced compared to systems with higher co-ordination numbers. A proper account of the important interaction of the d_σ orbital with the antibonding σ_g⁺ orbital is given using a cylindrically symmetric ‘void’ cell. A recent CLF analysis of CuCl₂ is shown to be incorrect because of the treatment of the void interaction. A new study of the ligand-field spectrum of CuCl₂ is presented, the results of which are consistent with the LDF and CLF studies on NiCl₂ and with recent molecular orbital and LDF calculations on CuCl₂.