Revealing charge-shift bonds in H3+ and their metallic analogs M3+ (M = Li, Na, K) through electron density topology

The bonding pattern of H3+ and its metallic isomers M3+ (M = Li, Na, and K) have been studied through the topological criterion by the quantum theory of atoms in molecules (QTAIM), interacting quantum atoms (IQA) and valence bond (VB) approach at the Coupled Cluster level. The results show that for the studied compounds, it is possible to state that they are not ring-type structures but structures in which the atoms are bound through electrostatic and covalent interactions (in that order of priority) to a non-nuclear attractor (NNA) located in the geometric center of the atomic positions. A series of resonance structures have been proposed following the VB model, including those of the covalent and ionic type with the participation of the NNA, which would explain the computed results. Additionally, a simple way of calculating the percentages of the contribution of each resonance structure using the delocalization and localization indexes is proposed. Calculated values show that the ionic resonance structures have a high contribution in the four studied systems, so it is possible to conclude that these compounds have charge-shift bonds.