Novel cobalt(II) complex of a new 24-membered macrocyclic bis-Schiff base bearing 3-mercapto-1,2,4-triazole: Synthesis, characterization, thermal and biological investigations

The synthesis of a new 24-membered macrocyclic bis-Schiff base, L1, and its corresponding binuclear cobalt(II) complex, [Co2(L1)2(Cl)4], 1, is reported. Compound L1 and complex 1 have been characterized by elemental analysis, FT-IR, 1H NMR, and UV-VIS spectroscopy as well as mass spectrometry. Furthermore, the molecular structures of the synthesized compounds were determined using single crystal X-ray diffraction analysis. The crystal structure of the binuclear cobalt(II) complex, 1, revealed that each ligand acts as a bidentate chelating one and links the metal ions through endocyclic nitrogen atoms of its 1,2,4-triazole moieties. The determined molecular structure as well as the UV-Vis studies indicated a tetrahedral geometry for complex 1. Moreover, the thermal stability of complex 1 has been investigated via thermogravimetric analysis (TGA). The product of pyrolysis of complex 1 was characterized as highly pure nano-scaled Co3O4 (mean crystallite size: 57 nm) by using a series of techniques including powder X-ray diffraction (P-XRD) and energy-dispersive X-ray spectroscopy (EDX). The biological activities of L1 and complex 1, including antibacterial and antifungal activities were evaluated. The antibacterial activity was tested against Gram-negative (Escherichia coli, E. coli ATCC 29232) and Grampositive (Staphylococcus aureus, S. aureus ATCC 25922) organisms. Also, the pathogenic fungi Candida albicans (C. albicans, ATCC 10231) and Saccharomyces cerevisiae (S. cerevisiae, BY 4741) were used for antifungal tests. The synthesized cobalt(II) complex displayed moderate to good antifungal activity.