Solvothermal syntheses, crystal structures and properties of five new thioantimonates(III) containing the [Sb4S7] anion

Five new thioantimonates have been synthesized in the presence of organic amines under solvothermal conditions and their structures determined by single-crystal X-ray diffraction. All of the compounds are layered and contain antimony-sulphide anions of stoichiometry Sb₄S₇]²⁻, but the structure of the anion formed is dependent on the amine used in synthesis. (H₃N(CH₂)₄NH₃)Sb₄S₇] (1) contains Sb₄S₇]²⁻ double chains directed along 010]. Weak interchain Sb-S interactions between neighbouring chains cause the double chains to pack into layers in the ab plane. In the 001] direction, the layers of double chains alternate with doubly protonated diaminobutane molecules to which the chains are hydrogen bonded. Compounds of general formula (TH)₂Sb₄S₇] (T=CH₃(CH₂)₂NH₂(2), (CH₃)₂CHNH₂(3), CH₃(CH₂)₃NH₂(4) and CH₃(CH₂)₄NH₂(5)) adopt a more complex structure in which Sb₃S₈]⁷⁻ units are linked by SbS₃³⁻ pyramids to form chains, which in turn are bridged by sulphur atoms to create sheets containing large heterorings. Pairs of such sheets form double layers of four atoms thickness that are stacked along 001]. Protonated amine molecules are located between anionic antimony-sulphide layers to which they are hydrogen bonded. Thermal analysis reveals that the decomposition temperature of materials containing Sb₄S₇]²⁻ anions is dependent both on the structure of the anion, the lowest decomposition temperature being that of the low-dimensional phase (1) and on the identity of the amine, the decomposition temperature decreasing with an increasing number of carbon atoms and decreasing density.