Nickel(II) complexes incorporating long-chain ester ligands: Synthesis, characterization, and exploration of mesophase behavior

This research synthesized a long-chain carboxylate ion and a cyclam ligand-enhanced Ni(II) ion-based heavy metal complex through a four-step reaction. In the first step, the long-chain ester ligand, CH3(CH2)13OC6H4COOC2H5, was synthesized through a classic esterification reaction from CH3(CH2)13Br and HOC6H4COOC2H5. Subsequently, in the second step, saponification yielded the CH3(CH2)13OC6H4COOK salt. In the third step, a dinuclear Ni(II) complex, [Ni2(CH3(CH2)13OC6H4COO)4(H2O)5]·H2O, was prepared by reacting nickel chloride hexahydrate with an alkoxy benzoic acid salt in ethanol. The final Ni(II) complex ionic liquid, [Ni(Cy)(CH3(CH2)13OC6H4COO)2]·2H2O, was obtained as a purple needle through a reflux reaction between the dinuclear complex and cyclam in ethanol. Elemental analysis confirmed the chemical formula of the final mesogenic complex, which is C52H94N4NiO8 with a molecular weight of 962.0 g mol⁻¹. The FTIR spectrum indicated monodentate coordination of the 4-CH3(CH2)13OC6H4COO- ligands. TGA analysis revealed a multi-step decomposition process, with a decomposition temperature of 286 °C. DSC analysis indicated a series of phase transitions, including crystal-to-mesophase and mesophase-to-isotropic liquid transitions. POM observations confirmed the formation of a mesophase upon cooling. KEY WORDS: Ionic liquid, Nickel complex, Cyclam, Organometallic compound, Metalomesogen Bull. Chem. Soc. Ethiop. 2026, 40(5), 1135-1146 DOI: https://dx.doi.org/10.4314/bcse.v40i5.14