Synthesis, electrochemistry and spectroscopy of lanthanide(III) homodinuclear complexes bridged by polyazine ligands

Six new complexes [Eu(tta)3]2bpm, [Er(tta)3]2bpm, [Tb(tta)3]2bpm, [Er(tta)3]2dpp, Pr(tta)3bpm and Nd(tta)3bpm (tta = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione, bpm = 2,2′-bipyrimidine, dpp = 2,3-bis(2-pyridyl)pyrazine) were prepared and studied. The electronic absorption spectra of the complexes display tta π → π* transitions in the UV region. Cyclic voltammetry of the complexes show an irreversible reduction followed by a reversible reduction both associated with the tta ligand. Eu(III) reduction in the homodinuclear [Eu(tta)3]2bpm complex occurs as an irreversible reduction at less negative potentials than the tta-based reductions. Emission spectra of the Eu(III) and Tb(III) bimetallics are typical of this type of bonding motif with ligand centered (tta) absorptions resulting in 4f–4f transitions in the visible and near infrared region.