The water soluble ruthenium-p-cymene complexes [Ru(eta(6)-p-cymene)X-2](2) (X = Cl, Br, I or NCS), [Ru(eta(6)-p-cymene)X-2(pta)] (X=Cl, Br, I, or NCS; pta=1,3,5-triaza-7-phosphatricyclo[126.96.36.199]decane) and the tetraruthenium cluster [H4Ru4(eta(6)-p-benzene)(4)](2+) have been prepared and their antimicrobial properties evaluated. They have been screened for antibacterial activity against Eschericia coli, Bascillus subtilis, Pseudomonas aeruginos, for antifungal activity against Candida albicans, Cladosporium resinae and Trichrophyton mentagrophytes and for antiviral activity against Herpes simplex and Polio viruses. The antimicrobial activity of these compounds does not appear to be correlated to DNA binding, but it could be due to specific interactions with proteins. The solid-state structure of the dimer complex [Ru(eta(6)-p-cymene)Cl-2](2), an important precursor complex in organometallic chemistry, is also reported. (C) 2002 Elsevier Science B.V. All rights reserved.