Synthesis of a cluster containing Eu(III) α2-P2W17O6110- and preliminary luminescence experiments

Recent advances in lanthanide-based POMs for photoluminescent applications

Since the first formation of the famous "Peacock-Weakley" anions [Ln(W5O18)2]8/9-, a steady stream of breakthroughs have been made in the chemistry of multitalented lanthanide (Ln)-based polyoxometalates (POMs) for their potentially desirable properties. In particular, LnIII ions are generally recognised as the "vitamins of the modern industry" owing to their ability to cover a wide emission range, endowing Ln-based POMs with great potential for versatile and diverse luminescence-related applications. In this frontier, we discuss the synthesis strategies and intramolecular energy transfer in Ln-based POM derivatives. Then, the progressive improvements achieved with Ln-based POMs in photoluminescence applications are highlighted, focusing mainly on luminescent and fluorescent probes. Finally, the challenges for Ln-based POM materials for photoluminescence applications are discussed.

An unprecedented polyhydroxycarboxylic acid ligand bridged multi-EuIII incorporated tellurotungstate and its luminescence properties

The first polyhydroxycarboxylic acid ligand bridged multi-EuIII-incorporated tellurotungstate K14H10[Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]·60H2O (H6glu = d-gluconic acid) (1) was synthesized via an organic ligand-driven self-assembly strategy. The polyhydroxycarboxylic acid ligand bridged tetrameric polyoxoanion [Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]24- in 1 can be viewed as an aggregation of four trivacant Keggin [B-α-TeW9O33]8- fragments and an innovative heterometallic [Eu4(H2O)4W6(H2glu)4O12]8+ cluster, in which four high-coordinate polyhydroxy flexible H2glu4- ligands chelate W and Eu centers through carboxyl and hydroxyl groups, giving rise to a heterometallic cluster. The hexagonal packing of the tetrameric polyoxoanions in 1 along the c axis provides excellent porous channels, which greatly increases the specific surface area of the whole framework and may be of benefit for fluorescence sensing in aqueous solution. 1 can function as a "turn-off" luminescence sensor to detect Cu2+ ions in aqueous solution. The limit of detection (LOD) of the 1-sensor is 8.82 × 10-6 mM, which is the lowest among the reported polyoxometalate-based fluorescence sensors. As for the Cu2+-quenching system, it can function as an "off-on" sensor to detect cysteine in an aqueous system, affording a LOD of 1.75 × 10-4 mM. This work opens up an avenue to broaden the applications of polyoxometalate-based materials in the optical intelligence detection field.

An organic chromophore -modified samarium-containing polyoxometalate: excitation-dependent color tunable behavior from the organic chromophores to the lanthanide ion

An organic–inorganic hybrid Ln-POM display reversible color-tunable photoluminescence properties based on excitation from 260 nm to 350 nm, emitting color from blue to pink.

Well-tuned white-light-emitting behaviours in multicenter-Ln polyoxometalate derivatives: A photoluminescence property and energy transfer pathway study

White light-emitting diodes (WLEDs) are of scientific significance in terms of their wide applications, and few uminescent materials based on white-light-emitting polyoxometalate (POM) derivatives have been reported till now. Herein, a series of organic chromophores modified POM derivatives [N(CH₃)₄]₃K₂Ln(C₇H₅O₂)(H₂O)₂(α-PW₁₁O₃₉)]·11H₂O (Ln³⁺ = Eu³⁺ (1), Tb³⁺ (2), Tm³⁺ (3), Lu³⁺ (4)) and multicenter-Ln analogues [N(CH₃)₄]₃K₂Eu_xTb_yTm_1-x-y(C₇H₅O₂)(H₂O)₂(α-PW₁₁O₃₉)·11H₂O (5-11) were synthesized successfully and were characterized by various physico-chemical analysis. The investigations indicate the white-light-emitting behavior can be well tuned by adjusting the molar ratio of Eu³⁺/Tb³⁺/Tm³⁺ = 0.06:0.10:0.84 in 9. The energy transfer process from organic benzoic and POM ligands to Eu³⁺, Tb³⁺ and Tm³⁺ emitting centers were detected through time-resolved emission spectroscopy (TRES) and the comparison of excitation of single-, double-, treble-Ln³⁺ mixed, indicating the energy can transfer from the photoexcitation O → M LMCT state of POM components and π → π* transition of organic ligand to sensitize the emissions of Ln³⁺ ions via intramolecular energy transition mechanism. The energy transfer between Eu³⁺ and Tb³⁺, Tm³⁺ and Eu³⁺, Tm³⁺ and Tb³⁺ ions also have been recorded and carefully studied by TRES and variations of Tm³⁺ luminescence lifetime in this context, and the results show a low-effectively process of energy transfer between Tm³⁺/Eu³⁺, Tm³⁺/Tb³⁺ ions and a relatively good energy transfer efficiency between Eu³⁺/Tb³⁺ ions.

The Monolanthanide-Containing Silicotungstates [Ln(β2-SiW11O39)2]13- (Ln = La, Ce, Sm, Eu, Gd, Tb, Yb, Lu): A Synthetic and Structural Investigation

We have synthesized and structurally characterized the monolanthanide-containing polyanions [Ln(beta2-SiW11O39)2]13- (Ln = La (1), Ce (2), Sm (3), Eu (4), Gd (5), Tb (6), Yb (7), Lu (8)). Synthesis was accomplished by reaction of the respective lanthanide ion with the monolacunary Keggin-type precursor [beta2-SiW11O39]8- in a 1:2 molar ratio in 1 M KCl medium at pH 5. Polyanions 1-8 were isolated as potassium salts and then characterized by IR, single-crystal X-ray diffraction, and elemental as well as thermogravimetric analysis. The structures of 1-8 are composed of an eight-coordinated Ln3+ center sandwiched by two chiral (beta2-SiW11O39) units. Large Ln3+ ions appear to favor an (R,R) (or (S,S)) configuration (point group C2) of the Keggin units, with an increasing amount of (R,S) (or (S,R)) configuration (point group C1) found in the solid state as the Ln3+ ion decreases in size. This trend is also supported by solution 183W NMR results for the diamagnetic La3+ and Lu3+ derivatives.

Excited State Behaviors of the Dodecamolybdocerate (IV) Anion: (NH4)6H2(CeMo12O42)·9H2O

The polyoxometalate (NH(4))(6)H(2)(CeMo(12)O(42)).9H(2)O (abbreviated as Ce(IV)Mo(12)) was synthesized, and its Ce(III) form was obtained by exhaustive electrochemical reduction. Both forms are fairly stable in pH 0.0 media. This stability decreases when the pH increases. The Ce(IV) species, in which the central metal is in the f(0) electronic configuration, is found to fluoresce, a feature that is only straightforwardly explained with the Ce(III) state. As the results of a series of experiments converge to confirm the stability of Ce(IV)Mo(12) in the media studied, a suggested rationale is that the emission originates from a higher-energy ligand-to-metal charge transfer and follows a scheme which is ultimately equivalent to the classical metal-centered fluorescence of Ce(III). Detailed studies of the influences of pH and ionic strength were carried out and suggest that protonated and/or ion-paired assemblies are the fluorescent species. A reproducible increase of the fluorescence intensity of Ce(IV)Mo(12) as a function of time was also observed.

Polynuclear Molybdenum and Tungsten Complexes containing 3-Hydroxypicolinic Acid and Europium (III)

Novel polynuclear tungsten and molybdenum (VI) complexes with 3-hydroxypicolinic acid (HpicOH) and europium(III) [M4O12Eu(picOH)3] (M(VI) = W, Mo) were prepared by hydrothermal methods. The solid compounds were characterized by FT-IR and FT-Raman spectroscopy and elemental analysis. The photoluminescent properties of the materials were investigated, showing sensitization of the europium(III) luminescence by both the 3- hydroxypicolinate ligand and the polyoxometalate moiety