Bridged 3,5-disubstituted pyrazolate ligands as support of metallomesogens containing [Pd(η3-C3H5)]+ fragments

Improving the mesomorphism in bispyrazolate Pd(II) metallomesogens: an efficient platform for ionic conduction

The introduction of structural asymmetry in metallomesogens is an established strategy to improve their mesomorphic behaviour in terms of lower melting temperatures and higher stability ranges of the mesophase, which is particularly important for metallomesogens that have potential application as electrolytes that require wide operational temperature ranges. Here in this work, a novel series of unsymmetrical bis(isoquinolinylpyrazolate)palladium(II) compounds bearing four alkyl side-chains with different lengths are described. Rectangular and hexagonal columnar mesophases were formed with low melting temperatures of 42-45 °C in most cases, whereas the clearing temperatures reached values up to 412 °C. The charge transport properties have been studied by complex impedance spectroscopy, showing that the mesophase favours proton conduction in the absence of water or humidity. The exceptional thermal stability of these species makes them promising candidates to act as a platform for ionic conduction via the nanochannels originated in the columnar mesophases. The results presented confirm that introducing structural asymmetry in the Pd(II) metallomesogens studied is a valid strategy to enhance the liquid crystalline properties, which opens new ways to develop water-free electrolytes based on unsymmetrical bis(isoquinolinylpyrazolate) Pd(II) compounds for potential applications such as proton exchange membranes (PEMs).

Mesomorphism of ionic allylpalladium(II) complexes containing pz(R2)py as ligands and [BF4]-, [PF6]- or [CF3SO3]- as counteranions

The synthesis and thermal behaviour is reported of some ionic liquid-crystalline complexes formed when a mesogenic, two-chained, pyrazolylpyridine ligand is bound to a eta3-allylpalladium(II) fragment. The phase behaviour of the complexes is dominated by the formation of the SmA phase and, while the stability of the crystal phase appears to be controlled by intermolecular solid-state interactions, the stability of the liquid crystal phases is controlled by the length of the ligand alkoxy chains. Some of the complexes also show a complex polymorphism leading to the observation of double-melting behaviour.