On the properties of XN noncovalent interactions for first-, second-, and third-row X atoms

摘要

In addition to a structure with a PHN H-bond, a second complex of greater stability is formed when the PH3 is rotated such that its P-H bond is pointing away from the approaching N lone pair of NH_3. Quantum calculations are applied to examine whether such a complex is characteristic only of P, or may occur as well for other atoms of the first, second, or third rows of the periodic table. The molecules PH_3, H_2S, HCl, AsH_3, and NH_3 are all paired with NH_3 as electron donor. While NH_3 will not engage in an NN attraction, all the others do form a XN complex. The energetics, geometries, and other properties of these complexes are relatively insensitive to the nature of the X atom. This uniformity contrasts sharply with the H-bonded XHN complexes where a strong sensitivity to X is observed. The three-dimensional nature of the electrostatic potential, in conjunction with the striving for a linear H-XN orientation that maximizes charge transfer, serves as an excellent tool in understanding both the shape of the potential energy surface and the proclivity to engage in a X...N interaction.