Crystal structure of Kuzel's salt 3CaO·Al2O3·1/2CaSO4·1/2CaCl2·11H2O determined by synchrotron powder diffraction

The crystal structure of Kuzel's salt has been successfully determined by synchrotron powder diffraction. It crystallizes in the rhombohedral R (3) over bar symmetry with a = 5.7508 (2) angstrom, c = 50.418 (3) angstrom. V = 1444.04 (11) angstrom(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 [Ca2Al(OH)(6)](+) and negatively charged interlayer [Cl-0.50 center dot(SO4)(0.25)center dot 2.5H(2)O](-). 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 center dot 2H(2)O](-) and [(SO4)(0.5)center dot 3H(2)O](-). 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. (C) 2011 Elsevier Ltd. All rights reserved.