Novel liquid-crystalline derivatives of transition metals. The effect of the molecular geometry of the ligands on the mesogenic properties of tetracoordinated copper(II) complexes

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Abstract
The synthesis, characterization and thermal behaviour of several new series of copper(II) complexes derived from carbonylic compounds and their Schiff's bases are reported. The complexes are of two types; [Cu(C6H3O(R)-C(X) = O)2], (type I) and [Cu(C6H3O(R)-C(X) = N-R′)2] (type II) where R = - OOC-C6H4OC10H21-p, and the position of R is 4 or 5; R′ = CH3, n-C10H21, p-n-C10H21O(C6H4)-; X ˭ H, CH3. In type I complexes, only the compound with X ˭ H and R in position 5 showed mesomorphism. For type II complexes, all the Schiff's bases complexes of copper(II) derived from 2,4-dihydroxybenzaldehyde showed thermotropic mesophases (smectic C and nematic), whereas the complexes derived from 2,5-dihydroxybenzaldehyde were only mesogenic when the imine was derived from methylamine. None of the complexes derived from the ketone (2,4 or 2,5-dihydroxy derivatives) showed liquid-crystalline properties. X-ray studies of four complexes of type II were carried out. The anisotropy of the magnetic susceptibility has a negative sign for complexes with R in position 4 and a positive sign for 2,5-derivative complexes. The relationship between molecular structure and mesomorphic behaviour is discussed.

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