Impact of POM's coordination mode and Mo-hybrid constituents on the binding, stability, and catalytic properties of hybrid (pre)catalysts

The assembly of MoVIO2 2+ and methoxy-substituted salicylaldehyde nicotinoyl hydrazone ligands afforded two classes of hybrid polyoxometalates (POMs). In the Class I architectures, [MoO2(HL1-3)(D)]2[Mo6O19]·xCH3COCH3 (D = CH3COCH3 or H2O, x = 0 or 2, and L1-3 = ligands bearing the OMe group at position 3, 4 and 5, respectively), the main driving force for self-assembly is the electrostatic interaction between the components. Class II architectures are composed of a POM anion covalently linked to two Mo-complex units through the terminal Ot or bridging μ2-OPOM oxygen atoms, as found in Lindqvist-based hybrids [{MoO2(HL1-3)}2Mo6O19]·xCH3CN (x = 0 or 2) and the asymmetrical β-octamolybdate-based hybrid [{Mo2O4(HL2)(H2L)}{MoO2(HL2)}2Mo8O26]·CH3CN·H2O. Quantum chemical calculations were applied to evaluate the impact of the POM hybrid constituents on the hybrid-type stability, showing that it strongly depends on the ligand substituent position and ancillary ligand nature. Hybrids were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP in water or decane) and with or without the addition of acetonitrile (CH3CN) as an organic solvent. The catalytic results provided by the use of TBHP in decane are the best ones and classify all the prepared catalysts as very active, with the conversion of cyclooctene >90%, and high selectivity towards epoxide, >80%. We also examined the influence of the ligand structure, POM's hybrid type, and coordination mode on the Mo-hybrid activity and selectivity.

Electrochemical and fluorescence sensing performance of four new coordination polymers tuned by different metal ions and dicarboxylic acids

Four new ZnII, CdII, CoII, and NiII coordination polymers (CPs) were successfully prepared from a bis-pyridyl–bis-amide and various dicarboxylate mixed ligands, which show good electrochemical and fluorescence sensing performance.

Four Anderson-type [TeMo6O24]6−-based metal–organic complexes with a new bis(pyrimidine)-bis(amide): multifunctional electrochemical and adsorption performances

Four isostructural Anderson-type POM-based metal–organic complexes derived from a new bis(pyrimidine)-bis(amide) ligand were synthesized, showing multifunctional electrochemical sensing activities and good adsorption performances for organic dyes.

Assembly of a coordination polymer with sulphate-capped pentamolybdate units and copper: Synthesis, Structure, Magnetic and Catalytic studies

A new coordination polymer based upon the sulphate-capped pentamolybdate unit has been synthesized from the reaction of {Mo3S7Br6}2- with copper(II) bromide and pyridine, in DMF. The as-synthesized compound, formulated as...

Four Keggin-type polyoxometalate-based complexes derived from bis(pyrazine)–bis(amide) ligands for electrochemical sensing of multiple analytes and adsorbing dye molecules

Four new Keggin-based complexes derived from bis(pyrazine)–bis(amide) ligands are used to detect multiple analytes (BrO3− NO2−, Cr(vi) and Fe(iii) ions) and adsorb organic dye molecules from aqueous solution.

POM-based metal–organic compounds: Assembly, structures and properties

Four POM-based inorganic-organic hybrid compounds, which are {[(Cu·L1’·H2O)·(α-Mo8O26)0.5]·H2O}n (1), {(Cu·L2’·H2O)·(α-Mo8O26)0.5}n (2), {[(Cu·L3’·H2O)·(β-Mo8O26)0.5]·5H2O}n (3), {(Cu·L4’·H2O)·(β-Mo8O26)}n (4)[L1’ = 1,5-bis (4-carboxylpyridine) pentane dibromide, L2’ = 1,7-bis (4-carboxylpyridine) heptane dibromide, L3’ = 1,2-bis [(4-carboxylpyridine) - N-methylene] benzene dibromide, L4’ = 1,4-bis [(4-carboxylpyridine) - N-methylene] benzene dibromide] have been successfully synthesized under hydrothermal conditions by tuning ligands. Compounds 1–4 were characterized by single crystal X-ray diffraction, infrared spectrum (IR), powder X-ray diffraction (PXRD), and thermogravimetric (TG). The transformation of ligands have a momentous effect on the [Mo8O26]4 - structures of this series. In addition, the adsorption and photocatalytic properties of organic dyes for compounds 1–4 have been investigated.

Polyoxometalate-Incorporated Framework as a Heterogeneous Catalyst for Selective Oxidation of C-H Bonds of Alkylbenzenes

Developing new catalysts for highly efficient and selective oxidation of saturated C-H bonds is significant due to their thermodynamic strength. Via incorporation of PW₁₂O₄₀^3-, pyridine-2,5-dicarboxylic acids (pydc), and Fe(III) ions into one framework, a new polyoxometalate-based metal-organic framework, [HFe₄O₂(H₂O)₄(pydc)₃PW₁₂O₄₀]·10.5H₂O (FeW-PYDC), was successfully prepared by a hydrothermal method. Interestingly, FeW-PYDC features a three-dimensional porous structure with {Fe₄O₂} interconnecting with PW₁₂O₄₀^3- units. FeW-PYDC displayed excellent performance in the selective oxidation of C-H bonds of alkylbenzenes with high conversion (95.7%) and selectivity (96.6%). As an effective heterogeneous catalyst, FeW-PYDC demonstrates good reusability and structural stability.

Anderson-type polyoxometalates: from structures to functions

Anderson-type polyoxometalates (POMs) are one of the most important groups of the POM family. In the past decade, the functionalization of Anderson-type POMs has achieved significant progress and these materials have already shown unique charm in catalysis, molecular devices, energy materials, and inorganic biochemical drugs. In particular, their highly flexible topological structure and diverse functionalization methods make them the most convenient and universal platforms for rational design and controllable synthesis. This review provides a deep discussion on the recent progress in the synthetic methodology, structural exploration, and promising applications of Anderson-type POMs. It also summarizes the latest research directions and provides future prospects.

Microwave-Assisted Synthesis of Tris-Anderson Polyoxometalates for Facile CO2 Cycloaddition

Four new tris-Anderson polyoxometalates (POMs), (NH₄)₄[ZnMo₆O₁₈(C₄H₈NO₃)(OH)₃]·4H₂O (1), (NH₄)₄[CuMo₆O₁₈(C₄H₈NO₃)(OH)₃]·4H₂O (2), (TBA)₃(NH₄)[ZnMo₆O₁₇(C₅H₉O₃)₂(OH)]·10H₂O (3) (TBA = n-C₁₆H₃₆N), and (NH₄)₄[CuMo₆O₁₈(C₅H₉O₃)₂]·16H₂O (4), were synthesized by a microwave-assisted method. Single-crystal X-ray diffraction revealed that 1 and 2 contained a tris (trihydroxyl organic compounds) ligand grafted on one side, while two tris ligands were grafted on two sides to form χ/δ and δ/δ isomers in 3 and 4, respectively. ¹H and ¹³C NMR spectra of the χ/δ isomer 3 were obtained for the first time, with six methylenes showing six peaks in the ¹H NMR spectrum and only four peaks in the ¹³C NMR spectrum. Mass spectrometry monitoring revealed that during the microwave-assistant process the tris ligand can graft onto POMs to form 1, while tris directly coordinates with metallic heteroatoms to form isopolymolybdates during the conventional reflux synthesis process. In addition, 1-4 can catalyze CO₂ with epoxides into cyclic carbonates with high selectivity and yields at an atmospheric pressure of CO₂, which is lower than the pressure of CO₂ in other catalysis using POMs as catalysts. Furthermore, 1-4 showed good catalytic stability and cycling properties. Mechanism studies substantiated POMs cocatalyzed with Br^- to improve the catalytic yields.

Aliphatic amine mediated assembly of [M6(mna)6] (M = Cu/Ag) into extended two-dimensional structures: synthesis, structure and Lewis acid catalytic studies

New aliphatic amine directed two-dimensional cadmium coordination polymers were shown to exhibit Lewis-acid catalytic activity for the cyanation of imines.

Polyoxometalate-based metal–organic frameworks for heterogeneous catalysis

POM-based MOFs simultaneously possessing the virtues of POMs and MOFs exhibit excellent heterogeneous catalytic properties.

Luminescence sensing and photocatalytic activities of four Zn(ii)/Co(ii) coordination polymers based on a pyridinephenyl bifunctional ligand

Four Zn(ii)/Co(ii) CPs act as bifunctional materials in the detection of Fe(iii) cation, Cr(vi) anion, and nitrofuran antibiotics and removal of methylene blue in aqueous media.

Extending the structural landscape of Mo(vi) hydrazonato inorganic–organic POM-hybrids: an experimental and computational study

Novel Mo(vi) hydrazonato octamolybdate and hexamolybdate hybrids have been synthesized and structurally characterized. Quantum chemical calculations have been applied to determine the possibility of developing the covalently anchored hybrids.

The rational design of four multifunctional octamolybdate-based complexes for detecting different ions and removing organic dyes from aqueous solution

Four new octamolybdate-based complexes were obtained and used not only as electrochemical sensors for sensing Cr(vi), Fe(iii), BrO₃⁻, and NO₂⁻ ions, but also as adsorbents to adsorb organic dyes.

An organic-inorganic hybrid nanomaterial composed of a Dowson-type (NH4)6P2Mo18O62 heteropolyanion and a metal-organic framework: synthesis, characterization, and application as an effective adsorbent for the removal of organic dyes

In this work, an inorganic-organic hybrid nanomaterial, P2Mo18/MIL-101(Cr), based on Wells-Dawson-type (NH4)6P2Mo18O62 polyoxometalate (abbreviated as P2Mo18) and the MIL-101(Cr) metal-organic framework was fabricated by the reaction of (NH4)6P2Mo18O62, Cr(NO3)3·9H2O and terephthalic acid under hydrothermal conditions. The as-prepared recyclable nanohybrid was fully characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) equipped with energy dispersive X-ray microanalysis (EDX), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy and Brunauer-Emmett-Teller (BET) specific surface area studies. All the analyses confirmed the successful insertion of P2Mo18O62 6- heteropolyanion within the cavities of MIL-101(Cr). The encapsulated MIL-101(Cr) showed a considerable decrease in both pore volume and surface area compared with MIL-101(Cr) due to incorporation of the very large Dowson-type polyoxometalate into the three-dimensional porous MIL-101(Cr). The nanohybrid had a specific surface area of 800.42 m2 g-1. The adsorption efficiency of this nanohybrid for removal of methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) from aqueous solutions was evaluated. Surprisingly, the composite not only presented a high adsorption capacity of 312.5 mg g-1 for MB, but also has the ability to rapidly remove 100% MB from a dye solution of 50 mg L-1 within 3 min. These results confirmed that this adsorbent is applicable in a wide pH range of 2-10. The nanohybrid showed rapid and selective adsorption for cationic MB and RhB dyes from MB/MO, MB/RhB, MO/RhB and MB/MO/RhB mixed dye solutions. The equilibrium adsorption data were better fitted by the Langmuir isotherm. Kinetics data indicate that the adsorption of the dye follows a pseudo-second order kinetics model. Also, this material could be effortlessly separated and recycled without any structural modification. Accordingly, it is an efficient adsorbent for removing cationic dyes.

Selective fluorescence sensing properties of a novel two-fold interpenetrating coordination polymer

One novel 3D interpenetrated Zn(ii) CP acts as multi-functional chemosensors in detection of acetone, Fe³⁺, Cu²⁺, Cr₂O₇²⁻, CrO₄²⁻ and nitrofurantoin (NFT).