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 = NdIII for 1 and GdIII for 2) and [{(α-PW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO}2]10− (Ln = SmIII for 3, EuIII for 4, GdIII for 5, TbIII for 6, HoIII for 7 and ErIII 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.