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X-Ray Crystal Structure of the Dyes 2-Nitro-4'-[N,N-Bis(β- Hydroxyethyl)amino]azobenzene and 2-Cyano-4'- [N,N-Bis-(β-Hydroxyethyl)amino]azobenzene

X-ray diffractometer data have been used to determine the crystal structure of the 2-nitro and 2-cyano derivatives of 4'-[N,N-bis(β-hydroxyethyl)amino]azobenzene. The structures were solved by direct methods and refined by least squares to R = 0.0352 (CN) and 0.0486 (NO2) for 1294 and 2661 independent reflections, re spectively. The nitro derivative is nonplanar with a dihedral angle of 42.1° between the two phenyl rings. The effect of the nitro group on the geometry of the molecule is discussed. On the other hand, the cyano derivative possesses a planar azobenzene skeleton. The dihedral angle between the two phenyl rings is 5.5° in this case. The O(4)-atom of the nitro substituent lies very close to the N(1)-atom of the azo moiety, as had been suggested previously to account for the low lightfastness of some closely related ortho-nitro azo dyes. The C(1)—N(1),N(1)—N(2), and N(2)—C(7) bond lengths of the azobenzene skeleton are surprisingly similar for the two dyes.