The layer crystal structure of [In_2(C_2O_4)_3(H_2O)_3]·7H_2O and microstructure of nanocrystalline In_2O_3 obtained from thermal decomposition

摘要

A new indium oxalate, [In_2(C_2O_4)_3(H_2O)_3]·7H_2O, with a layered structure has been synthesised from precipitation methods at room temperature. It crystallises with a monoclinic symmetry, space group P2_(1/c)(No.14), a = 8.7456(1)a, b = 11.1479(2)A, c = 21.9376(4)A, β = 112.1(1)°, V = 1979.98(6)A~3 and Z = 4. The structure is built from neutral [In_2(C_2O_4)_3(H_2O)_3] corrugated layers, between which water molecules are intercalated. The layers are built from chains with two different sequences of indium atoms and bichelating oxalate groups. Two independent indium atoms are present in the structure with two coordination polyhedra, i. e., InO_8 as a distorted square-based antiprism and InO_7 as a nearly regular pentagonal-based bipyramid. The thermal decomposition has been studied in situ by temperature dependent X-ray diffraction and thermogravimety. The final product is nanocrystalline indium oxide. The microstructure of the oxide has been characterised with both the Voigt/Langford method based on the integral breadth and the whole pattern fitting approach. The size of the isotropic crystallites increases from 322 to 924 A, while microstrains decrease, in the annealing temperature range 500-750 ℃.