[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight

Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW₉O₃₃]^9- based lanthanide-containing polyoxometalates [Cs_xK_36-x{Ln₆(H₂O)₁₂(α-AsW₉O₃₃)₆}]·yH₂O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln₃(H₂O)₆(α-AsW₉O₃₃)₃]^18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H₂O)₂(α-AsW₉O₃₃)]^6- as a building unit. In all the complexes, [α-AsW₉O₃₃]^9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW₉O₃₃]^9- unit bridges two Ln(III) centers through four μ₂-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of m_J states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.

Controlled assembly and reversible transformation of tuneable luminescent Mo8-R6G hybrids

This work reports that two new assemblies based on POM and AIE-quenched R6G display tuneable fluorescence intensity; furthermore two hybrids can be controllably synthesized and reversible transformation can also be achieved.

Shape-control of CeF3 nanocrystals by doping polyoxometalates: syntheses, characterization and tunable photoluminescence

A series of CeF₃ nanocrystals with uniform morphologies have been synthesized by introducing various polyoxometalates as dopants and shape modifiers.

Synthesis and spectroscopic properties of silver-fluorescein co-doped phosphotungstate hollow spheres

Herein, silver-fluorescein co-doped phosphotungstate hollow spheres have been successfully synthesized using a chemical precipitation method by introducing silver ions and fluorescein at room temperature. This hybrid nanomaterial possesses a uniform structure, exhibiting a strong emission spectrum with a peak centered at 517 nm. It is anticipated that silver and fluorescein as functionalized dopants for the phosphotungstate hollow sphere structure would provide this material with multiple properties. The control experiments indicate that fluorescein plays a key role in the formation of the hollow sphere structure. Hence, the co-doping strategy is proposed to be a general method to endow polyoxometalate nanomaterials with new structures, new functions and potential applications in bioimaging, fluorescent chemical sensors, and antibacterial or optoelectronic devices.

Reversible proton-switchable fluorescence controlled by conjugation effect in an organically-functionalized polyoxometalate

A novel monosubstituted organoimido hexamolybdate containing 6-nitroquinoline moiety has been successfully synthesized. This organically-functionalized polyoxometalate exhibits proton-induced switchable fluorescence property in aqueous acetonitrile solution at room temperature. Experimental and theoretical investigations of this reversible “on” and “off” switching mechanism have been carried out, and it is found that the protonation and deprotonation at the heterocyclic nitrogen atom within quinoline fragment leads to the breaking and reformation of the conjugation through strong d-π interaction between the hexamolybdate anionic cluster and the quinoline moiety, resulting in “on” and “off” luminescence signal.

Layer-by-layer assembly of polyoxometalate–pyrene-decorated fluorescent microspheres for the suspension immunoassay of Listeria monocytogenes

A new class of polyoxometalate–pyrene-decorated fluorescent microspheres prepared by a layer-by-layer self-assembly method were used in the suspension immunoassay technique to detectListeria monocytogenes.

Synthesis and characterization of conjugated Dawson-type polyoxometalate-porphyrin copolymers

Hybrid polyoxometalate-porphyrin copolymeric films were obtained by the electro-oxidation of zinc octaethylporphyrin (ZnOEP) in the presence of a Dawson type polyoxophosphovanadotungstate bearing two pyridyl groups (POM(py)2). The synthesis of a series of POM(py)2 consisting of [P2W15V3O62](9-) functionalized with diol-amide or triol moieties, as well as the characterization of the copolymers are presented.