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11. An organic-organometallic CO-releasing material comprising 4,4′-bipyridine and molybdenum subcarbonyl building blocks.

Author

Calhau, Isabel B., Gomes, Ana C., Mendes, Ricardo F., Almeida Paz, Filipe A., Gonçalves, Isabel S., and Pillinger, Martyn

Subjects
MAGIC angle spinning, X-ray powder diffraction, CARBON monoxide, THERMOGRAVIMETRY, ULTRAVIOLET-visible spectroscopy
Abstract

Over the past two decades, following the discovery of the important biological roles of carbon monoxide (CO), metal carbonyl complexes have been intensively studied as CO-releasing molecules (CORMs) for therapeutic applications. To improve the properties of "bare" low molecular weight CORMs, attention has been drawn to conjugating CORMs with macromolecular and inorganic scaffolds to produce CO-releasing materials (CORMAs) capable of storing and delivering large payloads of the gasotransmitter. A significant obstacle is to obtain CORMAs that retain the beneficial features of the parent CORMs. In the present work, a crystalline metal–organic framework (MOF) formulated as Mo(CO)3(4,4′-bipyridine)3/2 (Mobpy), with a structure based on Mo(CO)3 metallic nodes and bipyridine linkers, has been prepared in near quantitative yield by a straightforward reflux method, and found to exhibit CO-release properties that mimic those typically observed for molybdenum carbonyl CORMs. Mobpy was characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-IR, FT-Raman and diffuse reflectance (DR) UV-vis spectroscopies, and 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR. The release of CO from Mobpy was studied by the deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (MbCO) UV-vis assay. Mobpy liberates CO upon contact with a physiological buffer in the dark, leading to a maximum released amount of 1.3–1.5 mmol g−1, after 1.5 h at 37 °C, with half-lives of 0.5–1.0 h (time to transfer 0.5 equiv. of CO to Mb). In the solid-state and under open air, Mobpy undergoes complete decarbonylation over a period of 42 days, corresponding to a theoretical CO-release of 7.25 mmol g−1. [ABSTRACT FROM AUTHOR]

Published
2024
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16. Inclusion complexes of cucurbit[n]urils (n = 7, 8) with η5‐cyclopentadienyl methyl tricarbonyl molybdenum(II) and their use in epoxidation catalysis.

Author

Neves, Patrícia, Gomes, Ana C., Monteiro, Rodrigo P., Santos, Mirela J., Valente, Anabela A., Lopes, André D., Gonçalves, Isabel S., and Pillinger, Martyn

Subjects
INCLUSION compounds, EPOXIDATION, FATTY acid methyl esters, MOLYBDENUM, CATALYSTS recycling, COORDINATION polymers
Abstract

There are very few known examples of supramolecular compounds comprising molybdenum species hosted inside the portals/cavities of cucurbit[n]urils (CBn). In this work, CB7 and CB8 macrocycles have been studied as hosts for the carbonyl complex [CpMo(CO)3Me] (1) (Cp = η5‐C5H5). Compounds were isolated in the solid state and characterized as genuine 1:1 inclusion complexes (1@CBn) by elemental and thermogravimetric analyses, powder X‐ray diffraction, scanning electron microscopy, 13C{1H} cross‐polarization magic‐angle spinning NMR, FT‐IR, Raman, and diffuse reflectance UV–Vis spectroscopies. The host–guest structures can act as supramolecular precatalysts for olefin epoxidation. Based on the model reaction of cis‐cyclooctene with hydroperoxide oxidants (tert‐butylhydroperoxide or hydrogen peroxide), the structural features of 1@CBn as well as the operating conditions influence the catalytic process. The metal species in 1@CBn undergo oxidative decarbonylation in situ, giving oxidized metal species that are catalytically active for olefin epoxidation. The type of oxidant and solvent influences the catalytic activity and stability. 1@CB8 was more stable than 1@CB7 with regard to catalyst recycling and reuse. Based on the substrate scope investigation, for relatively large olefins, such as the fatty acid methyl ester methyl oleate, the size of the macrocyclic host may be a determining factor for catalytic activity. [ABSTRACT FROM AUTHOR]

Published
2024
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26. EXAFS studies of polyoxometalates and polyoxometalate-pillared layered double hydroxides

Author

Pillinger, Martyn

Subjects
546, Molecular sieve, Zeolites, Catalysts
Abstract

Extended X-ray Absorption Fine Structure (EXAFS) data has been analyzed for a series of polyoxometalates (POMs) of the type [MyOz]n- (isopolymetalates) and [XxMyOz]n- (heteropolymetalates) using spherical wave methods with ab initio phase shifts and backscattering factors. The raw X-ray absorption spectra were acquired mostly in the solid state at low temperature (80K) but also in some cases in solution at room temperature. The EXAFS data so derived is rich in detail about the M-O bonds (M-(η1-O) at 1.63-1.79Å, M-(η2-O) at 1.87-1.99Å and M-(η4-O or η6-O) at 2.16-2.39Å) and also the non-bonded M...M relationships (3.0-6.0Å) which arise from pairs of edge or corner sharing distorted MO₆ octahedra and define the whole cluster geometry. Analysis of the Mo K-, Nb K-, V K- and W Lm-edge EXAFS of the hexametalates [Mo₆O19]2-, [NbxW6-xO19](x+2)- (x=6,2-4) and [V₂W₄O19]4- enables a complete structural characterisation with both the short (3.22-3.34Å) and long (4.63-4.78Å) M...M distances being accessible. The M-(η2-O)-M bond angles were determined as 113° for [Mo₆O19]2- and 112° for [HNb₆O19]7- by allowing multiple scattering for these units. Examination of the Mo K-edge solution EXAFS of [(C₄H9)₄N]₂Mo₆O19, [(C₄H9)₄N]₃PMo12O40 (both in CH₃CN) and Na₃TeMo₆O24.nH₂O (in water) indicates very little difference between the solid and solution structures. In general the EXAFS-derived distances compare favourably with single crystal X-ray diffraction (XRD) data, where available, suggesting that the technique could be useful in studying POMs which are important as soluble metal oxide-like analogues.

Published
1994

28. A Molybdenum(VI) Complex of 5-(2-pyridyl-1-oxide)tetrazole: Synthesis, Structure, and Transformation into a MoO3-Based Hybrid Catalyst for the Epoxidation of Bio-Olefins

Author

Nunes, Martinique S., primary, Gomes, Diana M., additional, Gomes, Ana C., additional, Neves, Patrícia, additional, Mendes, Ricardo F., additional, Paz, Filipe A. Almeida, additional, Lopes, André D., additional, Pillinger, Martyn, additional, Valente, Anabela A., additional, and Gonçalves, Isabel S., additional

Published
2023
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