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)]·xH2O (Ln = Eu, Tb, 50:50 Eu/Tb; LnHg: M = Hg, x = 1; LnPb: M = Pb, x = 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 EuHg 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 LnPb strongly suggested similarity with the LnHg 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 LnPb. An N,N-dimethylformamide (DMF) solvate [Eu(OAc)2(DMF)3](PbBr3)] (EuPb·DMF) was structurally characterized, showing the same heteropolymeric motif as EuHg 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 LnM 50:50 Eu/Tb solid-solutions are described.