Coordination and solvation structures of the Cu + (H 2 O) n ions with n = 1-4 are studied by infrared photodissociation spectroscopy and density functional theory calculations. Hydrogen bonding between H 2 O molecules is detected in Cu + (H 2 O) 3 and Cu + (H 2 O) 4 through a characteristic change in the position and intensity of OH-stretching transitions. The third and fourth waters prefer hydrogen-bonding sites in the second solvation shell rather than direct coordination to Cu +. The infrared spectroscopy verifies that the gas-phase coordination number of Cu + in Cu + (H 2 O) n is two and the resulting linearly coordinated structure acts as the core of further solvation processes.

The infrared photodissociation spectra of mass-selected Mg + (NH 3) n (n = 3-6) are measured and analyzed with the aid of density functional theory calculations. No large frequency reduction is observed for the NH stretches of ammonia, suggesting that either all the ammonia molecules coordinate directly to the Mg + ion or an additional ammonia in the second shell bridges two ammonias in the first shell through hydrogen bonds. Four or possibly five ammonia molecules are allowed to occupy the first shell, in striking contrast to the closure of the first shell in Mg + (H 2 O) 3 .

No abstract

Solvation structure of the zinc(II) ion in N,N-dimethylpropionamide (DMPA) was studied by Raman spectroscopy at varying temperature and by quantum mechanical calculations. No significant ion-pair formation was found for the Zn(ClO4)2 solution in the molality range m(Zn) < 1.5 mol kg(-1), and the solvation number of the zinc(II) ion was determined to be 4, indicating that 6-coordination of DMPA is sterically hindered. Interestingly, DMPA molecules are under equilibrium between planar cis and nonplanar staggered conformers, and the latter is more preferred in the coordination sphere, while the reverse is the case in the bulk. The DeltaG degrees , DeltaH degrees , and TDeltaS degrees values of conformational change from planar cis to nonplanar staggered in the coordination sphere were obtained to be -0.9, -8.5, and -7.5 kJ mol(-1), respectively. Density functional theory (DFT) calculations show that the planar cis conformer is more favorable than the nonplanar staggered one in the 1:2 cluster, as is the case for a single DMPA molecule and H(DMPA)+, indicating that there hardly occurs solvent-solvent interaction through the metal ion in the Zn2+-DMPA 1:2 cluster. On the other hand, the SCF energy of [Zn(planar cis-DMPA)4-n(nonplanar staggered DMPA)n]2+ (n = 0-4) decreases with increasing n, implying that the nonplanar staggered conformer is preferred in the solvate ion. It is thus concluded that solvent-solvent interaction through space, or solvation steric effect, plays a crucial role in the conformational equilibrium in the coordination sphere of the four-solvate metal ion.

The [Al(NH 3) n ] + ions with n = 1-5 are studied by infrared photodissociation spectroscopy and density functional theory calculations. The inserted [H-Al-NH 2 ] + structure is calculated to be higher in energy than the adduct [Al-NH 3 ] + structure. However, incremental solvation stabilizes the inserted structure more efficiently than the adduct structure, because of a larger effective charge on the Al atom in [H-Al-NH 2 ] +. Actually, the infrared spectra demonstrate that the [(H-Al-NH 2)(NH 3) n-1 ] + ions are predominant over [Al-(NH 3) n ] + for n ≥ 4, while the adduct structures dominate the spectra of [Al(NH 3) n •Ar] + for n = 1-3.