Synthesis of radical-bridged lanthanide heterobimetallic complexes

Heteromultimetallic lanthanide (Ln) molecules are used in sensing and imaging, and have recently demonstrated Ln to-Ln energy transfer and potential as quantum logic processors. However, the selective synthesis of molecular Ln heteromultimetallics is challenging, limiting further investigation of their properties and applications. For example, redox active ligands mediate f-block reactivity with small molecules and have applications in molecular magnetics in homometallic Ln systems, yet have not been incorporated into heteromultimetallic complexes. Herein, we utilise the chemically distinct binding sites and redox chemistry of 1,10-phenanthroline-5,6-dione (pd) to synthesise radical-bridged Ln heterobimetallic complexes. In a stepwise, modular, and extendable synthesis, we tailor the ancillary ligand environment to generate selectivity within the non-directional ionic bonding regime typical for Ln ions. The selectivity of binding for two lanthanide combinations with different ionic radius ratios is demonstrated by solution-state spectroscopy (NMR, UV-vis, photoluminescence), and confirmed in the solid-state by crystallographic determination of the molecular structures. In preliminary photoluminescence studies, we observe complex, selective energy transfer unusually involving the radical ligand. Our synthetic strategy enables any pair of lanthanide ions to be combined and will be widely applicable in the preparation of heteromultimetallic complexes of otherwise non-selective metal ions.