3‑D Silver(I)Lanthanide(III) Heterometallic-Organic Frameworks Constructed from 2,2′-Bipyridine-3,3′-dicarboxylic Acid: Synthesis, Structure, Photoluminescence, and Their Remarkable Thermostability

A new family of silver­(I)–lanthanide­(III) heterometallic-organic frameworks having the formula [AgLn­(bpdc)₂] (Ln = Eu (1), Tb (2), Sm (3), Dy (4), Y (5), Yb (6), Er (7), Ho (8); H₂bpdc = 2,2′-bipyridine-3,3′-dicarboxylic acid), each of which crystallizes in the monoclinic space group C2/c with Z = 4, has been hydrothermally synthesized. The compounds were characterized by means of IR, elemental analysis, thermogravimetric-differential thermal analysis, and powder X-ray diffraction (XRD), wherein compounds 1, 2, and 4–8 were structurally characterized. The powder XRD and single-crystal structures of the title compounds indicate that all the compounds are isostructural and feature a three-dimensional (3-D) open framework. In the structures of the compounds, bpdc^2– ligands link Ln³⁺ through their carboxylic groups, resulting in the formation of a one-dimensional {Ln­(bpdc)₂}_n infinite chain along the c direction. The adjacent chains are then connected to each other through the coordination interaction between Ag⁺ and the pyridyl N atoms of bpdc^2– ligands from the chains, resulting in a 3-D (2,4,6)-connected open framework with (4¹¹·6⁴)­(4³·8²·10)­(8)₂ topology. The compounds show remarkable good thermally stability up to 370 °C because neither aquo ligands nor lattice water molecules exist in the composition of the compounds. The photoluminescent properties of compounds 1 and 2 were studied in detail. The energy level of the triplet states of the ligand H₂bpdc 21 505 cm^–1 (465 nm) was determined based on the 77 K emission spectrum of the compound [Gd₂(bpdc)₃­(phen)₂(H₂O)₂]·6H₂O 9. The ⁵D₀ and ⁵D₄ emission lifetimes (1.58 and 1.76 ms) and the overall quantum yields (21% and 22%) were determined for the compounds 1 and 2, respectively.