科研之友
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摘要
In the presence of the larger [H2N(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 [H2N(CH3)(2)](2)Na9K2H19{[Ln(4)W(4) Se4O22(H2O)(5)](Se2W14O52)(2)}(2)60H(2)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 Na2WO4 center dot 2H(2)O, Ln(NO3)(3)center dot 6H(2)O, and Na2SeO3 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 {[Ln(4)W(4)Se(4)O(22)(H2O)(5)](Se2W14O52)(2)}(16-) half-units linked through two W-O-Ln bridges. The sandwich-type half-unit comprises two tetra-vacant Dawson-like [Se2W14O52](12-) fragments encapsulating a unique dodecanuclear Se-Ln-W [Ln(4)W(4)Se(4)O(22)(H2O)(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 Ln(3+) 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.
