resistance of microorganisms to existing drugs necessitates a constant search for new compounds with antibacterial and antiviral properties. Hexaammine cobalt(III) chloride [Co(NH3)6]Cl3 showed remarkable antiviral properties against Sindbis virus, adenovirus, human immunodeficiency virus (HIV) and Zaire Ebola strain. Four multi-component compounds containing [Co(NH3)6]3+ cations and different N-, O-, and N,O-donor ligands with the formula [Co(NH3)6]Cl3.2(phen).3H2O (1) (Figure), [Co(NH3)6]Cl2(Hpht).3H2O (2), [Co(NH3)6]Cl(Hpht)2.3H2O (3), and [Co(NH3)6][Co(pdc)2(H2O)4]Cl.3H2O (4) (phen = 1,10-phenanthroline; H2pht = o-phthalic acid; H2pdc = 3,5-pyridinedicarboxylic acid) were synthesized and tested for their potential to inhibit the replication of HIV-1 (strain IIIB) and HIV-2 (strain ROD) in acutely infected MT-4 cells with parallel determination of their toxicity. Compound 1 exhibited the best activity among all tested with IC50 of 0.46 mg/mL.Figure. View of formula unit of [Co(NH3)6]Cl3.2(phen).3H2O.