Non-covalent interactions in NH4+•••(C2H2)n ammonium cation-acetylene

MP2/6-311++G(d,p) calculations on NH4+, center dot center dot center dot (C2H2)(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 NH4+ center dot center dot center dot (C2H2)(4) cluster since all C2H2 molecules are connected with NH4+ ion through N-H center dot center dot center dot pi 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 N-H center dot center dot center dot pi 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 center dot center dot center dot pi and C-H center dot center dot center dot pi non-covalent interactions. (C) 2012 Elsevier B.V. All rights reserved.