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 _∞¹[EuBr₂(phen)] chains. Seven new divalent europium complexes, [Eu(phen)₄(H₂O)]Br₂·2MeCN, [Eu(phen)₄]I₂·1.7Tol, [EuBr(phen)₃]₂Br₂·4MeCN, [EuCl₂(phen)₂]₂·2MeCN, [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 Eu^II 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.

Modulation of the structural information in shape-defined heterocyclic strands: the case of a (pyridine-hydrazone)2pyrazine ligand

Metal ions (Ag⁺, Cd²⁺, Eu³⁺, Sm³⁺) and protons can, through coordination and protonation, modulate in three specific ways the structural information contained in the pyrazine-based heterocyclic strand L (obtained from 2,5-bis(methylhydrazino)pyrazine and 2 equivalents of 2-pyridinecarboxaldehyde), thus generating two linear rod-like conformations and a bent one. This conformational diversity is associated with a structural one that consists of two diprotonated forms (H₂L(PF₆)₂ and H₂L(CF₃SO₃)₂), a polymeric architecture [AgL]_n(CF₃SO₃)_n, two rack-like complexes ([Eu₂H₂L₃(CF₃SO₃)₆](PF₆)₂ and [Sm₂H₂L₃(CF₃SO₃)₆](PF₆)₂) and a grid-like structure ([Cd₄L₄](CF₃SO₃)₈).