SH···N and SH···P blue-shifting H-bonds and N···P interactions in complexes pairing HSN with amines and phosphines.

Quantum calculations at the MP2/aug-cc-pVDZ level examine complexes pairing HSN with aliphatic amines and phosphines. Complexes are cyclic and contain two attractive interactions. The first is a SH···N/P H-bond in which the S-H covalent bond contracts and shifts its stretching frequency to the blue, more so for amines than for phosphines. The second interaction is different for the amines and phosphines. The amines engage in a NH···N H-bond comparable in strength to the aforementioned SH···N interaction. In contrast, the second interaction in the phosphine complexes is a direct N···P attraction without an intervening H. This interaction is due in part to opposite partial charges on the N and P atoms, as well as covalent forces generated by charge transfer effects.