Structure of trimers of group-2B metal dihalides from relativistic density-functional calculations

We report density-functional calculations, carried out in a quantum-chemical approach using localised-Gaussians expansions of the Kohn–Sham orbitals, for metal dihalides trimers (MX2)3, where X = Cl, Br, or I and M = Zn, Cd, or Hg. The reliability of the method and the relevance of relativistic terms are assessed by comparisons with previous results on bond lengths in the monomer and dimer of these compounds. In a viewpoint regarding the trimer as a possible structural component of expanded liquid states and of compressed gaseous states, we stress the character of the local coordination of the metal ion in the ground state as being of a distorted tetrahedral type in the case of the trimer of the Zn and Cd dihalides and of a twofold type in the Hg dihalides. We also discuss the presence of metastable and unstable structures at higher energies and the quantum-chemical topology of the trimer.