Preparation and characterization of metastable trigonal layered MSb2O6 phases (M = Co, Ni, Cu, Zn, and Mg) and considerations on FeSb2O6Electronic supplementary information (ESI) available. See DOI: 10.1039/c6dt04859e

MSb 2 O 6 compounds (M = Mg, Co, Ni, Cu, Zn) are known in the tetragonal trirutile forms, slightly distorted monoclinically with M = Cu due to the Jahn-Teller effect. In this study, using a low-temperature exchange reaction between ilmenite-type NaSbO 3 and molten MSO 4 -KCl (or MgCl 2 -KCl) mixtures, these five compositions were prepared for the first time as trigonal layered rosiaite (PbSb 2 O 6 )-type phases. Upon heating, they irreversibly transform to the known phases via amorphous intermediates, in contrast to previously studied isostructural MnSb 2 O 6 , where the stable phase is structurally related to the metastable phase. The same method was found to be applicable for preparing stable rosiaite-type CdSb 2 O 6 . The formula volumes of the new phases show an excellent correlation with the ionic radii (except for M = Cu, for which a Jahn-Teller distortion is suspected) and are 2-3% larger than those for the known forms although all coordination numbers are the same. The crystal structure of CoSb 2 O 6 was refined via the Rietveld method: P 3&cmb.macr;1 m , a = 5.1318(3) Å, and c = 4.5520(3) Å. Compounds with M = Co and Ni antiferromagnetically order at 11 and 15 K, respectively, whereas the copper compound does not show long-range magnetic order down to 1.5 K. A comparison between the magnetic behavior of the metastable and stable polymorphs was carried out. FeSb 2 O 6 could not be prepared because of the 2Fe 2+ + Sb 5+ = 2Fe 3+ + Sb 3+ redox reaction. This electron transfer produces an additional 5s 2 shell for Sb and results in a volume increase. A comparison of the formula volume for the stable mixture FeSbO 4 + 0.5Sb 2 O 4 with that extrapolated for FeSb 2 O 6 predicted that the trirutile-type FeSb 2 O 6 can be stabilized at high pressures. New forms of MSb 2 O 6 (M = Co, Ni, Cu, Zn, and Mg) have been prepared by ion exchange.