G. Licheri

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.

On NO−3–H2O interactions in aqueous solutions

The scattering of x rays from a concentrated NH4NO3 aqueous solution has been measured and analyzed at 25°C. It is shown that the sample may be considered as a solution of nitrate ions in water. In this way the existence of discrete NO−3–H2O interactions is demonstrated unequivocally. Good agreement with experimental data is achieved through a model in which each O atom in the nitrate ion gives rise to three weak hydrogen bonds with water molecules.

Coordination of Ag+ ions in AgI–Ag2O–B2O3 glasses by x‐ray diffraction

X‐ray diffraction measurements have been performed on glasses of the Ag2O–B2O3 and AgI–Ag2O–B2O3 systems. When silver iodide is present, the radial distribution function is dominated by a large peak at 2.85 A, due to Ag–I interactions, with a shoulder at ∼2.40 A, due to Ag–O pairs. The average number of Ag–I contacts has been calculated through analysis of the high angle structure functions si(s)’s, either by using the total si(s)’s or by using the partial si(s)’s, the latter obtained by subtracting the experimental structure function of the Ag2O–B2O3 glasses from that of the corresponding AgI‐doped glasses. The compatibility of the results obtained with recently proposed models of AgI–Ag2O–B2O3 glasses is examined.

Order phenomena in aqueous AlCl3 solutions

X‐ray diffraction data of two aqueous solutions of AlCl3 are interpreted using a model in which the Cl− ions have a coordination number of six and the Al(H2O)3+6 ions interact with twelve water molecules through short and linear H bonds, the water molecules nearest neighbor to the Al3+ ions having a trigonal orientation. Moreover, evidence is given that such a hydration structure tends to persist even when the total amount of water present in the system is rather small.

X-ray diffraction study of LiBr aqueous solutions

Abstract LiBr aqueous solutions were investigated by X-ray diffraction in order to study the structure of hydrated Br− ions. A simple model describing the coordination around the ions only in terms of nearest-neighbour interactions is shown to be consistent with experimental data. Octahedral coordination about Br− appears to be sufficiently established.

Hydration water–external water interactions around Cr3+ ions

A hydration model for the Cr3+ ion, suggested by the bond valence analysis, is tested against x‐ray diffraction data obtained from aqueous solutions of chromium chloride and nitrate about 1–2M. According to this model, the [Cr(H2O)6]3+ ions interact with 12 water molecules through short and linear H bonds, the water molecules nearest neighbor to the Cr3+ ion having a trigonal orientation (i.e., they point the negative end of their dipole vector towards the metal ion). The results show that such a model agrees with experimental data somewhat better than a model in which the water molecules nearest the cations have a pyramidal orientation (i.e., they point a lone pair towards the ion).

X-ray diffraction study of a “three-ion” aqueous solution

Abstract X-ray diffraction data on an aqueous solution 2 M in MgCl 2 are shown to be consistent with octahedral coordinations for the three ions as already found in solutions of single electrolytes. The rare-gas-like ion hydration thus appears not affected by the presence of other ions independently hydrated.

X‐ray diffraction study of CaBr2 aqueous solutions

CaBr2 aqueous solutions were investigated by x‐ray diffraction in order to study the structure of hydrated ions. The experimental data were analyzed using a model describing coordinations around the ions only in terms of nearest‐neighbor interactions. For the Br− ion, the octahedral coordination, already obtained in LiBr solutions, is confirmed. As regards the coordination of Ca++ ion, the experimental data can be interpreted both with six and eight coordination numbers.