Synthesis, Mesomorphism, and Spectroscopic Characterization of Bis[4-(n-alkoxy)-5-(p-n-tetradecylphenylazo)]-Substituted (N,N-Salicylidenediaminato)nickel(II) Complexes

The bis[4-(n-CmH2m+1O)-5-(p-C14H29C6H4N=N)]-substituted N,N′-salicylidenediamines H2[LN(m,14)] (N = 1: 1,2-diaminoethane; N = 2: 1,3-diaminopropane; N = 3: 1,3-diamino-2,2-dimethylpropane; m = 6 or 18) have been synthesized. Both the N = 2 and 3 series of compounds display a smectic C (SmC) mesophase, with clearing points well below 100 °C. By treating the H2[LN(m,14)] ligands with an NiII salt, liquid crystalline mononuclear complexes with “unconventional” (lateral-tailed) molecular shape form. These Ni[LN(m,14)] complexes, showing nematic and smectic disordered phases, are stable over a quite large temperature range and have been characterized by different spectroscopic techniques. The newly synthesized mesogens exhibit lower transition temperatures and higher thermal stability than homologous complexes Ni[LN(14)] with a “conventional” rod-like molecular geometry.