Solute structuring in aqueous [Cr(H2O)6]Cl3

Abstract
A [Cr(H2O)6]Cl3 aqueous solution ∼1M at T=18 °C is investigated by x‐ray diffraction. The experimental correlation function shows three main peaks, centered at about 2.00, 2.85, and 3.25 Å, which are ascribed, respectively, to Cr3+–H2O, H2O–H2O, and Cl–H2O nearest neighbor interactions. A simple model describing the coordination around the ions only in terms of nearest neighbor interactions is shown to be inconsistent with experimental data. A satisfactory agreement with experiments is reached with a model in which the hydrated [Cr(H2O)6]3+ ions are considered as interacting with a second shell of water molecules. This fact demonstrates that in the experimental conditions the Cr3+ ions hexa‐aquo must be considered as real kinetic units.