Acta Crystallographica Section B

Structural Science

Volume 55, Part 4 (August 1999)

Acta Cryst. (1999). B55, 530-542 [doi:10.1107/S0108768199000348]

Packing similarities of three isosteric molecules: 4,5-dichlorophthalic anhydride, 4,5-dibromophthalic anhydride and 5,6-dichlorobenzfurazan 1-oxide, including three polymorphs of 5,6-dichlorobenzfurazan 1-oxide

C. R. Ojala, W. H. Ojala, D. Britton and J. Z. Gougoutas

Abstract: 4,5-Dichlorophthalic anhydride (CPA) lies on a twofold axis in space group C2/c; the molecules pack as stacks of two-dimensional sheets. Polymorph A of 5,6-dichlorobenzfurazan 1-oxide (CBF; systematic name 5,6-dichloro-2,1,3-benzoxadiazole 1-oxide) is isomorphous with CPA with disordered CBF molecules being pseudo-isosteric with the CPA molecule. Polymorph C of CBF has similar unit-cell dimensions but the arrangement of the molecules in the cell is different. 4,5-Dibromophthalic anhydride occurs in space group P1 in a structure derived from the CPA structure. The four structures all have similar two-dimensional sheets of molecules, but differ, in addition to the disorder of the CBF molecules, in the stacking of successive sheets. There are three polymorphs of 5,6-dichlorobenzfurazan 1-oxide. In all three the molecules are disordered about twofold or pseudo-twofold axes. In all three the molecules form chains involving similar ClO contacts along the direction of the twofold axis. In polymorphs A and C these chains form virtually identical two-dimensional sheets with inter-chain C-HO, C-HN and ClCl contacts, but with different stacking arrangements between the sheets. In polymorph B the chains are associated in face-to-face pairs with the same face-to-face overlap as in A, at an average distance of 3.42 Å compared to an average distance of 3.38 Å in A (cf. Table 8); there are no two-dimensional sheets.

Online 1 August 1999


	Structure factor file (CIF format) (57.6 kbytes) Contains datablock 15110

	Structure factor file (CIF format) (100.9 kbytes) Contains datablock 15130b

	Structure factor file (CIF format) (62.3 kbytes) Contains datablock 15113

	Structure factor file (CIF format) (44.8 kbytes) Contains datablock 15112

	Structure factor file (CIF format) (64.2 kbytes) Contains datablock 15221

	Structure factor file (CIF format) (65.4 kbytes) Contains datablock 15220b

	Structure factor file (CIF format) (32.6 kbytes) Contains datablock 15166a

	Structure factor file (CIF format) (36.9 kbytes) Contains datablock 15164a

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