The reaction of Re(CO) 5 Cl with o- or p-N-(nitrophenyl)ethylenediaminediacetic acid (H 2 L 1 , H 2 L 2 ) and o- or p-N-(nitrophenyl)propylenediaminediacetic acid (H 2 L 3 , H 2 L 4 ) in methanol leads to the formation of stable anionic [Et 3 NH][Re(CO) 3 (L)]·H 2 O complexes 1–4. These compounds have been characterized by means of IR, mass spectrometry, elemental analysis, NMR and conductimetry, as well as X-ray crystallography for 2 and 3. The [Re(CO) 3 ] + moiety is coordinated via the nitrogen of the iminodiacetic acid unit and two oxygens of monodentate carboxylate groups. In each case, the nitro group of the aromatic ring remains uncoordinated. The analogous technetium-99m complexes 1′ and 3′ were also prepared quantitatively by the reaction of H 2 L 1 and H 2 L 3 , respectively, with the fac-[ 99m Tc(CO) 3 (H 2 O) 3 ] + precursor in ethanol. The corresponding Re and 99m Tc compounds were shown to possess the same structure by means of HPLC studies. The high affinity of these ligands for the Tc(I) or Re(I) core, coupled with the easiness of their derivatization (by reduction of the nitro group in amino group), implies that the utilization of this ligand system to develop target-specific radiopharmaceuticals for diagnosis and therapy is promising.