Tetrel-Bond Interactions Involving Metallylenes TH₂ (T = Si, Ge, Sn, Pb): Dual Binding Behavior

The dual binding behavior of the metallylenes TH₂ (T = Si, Ge, Sn, Pb) with some selected Lewis acids (T'H₃F, T' = Si, Ge, Sn, Pb) and bases (N₂, HCN, CO, and C₆H₆) has been investigated by using the high-level quantum chemical method. Two types (type-A and type-B) of tetrel-bonded complexes can be formed for TH₂ due to their ambiphilic character. TH₂ act as Lewis bases in type-A complexes, and they act as Lewis acids in type-B ones. CO exhibits two binding modes in the type-B complexes, one of which is TH₂···CO and the other is TH₂···OC. The TH₂···OC complexes possess a weaker binding strength than the other type-B complexes. The TH₂···OC complexes are referred to as the type-B2 complexes, and the other type-B complexes are referred to as the type-B1 complexes. The type-A complexes exhibit a relatively weak binding strength with E_int (interaction energy) values ranging from -7.11 to -15.55 kJ/mol, and the type-B complexes have a broad range of E_int values ranging from -9.45 to -98.44 kJ/mol. The E_int values of the type-A and type-B1 complexes go in the order SiH₂ > GeH₂ > SnH₂ > PbH₂. The AIM (atoms in molecules) analysis suggests that the tetrel bonds in type-A complexes are purely closed-shell interactions, and those in most type-B1 complexes have a partially covalent character. The EDA (Energy decomposition analysis) results indicate that the contribution values of the three energy terms go in the order electrostatic > dispersion > induction for the type-A and type-B2 complexes, and this order is electrostatic > induction > dispersion for the type-B1 complexes.