Pyrazine Dicarboxylic\nAcid and Phosphite-Bridging\nLanthanide-Incorporated Tellurotungstates and Their Fluorescence Performances

Two pyrazine dicarboxylic acid and phosphite-bridging\nlanthanide-incorporated\ntellurotungstates [H<sub>2</sub>N(CH<sub>3</sub>)<sub>2</sub>]<sub>12</sub> Na<sub>4</sub>[Ln<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>(H<sub>2</sub>PDBA)<sub>2</sub>(HPO<sub>3</sub>)<sub>2</sub>W<sub>6</sub>O<sub>10</sub>][B-α-TeW<sub>8</sub>O<sub>31</sub>]<sub>4</sub> · 70H<sub>2</sub>O [Ln = Eu<sup>3+</sup> (<b>1</b>), Tb<sup>3+</sup> (<b>2</b>); H<sub>2</sub>PDBA = 2,5-pyrazine\ndicarboxylic acid) were prepared, which contain four [B-α-TeW<sub>8</sub>O<sub>31</sub>]<sup>10–</sup> subunits and a deca-nuclear\nheterometallic [Ln(H<sub>2</sub>O)<sub>2</sub>(HPO<sub>3</sub>)<sub>2</sub> (H<sub>2</sub>PDBA)<sub>2</sub>(W<sub>3</sub>O<sub>5</sub>)<sub>2</sub>]<sup>24+</sup> cluster. Strikingly, two H<sub>2</sub>PDBA ligands connect two equivalent {W<sub>3</sub>Eu<sub>2</sub>O<sub>5</sub>(H<sub>2</sub>O)(B-α-TeW<sub>8</sub>O<sub>31</sub>)<sub>2</sub>(HP<sup>III</sup>O<sub>3</sub>)}<sup>8–</sup> moieties\nto form the polyanion skeleton, while the phosphite plays a bridging\nrole in joining two lanthanide centers in the {W<sub>3</sub>Eu<sub>2</sub>O<sub>5</sub>(H<sub>2</sub>O)(B-α-TeW<sub>8</sub>O<sub>31</sub>)<sub>2</sub>(HP<sup>III</sup>O<sub>3</sub>)}<sup>8–</sup> moiety. In addition to the fluorescence (FL) properties of <b>1</b> and <b>2</b> at room temperature, their temperature-dependent\nFL properties were also investigated. In 80–298 K, FL intensities\nof <b>1</b> and <b>2</b> decrease as temperature increases,\nand their maximum relative sensitivities (<i>S</i><sub>r</sub>) are 3.70 and 1.99% K<sup>–1</sup>, whereas the minimum temperature\nuncertainties (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\ntemperature, FL intensities of <b>1</b> and <b>2</b> initially\nrise to their maxima at 373 K and subsequently decrease. This is because\nsamples of <b>1</b> and <b>2</b> undergo dehydration together\nwith amorphization below 473 K and decomposition above this temperature.\nThis work lays a foundation for the development for luminescent thermometers\nbased on lanthanide-incorporated polyoxometalates.