title: Concomitant but disappearing: two polymorphs of 1,4-bis(tribromomethyl)benzene.
abstract: The title compound, C(8)H(4)Br(6), (I), initially crystallized from deuterochloroform as the comcomitant polymorphs (Ia) (prisms, space group P2(1)/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 CBr(3) 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-CBr(3) groups to form double layers parallel to (001) in the regions z ≃ ¼, ¾.
authors: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Postfach 3329, 38023 Braunschweig, Germany. p.jones@tu-bs.de
authors: Peter G
authors: PG
authors: Jones
authors: Henning
authors: H
authors: Hopf
authors: Anamaria
authors: A
authors: Silaghi
authors: Christian
authors: C
authors: Näther