Two Ce(SO4)2•4H2O polymorphs:: Crystal structure and thermal behavior

Syntheses, crystal structures and thermal behavior of two polymorphic forms of Ce(SO4)(2)center dot 4H(2)O are reported. The first modification, alpha-Ce(SO4)(2)center dot 4H(2)O (1), crystallizes in the orthorhombic space group Fddd, with a = 5.6587(1), b = 12.0469(2), c = 26.7201(3) angstrom and Z = 8. The second modification, beta-Ce(SO4)(2)center dot 4H(2)O (II), crystallizes in the orthorhombic space group Pnma, with a = 14.6019(2), b = 11.0546(2), c = 5.6340(1) angstrom and Z = 4. In both structures, the cerium atoms have eight ligands: four water molecules and four sulfate groups. The mutual position of the ligands differs in (1) and (11), resulting in geometrical isomerism. Both these structures are built up by layers of Ce(H2O)(4)(SO4)(2) held together by a hydrogen bonding network. The dehydration of Ce(SO4)(2)center dot 4H(2)O is a two step (1) and one step (II) process, respectively, forming Ce(SO4)(2) in both cases. During the decomposition of the anhydrous form, Ce(SO4)(2), into the final product CeO2, intermediate XCeO2 center dot YCe(SO4)(2) species are formed. (c) 2007 Elsevier Inc. All rights reserved.