Synthesis of Tetranuclear Zinc(II) Azomethine Complex: A Comparative Appraisal Between Conventional and Microwave-Assisted Methods

Symmetrical Schiff base ligand L1: 6,6'-(1E,1'E)-(1,3-phenylenebis(azan-1-yl-1-ylidene))-bis(methan-1-yl-1-ylidene)bis(2-methoxyphenol) was synthesized from a condensation reaction of m-phenylenediamine and o-vanillin in 1:2 molar ratio. The tetranuclear complex Zn4(L1)2 was synthesized via two methods, namely (a) the conventional method of refluxing and (b) the green method of microwave irradiation. Structural elucidation of the products was carried out through elemental analysis, melting point, and infrared and 1H-NMR spectroscopies. The signature n(C=N) of L1 at 1616 cm-1 experienced a shift towards a lower wavenumber at 1608-1613 cm-1 upon coordination to Zn(II) centers. A quantitative comparison between the two complexation methods was performed in terms of product yield, reaction time, solvent, electricity, and water utilization. It was found that not only the microwave-assisted complexation method produced a higher yield and required a much shorter reaction time, it was also the more resource-efficient method in terms of solvent, electricity, and water usages.