分别以吡嗪和4,4’-联吡啶为共配体, Cd2+、Zn2+与4,4’-偶氮苯二甲酸(H2(4,4’-azo))配位反应得到了两个金属-有机框架(MOFs)。X射线单晶衍射研究结果表明, 其结构中均不含共配体, 与之前报道的 ［Cd(4,4’-azo)(H2O)］n(1)和［Zn(4,4’-azo)(H2O)2］n(2)的晶体结构一致。将共配体变为几何尺寸更长的1,3-二(四吡啶基)丙烷(bpp), 金属离子变为Co2+, 合成了一个共晶［H2(4,4’-azo)(bpp)］n(3), 其为单斜晶系, C2/c空间群, 晶胞参数: a=3.216 8(19) nm, b=0.475 5(3) nm, c=1.873 2(14) nm。用热重分析仪和荧光分光光度计分别研究了三个化合物的热稳定性和两个MOFs的发光性质。1和2都具有优异的热稳定性, 尤其是2的初始失重温度高达247 ℃。由于1是由4,4’-azo双齿配位两个Cd2+形成双核3D网络结构, 而2是4,4’-azo单齿配位Zn2+形成的1D “zig-zag”链, 两者的紫外光谱和荧光光谱不同。2除具有配体固有的荧光发射(359 nm)外, 由于Zn2+与4,4’-azo配位后产生的配体到金属的电荷跃迁(LMCT), 还在420 nm处新增一个增强的荧光发射峰。

Using pyrazine and 4,4’-bipyrine as co-ligand, respectively, two metal-organic frameworks (MOFs) were synthesized by complexzation of Cd2+ and Zn2+ with 4,4’-azobenzoic acid (H2(4,4’-azo)). X-ray single crystal diffraction shows that their crystal structures are as same as those of the previously published ［Cd(4,4’-azo)(H2O)］n (1) and ［Zn(4,4’-azo)(H2O)2］n (2) where the co-ligands are not involved into the structures. Varying the co-ligand to 1,3-bi(tetrapyridyl)propane (bpp) with larger size and metal ions to Co2+, a co-crystal ［H2(4,4’-azo)(bpp)］n (3) was isolated successfully, which is monoclinic, space group of C2/c with crystal cell parameters a=3.216 8(19) nm, b=0.475 5(3) nm and c=1.873 2(14) nm. The thermal stabilities of the three compounds were investigated by thermal gravimetric analyzer and the fluorescence of two MOFs were examined by fluorescence spectrometer, respectively. Both 1 and 2 display excellent thermal stabilities. Especially, 2 keeps stable up to 247 ℃. UV-Vis spectra and fluorescence spectra of 1 and 2 are different, which are ascribed to that 1 is a 3D network formed by 4,4’-azo bi-dentated coordinating with two Cd2+ whereas 2 is a 1D zig-zag chain constructed by 4,4’-azo mono-dentated coordinating with Zn2+. In addition to the ligand emission at 359 nm, 2 exhibits a new enhanced emission at 420 nm due to the ligand to metal charge transfer (LMCT) upon Zn2+ coordination with 4,4’-azo.