[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 a=29.679(2), b=9.9798(6), c=11.7155(7)Å, V=3470.1(4)Å3, Z=4. 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 7.7Å×8.3Å. 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 2.03eV 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.