A water-stable metal-organic framework as a luminescent Fe3+ sensor under weak acidic and weak basic conditions

A three-dimensional (3D) metal-organic framework (MOF) ZnL·0.5H2O·0.75DMF (H2L=9-(pyridin-4-yl)-9H-carbazole-3,6-dicarboxylic acid, DMF=N,N-dimethylformamide) has been synthesized under solvothermal condition. Crystal structure analysis shows that, in ZnL, each dinuclear Zn2(COO)2 unit is doubly-bridged to the other two by the carbazole moieties to form the 1D chains, which are further connected together by pyridine moieties to lead to the 3D framework. ZnL exhibits both high structural stability and good luminescent stability in water with the pH range of 4–10. ZnL displays the luminescent quenching response for Fe3+ in water with good linear correlation between the quenching efficiency and the concentration with Ksv of 10800 M−1 in the low concentration range of 0–0.1 mM. Interestingly, it is observed that the sensing performance for Fe3+ is stable in the pH range of 4–9, enabling ZnL to detect Fe3+ ions in weak acidic and weak basic solutions.