A dual-heteroatom–lanthanide cluster-embedded polyoxotungstate for sequential fluorescence detection of Fe3+ and pyrophosphate

Abstract

A neoteric inorganic–organic hybrid dual-heteroatom (HA) and lanthanide (Ln) cluster-bridged polyoxotungstate (POT) [H₈BTHMMAP]_1.5[H₂N(CH₃)₂]₄Na₃H[Eu₂Bi₃(Hpdca)₃(H₂O)₃Te₂W₃O₁₄][(W₅O₁₈)(B-α-BiW₉O₃₃)₂]·44H₂O (1, H₆BTHMMAP = 1,3-bis[tris-(hydroxymethyl)methylamino]propane, Hpdca = 2-pyridinic acid) was prepared by the dual-HA template strategy. The skeleton of 1 possesses a three-bladed propeller-shaped [Eu₂Bi₃(Hpdca)₃(H₂O)₃Te₂W₃O₁₄]¹³⁺ core wrapped by two Keggin [B-α-BiW₉O₃₃]⁹⁻ and one Lindqvist [W₅O₁₈]⁶⁻ segments. Noteworthily, the intricate [Eu₂Bi₃(Hpdca)₃(H₂O)₃Te₂W₃O₁₄]¹³⁺ unit consisting of a Bi–Te dual-HA-bridged Ln–W polynuclear cluster is rather attractive and rarely seen in POT crystal engineering. Prominently, 1 exhibits an “ON–OFF” luminescence response triggered by Fe³⁺ based on dynamic quenching and competitive absorption, and the subsequent addition of pyrophosphate (PPi) leads to the recovery of luminescence due to the efficient interaction of Fe³⁺ and PPi. The developed “ON–OFF–ON” switch allows the consecutive discrimination of Fe³⁺ and PPi with low detection limits of 1.23 μM and 2.16 μM, respectively. This work provides a profound understanding of the dual-HA template approach in assembling complicated POTs, and shows the great potential of POT materials in environmental and biological detection.