Ce ³⁺ -and-SeO ₃ ²– -Cobridged Asymmetric Sandwich-Type Sb III –Se IV -Templated Polyoxotungstate Applied to a Molecularly Imprinted Electrochemical Sensor for Melamine Detection

Exploring and synthesizing polyoxometalates (POMs) with innovative building blocks (BBs) has become a key direction for advanced functional materials. In this work, a unique Ce³⁺-and-SeO₃²⁻-cobridged asymmetric sandwich-type SbIII-SeIV-templated POM [H₂N(CH₃)₂]₂H₆[Ce₂(H₂O)₄][W₂O₄(HPA)₂][SeSbW₈O₃₁][B-β-SeW₈O₃₀]·25H₂O (1, HPA = 2-picolinic acid) was synthesized. The anionic framework of 1 features a unique asymmetric sandwich architecture, in which a heterometallic [Ce₂(H₂O)₄W₂O₄(HPA)₂]¹⁰⁺ cluster bridges a conventional tetravacant Keggin [B-β-SeW₈O₃₀]⁸⁻ fragment and an uncommon {SeO₃}-functionalized tetravacant Keggin [SeSbW₈O₃₁]⁷⁻ moiety. Leveraging the exceptional electron storage and charge transfer capabilities of POMs, a hybrid 1-PEDOT film based on 1 and PEDOT (PEDOT = poly(3,4-ethylene dioxythiophene)) was fabricated and employed as an electrode modifier for the construction of a molecularly imprinted electrochemical sensor for the detection of melamine. The resulting sensor demonstrates high selectivity, excellent stability, a wide detection range (1 μM-10 pM), and a low detection limit of 1.95 × 10⁻¹² M. This work provides an efficient strategy for designing and synthesizing new POM-based materials, enriches the structural and functional diversity of POMs, extends their applications in food safety monitoring, and realizes the transformation from molecular design to practical public health and environmental safety technologies.