H-2 NMR study of the cyclopalladated 4,4'-bis(hexyloxy)-azoxybenzene, a complex showing a nematic phase

The Pd complex Azpac, synthesised from the 4,4'-bis(hexyloxy) azoxybenzene mesogen, shows a nematic phase between 90 degrees and 105 degrees C. The present work concerns the study of the orientational ordering of the ligand and complex molecules in their respective nematic phases, by H-2 NMR spectroscopy To this aim, 4,4'-bis(hexyioxy)azoxybenzene, HL, has been specifically deuterated in the positions 3 and 5 of both the rings and the complex Azpac-d(4) synthesised from it. Complex Azpac-d(26) was also synthesised starting from the ligand fully deuterated in the alkoxy chains. The morphism of Azpac-d(4) and Azpac-d(26) was investigated by optical microscopy and differential scanning calorimetry. H-2 NMR spectra were recorded on samples of HL-d(4), Azpac-d(4) and Azpac-d(26) in their mesophases as a function of temperature. By a procedure of best fitting of the experimental quadrupolar and dipolar splittings the order parameters and some structural data of the metallomesogen molecules were determined. The results are discussed with reference to the ligand.