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Complex formation equilibrium processes of the (N,N) donor containing 2,2ʹ-bipyridine (bpy) and ethylenediamine (en) with (η⁵-pentamethylcyclopentadienyl)rhodium(III) were investigated in aqueous solution via pH-potentiometry, ¹H NMR spectroscopy, and UV–vis spectrophotometry in the absence and presence of chloride ions. The structure of [RhCp*(en)Cl]ClO₄ (Cp*, pentamethylcyclopentadienyl) was also studied by single-crystal X-ray diffraction. pK_a values of 8.56 and 9.58 were determined for [RhCp*(bpy)(H₂O)]^2 + and [RhCp*(en)(H₂O)]^2 +, respectively resulting in the formation of negligible amount of mixed hydroxido complexes at pH 7.4. Stability and the H₂O/Cl⁻ co-ligand exchange constants of bpy and en complexes considerably exceed those of the bidentate O-donor deferiprone. The strong affinity of the bpy and en complexes to chloride ions most probably contributes to their low antiproliferative …