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, La2(H2O)4(SO4)2(C4O4), has been synthesized hydrothermally with squaric acid at 180 °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 P21/nP21/n, with a=6.5965(1) Åa=6.5965(1) Å, b=10.9595(3) Åb=10.9595(3) Å, c=9.6633(2) Åc=9.6633(2) Å, β=96.457(1)°β=96.457(1)°, V=694.17(3) Å3V=694.17(3) Å3, Z=2Z=2. Its framework is built up from dimers of OO 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 (101¯) 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 C4-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 La2(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 °C is stable up to 150 °C.

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