Unprecedented Selenium and Lanthanide Simultaneously Bridging Selenotungstate Aggregates Stabilized by Four Tetra-vacant Dawson-like {Se₂ W₁₄ } Units

In the presence of the larger [H₂ N(CH₃ )₂ ]⁺ and K⁺ counter cations as structure-stabilizing agents, a class of unprecedented selenium and lanthanide (Ln) simultaneously bridging tetra-vacant Dawson-like selenotungstate aggregates [H₂ N(CH₃ )₂ ]₂ Na₉ K₂ H₁₉ {[Ln₄ W₄ Se₄ O₂₂ (H₂ O)₅ ](Se₂ W₁₄ O₅₂ )₂ }₂ ⋅60 H₂ O [Ln=Tb^III (1), Dy^III (2), Ho^III (3), Er^III (4), Tm^III (5), Yb^III (6)] have been obtained by the one-pot assembly reaction of Na₂ WO₄ ⋅2 H₂ O, Ln(NO₃ )₃ ⋅6 H₂ O, and Na₂ SeO₃ under moderately acidic aqueous conditions and the complexes were structurally characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. It should be noted that the appropriate molar ratio of Se/W is extremely important in the formation of 1-6 and can effectively ameliorate the yield of 1-6. Moreover, dimethylamine hydrochloride is also indispensable and plays a considerably important role in improving the solubility of Ln ions and stabilizing the structures of 1-6. The main polyoxoanion skeletons of 1-6 are constructed from two sandwich-type tetra-vacant Dawson-like {[Ln₄ W₄ Se₄ O₂₂ (H₂ O)₅ ](Se₂ W₁₄ O₅₂ )₂ }^16- half-units linked through two W-O-Ln bridges. The sandwich-type half-unit comprises two tetra-vacant Dawson-like [Se₂ W₁₄ O₅₂ ]^12- fragments encapsulating a unique dodecanuclear Se-Ln-W [Ln₄ W₄ Se₄ O₂₂ (H₂ O)₅ ]⁸⁺ oxo cluster. Their solid-state visible and NIR fluorescent properties and lifetime decay behaviors were measured and their solid-state luminescent spectra mainly demonstrate the characteristic emission bands of Ln³⁺ ions. Moreover, the dominant wavelengths, the color purity, and correlated color temperatures of 1-5 have been also calculated. In addition, the luminous flux values of 1-5 are 2031, 6992, 3071, 921, and 477 lumen, respectively.