The curious case of co-planarity in di-nuclear triel complexes: a density functional investigation

Density functional investigation of intramolecular triel (Tr) bonding present in di-nuclear aryl complexes of group 13 elements having general formula [(Tr)Me₂(2,6-(X)₂C₆H₃O)]₂ (Tr = B, Al, Ga, In & Tl and X = OMe, OEt, OH, OPh, NH₂, SH, Cl, F) has been performed. Conclusive evidence of the concurrent two σ-hole interaction has been provided by analysis of the Tr bond length, interaction energy (ΔE), second order perturbation energy (E²), charge transfer (Δq), quantum theory of atom in molecules (QTAIM) and noncovalent interaction (NCI) plots for 12 complexes. The Tr bond length in the optimized geometry varies from 2.49 to 2.89 Å in Al complexes (1-8) and 2.66 to 2.83 Å in other group 13 element complexes (9-12) at the PBE0-D3 functional. The interaction energy calculation reveals that the co-planar structure of complexes containing Al (1-8) are more stable than their rotamers by 8-15 kcal mol^-1, whereas the di-nuclear complexes of other group 13 complexes (9-12) orient in a non-planar pocket structure. This loss of co-planarity reveals the fact that its presence relies on the Tr atom, not the intramolecular Tr bonding, which has a striking impact on the crystal engineering of di-nuclear complexes of Group 13.