Four Cd-Based Metal–Organic Frameworks with Structural Varieties Derived from the Replacement of Organic Linkers

Four
three-dimensional (3D) Cd-based metal–organic frameworks
(MOFs), [Cd­(pyip)­(dmf)] (1), [Cd­(pyip)­(doa)] (2), [Cd­(pyip)­(pz)] (3) and [Cd­(pyip)­(bipy)­(H2O)0.5] (4) (dmf = N,N′-dimethylformamide, doa = 1,4-dioxane,
pz = pyrazine, bipy = 4,4′-bipyridine) have been rationally
designed and systematically synthesized by using 5-(pyridine-4-yl)­isophthalic
acid (H2pyip) and Cd­(NO3)2·4H2O under solvothermal conditions. Compound 1 possesses
a mineral-like 3,6-connected rtl network, and compounds 2–4 exhibit a 3,5-connected interpenetrating hms network constructed with 2-fold layers and bridging coligands
pillars (doa, pz, and bipy), respectively. In compounds 2–4, doa, pz, and bipy act as pillars to extend
the distance between the two layers from 7.34 to 11.36 Å, and
the different conformations and lengths of the coligands have influenced
the angles between the bridging ligands and the layers. Additionally,
the four compounds exhibit strong luminescent emissions in the solid
state at room temperature, and the latter three compounds exhibit
robust architectures as evidenced by their permanent porosity and
high thermal stability.

本研究经合理设计，以5-(吡啶-4-基)间苯二甲酸（5-(pyridine-4-yl)isophthalic acid, H₂pyip）和四水合硝酸镉[Cd(NO₃)₂·4H₂O]为原料，于溶剂热条件下系统合成了四种三维镉基金属有机框架（metal–organic frameworks, MOFs），其化学式分别为[Cd(pyip)(dmf)] (1)、[Cd(pyip)(doa)] (2)、[Cd(pyip)(pz)] (3) 与 [Cd(pyip)(bipy)(H₂O)₀.₅] (4)。其中，dmf为N,N'-二甲基甲酰胺（N,N′-dimethylformamide），doa为1,4-二氧六环（1,4-dioxane），pz为吡嗪（pyrazine），bipy为4,4'-联吡啶（4,4′-bipyridine）。化合物1具有类矿物型3,6连接rtl拓扑网络；化合物2至4则呈现由双层结构与桥联辅助配体柱撑构筑的3,5连接互穿hms拓扑网络。在化合物2至4中，doa、pz与bipy分别作为柱撑配体，将双层间距从7.34 Å拓展至11.36 Å；辅助配体的不同构象与长度会对桥联配体与层平面的夹角产生影响。此外，四种化合物在室温固态下均展现出强发光发射；后三种化合物具备稳定的骨架结构，其永久孔隙率与高热稳定性可佐证该结构特性。