Iino Takuro, Ohashi Kazuhiko, Inoue Kazuya, Judai Ken, Nishi Nobuyuki, Sekiya Hiroshi
Department of Chemistry, Faculty of Sciences, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan.
J Chem Phys. 2007 May 21;126(19):194302. doi: 10.1063/1.2730830.
M(+)(H(2)O)(n) and M(+)(H(2)O)(n)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(+)(H(2)O)(1) x Ar indicates that the complex is quasilinear in an Ar-Ag(+)-O configuration with the H atoms symmetrically displaced off axis. The spectra of the Ar-tagged M(+)(H(2)O)(2) are consistent with twofold coordination with a linear O-M(+)-O arrangement for these ions, which is stabilized by the s-d hybridization in M(+). Hydrogen bonding between H(2)O molecules is absent in Ag(+)(H(2)O)(3) x Ar but detected in Cu(+)(H(2)O)(3) x Ar through characteristic changes in the position and intensity of the OH-stretch transitions. The third H(2)O attaches directly to Ag(+) in a tricoordinated form, while it occupies a hydrogen-bonding site in the second shell of the dicoordinated Cu(+). The preference of the tricoordination is attributable to the inefficient 5s-4d hybridization in Ag(+), in contrast to the extensive 4s-3d hybridization in Cu(+) which retains the dicoordination. This is most likely because the s-d energy gap of Ag(+) is much larger than that of Cu(+). The fourth H(2)O occupies the second shells of the tricoordinated Ag(+) and the dicoordinated Cu(+), as extensive hydrogen bonding is observed in M(+)(H(2)O)(4) x Ar. Interestingly, the Ag(+)(H(2)O)(4) x Ar ions adopt not only the tricoordinated form but also the dicoordinated forms, which are absent in Ag(+)(H(2)O)(3) x Ar but revived at n=4. Size dependent variations in the spectra of Cu(+)(H(2)O)(n) for n=5-7 provide evidence for the completion of the second shell at n=6, where the dicoordinated Cu(+)(H(2)O)(2) subunit is surrounded by four H(2)O molecules. The gas-phase coordination number of Cu(+) is 2 and the resulting linearly coordinated structure acts as the core of further solvation processes.
研究了M(+)(H₂O)ₙ和M(+)(H₂O)ₙAr离子（M = Cu和Ag），以探索贵金属离子的配位和溶剂化结构。这些物种在激光蒸发团簇源中产生，并使用三重四极杆质谱仪在OH伸缩区域通过红外（IR）光解离光谱进行探测。还进行了密度泛函理论计算以分析实验红外光谱。在Ag(+)(H₂O)₁ x Ar的光谱中观察到的部分分辨的转动结构表明，该配合物在Ar-Ag(+)-O构型中为准线性，H原子对称地偏离轴。Ar标记的M(+)(H₂O)₂的光谱与这些离子的线性O-M(+)-O排列的二重配位一致，这通过M(+)中的s-d杂化得以稳定。Ag(+)(H₂O)₃ x Ar中不存在H₂O分子之间的氢键，但通过OH伸缩跃迁的位置和强度的特征变化在Cu(+)(H₂O)₃ x Ar中检测到。第三个H₂O以三配位形式直接与Ag(+)结合，而它占据二配位Cu(+)第二壳层中的一个氢键位点。三配位的偏好归因于Ag(+)中低效的5s-4d杂化，与Cu(+)中广泛的4s-3d杂化形成对比，后者保留了二配位。这很可能是因为Ag(+)的s-d能隙比Cu(+)的大得多。第四个H₂O占据三配位Ag(+)和二配位Cu(+)的第二壳层，因为在M(+)(H₂O)₄ x Ar中观察到广泛的氢键。有趣的是，Ag(+)(H₂O)₄ x Ar离子不仅采用三配位形式，还采用二配位形式，这些形式在Ag(+)(H₂O)₃ x Ar中不存在，但在n = 4时恢复。对于n = 5 - 7，Cu(+)(H₂O)ₙ光谱的尺寸依赖性变化为在n = 6时第二壳层的完成提供了证据，其中二配位的Cu(+)(H₂O)₂亚基被四个H₂O分子包围。Cu(+)的气相配位数为2，所得的线性配位结构充当进一步溶剂化过程的核心。
