Synthesis and thermotropic behavior of cholesteric mixtures containing metallomesogen Cu(II), Ni(II), Pd(II) and vanadyl complexes

In this work the synthesis of a series of Ni(II), vanadyl and Pd(II) metallomesogen complexes with a chiral ligand is reported. Cholesteric mixtures were obtained by mixing such complexes with analogous achiral complexes and their thermotropic behavior was studied by means of differential scanning calorimetry, temperature dependent UV–Visible spectroscopy and optical observation. The results show a strong dependence of the cholesteric pitch on the temperature for Ni/Ni mixtures, minor and no dependence respectively for VO/VO and Pd/Pd mixtures, this last in accordance with the known behavior of Cu/Cu mixtures. The study reveals an influence of the metal and its coordination geometry on the temperature dependence of the cholesteric pitch.