Nucera, AlessandroCarniato, FabioBaranyai, ZsoltPlatas-Iglesias, CarlosBotta, Mauro2024-10-242024-10-242023-03-02Inorg. Chem. 2023, 62, 10, 4272–42831520-510Xhttp://hdl.handle.net/2183/39789[Abstract]: The Fe(III)-Tiron system (Tiron = 4,5-dihydroxy-1,3-benzenedisulfonate) was investigated using a combination of 1H and 17O NMR relaxometric studies at variable field and temperature and theoretical calculations at the DFT and NEVPT2 levels. These studies require a detailed knowledge of the speciation in aqueous solution at different pH values. This was achieved using potentiometric and spectrophotometric titrations, which afforded the thermodynamic equilibrium constants characterizing the Fe(III)-Tiron system. A careful control of the pH of the solution and the metal-to-ligand stoichiometric ratio allowed the relaxometric characterization of [Fe(Tiron)3]9–, [Fe(Tiron)2(H2O)2]5–, and [Fe(Tiron)(H2O)4]− complexes. The 1H nuclear magnetic relaxation dispersion (NMRD) profiles of [Fe(Tiron)3]9– and [Fe(Tiron)2(H2O)2]5– complexes evidence a significant second-sphere contribution to relaxivity. A complementary 17O NMR study provided access to the exchange rates of the coordinated water molecules in [Fe(Tiron)2(H2O)2]5– and [Fe(Tiron)(H2O)4]− complexes. Analyses of the NMRD profiles and NEVPT2 calculations indicate that electronic relaxation is significantly affected by the geometry of the Fe3+ coordination environment. Dissociation kinetic studies indicated that the [Fe(Tiron)3]9– complex is relatively inert due to the slow release of one of the Tiron ligands, while the [Fe(Tiron)2(H2O)2]5– complex is considerably more labile.engCopyright © 2023 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)http://creativecommons.org/licenses/by/3.0/es/Relaxometric dataThermodynamic dataKinetic dataNuclear magnetic relaxation dispersionpH valuePotentiometric titrationsjournal articleopen access10.1021/acs.inorgchem.2c04393