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The self-assembly mechanism leading to the exclusive formation of a triple-stranded bimetallic helicate upon reaction of Eu^III with a ditopic hexadentate ligand L bearing two carboxylate moieties has been fully elucidated in water for a wide range of [Eu]tot/[L]tot ratios. Using a fruitful combination of electrospray mass spectrometry, potentiometry, UV/Vis spectrophotometry, luminescence, and ¹H NMR spectroscopy, the final product Eu2L3 and the intermediate species EuL2 and Eu2L2 have been characterised. The presence of terminal carboxylates in L significantly reduces the electrostatic repulsions of the coordination sites in Eu2L2 and Eu2L3 compared with the corresponding complexes formed with analogous neutral ligands and thus increases the stability of the L-europium(III) complexes. Kinetic investigations carried out with an excess of L and with an excess of Eu^III, show that the self-assembly proceeds through either EuL2 or Eu2L intermediates depending on the experimental conditions and leads to a pre-organized Eu2L2 complex by either a “braiding” or a “keystone” mechanism. In the last step, a fast and efficient wrapping of the third ligand strand leads to the target Eu2L3 helicate. The overall process is mainly governed by electrostatic interactions and proceeds via a key double stranded intermediate helicate Eu2L2. To the best of our knowledge, as a result of the fine-tuning of the coordination properties of L, we present one of the most efficient and cooperative metal/ligand systems for the spontaneous organization of a bimetallic triple-stranded structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The iron(III) chelating properties of two heteropodands with 8‐hydroxyquinoline and catechol binding groups were examined and compared to those of the corresponding homopodal analogues, O‐TRENSOX and TRENCAMS. Like the parent homopodands, the two heteropodands are based on the TREN scaffold and the chelating units are connected by amide groups, TRENSOX2CAMS having two 8‐hydroxyquinoline and one catechol arms and TRENSOXCAMS2 one 8‐hydroxyquinoline and two catechol moieties. The aqueous coordination chemistry of these ligands was examined by potentiometric and spectrophotometric methods in combination with 1H NMR spectroscopy. The respective pFeIIIvalues showed a cooperative effect of the mixed chelating units. Moreover, the pFeIIIdependence on pH showed that the mixed ligands exhibit a higher complexing ability than the parent ligands over the pH range 5−9 which is of biological relevance. This result could be of great interest for medical applications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)