Synthesis, Mesomorphism and Spectroscopic Characterization of Bis-[(4-N-Alkoxy)-5-(p-n-Tetradecyl Phenylazo)]-Substituted (N,N'-Salicylidenediaminato) Nickel(II) Complexes

The bis[4-(n-CmH2m+1O)-5-(p-C14H29C6H4N=N)]-substituted N,N'-salicylidenediamines H-2[L-N(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 degrees C. By treating the H-2[L-N(m,14)] ligands with an Ni-II salt, Liquid crystalline mononuclear complexes with "unconventional" (lateral-tailed) molecular shape form. These Ni[L-N(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[L-N(14)] with a "conventional" rod-like molecular geometry.