On the Significance of Lone Pair/Lone Pair and Lone Pair/Bond Pair Repulsions in the Cation Affinity and Lewis Acid/Lewis Base Interactions

[Image: see text] Interaction of H(2)O, H(2)S, H(2)Se, NH(3), PH(3), and AsH(3) with cations H(+), CH(3)(+), Cu(+), Al(+), Li(+), Na(+), and K(+) was studied from the energetic and structural viewpoint using B3LYP/6-311++G(d,p) method. The charge transfer from the Lewis bases to the cations reduces lone pair/lone pair (LP/LP) repulsion in H(2)O, H(2)S, and H(2)Se and LP/bond pair (LP/BP) repulsion in NH(3), PH(3), and AsH(3). In parallel, changes in the H–M–H angles (M = O, S, Se, N, P, and As) are observed. The change in the H–M–H angle during the interactions was proportional to the amount of charge transferred from the bases to the cations and electron density (ρ) at the molecule/cation bond critical point. Also, the opposite trend for proton affinities of these two families, that is, NH(3) > PH(3) > AsH(3) and H(2)O < H(2)S < H(2)Se, was interpreted on the basis of LP/BP repulsion in their neutral and protonated forms. Interaction of the Lewis bases with neutral Lewis acids including BeH(2), BeF(2), and BH(3) was studied energetically and structurally. The calculated energies for interactions of H(2)O and NH(3) with BeH(2), BeF(2), and BH(3) are larger than the corresponding values for H(2)S, H(2)Se, PH(3), and AsH(3). This difference was interpreted on the basis of the lower stability of H(2)O and NH(3) because of large LP/LP and LP/BP repulsion in H(2)O and LP/BP repulsion in NH(3).