Assembly Chemistry between Lanthanide Cations and Monovacant Keggin Polyoxotungstates: Two Types of Lanthanide Substituted Phosphotungstates [{(α-PW<sub>11</sub>O<sub>39</sub>H)Ln(H<sub>2</sub>O)<sub>3</sub>}<sub>2</sub>]<sup>6−</sup> and [{(α-PW<sub>11</sub>O<sub>39</sub>)Ln(H<sub>2</sub>O)(η<sup>2</sup>,μ-1,1)-CH<sub>3</sub>COO}<sub>2</sub>]<sup>10−</sup>

Two 2:2 types of monolanthanide substituted polyoxometalates [{(α-PW<sub>11</sub>O<sub>39</sub>H)Ln(H<sub>2</sub>O)<sub>3</sub>}<sub>2</sub>]<sup>6−</sup> (Ln = Nd<sup>III</sup> for <b>1</b> and Gd<sup>III</sup> for <b>2</b>) and [{(α-PW<sub>11</sub>O<sub>39</sub>)Ln(H<sub>2</sub>O)(η<sup>2</sup>,μ-1,1)-CH<sub>3</sub>COO}<sub>2</sub>]<sup>10−</sup> (Ln = Sm<sup>III</sup> for <b>3</b>, Eu<sup>III</sup> for <b>4</b>, Gd<sup>III</sup> for <b>5</b>, Tb<sup>III</sup> for <b>6</b>, Ho<sup>III</sup> for <b>7</b> and Er<sup>III</sup> for <b>8</b>) have been synthesized in aqueous solution and characterized by elemental analyses, IR spectra, UV−vis−NIR spectra, thermogravimatric analyses and single-crystal X-ray diffraction. The common structural features are that they are constructed from monovacant Keggin-type polyoxoanions [α-PW<sub>11</sub>O<sub>39</sub>]<sup>7−</sup> and trivalent lanthanide cations. Both <b>1</b> and <b>2</b> are essentially isomorphous, and the molecular structure is built by two symmetrically related monolanthanide substituted Keggin units [α-PW<sub>11</sub>O<sub>39</sub>Ln(H<sub>2</sub>O)<sub>3</sub>]<sup>4−</sup> linked via two Ln−O−W bridges, representing the first monovacant Keggin polyoxotungstate dimers constituted by two [α-PW<sub>11</sub>O<sub>39</sub>]<sup>7−</sup> polyoxoanions and two lanthanide cations in polyoxometalate chemistry. <b>3</b>−<b>8</b> are also isostructural and display another dimeric structure constructed from two monolanthanide substituted units [(α-PW<sub>11</sub>O<sub>39</sub>)Ln(H<sub>2</sub>O)(η<sup>2</sup>,μ-1,1)-CH<sub>3</sub>COO]<sup>5−</sup> bridged by two (η<sup>2</sup>,μ-1,1)-acetato ligands. The photoluminescence properties of <b>4</b> and <b>6</b> were investigated at room temperature. Magnetic susceptibility measurements of <b>1</b>, <b>3</b>, <b>4</b>, <b>7</b> and <b>8</b> between 2 and 300 K exhibit that their magnetic behaviors mainly result from the spin−orbital coupling interactions as well as weak antiferromagnetic exchange interactions within magnetic centers. The electrochemical properties of <b>1</b>, <b>3</b>, <b>4</b>, <b>5</b>, <b>7</b> and <b>8</b> were studied by means of cyclic voltammetry in aqueous solution with 0.5 M Na<sub>2</sub>SO<sub>4</sub> as supporting electrolyte.