A comprehensive theoretical study on the structure and stability of linear and triangular isomers of anionic clusters of zinc, cadmium and mercury (Y2 3 Þ and their binding with one and two alkali metal cations (Xþ ¼ Liþ, Naþ, Kþ) has been investigated at the density functional (BP86 and B3LYP) and ab initio (MP2, MP4 and coupled cluster single and double (CCSD)) methods. The results showed that in all cases, the triangular geometry with D3h symmetry is more stable than linear one. The calculated values of interaction energies (IE) between Y2 3 anions and two Xþ cations, Wiberg bond indices (WBI) and the electron densities at bond critical points (BCP), (BCP), for Y–X bonds show that among all complexes investigated here at all levels of theory Zn3Li2 and Hg3K2 have the largest and the smallest values of IE, WBI and (BCP), respectively. The natural charges of the atoms and WBI involved in the bonding as well as the global value of the charge transfer Q from Y2 3 to Xþ cation in X2Y3 clusters, evaluated through natural population analysis, con¯rmed that covalent contribution in Y–X bond formation increases from Kþ to Liþ. Also the energy decomposition analyses (EDA) were used to detect the nature of interaction in the complexes. The results con¯rmed that the contribution of electrostatic interactions in present complexes is almost more than 70%.
