X-ray structure and temperature dependent luminescent properties of two bimetallic europium complexes

The structural, luminescent and temperature dependent luminescent properties of two homodinuclear europium complexes bridged by 2,2′-bipyrimidine (bpm) are reported. β-Diketonate ligands 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (tfa) and 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (tta) are used as capping ligands resulting in complexes of the form [Eu(tfa)3]2bpm (1) and [Eu(tta)3]2bpm (2). All EuIII ions are eight coordinate with six O atoms from the β-diketones and two N atoms from the polyazine bridging ligand. Excitation of the β-diketonate ligands tfa or tta at ca. 340 nm in toluene solutions results in the characteristic EuIII emission in the visible region of the spectrum. The emission intensity and lifetime associated with the EuIII centers decrease as the temperature of the solution is increased. Lifetime measurements are fit to a monoexponential while the temperature dependent lifetime data is fit to an Arrhenius-type equation. Evaluation of the data in comparison to data obtained from the monometallic EuIII analogs reveal very similar photoluminescent properties. This suggests little electronic communication between EuIII ions via the polyazine bpm bridging ligand.

Graphical abstractHomodinuclear europium complexes bridged by the polyazine ligand 2,2′-bipyrimidine display temperature dependent luminescent properties in toluene solutions.Figure optionsDownload full-size imageDownload as PowerPoint slide