Synthesis, Characterization And Liquid Crystalline Behavior Of [1,2,3]- Triazole-Based Bidentate Schiff Bases And Related Cu(Ii) Complexes
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Date
2016-10
Authors
Heng, Boon Teck
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Seven new homologous series of Cu(II) complexes with ligands derived from
[1,2,3]-triazole-based bidentate Schiff bases had been successfully synthesized. All
the molecular structures were elucidated by elemental analysis and various
spectroscopic techniques (UV-visible, FT-IR, 1D, 2D 1H and 13C-NMR). The optical
properties and phase transition temperatures were investigated by polarising optical
microscope (POM), differential scanning calorimetry (DSC) and X-ray diffraction
(XRD). The first series is Cu(II) complexes with ligands bearing F, Cl, Br and I
atoms as terminal substituent or without substituent. This is notable that fluorosubstituted
Cu(II) complexes (C14H29 and C16H33) showed enantiotropic N phase
which was absent in their corresponding ligands. X-ray diffraction studies had
suggested the alkyl chain self-ordering of SmA and SmC phases in complexes with
even parity C14H29 to C18H33. In second series, the effects due to the presence of two
terminal flexible chains in ligands had been investigated. X-ray diffraction studies
had substantiated the emerging of SmC phase in all ligands and complexes with tilt
angle of 37.2-39.5o. This study revealed that the existence of two terminal flexible
chains at both sides of ligands could prevent the change in aspect ratio through
complexation. The third series is the Cu(II) complexes containing halogenated
ligands with three rings system instead of the four rings system in first and second
series. The ligands with fluoro and iodo-substituent showed non-stable SmA phase.
The ultimate Cu(II) complexes show stable SmA phase. This indicated the important
of Cu(II) ion in enhancing the colinearity and molecular anisotropic of ligands.
Comparison studies discovered the introduction of an extra aromatic ring could also
lead to the stabilization of mesophase. The ligands and complexes in fourth series
comprised either bromine atom as terminal substituent or an additional terminal nhexadecyloxy
flexible chain. All the ligands are enantiotropic but their corresponding
Cu(II) complexes were non-mesomorphic. Comparison studies with ligands and
complexes in third series showed that the various location of ortho-hydroxyl group
could greatly affect the thermal and mesomorphic behavior. In the fifth series, all the
ligands and complexes demonstrated the similar mesomorphic behaviour. This
finding further supported the concept as mentioned in second series whereby the
aspect ratio will not be affected by complexation due to the presence of two terminal
flexible chains in ligands. The sixth series is the complexes with dimesogenic ligands
containing cholesterly moiety. The ligands with dodecanoate chain exhibited
enantiotropic N* and SmC* phase while the other members exhibited SmC* only.
This is worth to mention that all Cu(II) complexes exhibited SmA* phase which was
not observed in their respective ligands. This suggested that a new molecular
architecture had achieved through the formation of Cu(II) complexes. The final
series had molecular structures that are approximately analogous to the
aforementioned series but all the ligands and complexes in this series were
incorporated with ferroceny moiety instead of the cholesteryl moiety. All the ligands
prepared in the final series are non-mesomorphic. However, all their respective Cu(II)
complexes showed enantiotropic SmC and SmA phases. The comparison studies had
further evidenced the suppression of mesophase by the repulsive effect in between
the L-shaped ligands.
Description
Keywords
Seven new homologous series , of Cu(II) complexes