Orthorhombic polymorphs of twotrans-4-aminoazoxybenzenes

Abstract

The two isomeric compounds 4-amino-ONN-azoxybenzene [or 1-(4-aminophenyl)-2-phenyldiazene 2-oxide], i.e. the alpha isomer, and 4-amino-NNO-azoxybenzene [or 2-(4-aminophenyl)-1-phenyldiazene 2-oxide], i.e. the beta isomer, both C(12)H(11)N(3)O, crystallized from a polar solvent in orthorhombic space groups, and their crystal and molecular structures have been determined using X-ray diffraction. There are no significant differences in the bond lengths and valence angles in the two isomers, in comparison with their monoclinic polymorphs. However, the conformations of the molecules are different due to rotation along the Ar-N bonds. In the alpha isomer, the benzene rings are twisted by 31.5 (2) and 14.4 (2) degrees towards the plane of the azoxy group; the torsion angles along the Ar-N bond in the beta isomer are 24.3 (3) and 23.5 (3) degrees. Quantum-mechanical calculations indicate that planar conformations are energetically favourable for both isomers. The N-H.O hydrogen bonds observed in both networks may be responsible for the deformation of these flexible molecules.

trans-Diphenyldiazene oxide

“…In both complexes, azoxybenzene is found in an almost planar conformation, the dihedral angle between phenyl rings being 13.2 and 7.4°, respectively. The same conformation has been observed in derivatives of (I) including a parasubstituted phenyl ring (Ejsmont et al, 2000, 2002, 2004, 2005Domański et al, 2001. Non-planar conformations have been observed e.g.…”

“…Non-planar conformations have been observed e.g. in the case of trans-4-aminoazoxybenzene: the α isomer is stabilized in a planar (2.6°) conformation at 293 K (Domański et al, 2001) but is twisted [43.7 (1)°] at 90 K (Ejsmont et al, 2002). A similar flexible behavior is described for the β isomer.…”

“…Two coordination complexes including the title molecule have been structurally characterized (Bassi & Scordamaglia, 1975;Cambie et al, 1996). For structures of para-substituted azoxybenzenes, see: Ejsmont et al (2000Ejsmont et al ( , 2002Ejsmont et al ( , 2004Ejsmont et al ( , 2005; Domań ski et al (2001). Data collection: XSCANS (Siemens, 1999); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXTL-Plus (Sheldrick, 1998); program(s) used to refine structure: SHELXTL-Plus; molecular graphics: Mercury (Macrae et al, 2006); software used to prepare material for publication: SHELXTL-Plus.…”

Bis[4-(n-octyloxy)phenyl]diazene oxide

“…The bond angles within the C12-N1-N2(O1)-C15 fragment are expected to be close to 120 for trigonal sp 2 hybridization, but the angles for N1-N2-O1 and C13-C12-N1 exceed this value by 6.5 (2) and 9.5 (2) , respectively (Table 1). This deformation is believed to originate from the steric interaction between atom O1 and the H atoms in the ortho positions (Ejsmont et al, 2002).…”