Solvothermal synthesis of a bimetallic thiometallate containing germanium in two oxidation states

A new layered germanium-antimony sulphide, Ge(C₂N₂H₈)₃]GeSb₂S₆], has been prepared at 463 K under solvothermal conditions in the presence of ethylenediamine. The compound has been characterised by single-crystal X-ray diffraction, thermogravimetry, elemental analysis and reflectance spectroscopy. Ge(C₂N₂H₈)₃]GeSb₂S₆] crystallises in the space group Pbca (a=13.3284(5), b=17.4801(6), c=18.5447(7) Å). The structure consists of cyclic GeSb₂S₈]⁶⁻ units that form chains which are cross-linked through Sb₂S₂ rings to generate layers of stoichiometry GeSb₂S₆]²⁻, between which Ge(en)₃]²⁺ cations are located. Ge(C₂N₂H₈)₃]GeSb₂S₆] contains germanium in both the divalent and tetravalent states. The optical band gap of 2.49(4) eV is in excellent agreement with the value expected on the basis of the correlation with the density of metal centres previously identified for thioantimonates, and is consistent with states at the top of the valence band being predominantly of sulphur 3p character.