A Penta‐Eu III Sandwiched Dawson Selenotungstate and Its Unique Luminescence Properties

A new penta‐Eu III sandwiched Dawson‐type selenotungstate (ST) [H 2 N(CH 3 ) 2 ] 10 H 3 {SeO 4 Eu 5 (H 2 O) 8 [Se 2 W 14 O 52 ] 2 } · 40H 2 O ( 1 ) was constructed by an in‐situ self‐assembly strategy. The unique architectural feature of 1 is that two [Se 2 W 14 O 52 ] 12– segments graft each other by five Eu 3+ ions via oxygen linkers. Meanwhile, a disordered tetra‐coordinate Se IV ion locates on the central symmetric site of the structure. What's more, based on its benign fluorescence properties and excellent water solubility, 1 was prepared to be an efficient chemosensor for the selective detection of the Cu 2+ ion in aqueous solution. The detection was found to be 1.24 × 10 –3 m m . The fluorescence quenching mechanism of the Cu 2+ ion towards the 1 ‐based sensor might be caused by the LMCT absorption of the Cu 2+ ion hindering energy transfer from ST fragments to the Eu 3+ ion in 1 in aqueous solution. More interestingly, the Cu 2+ ‐quenched system could be recovered by addition of cysteine (cys) because the strong chelation between cys and Cu 2+ . The LOD value of detecting cys is 2.17 × 10 –4 m m for the continuous “off‐on” chemosensor, which provides a promising prospect of polyoxometalate‐based materials for environmental monitoring and clinical medical testing.