White powder, monoclinic, P21/c, a = 9.78(2), b = 13.33(2), c = 17.69(3) A, fl = 116.3(5) °, U = 2068.13(15) A3, Z = 8, Dx = 1.60 Mg m-3, Mo Kct radiation, 2 = 0-71069 A, /~ = 38-42 mm-1, F(000) = 992, T = 293K. Intensity data were only observable to a resolution of 1-1 A. 392 reflections were measured from a single crystal. 4,4'-disubstituted biphenyls crystallize in spacegroup No. 14 with either Z = 8 or Z = 2 [Brock, Kuo & Levy (1978). Acta Cryst. B34, 981-985]. The 4F,4'F compound is of the latter type, the 4Br,4'Br is of the former. This study was undertaken to find out to which group (if either) the mixed 4Br,4'F compound belonged. It is in fact isostructural with 4,4'-dibromobiphenyl.
