Discotic Liquid Crystals of Transition Metal Complexes, 5: Double Melting Behavior and Double Clearing Behavior of Discogens

Two new octa-substituted disk-like bis(β-diketonato) copper(II) complexes, 8C8-Cu and 8C8O-Cu, have been synthesized. The same type of octa-substituted copper complexes, SC9O-Cu, which was synthesized for the first time by A. M. Giroud-Godquin et al., has also been prepared. The thermal behavior of these three complexes was investigated by means of microscopic observations and DSC measurements. It was found that the 8C8-Cu exhibits not a discotic mesomorphism but a usual double melting behavior via the isotropic liquid, and that the 8C8O-Cu exhibits an unusual double melting behavior via the discophase which had not been reported by A. M. Giroud-Godquin et al. Furthermore, it was found that the 8C8O-Cu exhibits a new thermal phenomenon of “double clearing behavior” which is originated from a superheating of the transition from the crystalline phase to the discotic phase. Such double clearing behavior of the 8C8O-Cu is the first example in the mesomorphic compounds, so far as we know.