Coordination of ions in aqueous solutions of erbium chloride from X-ray diffraction data

Aqueous solutions of erbium chloride were studied by X-ray diffraction over a broad range of concentrations under standard conditions. The prepeaks observed in the experimental scattering intensity curves were interpreted. The solutions were found to possess two types of structures. Saturated and concentrated solutions down to molar ratio of 1 : 20 have a quasi-crystalline structure defined by inter-ion interactions. Dilute solutions form a water-like structure characterized by a tetrahedral network of hydrogen bonds between water molecules. It was found that prepeaks can also be seen in the intensity curves of dilute solutions, which implies that these solutions retain the so-called long-range order.