Synthesis and Mesogenic Properties of Rodlike Bis(alkylphenylazo)-Substituted N,N′-Salicylidenediaminato Nickel(II), Copper(II), and Oxovanadium(IV) Complexes

The tetradentate Schiff base ligands N,N‘-bis[5-(4‘-n-alkyl)phenylazosalicylidene]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[LN(n)] (M = Cu, Ni, VO) were readily obtained, which contained two free azo functions. The three series of complexes M[LN(n)] (N = 1−3) were investigated for mesomorphism. This was observed only for N = 1 or 2, in the form of enantiotropic nematic (lower homologues) or smectic (higher homologues) mesophases. The thermal behavior of complexes is discussed on the basis of the structural characteristics of the N,N chelate rings.