Hydrothermal synthesis, crystal structure and thermal behaviour of the first lanthanide sulfato-squarate, La2(H2O)4(SO4)2(C4O4)

A new three-dimensional lanthanum(III) sulfate squarate, La-2(H2O)(4)(SO4)(2)(C4O4), has been synthesized hydrothermally with squaric acid at 180 degrees C and its structure has been solved by single-crystal X-ray diffraction methods. A relevant feature of this new material is that it constitutes the first member of a family of hybrids based on this composition. It crystallizes in the monoclinic space group P(2)1/n, with a = 6.5965(1) angstrom, b = 10.9595(3) angstrom, c = 9.6633(2) angstrom, beta = 96.457(1)degrees, V = 694.17(3) angstrom(3), Z = 2. Its framework is built up from dimers of O-O edged-sharing nine-coordinated LaO7(H2O)(2) polyhedra described as monocapped square antiprisms. The linking of the binuclear La species by sulfate groups occurs in planes parallel to (11(1) over bar) and subsequently generates inorganic layers showing cavities. The stacking of them along the a-axis generates tunnels filled with bonded water molecules and squarate moieties. The three-dimensionality is ensured by one sulfate oxygen atom and the C-4-cycles. Thus, according to this structural description, the material presents a novel 3D-type structure in the field of the mixed anionic lanthanide compounds. The thermal behavior of La-2(H2O)(4)(SO4)(2)(C4O4) has been investigated using TG-DTA and X-ray thermodiffractometry showing that this precursor of crystallized lanthanum oxide at 900 degrees C is stable up to 150 degrees C. (C) 2006 Elsevier SAS. All rights reserved.