Discotic metallomesogens: mesophase crossover of columnar rectangular to hexagonal arrangements in bis(hydrazinato)nickel(II) complexes

Abstract

Three series ofN-(3,4-dialkoxybenzylidene)-N′-(3′,4′,5′-trialkoxybenzoyl)hydrazine and their nickel(ii) complexes, bis[N-(3,4-dialkoxybenzylidene)-N′-(3′,4′,5′-trialkoxybenzoyl)hydrazinato]nickel(ii), were prepared and characterized. The mesomorphic properties of these disc-like compounds were also studied in terms of liquid crystallinity. The orange nickel(ii) complexes with ten soft alkoxy side chains exhibited columnar disordered mesophases, which were characterized based on DSC analysis and optical polarized microscopy. Nickel complexes with shorter side chains (n=5–8) displayed a monotropic columnar rectangular disordered (Col_rd) phase; however, complexes with longer side chains showed monotropic (n=10) and enantiotropic (n=12, 14) columnar hexagonal disordered (Col_hd) phases. Similar nickel complexes (n=14) with eight side chains exhibited a columnar hexagonal phase, whereas complexes (n=14) with six side chains formed crystalline phases. The structures of these columnar disordered phases were confirmed by X-ray powder diffraction. XRD data indicated that mesophase crossover from columnar rectangular (Col_r) to hexagonal arrangements (Col_h) was observed with increasing side chain lengths.