Infrared spectroscopy of Cu+(H2O)n and Ag+(H2O)n: Coordination and solvation of noble-metal ions

Abstract

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.

Hydration of the Calcium Dication: Direct Evidence for Second Shell Formation from Infrared Spectroscopy

“…One strategy to gain a detailed understanding of how ions and water molecules interact is to build up a solution, one molecule of water at a time. [1] Vibrational spectroscopy is a powerful structural tool for investigating hydrated ions, and has been used to investigate the structures of hydrated monovalent cations, including Ag + , [2] H + , [3][4][5][6] Cs + , [7,8] Cu + , [2] K + , [9] Mg + , [10] NH 4 + , [11,12] and Ni + , [13] and hydrated anions, including Cl À , [14,15] e À , [16] F À , [15,17] HO À , [18] and SO 4 2À . [19] Despite serving critical regulatory and structural roles in biology, experimental studies of hydrated, multiply charged ions have lagged behind those of singly charged ions, owing to the great difficulty in producing them in significant abundances; for example, formation of doubly hydrated, divalent calcium by condensation results in rapid dissociation aided by Coulomb repulsion [Eq.…”

“…[19] Despite serving critical regulatory and structural roles in biology, experimental studies of hydrated, multiply charged ions have lagged behind those of singly charged ions, owing to the great difficulty in producing them in significant abundances; for example, formation of doubly hydrated, divalent calcium by condensation results in rapid dissociation aided by Coulomb repulsion [Eq. (1)]: [20] Ca 2þ ðH 2 …”

Near ultraviolet photodissociation spectroscopy of Mn+(H2O) and Mn+(D2O)

“…4 In fact, along the periodic 14 V, 15 Cr, 16 Mn, 17 Fe, 18 Ni, 19 Cu, 20 Zn 21 ) and M 2+ (H 2 O) (M = Sc, 14 V, 22 Cr, 16 Mn 17 ) in the O−H stretching region. Likewise, Nishi and co-workers measured vibrational spectra of M + (H 2 O) n for M = V, 23 Co, 24 Cu and Ag, 25 while Zhou and co-workers measured the vibrational spectra of Au + (H 2 O) n (n = 1-8). 26 In addition, van der Linde and Beyer have examined water activation in larger clusters of M + (H 2 O) n (n < 40) (M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn) in a FT-ICR mass spectrometer, with particular emphasis on water activation in Mn + (H 2 O) n .…”

Gas phase structure of micro-hydrated [Mn(ClO4)]+ and [Mn2(ClO4)3]+ ions probed by infrared spectroscopy

“…This is not often realized, but as the water cluster size increases, the water binding energy decreases, so that the IR induced photodissociation can be monitored [18,19,22,26]. For smaller size and more strongly bound water solvated metal cluster ions, a rare gas "tag" can be employed [23,24,28,29]. Alternatively, highly intense IR free electron lasers offer a complementary IR spectral range (100 -2000 cm Ϫ1 ) [31,32], which can provide information on the coordination mode of ligands bound to transition-metal cations [33][34][35][36][37][38].…”

“…As in the case of protonated water clusters [11], the frequencies of the water OH stretches can shift substantially with water-water hydrogen bond formation, and information about ionwater interaction and metal coordination number can be derived. Water solvated alkali [10,[12][13][14][15] and alkaline earth [16 -21] metals, as well as various transitionmetals [17,[22][23][24][25][26][27][28][29][30] have been studied. IR spectroscopy in the OH stretching region is usually carried out with a relatively low intensity table-top laser.…”