Pyrazine Dicarboxylic Acid and Phosphite-Bridging Lanthanide-Incorporated Tellurotungstates and Their Fluorescence Performances

Two pyrazine dicarboxylic acid and phosphite-bridging lanthanide-incorporated tellurotungstates [H₂N(CH₃)₂]₁₂ Na₄[Ln₄(H₂O)₂(H₂PDBA)₂(HPO₃)₂W₆O₁₀][B-α-TeW₈O₃₁]₄ · 70H₂O [Ln = Eu³⁺ (<b>1</b>), Tb³⁺ (<b>2</b>); H₂PDBA = 2,5-pyrazine dicarboxylic acid) were prepared, which contain four [B-α-TeW₈O₃₁]^10- subunits and a deca-nuclear heterometallic [Ln(H₂O)₂(HPO₃)₂ (H₂PDBA)₂(W₃O₅)₂]²⁴⁺ cluster. Strikingly, two H₂PDBA ligands connect two equivalent {W₃Eu₂O₅(H₂O)(B-α-TeW₈O₃₁)₂(HP^IIIO₃)}^8- moieties to form the polyanion skeleton, while the phosphite plays a bridging role in joining two lanthanide centers in the {W₃Eu₂O₅(H₂O)(B-α-TeW₈O₃₁)₂(HP^IIIO₃)}^8- moiety. In addition to the fluorescence (FL) properties of <b>1</b> and <b>2</b> at room temperature, their temperature-dependent FL properties were also investigated. In 80-298 K, FL intensities of <b>1</b> and <b>2</b> decrease as temperature increases, and their maximum relative sensitivities (<i>S</i>_r) are 3.70 and 1.99% K^-1, whereas the minimum temperature uncertainties (δ<i>T</i>) are 1.25 and 1.18 K for <b>1</b> and <b>2</b>. In 298-973 K, upon increasing temperature, FL intensities of <b>1</b> and <b>2</b> initially rise to their maxima at 373 K and subsequently decrease. This is because samples of <b>1</b> and <b>2</b> undergo dehydration together with amorphization below 473 K and decomposition above this temperature. This work lays a foundation for the development for luminescent thermometers based on lanthanide-incorporated polyoxometalates.