Rare-Earth-Incorporated Tellurotungstate Hybrids Functionalized by 2-Picolinic Acid Ligands: Syntheses, Structures, and Properties.

A series of organic-inorganic rare-earth-incorporated tellurotungstate hybrids, Na4 [RE2 (H2 O)4 (pica)2 W2 O5 ][(RE(H2 O)W2 (Hpica)2 O4 )(B-β-TeW8 O30 H2 )2 ]2 ·38H2 O (RE = LaIII (1), CeIII (2), NdIII (3), SmIII (4), EuIII (5); Hpica = 2-picolinic acid), were prepared via a one-step assembly reaction of Na2 WO4 ·2H2 O, RE(NO3 )3 ·6H2 O, K2 TeO3 , Hpica, and triethylamine (tea). Notably, the solubilization of tea toward Hpica and the solubilization of Hpica toward RE cations in the reaction system play an important role in the formation of 1-5. The most significant feature of 1-5 consists of an intriguing tetrameric [RE2 (H2 O)4 (pica)2 W2 O5 ][(RE(H2 O)W2 (Hpica)2 O4 )(B-β-TeW8 O30 H2 )2 ]2 4- polyoxoanion constructed from two tetravacant Keggin sandwich-type [(RE(H2 O)W2 (Hpica)2 O4 )(B-β-TeW8 O30 H2 )2 ]5- entities linked by a RE-W-Hpica {RE2 (H2 O)4 (pica)2 W2 O5 }6+ cluster, in which Hpica ligands not only play a key bridging role in linking RE and W centers by carboxylic groups in an irregular N-O-RE-O-W-O six-membered-ring motif but also can directly chelate with W centers via N and O atoms in a stable N-O-C-O-W five-membered-ring fashion. 1-5 represent rare organic-inorganic hybrid RE-substituted tellurotungstates. Moreover, the solid-state photoluminescence properties of 3-5 have been deeply investigated, and these compounds exhibit the characteristic emission stemming from intra-4f transitions of RE ions. The energy transfer of the O → W transitions sensitizing the emission of SmIII centers in 4 is convincingly proved by time-resolved emission spectra (TRES); the increase in the strongest typical emission of SmIII ions at a decay time of 17 μs is accompanied by the decline of O → W emission, and the CIE 1931 diagram was obtained from the corresponding TRES. Furthermore, a comparison of the luminescence behaviors of 5 in the solid state and in solution reveals the structural skeletal integrity of 5 in solution and a shorter decay lifetime in the solution caused by the high-frequency O-H oscillators.