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.

本研究报道了一类通式为[AgLn(bpdc)₂]的银(I)–镧系(III)异金属有机框架（heterometallic-organic frameworks）新家族，其中Ln=Eu(1)、Tb(2)、Sm(3)、Dy(4)、Y(5)、Yb(6)、Er(7)、Ho(8)；H₂bpdc为2,2'-联吡啶-3,3'-二羧酸。所有化合物均结晶于单斜晶系空间群C2/c，晶胞参数Z=4，且均通过水热法合成。
采用红外光谱（IR）、元素分析、热重-差示热分析以及粉末X射线衍射（XRD）对上述化合物进行了表征，其中对化合物1、2及4~8完成了单晶结构解析。
粉末XRD与单晶结构表征结果表明，所有化合物均为同构体，均具有三维（3-D）开放骨架结构。在化合物结构中，bpdc²⁻配体通过其羧基与Ln³+离子配位连接，沿c轴方向形成一维{Ln(bpdc)₂}ₙ无限链。相邻链之间通过Ag+与来自该链的bpdc²⁻配体的吡啶氮原子之间的配位作用相互连接，最终构筑得到具有(4¹¹·6⁴)(4³·8²·10)(8)₂拓扑的三维(2,4,6)连接开放骨架。
由于该类化合物组成中既不含配位水配体也无晶格水分子，因此其热稳定性优异，可稳定至370℃。
对化合物1和2的光致发光性能进行了详细研究。
基于配合物[Gd₂(bpdc)₃(phen)₂(H₂O)₂]·6H₂O（文献9）在77K下的发射光谱，确定了配体H₂bpdc的三重态能级为21505 cm⁻¹（465 nm）。
分别测得化合物1和2的5D₀与5D₄发射寿命（分别为1.58 ms和1.76 ms）以及总量子产率（分别为21%和22%）。