Theoretical studies on the structure and aromaticity of Ti ₂P₆⁺

Cationic cluster Ti₂P₆⁺ has been studied within density functional theory. The structure of this cluster is predicted to be a slightly distorted tetragonal prism. The dissociation energy of this cationic cluster is higher than that of the known sandwich compound, [(P ₅)₂Ti]^2-, because of the different bonding in these two compounds. In Ti₂P₆⁺, the hybridization of P atoms of the ring is sp³. The bonding between the metal atoms and the P ring is mainly σ-π. While in [(P ₅)₂Ti]^2-, the P atoms take sp² hybridization, the bonding between the metal atom and the rings is the typical π-π interaction. The electronic delocalization is another stabilizing factor for Ti₂P₆⁺. The nuclear independent chemical shift indicates that Ti₂P₆⁺ is a three-dimensional aromatic molecule. The predicted infrared and NMR help to identify the Ti₂P₆⁺ conformations in experiment.