G. Pinna

X‐ray diffraction study of the average solute species in CaCl2 aqueous solutions

The structure of several CaCl2 aqueous solutions was studied by means of x‐ray diffraction. It is demonstrated that the solutions can be treated as being composed of independent hydrated ions, and for this reason the structural problem is limited to the study of close hydration. This description allows the calculation of structure functions in very good agreement with experimental data when using coordination number six and octahedral geometry for both the ionic species present.

Interactions and structure in aqueous NaNO3 solutions

Two concentrated (5 and 7 mol l−1) aqueous solutions of NaNO3 were investigated by x‐ray diffraction. The features of the total radial functions calculated from experimental intensity data show that the positional correlation is not very strong in the systems investigated. However, it is possible to account for experimental data only by using models in which hexahydrated Na+ ions have definite correlations with NO3− ions, even if not through formation of isolated ion pairs. The compatibility of our observations with spectroscopic results is also discussed.

X-ray diffraction study of MgCl2 aqueous solutions

X-ray diffraction data for three aqueous solutions of MgCl2 were analyzed. It is shown that in a very concentrated solution the structure and correlation functions can be reproduced almost completely by using a nearest-neighbor model of ionic hydration, whereas in the more dilute solutions a certain number of interactions between the hydrated cation and external water molecules must also be considered. The mean coordination geometry for the close hydration was found to be octahedral both for cation and anion with mean cation–water distances (2.10–2.12 A) and mean anion–water distances (3.11–3.14 A) in accordance with results found in other cases.

X-ray diffraction study of aqueous SrCl2 solutions

Two aqueous solutions of SrCl2 of concentration 1.53 and 2.00 mol dm−3 have been investigated by X-ray diffraction. A model in which the Sr2+ ion was considered as having eight nearest-neighbour water molecules at a distance of 2.64 A and a second outer shell came out in best agreement with the experimental data. Octahedral water coordination for Cl− ions has been confirmed in agreement with the results obtained by other X-ray studies.

Diffraction of X-rays and hydration phenomena in aqueous solutions of Mg(NO3)2

Abstract The ionic coordination of Mg(NO3)2 in aqueous solutions has been investigated by X-ray diffraction. The experimental correlation functions appear to be characterized by the hydration of the cation. Satisfactory agreement with the experimental data has been reached through a model in which: (i) the nitrate ions do not produce any structuring effect in their neighbourhood; (ii) the Mg2+ ions possess an inner hydration shell of six water molecules and a second coordination shell.

X-ray investigation of CoCl bonding in a concentrated aqueous solution of CoCl2 and LiCl

Abstract A concentrated CO(II) solution with a Cl − /Co 2+ ratio of≈4 was examined by X-ray diffraction. The Fourier-transformed scattering data indicated inner complex formation between Co 2+ and Cl − ions. The overall coordination of Co 2+ ions is very close to 6 and the average number of bonded Cl − ions per cobalt atom was found to be nearly 1. The similarity of this result to the one obtained from a solution of NiCl 2 of equal concentration is discussed. This result was also checked through EXAFS measurements.

Exafs study of Ni2+ coordination in concentrated aqueous solutions

Abstract EXAFS measurements are reported for NiCl2 and Ni(N03)2 aqueous solutions with molar concentrations of about 4, and for crystalline Ni(N03)2·6H2O. A comparative analysis of the Fourier filtered spectra confirms that the first coordination sphere essentially consists of water molecules. No evidence was found for outer-sphere Cl− ions approaching closely the inner sphere in NiCI2 solution.

X-ray Diffraction Study of Aqueous Solutions of ZnSO4

Five aqueous solutions of ZnSO4 of concentrations ranging from 0.6M to 3.1 M were examined by X-ray diffraction. In the correlation functions no concentration effect on structural phenomena is detectable. The same model was then successfuly used for all cases, attributing two hydration shells to Zn2+ and one hydration shell to SO42+ . The reliability of the structural parameters obtained is discussed.

X-Ray Diffraction and Structural Properties of Aqueous Solutions of Divalent Metal-Chlorides

Abstract X-ray diffraction data are reported for aqueous solutions of CaCl2 (6.30 M), CdCl2 (0.87 and 1.26 M) and NiCl2 (1.96 and 3.88 M). The highly concentrated CaCl2 solution shows a medium range order resembling that of the corresponding hydrate crystal. The CdCl2 solutions are characterized by the presence of complexes with chloride ions in the first coordination sphere of the cation. In NiCl2 solutions, a first sphere Ni-Cl coordination can be excluded and the existence of six Ni-H2O nearest neighbour contacts is clearly confirmed. In these solutions no evidence was found for the existence of highly ordered structures; hexa-aquo cations interact with external water molecules and, at the highest concentration, some outer sphere Ni-Cl correlation is possible as due to packing.

A general computer program for the analysis of X-ray diffraction data for liquids

A general computer program for the analysis of X-ray diffraction data for liquids is here described. It consists of a central part (main) and a number of subroutines, in which one single step of the elaboration of experimental intensities is performed. This arrangement allows the entire sequence of operations to be performed as far as the radial distribution functions; alternatively only a part can be performed, starting or stopping at any point. The program is flexible and easily modifiable for the users needs.