Crystal structure of Kuzel's salt 3CaO·Al 2O 3·1/2CaSO 4·1/2CaCl 2·11H 2O determined by synchrotron powder diffraction

Abstract

The crystal structure of Kuzel's salt has been successfully determined by synchrotron powder diffraction. It crystallizes in the rhombohedral R3̅ symmetry with a = 5.7508 (2) Å, c = 50.418 (3) Å, V = 1444.04 (11) Å 3. Joint Rietveld refinement was realized using three X-ray powder patterns recorded with a unique wavelength and three different sample-to-detector distances. Kuzel's salt is the chloro-sulfoaluminate AFm phase and belongs to the layered double hydroxide (LDH) large family. Its structure is composed of positively charged main layer [Ca 2Al(OH) 6] + and negatively charged interlayer [Cl 0.50·(SO 4) 0.25·2.5H 2O] −. Chloride and sulfate anions are ordered into two independent crystallographic sites and fill successive interlayer leading to the formation of a second-stage compound. The two kinds of interlayer have the compositions [Cl·2H 2O] − and [(SO 4) 0.5·3H 2O] −. The crystal structure explains why chloride and sulfate anions are not substituted and why the formation of extended solid solution in the chloro-sulfate AFm system does not occur.