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).