A new group of CO-releasing molecules, CO-RMs, based on cyclopentadienyl iron carbonyls have been identified. X-Ray structures have been determined for [(eta-C(5)H(4)CO(2)Me)Fe(CO)(2)X], X = Cl, Br, I, NO(3), CO(2)Me, [(eta-C(5)H(4)CO(2)Me)Fe(CO)(2)](2), [(eta-C(5)H(4)CO(2)CH(2)CH(2)OH)Fe(CO)(2)](2) and [(eta-C(5)H(4)CO(2)Me)Fe(CO)(3)][FeCl(4)]. Half-lives for CO release, (1)H, (13)C, and (17)OC NMR and IR spectra have been determined along with some biological data for these compounds, [(eta-C(5)H(4)CO(2)CH(2)CH(2)OH)Fe(CO)(3)](+) and [[eta-C(5)H(4)(CH(2))(n)CO(2)Me]Fe(CO)(3)](+), n = 1, 2. More specifically, cytotoxicity assays and inhibition of nitrite formation in stimulated RAW264.7 macrophages are reported for most of the compounds analyzed. [(eta-C(5)H(5))Fe(CO)(2)X], X = Cl, Br, I, were also examined for comparison. Correlations between the half-lives for CO release and spectroscopic parameters are found within each group of compounds, but not between the groups.