Mn(II) complexes of cyclen ligands tetra-substituted with amide, carboxylic acid, or phosphonic acid side arms are of interest due to the insights they can provide into the chemical origins of their pH-dependent relaxivities. A detailed investigation of the speciation of these complexes by potentiometric titration and solution IR spectroscopy has led to comprehensive models of the binding and protonation equilibria and, in some cases, the solution structures of the complexes. On the basis of these models we have assigned specific 1H longitudinal relaxivity values to each species present in the pH range 2-10. Details of the solution structures have also been probed through the use of diamagnetic analogs which can be characterized by conventional NMR techniques. In addition, variable temperature 17O studies provide insights into the chemical mechanisms responsible for exchange of coordinated protons with those of bulk water. These results have been applied to the design and synthesis of a new Mn(II) complex of a cyclen-based ligand with mixed carboxylic acid and amide side arms. The chemical, structural, and NMR properties of this complex will be presented.

Correlation of<sup> 1</sup>H relaxivities with solution speciation and structural features in a series of Mn(II) complexes of cyclen derivatives

247th National Meeting (2014)

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Correlation of 1H relaxivities with solution speciation and structural features in a series of Mn(II) complexes of cyclen derivatives

Correlation of¹H relaxivities with solution speciation and structural features in a series of Mn(II) complexes of cyclen derivatives