Liquid crystal behaviour of ionic allylpalladium complexes containing 2-pyrazolylpyridine as bidentate N,N′-ligand

The substitution at the 3 and 5 positions on the pyrazole ring of 2-pyrazolylpyridine (pzR2py) ligands was determinant to produce mesomorphic properties on themselves as well as on their PdCl2 complexes. This behaviour was absent on the related ligands and complexes containing an unique substituent at the 3-position (pzRpy). By contrast, the [Pd(η3-C3H5)]+ fragment induces mesomorphism on the complexes obtained upon coordination to pzRpy. In this work, the new cationic [Pd(η3-C3H5)(pzRpy)]+ compounds are characterised, and their liquid crystal properties are examined and related to their molecular structures determined by X-ray diffraction.