Competing non-covalent interactions in alkali metal ion-acetonitrile-water clusters
ABSTRACT 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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ABSTRACT: The competitive solvation of the potassium ion by benzene and water is investigated at molecular level by means of Molecular Dynamics simulations on the K+-(C6H6)n -(H2O)m (n = 1–4; m = 1–6) ionic aggregates. The preference of K+ to bind C6H6 or H2O is investigated in the range of temperatures in which isomerisation processes are likely by adding water and benzene to the K+-(C6H6)n and K+-(H2O)m aggregates, respectively. Hydrogen bonds and the π-hydrogen bond, in spite of their weakness with respect to the K+-π and K+-H2O interactions, play an important role in stabilising different isomers, thus favouring isomerisation processes. Accordingly with experimental information it has been found that K+ bind preferably C6H6 rather than H2O and that the fragmentation of C6H6 is only observed for aggregates containing four molecules of benzene.The European Physical Journal D 04/2013; 67(4). DOI:10.1140/epjd/e2013-30753-x · 1.40 Impact Factor
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ABSTRACT: We report a systematic theoretical study on the growth pattern and energetics of Na+(CH3CN)n clusters (n = 1–8,12) using density functional approach at the B3LYP/6-31++G(d,p) level. Geometry optimizations for all these clusters were carried out with various possible initial guess structures without any symmetry restriction and finally the stability of the lowest energy isomer was verified from Hessian calculations. It is found that the incorporation of a sodium ion completely rearrange the equilibrium structure of the neat acetonitrile cluster. The solvated clusters favor multiple shell structure with higher symmetry. The first solvation shell is formed by six CH3CN molecules, where the nitrogen atoms of each molecule points towards the central sodium ion. Here, the nature of binding between the solute and solvent has been attributed as strong ion–dipole interactions. The onset of the second solvation shell occurs at n = 7 and thereafter additional acetonitrile molecules interact with the molecules of the first solvation shell through N…H interaction. Such interactions are weak compared to the ion–dipole interactions leading to minimal perturbation to the inner shell structure. In consistent with this conjecture, the ion-solvation energy is found to increase very sharply upto n = 6, and becomes less steep from n = 7 onwards. Moreover, the calculated stepwise binding energies are found to be in good agreement with available experimental data, which provide confidence about the equilibrium geometries of the Na+(CH3CN)n clusters predicted in this study.Journal of Molecular Structure THEOCHEM 08/2009; 907(s 1–3):22–28. DOI:10.1016/j.theochem.2009.04.013 · 1.37 Impact Factor
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ABSTRACT: State of the art DFT calculations indicate that 3-(phenylamino)-2-cyclohexen-1-one (PACO), a β-enaminone, is capable of forming 1:1 microclusters with a variety of oxygen donor solvents in the ground state through its hydrogen bond donor unit (N–H). The computed N–H bond lengths and N–H stretching frequencies correlate fairly well with the H-bond donating and accepting abilities of the solvents together with their polarities through Kamlet–Taft type of equations. Experimental IR spectra in bulk solvents indicate that there could be additional microsolvation also through the H-bond accepting unit of the probe. Our calculations indicate that PACO forms 1:3 microclusters with water through simultaneous solvation at the CO and the N–H moieties. The computed IR spectrum of this 1:3 microcluster suggests that H-bonding at the H-bond donor site can be cooperatively affected by H-bond formation at the H-bond accepting site of PACO.Chemical Physics 06/2012; 402:96–104. DOI:10.1016/j.chemphys.2012.04.015 · 2.03 Impact Factor