Non-covalent interactions in ammonium cation–acetylene clusters

MP2/6-311++G(d,p) calculations on NH 4 + ⋯ ( C 2 H 2 ) n (n = 1–8) complexes have been carried out and their structures were analyzed. The stable shell of four acetylene molecules is formed for the NH 4 + ⋯ ( C 2 H 2 ) 4 cluster since all C2H2 molecules are connected with NH 4 + ion through NH⋯π hydrogen bonds. For the greater number of acetylene molecules within the cluster (n > 4) the stable shell structure of four acetylene molecules is partly destroyed and NH⋯π hydrogen bonds are weaker than such interactions for clusters containing fewer acetylene molecules. Additionally for n ⩾ 4 the other interactions play an important role in the stabilization of clusters, these are N⋯π and CH⋯π non-covalent interactions.