A comprehensive series of Group 14 derivatives of the plenary mixed-metal polyoxometalate [PNbW11O40]4−

Preparation and isolation of mono-Nb substituted Keggin-type phosphomolybdic acid and its application as an oxidation catalyst for isobutylaldehyde and Wacker-type oxidation

The potassium and proton mixed salt of mono-Nb substituted Keggin-type phosphomolybdate, KH3[PMo11NbO40], was isolated in a pure form by reacting Keggin-type phosphomolybdic acid (H3[PMo12O40]) and potassium hexaniobate (K8Nb6O19) in water, followed by freeze-drying. The all protonic form, H4[PMo11NbO40], was isolated via proton exchange with H-resin and subsequent freeze-drying. The most crucial factor to isolate KH3[PMo11NbO40] and H4[PMo11NbO40] in pure forms is the evaporation of water using the freeze-drying method. Using a similar procedure, the potassium salt of the di-Nb substituted compound K5[PMo10Nb2O40] was isolated. H4[PMo11NbO40] exhibited high catalytic activity for oxidizing isobutylaldehyde to methacrolein and moderate catalytic activity for the Wacker-type oxidation of allyl phenyl ether when combined with Pd(OAc)2.

Self-Assembly of Ag+/[PW11NbO40]4- Complexes in Nonaqueous Solutions

Self-assembly between Ag⁺ and [PW₁₁NbO₄₀]^4- in N- and O-donor solvents (nitriles and amides) has been studied. In the case of dimethylformamide (DMF), formation of a yellow [Ag₄(DMF)₁₂][PW₁₁NbO₄₀] (1a) metastable phase and a colorless [Ag₄(DMF)₁₀][PW₁₁NbO₄₀] (1) stable phase was observed. In acetonitrile (CH₃CN), the product was [Ag(CH₃CN)₄]₂{[Ag(CH₃CN)₃]₂[PW₁₁NbO₄₀]} (2a). By contrast, [SiW₁₂O₄₀]^4- of the same size and charge as [PW₁₁NbO₄₀]^4- produces [Ag(CH₃CN)₃]₄[SiW₁₂O₄₀] (3a). Partial desolvation of 2a and 3a leads to Ag₄[PW₁₁NbO₄₀]·7.5CH₃CN (2) and Ag₄[SiW₁₂O₄₀]·7.5CH₃CN (3), respectively. The CH₃CN molecules in the structure of 2 are labile, and this compound was used as the starting material to study solvent-exchange processes in N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMA), diethylformamide (DEF), and benzonitrile (PhCN) solutions. These solvent reactions yield [Ag(DMA)₄][Ag₃(DMA)₆][PW₁₁NbO₄₀] (4), [Ag₂(NMP)₄(CH₃CN)]₂[PW₁₁NbO₄₀]·1.3NMP (5a), [Ag₂(NMP)₅]₂[PW₁₁NbO₄₀] (5b), Ag₄[PW₁₁NbO₄₀]·9.5DEF (6), and [Ag(PhCN)₄]₂[{Ag(PhCN)₃}₂PW₁₁NbO₄₀] (7). All products were isolated and characterized by single-crystal X-ray diffraction (except for 2 and 3), IR, elemental analysis, and thermogravimetric analysis techniques. The O-donor solvents favor polynuclear, solvent-bridged cationic aggregates. In the case of DMF, DMA, and DEF discrete, tri- and tetranuclear polycations are observed, while in the case of NMP, the formation of infinite polycationic structures takes place. By contrast, the N-donor solvents (CH₃CN and PhCN) favor mononuclear cations, which can exist either as distorted tetrahedral, isolated [Ag(Solv)₄]⁺ cations or as pseudotriangular {Ag(Solv)₃}⁺ units, additionally coordinated to a polyoxometalate. Screening of the luminescent properties for solid samples of 1-7 revealed that only 5a/5b and 7 are emissive. In particular, the sample containing 5a and 5b demonstrates long-lived phosphorescence with a 30 ms lifetime.

Niobium uptake by a [P8W48O184]40−macrocyclic polyanion

Incorporation of Nb into the [P₈W₄₈O₁₈₄]⁴⁰⁻anionic macrocyclic cavitand leads to formation of new Nb–W POMs. Inclusion of up to five {NbO(H₂O)}³⁺groups was observed. Solution speciation of the Nb-encapsulating macrocycles was studied by HPLC-ICP-AES and SAXS.

A HPLC-ICP-AES technique for the screening of [XW11NbO40]n− aqueous solutions

In this research combined HPLC-ICP-AES technique was used to study formation of mixed [XW₁₁O₄₀]ⁿ⁻ (X = P, Ge, B) complexes.

Self-assembly of [PNbxW12−xO40]n− Keggin anions – a simple way to mixed Nb–W polyoxometalates

This paper summarizes preparations of mixed phosphoniobotungstates [PNb_xW_12−xO₄₀]^(3+x)− (x = 1–3) based on two different ways: incorporation of Nb into pre-existing lacunary-type phosphotungstates and self-assembly reactions.

19-Tungstodiarsenate(III) Functionalized by Organoantimony(III) Groups: Tuning the Structure-Bioactivity Relationship

A family of three discrete organoantimony(III)-functionalized heteropolyanions-[Na{2-(Me2HN(+)CH2)C6H4Sb(III)}As(III)2W19O67(H2O)](10-) (1), [{2-(Me2HN(+)CH2)C6H4Sb(III)}2As(III)2W19O67(H2O)](8-) (2), and [{2-(Me2HN(+)CH2)C6H4Sb(III)}{WO2(H2O)}{WO(H2O)}2(B-β-As(III)W8O30)(B-α-As(III)W9O33)2](14-) (3)-have been prepared by one-pot reactions of the 19-tungstodiarsenate(III) precursor [As(III)2W19O67(H2O)](14-) with 2-(Me2NCH2)C6H4SbCl2. The three novel polyanions crystallized as the hydrated mixed-alkali salts Cs3KNa6[Na{2-(Me2HN(+)CH2)C6H4Sb(III)}As(III)2W19O67(H2O)]·43H2O (CsKNa-1), Rb2.5K5.5[{2-(Me2HN(+)CH2)C6H4Sb(III)}2As(III)2W19O67(H2O)]·18H2O·Me2NCH2C6H5 (RbK-2), and Rb2.5K11.5[{2-(Me2HN(+)CH2)C6H4Sb(III)}{WO2(H2O)}{WO(H2O)}2(B-β-As(III)W8O30)(B-α-As(III)W9O33)2]·52H2O (RbK-3), respectively. The number of incorporated {2-(Me2HN(+)CH2)C6H4Sb(III)} units could be tuned by careful control of the experimental parameters. Polyanions 1 and 2 possess a dimeric sandwich-type topology, whereas 3 features a trimeric, wheel-shaped structure, representing the largest organoantimony-containing polyanion. All three compounds were fully characterized in the solid state via single-crystal X-ray diffraction (XRD), infrared (IR) spectroscopy, and thermogravimetric analysis, and their aqueous solution stability was validated by ultraviolet-visible light (UV-vis) and multinuclear ((1)H, (13)C, and (183)W) nuclear magnetic resonance (NMR) spectroscopy. Effective inhibition against six different types of bacteria was observed for 1 and 2, and we could extract a structure-bioactivity relationship for these polyanions.