Synthesis and mesogenic properties of acylhydrazinato metal complexes

Buckley, Christina Maria (1995) Synthesis and mesogenic properties of acylhydrazinato metal complexes. Doctoral thesis, University of Central Lancashire.

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Previous work at this institute involved the successful synthesis of liquid crystalline nickel(II) and copper(II) metal complexes based on the N-methylidene(4'-n-alkoxybenzoyl)hydrazone ligand. The primary aim of this study was to determine the structural variations which would still permit mesophase formation in these recently discovered liquid crystalline acyihydrazinato metal complexes.
The potential mesogens were synthesised, characterised spectroscopically and the effects of the structural changes on the mesophase characteristics determined by a combination of polarising microscopy, DSC and in certain cases by X-ray diffraction.
The following structural variations were examined:
Varying the alkoxy chain length of the known N-methylidene(4'-nalkoxybenzoyl) hydrazinato metal complexes; The replacement of the alkoxy chain by an alkyl chain; The introduction of a 3-fluoro-substituent on the aromatic ring of the alkoxy complexes; The replacement of the benzoyl group by a biphenyloyl group and introduction of N-alkylidene
groups into the biphenyloyl complexes;. The replacement of the N-methylidene group of the biphenyloyl complexes with alkylidene or aralkylidene groups; The introduction of alkylene or vinyl spacer groups between the aromatic and acylhydrazinatometal rings; Elongation of the molecule by the introduction of a 4-phenylazo group; The incorporation
of chiral centres into the alkyl chains of the alkoxy complexes; The alteration of the position of substitution on the acylhydrazinatometal ring from C-3 to N-5; The formation of polymeric structures; Change of the metal co-ordinated to the N-methylideneacylhydrazinato ligand from nickel(ll) to palladium(ll), zinc(ll) or cobalt(U).
In general, structural variations of the ligand proved to be successful in the formation of liquid crystalline materials; mostly forming SmC phases except for the N-alkyl and N-alkylidenebiphenyloyl complexes which formed SmA and nematic phases respectively. These complexes often had much wider liquid crystalline ranges and much higher melting ranges than the simple alkoxy complexes; the higher temperatures often resulting in extensive decomposition in the mesophase. Co-ordination to palladium(ll) gave liquid crystals with slightly higher melting ranges than their corresponding nickel(ll) analogues, whilst co-ordination to cobalt(II) and zinc(ll) supressed mesophase, formation. The synthesis of polymeric
structures were successful but the compounds did not exhibit any liquid crystalline tendencies. Changing the position of substitution on the acylhydrazinatometal ring from C-3 to N-5 also suppressed liquid crystalline behaviour in the system.

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