The detection of hexavalent chromium in the environment is important due to the acute toxicity of Cr^VI. Exposure can lead to damage of the respiratory tract and an increased risk of cancer. Luminescent metal-organic frameworks (LMOFs) have quick response times and excellent sensitivity and selectivity, and thus, could be a good candidate for detecting Cr^VI. However, a lack of stability in water and poor recyclability have impeded their application so far.

Tong-Liang Hu, Xian-He Bu, Nankai University, China, and colleagues have developed a water-stable LMOF for the detection of Cr^VI in aqueous solution. The team combined a luminescent anthracene-based ligand and an organic linker with Zn²⁺ ions to fabricate the LMOF {[Zn₃(bpanth)(oba)₃]·2DMF}_n (H₂oba = 4,4’-oxybis(benzoic acid), bpanth = 9,10-bis(4-pyridyl)anthracene, DMF = dimethylformamide).

This LMOF maintains its crystallinity in solution (pH = 3 to 11) and exhibits cyan light emission under UV irradiation. In detection experiments, it showed a selective and sensitive quenching response to Cr^VI ions in aqueous solution. The compound can easily be regenerated.  According to the researchers, the prepared LMOF holds promise for sensing Cr^VI ions in sewage systems.

• A Water-Stable Luminescent Zn^II Metal-Organic Framework as Chemosensor for High-Efficiency Detection of Cr^VI-Anions (Cr₂O₇²⁻ and CrO₄²⁻) in Aqueous Solution,
  Zhao-Quan Yao, Guang-Yu Li, Jian Xu, Tong-Liang Hu, Xian-He Bu,
  Chem. Eur. J. 2018.
  https://doi.org/10.1002/chem.201705328