Pyrazole-based allylpalladium complexes: Supramolecular architecture and liquid crystal behaviour

The co-ordination of non-mesomorphic 3-substituted pyrazoles HpzR to the [Pd(η3-C3H5)]+ fragment gives rise to four-coordinated complexes [Pd(η3-C3H5)(HpzR)2]+ (R = C6H4OCnH2n+1; n = 12 (I12), 14 (I14), 16 (I16), 18 (I18)), which were isolated with image as counteranion. The new complexes are proved to have liquid crystal properties exhibiting monotropic or enantiotropic smectic A (SmA) mesophases at low temperatures which range between ca. 40 and 80 °C. The crystal structure of I12 presents a 2D network highly interdigitated, which could be related with the layered structure proposed in the liquid crystalline phase through the X-ray diffraction at variable temperature.