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 (Δ<i>E</i>), second order perturbation energy (<i>E</i>²), charge transfer (Δ<i>q</i>), 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.