An unprecedented polyhydroxycarboxylic acid ligand bridged multi-EuIII incorporated tellurotungstate and its luminescence properties

Abstract

The first polyhydroxycarboxylic acid ligand bridged multi-Eu^III-incorporated tellurotungstate K₁₄H₁₀[Eu₄(H₂O)₄W₆(H₂glu)₄O₁₂(B-α-TeW₉O₃₃)₄]·60H₂O (H₆glu = D-gluconic acid) (1) was synthesized via an organic ligand-driven self-assembly strategy. The polyhydroxycarboxylic acid ligand bridged tetrameric polyoxoanion [Eu₄(H₂O)₄W₆(H₂glu)₄O₁₂(B-α-TeW₉O₃₃)₄]²⁴⁻ in 1 can be viewed as an aggregation of four trivacant Keggin [B-α-TeW₉O₃₃]⁸⁻ fragments and an innovative heterometallic [Eu₄(H₂O)₄W₆(H₂glu)₄O₁₂]⁸⁺ cluster, in which four high-coordinate polyhydroxy flexible H₂glu⁴⁻ ligands chelate W and Eu centers through carboxyl and hydroxyl groups, giving rise to a heterometallic cluster. The hexagonal packing of the tetrameric polyoxoanions in 1 along the c axis provides excellent porous channels, which greatly increases the specific surface area of the whole framework and may be of benefit for fluorescence sensing in aqueous solution. 1 can function as a “turn-off” luminescence sensor to detect Cu²⁺ ions in aqueous solution. The limit of detection (LOD) of the 1-sensor is 8.82 × 10⁻⁶ mM, which is the lowest among the reported polyoxometalate-based fluorescence sensors. As for the Cu²⁺-quenching system, it can function as an “off–on” sensor to detect cysteine in an aqueous system, affording a LOD of 1.75 × 10⁻⁴ mM. This work opens up an avenue to broaden the applications of polyoxometalate-based materials in the optical intelligence detection field.