SYNTHESIS AND MESOGENIC PROPERTIES OF RODLIKE BIS(ALKYLPHENYLAZO)-SUBSTITUTED N,N'-SILICYLIDENEDIAMINATO NICKEL(II), COPPER(II), AND OXOVANADIUM(IV) COMPLEXES

The tetradentate Schiff base Ligands s[5-(4'-n-alkyl)phenylazosalicyli dene]alkyldiamine H2LN(n) (n = 6, 14), based on 1,2-diaminoethane (N = 1), 1,3-diaminopropane (N = 2), and 1,3-diamino-2,2-dimethylpropane ( N = 3) were prepared and characterized. For all the ligands complexes M[L-N(n)] (M = Cu, Ni, VO) were readily obtained, which contained two free azo functions. The three series of complexes M[L-N(n)] (N = 1-3) were investigated for mesomorphism. This was observed only for N = 1 o r 2, in the form of enantiotropic nematic (lower homologues) or smecti c (higher homologues) mesophases. The thermal behavior of complexes is discussed on the basis of the structural characteristics of the N,N c helate rings.