Synthesis and antimicrobial activity of copper(II) and silver(I) complexes of hydroxynitrocoumarins: X-ray crystal structures of [Cu(hnc) 2(H 2O) 2] · 2H 2O and [Ag(hnc)] (hncH = 4-hydroxy-3-nitro-2 H-chromen-2-one)

Abstract

[Cu(hnc) 2(H 2O) 2] · 2H 2O ( 1) [hncH = 4-hydroxy-3-nitro- 2H-chromen-2-one] and [Ag(hnc)] ( 2) were prepared by deprotonating the hydroxy group of hncH with NaOH and then adding copper(II) chloride dihydrate and silver(I) nitrate, respectively. [Ag(hmnc)] ( 3) was synthesised in a similar manner [hmncH = 7-hydroxy-8-nitro-3-methyl- 2H-chromen-2-one]. The mixed-ligand Ag(I) complex [Ag(phen) 2hnc] ( 4) was prepared by treating silver(I) nitrate with 1,10-phenanthroline (phen) (1:1) and subsequent reaction with a solution containing hncH and NaOH. Molecular structures of 1 and 2 were determined by X-ray crystallography. The asymmetric unit in 1 contains two molecules of water in addition to one molecule of the copper complex. In 2 the asymmetric unit comprises one hnc − ligand moiety bonded in a bidentate fashion to the silver(I) ion with additional interactions from three other coumarin ligands. The geometry is best described as pentagonal bipyramidal. While none of the coumarin-based ligands or the free copper salt showed any significant anti-microbial activity, AgNO 3 and its’ phen and coumarin complexes exhibited good anti-microbial activity, particularly against the clinically important methicillin-resistant Staphylococcus aureus (MRSA) bacterium and also demonstrated good activity, comparable to that of the commercial fungicides clortrimazole and ketoconazole, against a clinical isolate of the fungal pathogen Candida albicans.