First Dimethyltin-Functionalized Rare-Earth Incorporated Tellurotungstates Consisting of {B-α-TeW7O28} and {W5O18} Mixed Building Units.

The facile one-step assembly reaction of Na2WO4·2H2O, Sn(CH3)2Cl2, RE(NO3)3·6H2O and K2TeO3 in the presence of dimethylamine hydrochloride as an organic solubilizing agent in acidic aqueous solution resulted in a family of dimethyltin-functionalized rare-earth (RE) incorporated tellurotungstates consisting of {B-α-TeW7O28} and {W5O18} mixed building units [H2N(CH3)2]8Na4H2[RE2(OH)(B-α-TeW7O28)Sn2(CH3)4(W5O18)]2·18H2O [RE = ErIII (1), YbIII (2), HoIII (3), YIII (4)]. The most striking structural characteristic of 1-4 is that they all contain a novel tetrameric S-shaped [RE2(OH)(B-α-TeW7O28)Sn2(CH3)4(W5O18)]214- moiety simultaneously including two pentavacant Keggin [B-α-TeW7O28]12- and two monovacant Lindqvist [W5O18]6- fragments connected by RE and dimethyltin linkers. To the best of our knowledge, such dimethyltin-functionalized RE-containing tellurotungstates have not been reported before. The visible or NIR solid-state emission spectra of 1 and 3 display the characteristic emission bands arising from ErIII and HoIII centers. Moreover, various 1-Er/Yb co-doped samples were prepared by controlling different mass ratio of Er(NO3)3·6H2O/Yb(NO3)·6H2O in the range of 0.96:0.04-0.02:0.98. In the visible region, the emission intensity of the 1-Er0.40/Yb0.60 co-doped sample reaches the maximum at the mass ratio of Er(NO3)3·6H2O/Yb(NO3)·6H2O being 0.40:0.60, and this observation is mainly derived from the fact that the Yb3+ ions can sensitize the Er3+ ions to enhance the emission intensity in the visible region. However, no such phenomenon for the 1-Er/Yb co-doped samples is seen in the NIR region. Besides, the upconversion spectra of the 1-Er/Yb co-doped samples were first observed. In addition, the thermal stabilities of 1-4 were also investigated on the crystalline samples and the thermal decomposition process of 1 has been deeply studied.