Syntheses, Characterization, and Luminescence Properties of Four Metal–Organic Frameworks Based on a Linear-Shaped Rigid Pyridine Ligand

Solvothermal syntheses in DMF (or DMA) and H2O afforded four novel metal–organic frameworks: {[Cd(DPBT) (BDC)]·2(H2O)}n (1), {[Zn2(DPBT)2(IPA)2]·2(DMA)}n (2), {[Co2(DPBT)2(BDC)2]·2(DMF)·5(H2O)}n (3), and {[Ni(DPBT)2(H2O)4]·(BDC)}n (4) (DPBT = 4,7-di(4-pyridyl)-2,1,3-benzothiadiazole, BDC = 1,4-benzene dicarboxylate, IPA = isophthalic acid, DMA = N,N-dimethylacetamide, and DMF = N,N-dimethylformamide). X-ray analyses show that 1 and 3 show similar structures with the same building blocks and possess 3-dimensional 6-connected pcu net. Compounds 1 and 3 are based on a 2-fold interpenetrating network with solvent molecules located in the framework, whereas 3 is different in the absence of DMF solvent molecules. Compared with compounds 1 and 3, 4 is constructed under the same conditions except with metal ions and possesses a completely different structure type. Luminescence properties of 1 and 2 without any activation well-dispersed in common solvents have also been investigated systematically; the luminescence properties show different intensities depending on the nature of the solvents, especially for nitrobenzene (NB), which exhibits a significant quenching effect. Compound 2 possesses a layered structure; the distance between two parallel layers is big enough to allow small molecules to more easily move into the crystal skeleton and interact with each other. Thus, the luminescence responses of 2 were investigated for various nitro compounds. When the concentration of PA is up to 0.1 mM, the emission of 2 is completely quenched. These results show that compound 2 has great potential to be developed as the favorable sensor for highly selective detection of PA. Furthermore, the magnetic properties of compound 3 were investigated.