Na9Sb(Ge2Q6)2 (Q = S, Se): two new antimony(iii) quaternary chalcogenides with ethane-like [Ge2Q6]6− ligands

Abstract

Two new antimony(III) quaternary chalcogenides, Na₉Sb(Ge₂S₆)₂ and Na₉Sb(Ge₂Se₆)₂, were successfully synthesized in vacuum-sealed silica tubes. They crystallize in different space groups: C2/m for Na₉Sb(Ge₂S₆)₂ and C2/c for Na₉Sb(Ge₂Se₆)₂. In comparison with their structures, similar ethane-like [Ge₂Q₆]⁶⁻ ligands and infinite [(Na/Sb)Q₄]_n chains exist in both of them, but note that two interesting [Na₂Sb₂(Ge₂S₆)₂]⁸⁻ and [NaS₆] layers are discovered in the structure of Na₉Sb(Ge₂S₆)₂, rather than a 3D framework structure for Na₉Sb(Ge₂Se₆)₂. Moreover, overall investigation of the quaternary chalcogenides containing M–M bonds (M = Si, Ge) indicates that the orientation of the M–M bonds has a close relation with the number ratio of sodium/another cation and cation radius in the crystal structure, which may provide a feasible way to predict the orientations of the M–M bonds in the layers for new compounds. The UV-vis-NIR diffuse reflectance and IR spectra of Na₉Sb(Ge₂S₆)₂ are measured and show that it can be expected to be a promising IR optical window material with a wide IR transmission range from 0.48–22 μm. Raman spectra further verify the IR absorption edges and the presence of Ge–Ge bonds for the title compounds.