Tetrel bond of pseudohalide anions with XH3F (X = C, Si, Ge, and Sn) and its role in SN2 reaction

The complexes of XH3F center dot center dot center dot N-3(-)/OCN-/SCN- (X = C, Si, Ge, and Sn) have been investigated at the MP2/aug-cc-pVTZ(PP) level. The sigma-hole of X atom in XH3F acts as a Lewis acid forming a tetrel bond with pseudohalide anions. Interaction energies of these complexes vary from -8 to -50 kcal/mol, mainly depending on the nature of X and pseudohalide anions. Charge transfer from N/O/S lone pair to X-F and X-H sigma* orbitals results in the stabilization of these complexes, and the former orbital interaction is responsible for the large elongation of X-F bond length and the remarkable red shift of its stretch vibration. The tetrel bond in the complexes of XH3F (X = Si, Ge, and Sn) exhibits a significant degree of covalency with XH3F distorted significantly in these complexes. A breakdown of the individual forces involved attributes the stability of the interaction to mainly electrostatic energy, with a relatively large contribution from polarization. The transition state structures that connect the two minima for CH3Br center dot center dot center dot N-3(-) complex have been localized and characterized. The energetic, geometrical, and topological parameters of the complexes were analyzed in the different stages of the S(N)2 reaction N-3(-) + CH3Br -> Br- + CH3N3. Published by AIP Publishing.