Competition between intramolecular hydrogen and pnictogen bonds in protonated systems
A theoretical study of the competition between hydrogen (HB) and pnictogen bonds (ZB) in three different families of compounds, (Z)-1,2-disubstituted ethenes (Eth), 1,2-disubstituted benzenes (Phe) and 1,8-disubstituted naphthalenes (Naph), with a charged group, ZH3 + and a neutral one, Z′H2 (Z, Z′ = N, P, As) as interacting moieties, has been carried out. In those structures with a NH3 +motif, intramolecular hydrogen bond structures are minima while pnictogen interactions are transition states. The opposite is true for PH3 + and AsH3 + moieties. An analysis of isodesmic energies (Eiso), interaction energies (E b) and deformation energies (E def) shows that in Eth derivatives, the most stable compound corresponds to P+–N ZB while in the Phe and Naph ones, the N+–N HB interaction presents the largest negative isodesmic energy. Also, Eth and Phe derivatives show negative E iso values for all the compounds under study; however, in some cases of Naphderivatives positive isodesmic energies have been found. The Atoms in Molecules (AIM) analysis of the electron density, natural bond orbital (NBO) second-order orbital energies and electron density shift maps (EDS) have been used to better understand these intramolecular interactions.