Crystal structure of the high-temperature form of the trisulfide Cs₂S₃ and the (3+1)D modulated structure of the telluride K₃₇Te₂₈

The high-temperature polymorph of the trisulfide Cs₂S₃, which has been synthesized from Cs₂S₂ and elemental sulfur, crystallizes in a new structure type (monoclinic, space group P2₁/c, a=999.97(4), b=1029.30(5), c=2642.07(12) pm, β=90.083(2) , Z=16, R1=0.0324). The structure contains four crystallographically independent angled S₃^2- trisulfide ions with S-S distances of 205.7-208.3 pm. The distorted b.c.c. packing of the anions and their insertion in the five-membered rings of 3.5³ + 3.5.3.5. (1:1) Cs nets are similarly found in the r.t. form (Cmc2₁, K₂S₃-type structure) and the two polymorphs differ mainly in the orientation of the S₃ groups. The second title compound, K₃₇Te₂₈, was synthesized from stoichiometric melts of the elements. It forms a complex (3+1)D modulated tetragonal structure (space group I4₁/amd (00σ₃)s0s0, q=(0, 0, 0.5143), a=1923.22(2), c=2626.66(4) pm, Z=4, R1_all=0.0837). According to K₃₇Te₂₈=K₃₇[Te(1X)]₈[Te(2X)₂]₆[Te(3X)₈] the structure contains three different types of Te anions: The two crystallographically different isolated telluride anions [Te(1X)]^2- are coordinated by 9/10 K⁺ cations. Three [Te(2X)₂]^2- dumbbells (d_Te-Te=277.9/286.4 pm) are arranged to 'hexamers'. The Te(31) and Te(32) atoms are located in columns of face-sharing K square antiprisms. Their z position modulation, which is accompanied by a smaller shift of the surrounding K⁺ cations, results in the decomposition of the [Te(3X)₈]₂ chain in a sequence vertical stroke:Te₃-Te₂-Te₂-Te₃-Te₂-Te₂-Te₂: vertical stroke of dumbbells Te₂^2- (d_Te-Te=304 pm) and hypervalent linear trimers Te₃^4- (d_Te-Te=325 pm).