Crystal structures of 3,3′-bis(hydroxydimethylsilanyl)azobenzene and 4,4′-bis(hydroxydimethylsilane)azobenzene

The title compounds {systematic names (E)-[diazene-1,2-diylbis(3,1-phenylene)]bis(dimethylsilanol) and (E)-[diazene-1,2-diylbis(4,1-phenylene)]bis(dimethylsilanol)}, both of the sum formula C16H22N2O2Si2, were obtained by transmetallation of the respective bis-stannylated azobenzenes with dichlorodimethylsilane and esterification followed by hydrolysis. The asymmetric unit of 3,3′-diazenediylbis[dimethyl(phenyl)silanol] (with the silanol functional group in a meta position) consists of two molecules, of which one occupies a general position, whereas the second is located on a centre of inversion. In 4,4′-diazenediylbis[dimethyl(phenyl)silanol] (with the silanol functional group in a para position) likewise two molecules are present in the asymmetric unit, but in this case both occupy general positions. Differences between all molecules can be found in the torsions about the N=N bond, as well as in the dihedral angles between the benzene rings. In both structures, intermolecular O—H...O hydrogen bonding is observed, leading to the formation of layers parallel to (01-1) for (I) and to chains parallel to the a axis for (II).