Electronic effect related to the nonuniform distribution of ionic charges in metal-cluster chalcogenide halides

Recently, it was shown that the bond valence model is a unique tool to describe the lattice strains in (TM)₆ chalcogenide halides (TM = transition metal). Three different phenomena that result in valence violations were identified: (1) a steric conflict between countercations and the cluster-ligand framework, (2) a steric conflict between small (TM)₆ clusters and large coordination polyhedra around the cluster or the so-called matrix effect, and (3) nonuniform distribution of the anion valences (bond valence sums) around the clusters. This paper shows that the model is valid for a wide family of cluster compounds with different nuclearities. On the basis of the separation of the steric and electronic effects in the calculation procedure, the unusual distribution of the anion valences in the cluster compounds was assigned to the nonuniform spreading of ionic charges. Thus, stabilization mechanisms in cluster compounds were explained by simple electrostatic interactions.