Infrared spectroscopy of Cu{sup +}(H{sub 2}O){sub n} and Ag{sup +}(H{sub 2}O){sub n}: Coordination and solvation of noble-metal ions
- Department of Chemistry, Faculty of Sciences, Kyushu University, Hakozaki, Fukuoka 812-8581 (Japan)
M{sup +}(H{sub 2}O){sub n} and M{sup +}(H{sub 2}O){sub n}{center_dot}Ar ions (M=Cu and Ag) are studied for exploring coordination and solvation structures of noble-metal ions. These species are produced in a laser-vaporization cluster source and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region using a triple quadrupole mass spectrometer. Density functional theory calculations are also carried out for analyzing the experimental IR spectra. Partially resolved rotational structure observed in the spectrum of Ag{sup +}(H{sub 2}O){sub 1}{center_dot}Ar indicates that the complex is quasilinear in an Ar-Ag{sup +}-O configuration with the H atoms symmetrically displaced off axis. The spectra of the Ar-tagged M{sup +}(H{sub 2}O){sub 2} are consistent with twofold coordination with a linear O-M{sup +}-O arrangement for these ions, which is stabilized by the s-d hybridization in M{sup +}. Hydrogen bonding between H{sub 2}O molecules is absent in Ag{sup +}(H{sub 2}O){sub 3}{center_dot}Ar but detected in Cu{sup +}(H{sub 2}O){sub 3}{center_dot}Ar through characteristic changes in the position and intensity of the OH-stretch transitions. The third H{sub 2}O attaches directly to Ag{sup +} in a tricoordinated form, while it occupies a hydrogen-bonding site in the second shell of the dicoordinated Cu{sup +}. The preference of the tricoordination is attributable to the inefficient 5s-4d hybridization in Ag{sup +}, in contrast to the extensive 4s-3d hybridization in Cu{sup +} which retains the dicoordination. This is most likely because the s-d energy gap of Ag{sup +} is much larger than that of Cu{sup +}. The fourth H{sub 2}O occupies the second shells of the tricoordinated Ag{sup +} and the dicoordinated Cu{sup +}, as extensive hydrogen bonding is observed in M{sup +}(H{sub 2}O){sub 4}{center_dot}Ar. Interestingly, the Ag{sup +}(H{sub 2}O){sub 4}{center_dot}Ar ions adopt not only the tricoordinated form but also the dicoordinated forms, which are absent in Ag{sup +}(H{sub 2}O){sub 3}{center_dot}Ar but revived at n=4. Size dependent variations in the spectra of Cu{sup +}(H{sub 2}O){sub n} for n=5-7 provide evidence for the completion of the second shell at n=6, where the dicoordinated Cu{sup +}(H{sub 2}O){sub 2} subunit is surrounded by four H{sub 2}O molecules. The gas-phase coordination number of Cu{sup +} is 2 and the resulting linearly coordinated structure acts as the core of further solvation processes.
- OSTI ID:
- 20991268
- Journal Information:
- Journal of Chemical Physics, Vol. 126, Issue 19; Other Information: DOI: 10.1063/1.2730830; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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