Competing Non-covalent Interactions in Alkali Metal Ion−Acetonitrile−Water Clusters

Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
The Journal of Physical Chemistry A (Impact Factor: 2.69). 06/2005; 109(17):3880-6. DOI: 10.1021/jp050534s
Source: PubMed


Competitive ion-dipole, ion-water, and water-water interactions were investigated at the molecular level in M+ (CH3CN)n(H2O)m cluster ions for M = Na and K. Different [n,m] combinations for two different n + m cluster sizes were characterized with infrared predissociation spectroscopy in the O-H stretch region and MP2 calculations. In all cases, no differences were observed between the two alkali metal ions. The results showed that at the n + m = 4 cluster size, the solvent molecules interact only with the ion, and that the interaction between the ion and the large dipole moment of CH3CN decreases the ion-water electrostatic interactions. At the n + m = 5 cluster size, at least two different hydrogen-bonded structures were identified. In these structures, the ion-dipole interaction weakens the ability of the ion to polarize the hydrogen bonds and thus decreases the strength of the water-water interactions in the immediate vicinity of the alkali metal ion.

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