The interaction of fluoramines, fluorophosphines and fluoroarsines with hydrogen fluoride clusters (HF)n: Model studies on blue-shifted hydrogen bonds

Complexes formed between the molecules XH2F and XHF2, with X∈{N, P, As}, and hydrogen fluoride clusters (HF)n (1≤n≤3) were investigated within the framework of second-order Møller-Plesset perturbation theory applying extended basis sets. Two types of minima have been detected for each of the dimeric complexes. In one structure type, FH⋯XH2F and FH⋯XHF2, only F-H⋯X hydrogen bonds occur, but nevertheless blue shifts of the free X-H stretching vibrations are predicted. In the second type, a cyclic structure with weaker X-H⋯F contacts and stronger F-H⋯F hydrogen bonds is calculated. The latter type of complexes show weak red shifts of the X-H stretching vibrations, when X=N, and display blue shifts when X=P or X=As. All higher clusters XH2F-(HF)n and XHF2-(HF)n, with n=2 and 3, again form two types of cyclic structures. When X=N, red shifts as well as blue shifts of N-H stretching frequencies are encountered. When X=P or X=As, all X-H stretching vibrations are blue-shifted. This behavior is rationalized by considering the response of fluoramines, fluorophosphines and fluoroarsines to external electric fields and by selected scans of their potential energy surfaces.