Study on cooperativity of bonds in NH3…H2O−M (M= Li+, Na+, K+, Rb+,Cs+ and Sr2+) triads having metal cation and hydrogen bond

While the structure and properties of small molecules are determined by covalent bonding, in any larger system, noncovalent interactions become equally important[1].Among the non-covalent interactions, hydrogen bonds are the most common type of weak interactions[2]. The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation[3]. In this work, we try to investigate the cooperativity between a Mn+−OH2 bond and a NH3...H2O hydrogen bond in NH3…H2O−M(M= Li+, Na+, K+, Rb+,Cs+ and Sr2+) triads. The geometries of all dyads and triads in the gas-phase were fully optimized with def2-TZVPD basis set at MP2 and M06 levels of theory using the Gaussian 09 set of programs. The different types of interaction and stabilization energies[4]were calculated and corrected for the basis set superposition error (BSSE)[4].In order to study the cooperativity in these systems, a newly presented method was used[5].The data showed that the total cooperativity of triads correlateswell with the sum of the changes in values ofMn+−OH2andNH3...H2O interactions,upon the formation of NH3...H2O−Mn+ triad.