The toxic and therapeutic properties of Carbon monoxide (CO) are close together. However, the toxic properties of CO are far better known than the therapeutic applications. The low solubility in aqueous media and the lack of selectivity of free carbon monoxide are problematic for a specific therapeutic use. The research of the carbon monoxide-releasing molecules, (CORMs), is the decisive step for the use of carbon monoxide as a therapeutic. By CORMs are often at transition metal carbonyl compounds, which are inactivated by the CO coordination to the metal center. In solid state of these complexes, a dose control of CO is possible. The present work focuses on the synthesis and characterization of ruthenium and manganese carbonyl complexes. Additionally, some of the complexes obtained, were analyzed with respect to their CO release properties as photo-CORMs in a myoglobin-based assay. Two ruthenium carbonyl complexes with the general formula [Ru(CO)2(S^N)2] with (S^N) representing a bidentate amino thiolate ligand and one [Ru2(CO)5(R-APE)] complex with R-APE being an 1,2-bis(amido)-1,2-bis(pyridyl) ethane ligand are discusses. In the case of these ruthenium complexes it was not possible to observe light-induced loss of CO. In addition three different synthesis methods were employed for obtaining manganese carbonyl complexes. The reactions yielded dinuclear complexes of the general formula [Mn(CO)4(μ-SC6H4-4-R)]2 or tetranuclear [Mn(CO)3(μ-SR)]4 products of with a high amount of CO ligands and the CO release during irradiation with visible light occurred in some cases.