Proton acceptor response in hydrogen-bonded XH ... WZ (X = F, Cl, Br, FAr, FKr, NC, FCC; WZ = CO, FH, N2) complexes

An MP2/6-311++G(3df,3pd) computational study of the model complexes XH...WZ (X = F, Cl, Br, FAr, FKr, NC, FCC; WZ = CO, FH, N-2), which involve both red- and blue-shifting hydrogen bonds, was undertaken. The response of the hydrogen bond acceptors WZ, as gauged from their bond length change and the frequency shifts of their stretching modes, was investigated. The W-Z bond length change (extension or compression) depends on the sign of the WZ dipole moment derivative with respect to bond extension. The hydrogen bond strength and the WZ bond length change/frequency shift were found to be strongly correlated.