Crystal Structures of a Cubic Tin(II) Germanate, α-SnGeO, and a Tetragonal Tin(II) Silicate, γ-SnSiO.

A cubic tin(II) germanate, α-SnGeO (space group 4̅3, = 10.52521(2) Å, and = 4), has been synthesized by both regular hydrothermal and microwave-assisted hydrothermal methods, and the crystal structure of this material has been solved by Rietveld refinement of synchrotron powder X-ray diffraction (PXRD) data. The crystal structure is analogous to α-SnSiO and is therefore related to the zinc blende structure comprising a face-centered cubic array of [SnO] anionic clusters with Ge cations occupying half of the tetrahedral holes. Variable-temperature PXRD has revealed that tin(II) germanate has high thermal stability: remaining stable at 950 K and mostly decomposing over the range 984-1034 K. The tin(II) germanate has been further characterized by X-ray fluorescence (XRF), Raman, and diffuse reflectance (DR) UV-vis spectroscopies. In addition, variable-temperature PXRD studies have revealed the formation of a tetragonal tin(II) silicate polymorph, γ-SnSiO (space group 4̅, = 7.30414(6) Å, = 10.53731(6) Å, and = 2), at temperatures below 170 K. The crystal structure of γ-SnSiO has been elucidated by Rietveld refinement. While a transition to a tetragonal polymorph is observed upon cooling α-SnSiO, no corresponding transition is observed for α-SnGeO, which retains its cubic structure over the probed temperature range.