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

In addition to a structure with a PH center dot center dot center dot N 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 NH3. 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 PH3, H2S, HCl, AsH3, and NH3 are all paired with NH3 as electron donor. While NH3 will not engage in an N center dot center dot center dot N attraction, all the others do form a X center dot center dot center dot N 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 XH center dot center dot center dot N 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-X center dot center dot center dot N 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 center dot center dot center dot N interaction. (C) 2011 American Institute of Physics. [doi:10.1063/1.3585611]