Tri-α-PbO2 -Type Fe-Sb Tungstate by Topotactic Ion Exchange of LiSbWO6

A tri-alpha-PbO2-type oxide, Li0.08Fe0.46SbWO6 , is synthesized for the first time by topotactic ion exchange of LiSbWO6 in an aqueous Fe(II) solution at 60 degrees C for 4 days under an argon atmosphere. The structure of the resulting compound is ascertained by Rietveld refinement of PXRD data, and the topotactic nature of exchange is established. The Fe-Sb tungstate showed a considerable reduction in the band gap to 2.06 from 3.05 eV of the parent LiSbWO6. The compound is metastable in nature; it undergoes exothermic structural transitions or decompositions at around 790 and 950 degrees C and cannot be stabilized by conventional solid-state reactions. The compound shows an antiferromagnetic transition at similar to 20 K, which is ascribed to the presence of Fe(II) dimers in the edge-shared chains of Li/FeO6 octahedra running parallel to the c-direction in the tri-alpha-PbO2 structure. The applicability of the Fe-exchanged compound for visible-light-driven semiconductor photocatalysis is investigated by degradation of RhB dye. The topotactic ion exchange in the tri-alpha-PbO2 structure is unique and rare owing to its three-dimensional quasi-ordered structure with corner- and edge-connected moieties; however, plenty of them are reported in other structure types, including layered, tunnel, and framework structures. The strategy will be useful in constructing ordered or pseudo-ordered transition-metal arrays in three-dimensional structures with intriguing electronic properties.