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Issue 7, 2003
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Substituent effects in columnar β-diketonate metallomesogens

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A systematic study of the mesomorphic properties of two homologous series of copper(II) and palladium(II) complexes 1ab derived from unsymmetrical β-diketonate derivatives 2 containing a variety of functional substituents (X = H, CH3, C2H5, OCH3, Cl, Br, I, CN) on the phenyl ring is reported. These disc-like molecules all contain eight n-octyloxy chains, required for the formation of columnar phases appended to the central β-diketonate core. All complexes exhibited columnar phases studied by differential scanning calorimetry, polarized optical microscopy and powder X-ray diffraction. The mesomorphic results indicated that all compounds formed stable enantiotropic columnar mesophases, and the formation of columnar phases was strongly dependent on the electronic and/or the steric factors of the substituents. For compounds containing bulky substituents (i.e. X = Me, Et) a rectangular columnar phase (Colr) was observed, however, other compounds containing electron-withdrawing substituents (i.e. X = Cl, Br, I) exhibited a hexagonal columnar phase (Colh). Most of the palladium(II) complexes, except for X = CH3 and OCH3 derivatives, have lower clearing temperatures than those of the copper(II) analogues, and this is probably due to a weaker molecular interaction between the cores in the palladium(II) complexes. Lattice constants for these two types of compound obtained by powder X-ray diffraction were found to be insensitive to the metal center incorporated. These values were all relatively close in magnitude, which indicated that the two structures were quite similar. A satisfactory linear relationship with a correlation coefficient of 0.974 between the clearing temperatures and the Hammett σp constants of substituents was obtained only for the copper complexes.

Graphical abstract: Substituent effects in columnar β-diketonate metallomesogens

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The article was received on 12 Mar 2003, accepted on 29 Apr 2003 and first published on 16 May 2003

Article type: Paper
DOI: 10.1039/B302858E
Citation: J. Mater. Chem., 2003,13, 1588-1595

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    Substituent effects in columnar β-diketonate metallomesogens

    C. Chien, K. Liu and C. K. Lai, J. Mater. Chem., 2003, 13, 1588
    DOI: 10.1039/B302858E

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