Discotic mesomorphism of 2,3,7,8,12,13,17,18-octakis (alkyl-thio) 5,10,15,20 tetraaza porphyrin and its complexes with some divalent transition metal ions Synthesis and characterization

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Abstract
New discotic metallomesogens of 2,3,7,8,12,13,17,18-octakis (alkyl-thio) 5,10,15,20 tetraaza porphyrin (H2Pn) and some related complexes, obtained by reaction of first row transition metal ions Ni(II), Co(II), Cu(II), Zn(II) with the free porphyrin, have been prepared. All materials were characterized by DSC measurements and optical observations. The microscopic structure of all mesophases was checked and characterized by X-ray diffraction. Except for H2P(7–12), all of the compounds are mesogenic; a few of them exhibit mesomorphic polymorphism. Melting (C→D) temperatures range from 40 to 85°C. Only NiP4, CoP4 and CuP4 show higher values. Both temperature and ΔH of isotropization (D→I) show a regular trend with respect to the number of carbon atoms in the alkyl chains and of the nature of the metal. ΔH values for complexes with partially filled d-shell metals are very similar and show definite differences with respect to those of Zn(II). Optical and X-ray data in the case of n  7 indicate a columnar mesophase with hexagonal packing whereas in complexes with n < 7 the observed mesophase shows a non-hexagonal columnar packing. CuP6 and NiP6 probably show both mesophases which are connected by a phase transition, presumably of second order or with exceedingly low enthalpy change but easily detected by polarizing microscopy because of sharp texture changes. As expected, no odd–even effect is detectable on the properties of the liquid-crystalline phases as a function of the number of carbon atoms in the aliphatic chains.