Synthesis and crystal structure of (Sb2Te2)[AICl(4)], a compound containing a heteroatomic polymeric cation (Sb2Te2+)(n)

The reaction of tellurium, antimony, antimony trichloride, sodium chloride, and an excess of aluminium trichloride in a closed evacuated glass ampoule yields dark red crystals of (Sb2TC2)[AlCl4]. During the reaction a melt is formed from which needle shaped crystals of the title compound grow on sublimating off the volatile AlCl3 at 130degreesC. Energy dispersive X-ray emission analysis showed the 1:1 ratio of Sb:Te. The crystal structure analysis (triclinic, P (1) over bar, a 949.30(2), b = 1348.24(3), c = 1804.97(5)pm, alpha = 78.983(2), beta = 88.060(1), gamma = 88.444(1)degrees, V = 2239.65(9)(.)10(6) pm(3), Z = 8) shows that the structure is built of almost regular tetrahedral [AlCl4](-) anions and of one-dimensional polymeric (Sb2Te2+)(n)cations. The assignment of Sb and Te atoms to the respective atom positions of the cations was performed by an analysis of the occupation factors, a reasonable electron and charge distribution, and by the analysis of the cation-anion interactions. The unit cell contains two symmetrically independent but almost isostructural cations which form strands made up of four-membered stacked Sb2Te2 rings. These rings are connected with their neighboured rings alternatingly via two, three, and four covalent bonds. Predominantly Sb-Te bonds are present, in smaller degree Sb-Sb bonds, while Te-Te bonds are not observed. The cationic strands can be interpreted by the Zintl concept in the connectivity of the different atom types and the resulting charges.