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).