Two Eu3+ Based Complexes Containing Uncoordinated Lewis Basic Pyridyl Sites and Chemical Sensing of 4‑Nitrophenol and Fe3+ ions

Two pyridyl functionalized aromatic carboxylic acids HL1 (4,4′-[[3,5-bis­(4-pyridinyl)­phenyl]­imino]­mono-[benzoic acid]) and H2L2 (4,4′-[[3,5-bis­(4-pyridinyl)­phenyl]­imino]­bis-[benzoic acid]) were designed as linkers for construction of aggregation-induced emission active coordination polymers. Two complexes decorated with open Lewis basic pyridyl active sites have been successfully synthesized by using organic linker precursors. Complex 1, with the formula as Eu2(L1)6(H2O)4·3DMF, is constructed by one-dimensional infinite chains. Complex 2, with the formula as Eu2(L2)2(HCOO)2(H2O)4·H2O, possesses a (2,6)-connected three-dimensional framework. Fluorescence studies revealed that both 1 and 2 can quickly detect 4-nitrophenol (4-NP) in dimethylformamide (DMF) and Fe3+ ions in H2O through luminescence quenching. In comparison, complex 1 exhibits higher sensitivity and selectivity toward 4-NP and Fe3+ than those of 2. The synergistic competitive absorption and electrostatic interaction mechanism can explain the detection of 4-NP, and the selectivity of Fe3+ can be attributed to the synergistic effect of competitive absorption and coordination interactions between Fe3+ ions and pyridine N atoms. In addition, complex 2 can be excited at a long excitation wavelength of 380 nm, which is almost in the visible region. This is an important requirement for its application.