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, bpdc2– 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 bpdc2– 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.