Enhancing redox functionality in dinuclear europium complexes

Abstract

Europium stands out amongst the lanthanoid elements because of its accessibility in the divalent state, in addition to the more common trivalent state. To explore europium-based redox chemistry in the presence of redox-active ligands, we have synthesised a series of dinuclear europium complexes with different redox-active bridging ligands containing oxygen and nitrogen donor atoms. Here, we report three new dinuclear europium complexes containing different redox-active bridging ligands: [{Eu^II(I)₂(tpa)}₂(μ-bpym)] (1), [{Eu^III(I)₂(tpa)}₂(μ-bptz˙⁻)][I] (2), and [{Eu^III(tpa)₂}(μ-Br₄cat)₃] (3) (tpa = tris(2-pyridylmethyl)amine; bpym = 2,2′-bipyrimidine; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine and Br₄catH₂ = tetrabromocatechol). Across the series, the varying oxidation states of europium and the bridging ligands highlight the redox diversity accessible with these compounds. Characterization using X-ray crystallography, electronic spectroscopy, electrochemistry, and magnetometry has allowed confirmation of the oxidation states of both the metal centers and the ligands, showcasing the rich redox chemistry of these molecular europium systems.