2,5-Diaryl-1,3,4-selenadiazoles prepared from Woollins' reagent

Two polymorphs of 2,5-diphenyl-1,3,4-selenadiazole, C14H10N2Se, denoted (Ia) and (Ib), and a new polymorph of 2,5-bis(thiophen-2-yl)-1,3,4-selenadiazole, C10H6N2S2Se, (IIb), form on crystallization of the compounds, prepared using Woollins' reagent (2,4-diphenyl-1,3-diselenadiphosphetane 2,4-diselenide). These compounds, along with 2-(4-chlorophenyl)-5-phenyl-1,3,4-selenadiazole, C14H9ClN2Se, (III), and 2-(furan-2-yl)-5-(p-tolyl)-1,3,4-selenadiazole, C13H10N2OSe, (IV), show similar intermolecular interactions, with pi-pi stacking, C-H center dot center dot center dot pi interactions and weak hydrogen bonds typically giving rise to molecular chains. However, the combination of interactions differs in each case, giving rise to different packing arrangements. In polymorph (Ib), the molecule lies across a crystallographic twofold rotation axis, and (IV) has two independent molecules in the asymmetric unit.