Synthesis and antimicrobial activity of copper(II) and silver(I) complexes of hydroxynitrocoumarins: X-ray crystal structures of [Cu(hnc)(2)(H2O)(2)] center dot 2H(2)O and [Ag(hnc)] (hncH=4-hydroxy-3-nitro-2H-chromen-2-one)

[Cu(hnc)(2)(H2O)(2)] center dot 2H(2)O (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(l) 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(l) complex [Ag(phen)(2)hnc] (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 I 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(l) 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, AgNO3 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. (C) 2005 Elsevier Ltd. All rights reserved.