Impact of 1,10-Phenanthroline-Induced Intermediate Valence on the Luminesence of Divalent Europium Halides

Starting from EuX2 (X = Cl, Br, I), we systematically investigated a variety of divalent europium complexes containing bidentate 1,10-phenanthroline (Phen) ligands. Depending on the Eu/Phen ratio, mono-, di-, and polynuclear complexes are formed, with the latter yielding one-dimensional infinity 1[EuBr2(phen)] chains. Seven new divalent europium complexes, [Eu(phen)4(H2O)]Br2 center dot 2MeCN, [Eu(phen)4]I2 center dot 1.7Tol, [EuBr(phen)3]2Br2 center dot 4MeCN, [EuCl2(phen)2]2 center dot 2MeCN, [EuBr2(phen)2]2, [EuI2(phen)2]2, and [EuBr2(phen)]x, are presented in this work. All species show remarkable optical properties based on a partial electron transfer from the EuII center to the Phen ligand. The photophysical characterization is further supported by electrochemistry studies in order to describe the intermediate valence of the Eu center