Effect of counterions on hypervalent interactions in prereaction complexes of S N 2 reactions of bisphenoid compounds of the second and third period elements

Abstract

The electronic and molecular structures of the (LiF)nXFm complexes (X = C, N, O, F, Si, P, S, Cl; m = 1–4, n = 0, 1, 3) were studied by the ab initio (MP2(full)/6-311+G*) and density functional theory (B3LYP/6-311+G*) methods. All bisphenoid anionic structures XFm− (X = C, N, O, F, Si, P, S, Cl; m = 2–5) of elements of the second and third periods, except carbon fluorides, are most stable in the hypervalent state of atoms with strongly elongated axial bonds. Carbon tetrafluoride forms a stable intermolecular F−...CF4 complex. In all cases of addition of the Li atom as a counterion, the most stable intermolecular complex of lithium fluoride with fluorides of elements is stabilized by the hypervalent interaction. In all cases when the counterion is complicated to lithium trifluoride, except for (LiF)3CF4 and (LiF)3NF3, the hypervalent structure with equal and elongated X-F axial bonds is stabilized. In the cases of the (LiF)3CF4 and (LiF)3NF3 complexes, the prereaction structures bound by the strong hypervalent interaction are stabilized.