Hydroxyquinoline-Calix[4] arene Conjugates as Ligands for Polynuclear Lanthanide Complexes: Preparation, Characterization, and Properties of a Dinuclear EuIII Complex

The synthesis of calixarene-based N4O4-donor ligand H6L, in which two 8-hydroxyquinoline-2-carbaldehyde units are appended via hydrazone-carbonylmethoxy linkages in a 1,3 arrangement to the lower rim of tert-butylcalix[4] arene, and its coordination properties towards Eu-III are described. The reaction of H6L with Eu(NO3) (3).6H(2)O produced dinuclear complex [Eu-2(H3L)(2)(MeCN)(2)] (4). The EuIII ions in 4 are well separated from each other (d > 8 angstrom) and each is coordinated by two tetradentate hydroxyquinoline-2-carbaldehyde hydrazone substituents from two triply deprotonated (H3L)(3-) ligands in a dodecahedral geometry. As a consequence there are no exchange interactions between the Eu-III ions, and the magnetic properties are solely associated with thermal population of excited (F-7(1)-F-7(6)) terms. The spin-orbit coupling constant lambda is 325.2(4) cm(-1). Moreover, H6L was found to extract Eu-III and Tb-III from aqueous solution at pH 7-8, as established by radiotracing with Tb-160 and Eu-152.