Crystal data are reported for the binary n-molecular compounds with naphthalene, anthracene, phenanthrene, acenaphthene, fluoranthene, pyrene or triphenylene as donor and 1,3,5-trinitrobenzene, picric acid, picryl chloride or picryl bromide as acceptor (33 different crystals have been studied). In three out of seven pairs, the trinitrobenzene and picric acid molecular compounds of a particular hydrocarbon are isomorphous, and in four out of seven pairs the picryl chloride and picryl bromide molecular compounds are isomorphous. The structure of fluoranthene:picryl bromide, polymorph I [monoclinic; a=7.664(8), b=8.035 (2), c=31-631 (8)/~,, fl=91-8 (1) °, space group P21/c, Z=4] has been solved by Patterson and Fourier methods and refined by block-diagonal least-squares calculations to a final R of 0.062. The structure consists of quasi-hexagonally close-packed mixed stacks of alternating donor and acceptor molecules. The stack axes are parallel to [100]. The interplanar spacing is 3.49 A, suggesting a rather weak charge-transfer interaction.