Dication-water interactions: M(2+)(H2O)(n) clusters for alkaline earth metals M=Mg,Ca,Sr,Ba, and Ra

被引:147
作者
Glendening, ED
Feller, D
机构
[1] PACIFIC NW NATL LAB, ENVIRONM MOL SCI LAB, RICHLAND, WA 99352 USA
[2] INDIANA STATE UNIV, DEPT CHEM, TERRE HAUTE, IN 47809 USA
关键词
D O I
10.1021/jp952546r
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Gas-phase structures, binding energies, and enthalpies are reported for small M(2+)(H2O)(n) clusters consisting of an alkaline earth dication (Mg2+, Ca2+, Sr2+, Ba2+, and Ra2+) with one to six water molecules. Ab initio molecular orbital calculations were performed at the RHF and MP2 levels of theory using split-valence basis sets (6-31+G* with effective core potentials for the heavier alkaline earth metals). The water molecules in these clusters coordinate the dications in highly symmetric arrangements that tend to enhance electrostatic charge-dipole interactions while minimizing ligand-ligand repulsions. Comparisons of the calculated structures and binding energies to higher level treatments reveal fairly reasonable agreement. The optimized M-O distances are slightly long (by 0.02-0.03 Angstrom), and binding energies are somewhat weak (by 1-3 kcal mol(-1) per ligand). Natural energy decomposition analysis emphasizes the importance of polarization effects in the M(2+)(H2O)(n) clusters. Polarization is largely responsible for the nonclassical bent and pyramidal structures of the di- and trihydrates and for the nonadditive, many-body tens that contribute importantly to the binding energies. This study serves, in part, to calibrate the RHF/6-31+G* and MP2/6-31+G* approaches for applications to dication-ligand interactions in more extended systems (such as the ion-selective binding of crown ethers) for which calculations at higher levels of theory are not currently feasible.
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页码:4790 / 4797
页数:8
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