Synthesis, structure and characterization of two new antimony oxides–LaSb3O9and LaSb5O12: Formation of LaSb5O12from the reaction of LaSb3O9with Sb2O3

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Abstract
Two new lanthanum antimony oxides, LaSb3O9 and LaSb5O12, have been synthesized as bulk phase powders and single crystals by solid state reactions using La2O3 (or La(NO3)3·xH2O), Sb2O3 and Sb2O5 as reagents. The structures of LaSb3O9 and LaSb5O12 were determined by single crystal X-ray diffraction. LaSb3O9 contains exclusively Sb5+ cations, whereas LaSb5O12 contains both Sb3+ and Sb5+ cations. LaSb3O9 has a novel three-dimensional framework consisting of edge- and corner-shared Sb5+O6 octahedra. LaSb5O12 exhibits a layered crystal structure consisting of corner-shared Sb5+O6 octahedra. The Sb3+O3 groups cap the SbO6 layers from above and below. The Sb3+ cations are in asymmetric coordination environments attributable to their stereo-active lone-pair. We also report on the reaction of three-dimensional LaSb3O9 with Sb2O3 to form the two-dimensional LaSb5O12. Infrared, thermogravimetric and dielectric analyses are also presented.