Discotic Liquid Crystals of Transition Metal Complexes VI. Monotropic Lamella Mesomorphism of Tetrakis(N-Alkyldithiolato)Dinickel(II) and Bis(N-Alkylxanthato)Nickel(II) Complexes

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Abstract
It was found that each of the tetrakis(n-alkyldithiolato)dinickel(II), (Cn-DTA)4-Ni2, complexes where n-alkyl is n-pentyl through n-dodecyl, exhibits a broken-fan texture on cooling from an isotropic liquid, and that the phase gave a characteristic lamella structure X-ray diffraction powder pattern. Furthermore, the infrared spectrum of this phase is more similar to that of the isotropic liquid than that of the crystal. Therefore, the phase can be described as a monotropic lamella mesophase. Interestingly, each of the complexes of bis(n-alkylxanthato)nickel(II), (Cn-Xan)2Ni, (n = 5, 7, 9, 11) exhibits double (triple) melting behavior via the isotropic liquid, whereas each of the complexes of (Cn-Xan)2Ni (n = 4, 6, 8, 10, 12) shows ordinary single melting behavior. Such unique double melting accompanied by an even-odd effect appears to be the first example of this in the long chain substituted compounds. Each of the complexes of (Cn-Xan)2 Ni (n = 9, 11, 12) has a monotropic lamella mesophase exhibiting a large broken fan texture.