Troponoid metallomesogens with 5-alkoxy, 5-alkoxycarbonyl, 5-alkanoyloxy, 5-alkyl, 5-alkoxy-2-amino, and 5-alkoxy-2-alkylamino substituents

Abstract

Metal complexes (Cu, VO, Zn, Mn, and Ni) with 5-alkoxy-, 5-alkoxycarbonyl-, 5-alkanoyloxy-, and 5-alkyl-tropolonato structures as well as bis(5-alkoxy-2-aminotroponato)copper were synthesized. All bistropolonato Cu complexes showed ordered smectic phases such as hexatic smectic B, smectic G(J), and smectic H phases. The Zn, Mn, and Ni complexes were non-mesomorphic whereas the VO complexes with 5-alkoxy- and 5-alkanoyloxy-tropolonato groups had mesophases. Among the Cu complexes, bis(5-alkanoyloxytropolonato)copper complex had the highest clearing point. The mesomorphic properties depend on the kinds of substituents, metal ions, and heteroatoms of the core. The Cu complexes have a square planar coordination structure and the VO complexes a square pyramidal one. The thermal stability of the Cu complexes was explained by the size and symmetry of the core structure. To decrease the transition temperatures of bis(5-alkoxytropolonato)copper complexes, secondary alkoxyl groups were introduced at the C-5 positions and the two oxygen atoms of the bistropolonato core were replaced by two nitrogen atoms, which reduced the symmetry of the structure.