The structure of concentrated aqueous solutions of chromium nitrate and cerium chloride studied by X-ray diffraction and Raman spectroscopy

Concentrated aqueous solutions of chromium nitrate and cerium chloride were investigated by X-ray diffraction and Raman spectroscopy. The X-ray diffraction patterns of two sets of solutions (1.60 up to 2.48 mol dm(-3) for chromium nitrate and 0.98 up to 2.81 mol dm(-3) for cerium chloride) display an intense maximum, prepeak, in the angular region about Q(0) similar to 0.9 angstrom(-1) (Q=4 pi sin theta/lambda, theta being the diffracting angle). The value of Q(0) corresponding to these maxima is proportional to the power 1/3 of the molar concentration. The proportionality coefficient has the value that should be observed for a close packing (fee network) if assumed for cations. This study demonstrates, once more, the existence of an intermediate range order (up to similar to 10 angstrom) in very concentrated aqueous solutions of salts constituted by small ions of different valences, range order previously reported by these authors in many articles. Raman experiments are in consonance with X-ray diffraction results. (c) 2007 Elsevier B.V. All rights reserved.