The synthesis and mesomorphic behaviour of tetracatenar di-hydrazine derivatives

Symmetrical four-chained (tetracatenar) di-hydrazine derivatives, namely oxalyl N',N'-bis(3,4-dialkoxybenzoyl)-hydrazide (BFH-n, n = 4, 6, 8, 10), were synthesised. Investigations on the liquid crystalline properties by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarising optical microscopy (POM) showed that the di-hydrazine derivatives exhibited columnar mesophases and the symmetry of the mesophase changes from rectangular to hexagonal on increasing the temperature. The rectangular columnar mesophases of BFH-n (n = 6, 8, 10) remained stable down to 10°C during cooling and the subsequent recrystallisation from the Colr phase of BFH-n (n = 6, 8, 10) was observed on the second heating runs. Furthermore, the average number of molecules packing in a column slice was estimated to be three, based on their X-ray diffraction results. Intermolecular hydrogen bonding between –C=O and −N−H groups in crystalline and liquid crystalline phases was confirmed.

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