Novel Metal²⁺ complexes of N-(1,4-dihydro-1,4- oxonaphthalen-3-yl) pyrazine-2-carboxamide: Synthesis, structural characterization, magnetic properties and antimicrobial activities

Chioma Festus, Ozioma A. Ekpete and Chioma D. Don-Lawson

Background and Objective: Heterocyclic nitrogen-bearing cyclic compounds mostly of amine derivatives have long been associated with biological and industrial applications as antimycobacterial, fungicides, growth inhibitors, perfumes, cosmetics, insecticides and to impact flavour in pharmaceuticals. Hence, this research study tends to synthesize and characterize divalent metal complexes of N-(1,4-dihydro-1,4-oxonaphthalen-3-yl)pyrazine-2-carboxamide and evaluate same for bactericidal and fungicidal properties. Materials and Methods: The Elementar instrument; model Vario EL III and micrOTOF-Q II 10390 was adopted for the elemental and electron impact mass spectra analyses at North-West University, South Africa. Proton and carbon-13 NMR spectra were determined on Bruker DRX-300, 300 MHz NMR spectrometer, while vibrational bands stood evaluated on Shimadzu FTIR 8000 spectrophotometer as KBr pellets. The Lambda 25 UV/visible spectrophotometer was used to obtain the electronic spectra. The in vitro antibacterial and antifungal activities of the synthesized compounds were investigated against the strains of B. cereus, P. mirabilis, E. coli, S. aureus, K. oxytoca, P. aeruginosa, A. niger, A. flavus and R. stolonifer. Results: A new Fe²⁺, Co²⁺, Ni²⁺ and Cu²⁺ complexes of LH type ligand, derived from the condensation of 2-hydroxy-1,4-naphthoquinone with pyrazine-2-carboxamide were synthesized. Physical and analytical (molar conductance and magnetic moment measurements, melting point and solubility determination, elemental analysis) and spectral (¹H-¹³C-NMR, mass, UV-visible and FTIR) data were used to confirm the formation of the synthesized compounds. On spectral basis, the ligand LH, acts as bi-dentate, coordinating through the deprotonated secondary amide nitrogen and ketonic oxygen atoms, while analytical and spectral data indicate that all the complexes were mononuclear, non-electrolytic in dimethyl sulfoxide (CH₃)₂SO, coordinated with the ligand in 2L:1M molar ratio and also the presence of coordinated water molecule(s) in Fe²⁺, Co²⁺ and Cu²⁺ complexes. Furthermore, tetrahedral geometry for Ni²⁺ and Co²⁺ and octahedral geometry for Fe²⁺ and Cu²⁺ complexes were proposed. Conclusion: Generally, the metal²⁺ complexes exhibited moderate to good activity against the microorganisms better than the metal free ligand in one form or the other. The studied cobalt and nickel complexes had the best antibacterial and antifungal activities against the screened microbes with inhibitory zones of 25.0 and 22.0 mm separately.

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