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Abstract

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 degrees 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 degrees C to 400 degrees C, a high-temperature form h-SnBr2 crystallizes in the hexagonal space group P6(3)/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 6(3) to 3(4).6. Utilizing differential scanning calorimetry on o-SnBr2 endothermal processes at 224 degrees C and 226 degrees C were assigned as possible phase transition temperatures prior to the melting point at 227 degrees C, supported by temperature depending powder X-ray diffraction data.