Synthesis, structures, spectroscopy and antimicrobial properties of complexes of copper(II) with salicylaldehyde N-substituted thiosemicarbazones and 2,2′-bipyridine or 1,10-phenanthroline

Abstract

Among the biometals (Cu, Co, Ni-cofactors in many enzymes), copper derivatives of O, N, S-donor salicylaldehyde thiosemicarbazones have received considerable attention owing to their potential biological applications. Eight new complexes of salicylaldehyde-N-substituted thiosemicarbazones [5-MeO-2-HO–C6H4–C2(H)N3–N2H–C1(S)–N1HR; R = Me, H2L1; Et, H2L1, Ph, H2L3, H, H2L4] with copper(II), namely, [Cu(κ3-O,N,S-L)( κ2-N,N-L′)] {(L)2− = (L1)2−, L′ = bipy, 1, phen, 2; (L)2− = (L2)2−, L′ = bipy, 3, phen, 4; (L)2− = (L3)2-, L′ = bipy, 5, phen, 6; (L)2− = (L4)2−, L′ = bipy, 7, phen, 8} have been isolated. Complexes have slightly distorted square pyramidal geometry around the metal center (τ parameter = 0.243–0.357) and display weak to intense fluorescence in the region, 375–475 nm. These copper complexes have shown significant growth inhibitory activity (antimicrobial activity) against Staphylococcus aureus (MTCC740), methicillin resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae 1 (MTCC109), Shigella flexneri (MTCC1457), Pseudomonas aeruginosa (MTCC741) and Candida albicans (MTCC227). The activity against MRSA is an interesting observation as the commercially available gentamycin is found to be inactive against this bacterial strain. Specifically complex 5 formed by 5-methoxysalicylaldehyde-N-phenylthiosemicatbazone has shown novel antimicrobial activity against various bacteria and yeast investigated.