Acta Crystallographica Section B

Structural Science

Volume 60, Part 3 (June 2004)

Acta Cryst. (2004). B60, 333-342 [doi:10.1107/S0108768104005853]

Structural phase transitions, and BrN and BrBr interactions in 1-phenyl-2-methyl-4-nitro-5-bromoimidazole

M. Kubicki

Abstract: Crystals of C₁₀H₈N₃O₂Br undergo two reversible phase transitions between 295 and 100 K. The first, of an order-disorder nature, is a second-order transition and takes place continuously over a wide temperature range. This transition is connected with the doubling of the length of the c axis of the unit cell and with the change of the space group from P2₁/m with Z' = 1/2 (room-temperature [alpha] -phase) to P2₁/c, Z' = 1 ( [beta] -phase, 200-120 K). During this transition the molecule loses the C_s symmetry of the [alpha] -phase. The second transition takes place between 118 and 115 K, and is accompanied by a change of the crystal symmetry to the triclinic space group P $\bar 1$ (low-temperature [bold gamma] -phase). This second phase transition is accompanied by the twinning of the crystal. Neither the molecular geometry nor the crystal packing shows any dramatic changes during these phase transitions. Halogen bonds C-BrN and dihalogen interactions BrBr play a crucial role in determining the crystal packing and compete successfully with other kinds of weak intermolecular interactions.

Online 17 May 2004


	Structure factor file (CIF format) (76.5 kbytes) Contains datablock pw13a_1

	Structure factor file (CIF format) (74.2 kbytes) Contains datablock pw13b_1

	Structure factor file (CIF format) (136.2 kbytes) Contains datablock pw13c_3

	Structure factor file (CIF format) (133.9 kbytes) Contains datablock pw13d_3

	Structure factor file (CIF format) (134.1 kbytes) Contains datablock pw13e_3

	Structure factor file (CIF format) (139.7 kbytes) Contains datablock pw13f_3

	Structure factor file (CIF format) (86.4 kbytes) Contains datablock pw13g_1

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