Hydrothermal assembly strategy for the construction of oxygen-bridging lanthanide-substituted bilacunary Keggin-type germanotungstate tetramers encapsulating [W₃O₁₂]^6- connector

Under the hydrothermal condition and presence of organic amines, incorporating lanthanide (Ln) ions into monolacunary Keggin-type germanotungstate precursor resulted in the formation of two new complex clusters formulated as H-17(H(2)en)(5)[K-3(H2O)(GeW10O37TbOTb)(4)(mu(6)-W3O12)] & sdot; 45H(2)O (GeW-Tb) and H-22(H(2)en)(3)[K-2(GeW10O37EuOEu)(4)(H2O)(mu(6)-W3O12)] & sdot; 44H(2)O (GeW-Eu) (en=ethylenediamine), which have been structurally characterized by elemental analyses, ICP analysis, IR spectra, thermogravimetric analysis, bond valence sum calculations and single-crystal X-ray diffraction. The most prominent structural feature of GeW-Eu and GeW-Tb revealed an unprecedented oxygen-bridging Ln-substituted bilacunary Keggin-type germanotungstate tetramers encapsulating [W3O12](6-) connector. What's more interesting is that a versatile library of linkable units including bilacunary germanotungstate [alpha-GeW10O37](10-), internal oxo group between two Ln ions, as well as central tritungstate intermediate [W3O12](6-) are all generated in situ thanks to the potential promotion of hydrothermal reaction system. In particular, the possible assembly mechanism for the complex clusters is proposed, and their solid-state photoluminescence properties are also discussed in detail. To our knowledge, both [alpha-GeW10O37](10-) and [W3O12](6-) intermediates are the highly robust POM building blocks that were first discovered. The studies highlight the structural diversity of Ln-substituted germanotungstates and provide a new direction in the design of other functional germanotungstate based POMs in the future.