• Boon-Teck Heng

      Articles written in Journal of Chemical Sciences

    • Synthesis, optical and thermal behaviour of palladium(II) complexes with 4-(4-alkoxy-2-hydroxybenzylideneamino)azobenzene

      Boon-Teck Heng Guan-Yeow Yeap Daisuke Takeuchi

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      A series of new Pd(II) complexes derived from the reaction of palladium acetate with 4-(4-alkoxy-2-hydroxybenzylideneamino)azobenzene having the flexible terminal chain of OC$_n$H$_{2n+1}$, in which n are even numbers ranging from 8 to 16, has been successfully synthesized. The physical measurement and spectroscopic techniques (FTIR and 1H-NMR) reveal that the Pd(II) complexes possess the Pd-N and Pd-O coordination modes in which the central Pd(II) adopts square-planar geometry. The observation under the polarized light shows that all the ligands and Pd(II) complexes exhibit enantiotropic mesophases. The ligands with 𝑛-octyloxy and 𝑛-decyloxy flexible chains exhibit the nematic (N) and smectic A (SmA) phases whilst the Pd(II) complexes show exclusive SmA phase. The SmA phase observed in Pd(II) complexes can be supported by the presence of focal conic fan-shaped texture with the presence of curved lines which are prominent during the cooling process. On the other hand, the comparison studies show that Pd(II) complexes possess exceptional higher phase transition temperatures as compared to the corresponding Cu(II) and Ni(II) complexes.

    • Mesogenic copper(II) complexes with [1,2,3]-triazole-based bidentate Schiff bases

      Guan-Yeow Yeap Boon-Teck Heng

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      The first mesogenic Cu(II) complex with [1,2,3]-triazole-based bidentate Schiff bases with flexible terminal alkyl chain, C$_n$H$_{2n+1}$ (even parity of n = 10-18) has been successfully synthesized. The heterocyclic triazole core was introduced into the target compound through the click reaction between azidoalkane and propargyl aldehyde. All the uncoordinated ligands and target complexes were characterized by elemental analysis, FT-IR, 1H-NMR and UV-visible spectroscopic techniques. The observation under the polarized light and differential scanning calometry (DSC) shows that the triazole-based ligands exhibit unstable SmA phase which are not reproducible upon subsequent heating and cooling. Interestingly, the whole homologues of Cu(II) complexes show exclusively stable focal conic fan-shaped texture characteristic of SmA phase. This can be ascribed to the presence of Cu-N and Cu-O coordination modes which enhance the collinearity and molecular anisotropy. On the other hand, the Cu(II) complexes are thermally more stable as compared to their corresponding ligands.

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