Bonding and Metastability for Group 12 Dications

Abstract

Electronic structure and bonding properties of the Group 12 dications M2(2+) (M = Zn, Cd, Hg) are investigated and electron density-derived quantities are used to characterize the metastability of these species. Of particular interest are the complementary descriptions afforded by the Laplacian of the electron density ∇^2 ρ(r)) and the Bohm quantum potential (Q = ∇^2 √(ρ(r) )/2√(ρ(r) )) along the bond path. Further, properties derived from the pair density including the localization-delocalization matrices (LDMs) and the interacting quantum atoms (IQAs) energies are analyzed within the framework of the Quantum Theory of Atoms in Molecules (QTAIM). From the crossing points of the singlet (ground) and triplet (excited) potential energy curves, the barriers for dissociation are estimated to be 25.2 kcal/mol (1.09 eV) for Zn2(2+), 22.8 kcal/mol (0.99 eV) for Cd2(2+), and 26.4 kcal/mol (1.14 eV) for Hg2(2+). At the equilibrium geometries, LDMs, which are used here as an electronic fingerprinting tool, clearly discriminate and group together Group 12 M2+ from its isoelectronic Group 11 M2. While “classical” bonding indices are inconclusive in establishing regions of metastability in the bonding, it is shown that the Bohm quantum potential is promising in this regard.