Assembly Chemistry between Lanthanide Cations and Monovacant Keggin Polyoxotungstates: Two Types of Lanthanide Substituted Phosphotungstates [{(α-PW₁₁O₃₉H)Ln(H₂O)₃}₂]⁶⁻ and [{(α-PW₁₁O₃₉)Ln(H₂O)(η²,μ-1,1)-CH₃COO}₂]¹⁰⁻

Two 2:2 types of monolanthanide substituted polyoxometalates [{(α-PW₁₁O₃₉H)Ln(H₂O)₃}₂]⁶⁻ (Ln = Nd^III for 1 and Gd^III for 2) and [{(α-PW₁₁O₃₉)Ln(H₂O)(η²,μ-1,1)-CH₃COO}₂]¹⁰⁻ (Ln = Sm^III for 3, Eu^III for 4, Gd^III for 5, Tb^III for 6, Ho^III for 7 and Er^III for 8) 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-PW₁₁O₃₉]⁷⁻ and trivalent lanthanide cations. Both 1 and 2 are essentially isomorphous, and the molecular structure is built by two symmetrically related monolanthanide substituted Keggin units [α-PW₁₁O₃₉Ln(H₂O)₃]⁴⁻ linked via two Ln−O−W bridges, representing the first monovacant Keggin polyoxotungstate dimers constituted by two [α-PW₁₁O₃₉]⁷⁻ polyoxoanions and two lanthanide cations in polyoxometalate chemistry. 3−8 are also isostructural and display another dimeric structure constructed from two monolanthanide substituted units [(α-PW₁₁O₃₉)Ln(H₂O)(η²,μ-1,1)-CH₃COO]⁵⁻ bridged by two (η²,μ-1,1)-acetato ligands. The photoluminescence properties of 4 and 6 were investigated at room temperature. Magnetic susceptibility measurements of 1, 3, 4, 7 and 8 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 1, 3, 4, 5, 7 and 8 were studied by means of cyclic voltammetry in aqueous solution with 0.5 M Na₂SO₄ as supporting electrolyte.