An Unusual Bismuth–Antimony–Europium Cluster-Imbedded Polyoxotungstate and Its Bidirectional Luminescence Detection

An unprecedented aggregate formed by two bismuth-antimony-europium cluster-imbedded tungsten-oxo clusters and one Krebs-type polyoxotungstate linker [H₂N(CH₃)₂]₁₄Na₃₀H₆[W₄O₁₀][B-β-BiW₉O₃₃]₂{[Bi_5.35Sb_0.65Eu₃O₉(H₂O)₉][B-α-SbW₉O₃₃]₃}₂·124H₂O (1) was prepared. The polyoxoanion skeleton of 1 contains a Krebs-type polyoxotungstate [W₄O₁₀][B-β-BiW₉O₃₃]₂}^14- ({Bi₂W₂₂}) (1a) as a linker that offers six active coordinate O atoms (two μ₃-O and four μ₂-O atoms) to grasp two Bi-Sb-Eu cluster-imbedded tungsten-oxo clusters {[Bi_5.35Sb_0.65Eu₃O₉(H₂O)₉][B-α-SbW₉O₃₃]₃}^18- (1b) through Bi-O-W and Sb-O-W bonds. 1b comprises an unprecedented nona-nuclearity Bi-Sb-Eu [Bi_5.35Sb_0.65Eu₃O₉(H₂O)₉]⁹⁺ cluster encircled by three trivacant [B-α-SbW₉O₃₃]^9-segments in a triangular motif through Eu-O-W, Sb-O-W, and Bi-O-W linkages into a trilobal trimer. Moreover, a bidirectional detection method by using 1 as an effective luminescence probe was proposed to recognize both Mn²⁺ and CO₃^2- through an "on-off-on" mode. 1 can be used as an "on-off" luminescent sensor to detect Mn²⁺ ions in aqueous solution. The limit of detection was 0.05 μM (9 × 10^-6 mg L^-1), which is much lower than the World Health Organization (WHO) guideline for Mn²⁺ concentration in drinking water (0.05 mg L^-1). Then the Mn²⁺-quenching system can be used as an "off-on" sensor to detect CO₃^2- in water system. This work provides a new research idea for the application of rare-earth-imbedded polyoxotungstate-based materials in the field of optical smart detection.