Structure, energetics, and infrared spectra of weakly bound HC(2n+1)N···HCl complexes. A theoretical study

Three model systems, HCN···HCl, HC(3)N···HCl, and HC(5)N···HCl, have been investigated computationally with the use of the second-order Möller-Plesset (MP2) and the coupled cluster (with single and double excitations and noniterative inclusion of triples) methods. The global minima are linear hydrogen-bonded structures with HCl as a proton donor. Bent structures are proton-side complexes with HCl as an electron donor, while the bifurcated hydrogen bonds are predicted for t-shape complexes. One of the most important findings in this paper is that, according to symmetry-adapted perturbation analysis, the induction-to-dispersion ratios are the biggest for linear complexes, and it is the most noticeable difference between linear, bent, and t-shape structures.