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.