Emissive Ln(III)–Hg(II)/Pb(II) Coordination Polymers with Heteropolymeric 1-D Structures Synthesized Mechanochemically Using a Hard–Soft Acid–Base Mismatch Strategy

The mechanochemical synthesis of a family of heterobimetallic Ln(III)-M(II) coordination polymers of the form [Ln(OAc)₂(OH₂)₃](MBr₃)]·<i>x</i>H₂O (Ln = Eu, Tb, 50:50 Eu/Tb; <b>LnHg</b>: M = Hg, <i>x</i> = 1; <b>LnPb</b>: M = Pb, <i>x</i> = 0) is described. They are formed via the anion-exchange reaction between lanthanide(III) bromide and metal(II) acetate salts and driven by a mismatch in hard-soft acid-base character. The crystal structure of <b>EuHg</b> revealed a heteropolymeric 1-D structure, with cationic acetate-bridged and anionic bromide-bridged chains forming parallel arrays; IR, Raman, and photoluminescence spectroscopic data of <b>LnPb</b> strongly suggested similarity with the <b>LnHg</b> compounds. The analogous reaction with EuCl₃·6H₂O and Hg(OAc)₂ forms an isostructural material, but substituting Pb(OAc)₂ generates [Eu(OAc)₂(OH₂)₃]Cl and PbCl₂ instead of a mixed-metal product comparable to <b>LnPb</b>. An <i>N</i>,<i>N</i>-dimethylformamide (DMF) solvate [Eu(OAc)₂(DMF)₃](PbBr₃)] (<b>EuPb·DMF</b>) was structurally characterized, showing the same heteropolymeric motif as <b>EuHg</b> and resembling an organic-inorganic lead-halide perovskite due the anionic chain of face-sharing bromoplumbate(II) octahedra. Photoluminescence properties of the compounds, including lifetime measurements and Tb(III)→Eu(III) energy transfer parameters for the <b>LnM</b> 50:50 Eu/Tb solid-solutions are described.