Crystallographic and conformational analysis of two novel trans-azo benzene compounds

The molecular and crystal structure of (E)-2-Acetyl-4-(2-bromophenyldiazenyl)phenol (1) and (E)-2-Methyl-4-(o-tolyldiazenyl)phenol (2) were characterized and determined by single crystal X-ray diffraction method besides spectroscopic means. The periodic organization of 1 is stabilized by C-H···O type weak H-bond and Br···O type weak halogen bonding and thus, a two dimensional puckered network is established almost parallel to (101̄) the plane. Molecules of 2 are linked into C(7) chains generated by translation along the [1 0 1] direction with the aid of O-H···N type H-bonds, and these chains are strengthened by C-H···π interactions involving o-tolylphenol ring. Quantum chemical studies at B3LYP/6-311 ++G(d,p) level reveal that potential barrier of the compounds around Ar-N torsions is of double minimum character unless it is defected by the presence of o-substituent groups in the vicinity of the azo bridge. The results from crystallographic and quantum chemical studies suggest that azo benzene compounds may adapt non-planar geometry apart from the most stable planar conformation, which is located on the secondary minima of double potential barrier regarding rotational motion around Ar-N bonds. © Springer Science+Business Media, LLC 2009.