A metal tricarbonyl compound of the general formulawhereinM is rhenium or technetium or an isotope thereoftwo of X1, X2 and X3 are part of a bidentate ligand and the other one is optionally a monodentate ligand selected from the group consisting of halogens, CO, aromatic heterocycles, thioethers and isocyanides, wherein the aromatic heterocycles are selected from the group consisting of pyridine, pyrimidine, pyrazine, imidazole, pyrazole, triazole, tetrazole, thiazole, and oxazole, wherein the bidentate ligand is an amino acid.