Dimeric Lanthanoid Complexes with Diamine-based Polydentate Ligands

An early attempt to prepare heterometallic complexes of general formula [M(m-ox)₃{Ln(bbpen)}₃] (ox = oxalate; M = Cr³⁺) for magnetic studies accidentally produced dimeric complexes of Gd³⁺ and Dy³⁺ formulated as [{Ln(bbpXn)}₂(µ-C₂O₄)] (X = p or e) [3]. Subsequently, the dimers were rationally prepared from bbpen^2- and bbppn^2-, Ln³⁺ salts (Ln = Gd³⁺, Tb³⁺, Dy³⁺ and Eu³⁺), and oxalate ions. The dimeric structure (Fig. 1) was confirmed for [{Ln(bbpen)}₂(µ-C₂O₄)]·4MeOH·4H₂O, Ln = Gd³⁺ and Dy³⁺ by single-crystal XRD. Photophysical measurements of solids precipitated from the reaction mixtures revealed intense emission from the Tb³⁺ complexes (QLnL = 42.8% and t = 0.981 ms at 11 K for the bbppn^2- dimer) and temperature-dependent photoluminescence from the Eu³⁺ analogs (Fig. 1). Efforts are now focused on (re)crystallizing the dimers to enable precise determination of photophysical parameters and description of energy-transfer mechanisms.