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Concomitant but disappearing: two polymorphs of 1,4‐bis(tribromomethyl)benzene

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The title compound, C8H4Br6, (I), initially crystallized from deuterochloroform as the comcomitant polymorphs (Ia) (prisms, space group P21/n, Z = 2) and (Ib) (hexagonal plates, space group C2/c, Z = 4). The molecules in both forms display crystallographic inversion symmetry. All further attempts to crystallize the compound led exclusively to (Ib), so that (Ia) may be regarded as a `disappearing polymorph'. Surprisingly, however, the density of (Ia) is greater than that of (Ib). The only significant difference between the molecular structures is the orientation of the CBr3 groups. The molecular packing of both structures is largely determined by Br...Br interactions, although (Ia) also displays a C—H...Br hydrogen bond and both polymorphs display one Br...π contact. For (Ia), six of the eight contacts combine to form a tube‐like substructure parallel to the a axis. For (Ib), the two shortest Br...Br contacts link `half' molecules consisting of C—CBr3 groups to form double layers parallel to (001) in the regions z, .

Document Type: Research Article


Publication date: October 15, 2011

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