Carbene tetrel-bonded complexes

An ab initio calculation has been carried for the carbene tetrel bonded complexes CH(3)Ya (TM) a (TM) a (TM) CH2 (Y = F, CN, NC, and NO2), CH(3)Fa (TM) a (TM) a (TM) CZ(2) (Z = Cl and CH3), XH(3)Fa (TM) a (TM) a (TM) CF2 (X = C, Si, Ge, and Sn), SiF(4)a (TM) a (TM) a (TM) CF2, and XH(3)Fa (TM) a (TM) a (TM) NHC (N-heterocyclic carbene), where carbene is treated as a Lewis base and XH3Y is a Lewis acid. Formation of the tetrel bond is mainly attributed to charge transfer from the lone pair on the C atom in the carbene toward the sigma* X-Y orbital and also the sigma* X-H one in the strong tetrel bond. The carbene tetrel bond is strengthened/weakened by the electron-withdrawing group in the tetrel donor/acceptor and enhanced by the methyl group in C(CH3)(2). NHC forms a stronger carbene tetrel bond in XH(3)Fa (TM) a (TM) a (TM) NHC (X = Si, Ge, and Sn) where it exceeds that of the majority of H-bonds. Interestingly, the tetrel bond becomes stronger in the order of X = C < Ge < Sn < Si in XH(3)Fa (TM) a (TM) a (TM) NHC and the largest interaction energy occurs in SiH(3)Fa (TM) a (TM) a (TM) NHC, amounting to -103 kJ/mol. The carbene tetrel bond can be strengthened by cooperative effect with the Na (TM) a (TM) a (TM) M interaction in trimers H2Ca (TM) a (TM) a (TM) CH3CNa (TM) a (TM) a (TM) M (M = CH3CN, HCN, ICN, SbH2F, LiCN, and BeH2) and has doubled in H2Ca (TM) a (TM) a (TM) CH3CNa (TM) a (TM) a (TM) BeH2.