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

Abstract

A series of organic-inorganic rare-earth-incorporated tellurotungstate hybrids, Na[RE(HO)(pica)WO][(RE(HO)W(Hpica)O)(B-β-TeWOH)]·38HO (RE = La (1), Ce (2), Nd (3), Sm (4), Eu (5); Hpica = 2-picolinic acid), were prepared via a one-step assembly reaction of NaWO·2HO, RE(NO)·6HO, KTeO, 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 [RE(HO)(pica)WO][(RE(HO)W(Hpica)O)(B-β-TeWOH)] polyoxoanion constructed from two tetravacant Keggin sandwich-type [(RE(HO)W(Hpica)O)(B-β-TeWOH)] entities linked by a RE-W-Hpica {RE(HO)(pica)WO} 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 Sm centers in 4 is convincingly proved by time-resolved emission spectra (TRES); the increase in the strongest typical emission of Sm 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.

Multinuclear Lanthanide-Implanted Tetrameric Dawson-Type Phosphotungstates with Switchable Luminescence Behaviors Induced by Fast Photochromism

“…Liu’s group reported three cases of Keggin tetrameric LSLPs [(Ge 4 ­W 36 ­Nb 36 O 156 )­Eu­(H 2 O) 3 ] 17– based on the {GeW 9 Nb 3 O 40 } unit in 2012 . Afterward, Zhao’s group prepared five tetrameric organic–inorganic Ln-incorporated tellurotungstate hybrids, Na 4 ­[Ln 2 ­(H 2 O) 4 ­(pica) 2 ­W 2 O 5 ]­[(Ln­(H 2 O)­W 2 ­(Hpica) 2 ­O 4 )­(B-β-TeW 8 ­O 30 H 2 ) 2 ] 2 ·38H 2 O (Ln = La 3+ , Ce 3+ , Nd 3+ , Sm 3+ , and Eu 3+ ; Hpica = 2-picolinic acid) in 2017 . Two years later, they constructed another type of novel Ln and Sb–oxo tetrameric cluster simultaneously bridging antimono­tungstates, [H 2 N­(CH 3 ) 2 ] 8 ­Na 6 H 8 ­{[Ln 4 ­(H 2 O) 6 ­Sb 6 ­O 4 ]­(Sb­W 10 ­O 37 ) 2– ­(Sb­W 8 ­O 31 ) 2 }·24H 2 O (Ln = Dy 3+ , Er 3+ , Y 3+ , and Ho 3+ ) .…”

pH-Controlled Assembly of Two Polynuclear Dy(III)-Containing Polytungstoarsenates with Magnetic and Luminescence Properties

“…Notably, the POM ligands are also appropriate candidates to sensitize the emission of Ln ions through intramolecular energy transfer (ET) from the O → M (M = Mo or W) photoexcitation state of ligand-to-metal charge transfer (LMCT) state within Ln-containing POMs . Therefore, several Ln-substituted lacunary POMs have been reported to display outstanding luminescence properties . For example, the [EuP 5 W 30 O 110 ] 12– polyanions was encapsulated by polyelectrolytes to prepare photoluminescent multilayer films .…”

Roles of Organic Fragments in Redirecting Crystal/Molecular Structures of Inorganic–Organic Hybrids Based on Lacunary Keggin-Type Polyoxometalates

“…The addition of RE components (coordinated to the non-sandwiched {WO 2 (pic)} unit) led to the development of [(RE) 8 (pic) 6 (H 2 O) 22 (B- β -AsW 8 O 30 ) 4 (WO 2 (pic)) 6 ] 12− (RE = Tb, Eu) structures [ 137 ]. In the structure of tetrameric [RE 2 (H 2 O) 4 (pic) 2 W 2 O 5 ][(RE(H 2 O)W 2 (pic) 2 O 4 )(B- β -TeW 8 O 30 H 2 ) 2 ] (RE = La III , Ce III , Nd III , Sm III , Eu III ), Hpic ligand stabilized the structure by connecting W and RE atoms together by forming stable N−O−C−O−W five-membered-rings or N−O−RE−O−W−O six-membered-ring motifs [ 138 ]. The reaction of 3,4-pdc, RE ions, and monolacunary silicotungestate polyanions lead to monomeric (3,4-pdc) 2 RE(H 2 O) 2 SiW 11 O 39 (RE = La, Pr, Dy) structures.…”