title: (E)-(4-hydroxyphenyl)(4-nitrophenyl)diazene, (E)-(4-methoxyphenyl)(4-nitrophenyl)diazene and (E)-[4-(6-bromohexyloxy)phenyl](4-cyanophenyl)diazene.
abstract: Syntheses and X-ray structural investigations have been carried out for (E)-(4-hydroxyphenyl)(4-nitrophenyl)diazene, C(12)H(9)N(3)O(3), (Ia), (E)-(4-methoxyphenyl)(4-nitrophenyl)diazene, C(13)H(11)N(3)O(3), (IIIa), and (E)-[4-(6-bromohexyloxy)phenyl](4-cyanophenyl)diazene, C(19)H(20)BrN(3)O, (IIIc). In all of these compounds, the molecules are almost planar and the azobenzene core has a trans geometry. Compound (Ia) contains four and compound (IIIc) contains two independent molecules in the asymmetric unit, both in space group P1 (No. 2). In compound (Ia), the independent molecules are almost identical, whereas in crystal (IIIc), the two independent molecules differ significantly due to different conformations of the alkyl tails. In the crystals of (Ia) and (IIIa), the molecules are arranged in almost planar sheets. In the crystal of (IIIc), the molecules are packed with a marked separation of the azobenzene cores and alkyl tails, which is common for the solid crystalline precursors of mesogens.