Acta Crystallographica Section B

Structural Science

Volume 56, Part 3 (June 2000)

research papers

Acta Cryst. (2000). B56, 486-496 [ doi:10.1107/S0108768100000355 ]

Metastable -phase of benzophenone: independent structure determinations via X-ray powder diffraction and single crystal studies

H. Kutzke, H. Klapper, R. B. Hammond and K. J. Roberts

Abstract: Benzophenone was the first organic molecular material to be identified as polymorphic. It is well known that benzophenone crystallizes in a stable orthorhombic [alpha] -form (m.p. 321 K) with space group P2₁2₁2₁ and a = 10.28, b = 12.12, c = 7.99 Å, [Girdwood (1998). Ph.D. thesis. Strathclyde University, Glasgow, Scotland]. Here we report two separate structure determinations of the metastable [beta] -form (m.p. 297-299 K). Crystalline material of the metastable polymorph was obtained from a melt supercooled to 243 K. The structure was determined from X-ray powder diffraction data by employing a novel, computational systematic search procedure to identify trial packing arrangements for subsequent refinement. Unit-cell and space-group information, determined from indexing the powder diffraction data, was used to define the search space. The structure was also determined from single-crystal diffraction data at room temperature and at 223 K. The metastable phase is monoclinic with space group C2/c and a = 16.22, b = 8.15, c = 16.33 Å, [beta] = 112.91° (at 223 K). The structures derived from the individual techniques are qualitatively the same. They are compared both with each other and with the stable polymorph and other benzophenone derivatives.

Keywords: Benzophenone; Metastable; Polymorphism.