Ab initio calculations and X-ray diffraction experiments were carried out to study the structure of solutions of calcium chloride in water and methanol. Ab initio calculations were performed at MP2 level and density functional calculations at B3LYP level on calcium-water and calcium-methanol clusters yielding the formation of stable calcium-water clusters with up to eight water molecules and calcium-methanol clusters with up to seven methanol molecules. The experiments were performed in a wide concentration range both in water and in methanol (1-6 M and 1-2 M, respectively). The coordination number of the cation in low-concentration (1 M) aqueous and methanol solutions could only be determined with great uncertainty due to the low weights of cation-solvent contributions to the X-ray scattering intensity for both series of solutions. It was found that in 1 M solutions the Ca 2+ ion is surrounded by eight (five to ten) water and six (four to seven) methanol molecules, respectively. The coordination numbers decrease with an increase in concentration. The accuracy of the coordination numbers determined increases with increasing concentration. The solvation shell of Clion is composed of six solvent molecules in each solution. We have found evidence of both contact and solvent-separated Ca-Cl ion pair formation at higher concentrations. On the basis of the stoichiometry of the solution and structural parameters obtained, different models are suggested to explain the liquid structure of the solutions.

First principles molecular dynamics has been used to investigate the structural, vibrational, and energetic properties of [Ca(H2O)n]2+ clusters with n=1–9, and the hydration shell of a calcium ion in a periodically repeated box with 54 water molecules. We find that, while stable highly symmetric Ca–water clusters can be formed with up to eight water molecules, the n=9 cluster dissociates into the last stable [Ca(H2O8]2+ complex. In solution the first hydration shell around the Ca2+ ion contains six water molecules in an octahedral arrangement. The electronic structure of nearest neighbor hydration shell water molecules has been examined with a localized orbital analysis. The average dipole moments of hydration water molecules was found to be increased by about 0.4 Debye relative to that of pure water.

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We report the synthesis and solution- and solid-state characterization of gold(I) rings with short 1,9-transannular Au...Au interactions. The 9- and 16-membered gold(I) rings were prepared by reacting 9,9-dimethyl-4,5-bis(diphenylphosphino)-xanthene and (Me2S)AuCl in the presence of AgNO3 in the molar ratio of 1:0.5:1 and 1:1:1, respectively. X-ray crystallographic measurements in conjunction with solution X-ray diffraction and NMR methods have been used to determine the structure of gold(I) rings, and we also gained insight into the dynamics. The nine-membered gold(I) ring is chiral, and the crystal contains only one of the two enantiomers, either right- or left-handed. To the best of our knowledge this represents the first example of crystallization-induced spontaneous resolution of a binuclear gold(I) cycle. The 16-membered ring with 1,9-transannular Au...Au interaction is in a figure-eight conformation.

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Wide-angle X-ray scattering and diffusion NMR techniques have been used to obtain structural information on three self-assembled metallacyclic supramolecular complexes in solution: a rectangle, a triangle, and a three-diminsional cage. The low-angle region of the measured diffraction patterns and hydrodynamic radii calculations, determined from DOSY NMR experiments, suggest that the supramolecular assemblies retain their shape when dissolved in nitromethane. The experimental structure functions for the large-angle region have been analyzed, and the intramolecular contributions of the platinum-platinum interactions are discussed. These scattering measurements provide evidence that the supramolecular assemblies are not as rigid in solution as they are in the single crystal. Finally, by analysis of the radial distribution functions of the solutions, direct structural information (e.g., platinum-platinum intramolecular distances and coordination number) about the supramolecular assemblies has been obtained.