Metal-organic frameworks (MOFs) are porous materials that are spontaneously assembled through coordinative bonds between metal ions or atoms and organic ligands. A vast number of MOFs can be made by combining different metal centers and various ligands containing multiple donor groups. MOFs often have big pores, which can adsorb a variety of molecules. The size of these pores can be manipulated by varying the ligand size. MOFs can be used as separators, sensors, or in catalysis, for example.

Hongming He, Tianjin Normal University, Tianjin, China, and colleagues have developed a MOF with a new dendritic ligand. The aromatic linker 1,3,5-tris[3,5- bis(3-carboxylphenyl-1-yl)phenyl-1-yl]benzene (H₆TDCPB) has six “arms” with carboxylic groups as O-donors. It was synthesized via Suzuki coupling. The team then combined the linker and cadmium(II) nitrate in a mixture of N,-N-dimethyl acetimide (DMAc) and HNO₃ to obtain crystals of the desired MOF, {[Cd₃(TDCPB)·2 DMAc]·DMAc·4 H₂O}_n. They analyzed the structure with single-crystal X-ray analysis. The researchers found a porous 3D structure with Cd₆ clusters and an unusual accumulation of six adjacent linkers, which is facilitated by π-π stacking of the aromatic ligands.

The researchers studied the luminescence properties of the MOF in the presence of six common antibiotics using emission spectroscopy. The MOF selectively showed a strong decrease in luminescence (quenching) in the presence of the antibiotics nitrofurazone (NFZ) and nitrofurantoin (NFT), with quenching efficiencies of 81 % and 87 %, respectively. Only a weak decrease of luminescence was observed with the drugs dimetridazole and sulfamethazine, and no change was noticed with florfenicol, thiamphenicol, chloramphenicol, and penicillin.

The MOF can be recycled multiple times after use. This could allow its use as a detector for antibiotic pollution with NFZ and NFT in the environment.

• Design and Construction of a Metal–Organic Framework as an Efficient Luminescent Sensor for Detecting Antibiotics,
  Qian-Qian Zhu, Qiao-Shu Zhou, Han-Wen Zhang, Wen-Wen Zhang, Di-Qiu Lu, Mei-Tong Guo, Ye Yuan, Fuxing Sun, Hongming He,
  Inorg. Chem. 2020.
  https://doi.org/10.1021/acs.inorgchem.9b03032