[C6H21N4][Sb9S14O]: Solvothermal synthesis, crystal structure and characterization of the first non-centrosymmetric open Sb–S–O framework containing the new [SbS2O] building unit

[C6H21N4][Sb9S14O] represents the first known oxo-thioantimonate with an organic ion acting as structure director. The compound crystallizes in the non-centrosymmetric space group Cmc21 with image, image, image, image, image. The structure contains the hitherto unknown [SbS2O] unit as a structural motif. The [SbS3] trigonal pyramids and [SbS2O] units are joined to form a 10-membered ring with large pores having a diameter of 7.7 Å×8.3 Å. The organic template molecule acts like a tetra-dentate ligand around the O atom of the [SbS2O] group. Depending on the value chosen for the Sb–S bond lengths, the material contains a 1-, 2- or 3-dimensional anion. The optical band gap of 2.03 eV demonstrates that the material is an optical semi-conductor. Upon heating, the compound decomposes in two steps yielding finally a mixture of Sb and Sb2S3. The 121Sb Mössbauer spectrum shows a relative large line width in accordance with the superposition of the five signals.