Two Modifications of Tin(II) Bromide

• Published in: Zeitschrift für anorganische und allgemeine Chemie (1950) 2015-07, Vol.641 (8-9), p.1467-1472
• Main Authors: Eckold, Pierre, Hügel, Werner, Dinnebier, Robert E., Niewa, Rainer
• Format: Article
• Language: English
• Subjects: Crystal structure; Polymorphism; Tin(II) bromide; X-ray diffraction
• ISSN: 0044-2313; 1521-3749
• DOI: 10.1002/zaac.201500108

Different temperature conditions in crystal growth of tin(II) bromide, SnBr2, lead to the formation of two modifications of the title compound. Applying a temperature gradient from 650 °C to room temperature along a silica glass ampoule, the stable room‐temperature modification, o‐SnBr2 crystallizes in the orthorhombic space group Pnma (no. 62), with a = 839.08(4) pm, b = 423.54(2) pm, c = 1052.03(4) pm, and Z = 4. Changing the reaction conditions towards a decreased temperature gradient from 700 °C to 400 °C, a high‐temperature form h‐SnBr2 crystallizes in the hexagonal space group P63/m (no. 176), with a = 1228.24(5) pm, c = 435.68(2) pm, and Z = 6. The trigonal coordination of Sn with three Br atoms and the resulting one‐dimensional chains of corner sharing units 1∞[SnBrBr2/2] can be assigned as common structural motif of both modifications. In o‐SnBr2 pairs of these chains exhibit the motif of a hexagonal rod packing parallel to the crystallographic b axis. In h‐SnBr2 the chains are rearranged, which results in a lower packing density and in a change in topology from 63 to 34.6. Utilizing differential scanning calorimetry on o‐SnBr2 endothermal processes at 224 °C and 226 °C were assigned as possible phase transition temperatures prior to the melting point at 227 °C, supported by temperature depending powder X‐ray diffraction data.