2 Methyl 1 Propanethiol Oxidation

DOI: 10.1039/C9SC06217C (Border Article) Chem. Sci., 2020, eleven, 2388-2393

Embedding alkenes within an icosahedral inorganic fullerene {(NH ₄ ) ₄₂ [Mo ₁₃₂ O ₃₇₂ (L) ₃₀ (H ₂ O) ₇₂ ]} for trapping volatile organics†

Received 8th December 2019 , Accepted 19th January 2020

Commencement published on 23rd January 2020

Abstract

Eight alkene-functionalized molybdenum-based spherical Keplerate-blazon (inorganic fullerene) structures have been obtained via both straight and multistep synthetic approaches. Driven by the opportunity to blueprint unique host–guest interactions within hydrophobic, π-electron rich bars environments, we have synthesised {(NH _iv ) ₄₂ [Mo ₁₃₂ O ₃₇₂ (Fifty) ₃₀ (H _ii O) ₇₂ ]}, where L = (one) acrylic acrid, (ii) crotonic acid, (iii) methacrylic acid, (iv) tiglic acrid, (5) iii-butenoic acrid, (half dozen) 4-pentenoic acrid, (7) 5-hexenoic acid, and (eight) sorbic acrid. The compounds, which are obtained in good yield (10–40%), comprise 30 carboxylate-coordinated alkene ligands which create a fundamental crenel with hydrophobic character. Extensive Nuclear Magnetic Resonance (NMR) spectroscopy studies contribute significantly to the complete characterisation of the structures obtained, including both 1D and 2D measurements. In improver, unmarried-crystal X-ray crystallography and subsequently-generated electron density maps are employed to highlight the distribution in ligand tail positions. These alkene-containing structures are shown to effectively encapsulate small alkyl thiols (1-propanethiol (A), two-propanethiol (B), 1-butanethiol (C), 2-butanethiol (D) and 2-methyl-1-propanethiol (E)) equally guests inside the cardinal crenel in aqueous solution. The hydrophobically driven clustering of up to vi equivalents of volatile thiol guests within the central cavity of the Keplerate-type structure results in constructive thermal protection, preventing evaporation at elevated temperatures (ΔT ≈ 25 K).

Introduction

Host–guest encapsulation processes, facilitated by not-covalent interactions, are utilized in drug commitment,¹ sensing,² and separation processes.³ Inorganic systems accept provided insights into the driving force for host–guest interactions such every bit the hydrophobically driven uptake of alcohols^iv and the enthalpically dominated encapsulation of organic guests inside a M _eight L ₁₂ metal/ligand coordination muzzle.⁵ Polyoxometalates (POMs) are discrete metal-oxide clusters which exhibit varied architectures, sizes and compositions. High-nuclearity, spherical Keplerate-type POMs,^vi accept been used equally hosts in previous invitee encapsulation studies, giving insights into hydrophobic effects and pH-driven guest uptake.^4,7

Molybdenum-based Keplerate-type structures possess a metal-oxo framework containing 132 Mo atoms consisting of twelve {Mo ₆ } pentagonal units and thirty {Mo _ii } linkers. The pentagonal and linker-blazon units (Fig. 1) are bundled to form 20 hexagonal {Mo _nine O _nine } flexible pore-like voids, with bore ca. three.6 Å, on the surface of the structure. The linker units are stabilized by the introduction of coordinating ligands, such as sulfates,⁸ oxalates,⁹ and carboxylate-containing species,^4,10 which tin can replace coordinated water molecules on the inner surface of the structures.


	Fig. 1 Simplified brawl-and-stick representation of the {Mo ₁₃₂ } framework highlighting the pentagonal (blue polyhedra) and linker (red polyhedra) structural units. An enhanced view of one of the twenty surface pores is shown, presenting the coordination style of acrylate ligands at the inner surface. A simplified scheme of the overall ligand exchange process from {Mo ₁₃₂ (OAc) ₃₀ } to the formation of 1–8, followed past the uptake of thiol guest species, is presented. Finally, the ligands used for the synthesis of i–viii are shown, with labelled proton groups, as used for data analysis herein; Fifty = acrylic acid, 1; crotonic acid, 2; methacrylic acrid, 3; tiglic acrid, iv; 3-butenoic acid, 5; 4-pentenoic acid, 6; 5-hexenoic acid, vii; and sorbic acid, 8. Atom central: Mo; blueish, O; red, C; yellowish, and H; grey.

Coordination of upwards to 30 ligands allows for the targeted pattern of the internal surface character. For case, the introduction of butyrate ions results in a hydrophobic internal surface, in contrast to the hydrophilic grapheme expressed by the sulphate-containing structure.¹¹ Compounds with the inorganic super-fullerene structure can be produced by either straight syntheses, from molybdate salts, or via the exchange of ligands present on a precursor Keplerate cluster with new donors. The ligand commutation process is facilitated by the porous nature of the framework with the apertures lending these structures sieve-like backdrop, preventing coordination of bulky ligands on the inner surface of the spheres.¹²

In dissimilarity to the wide range of hydrophilic-ate ligands utilized in Keplerate synthesis, only a handful of, exclusively aliphatic, hydrophobic carboxylate-containing ligands have been incorporated into {Mo ₁₃₂ }. Nosotros sought to coordinate hydrophobic π-systems, provided by alkene ligands, resulting in an electron-rich inner surface. Ligands were selected containing coordinating carboxylic acid groups forth with alkene functionality with varied olefin regioisomers and alkyl tail length. Using straight and ligand exchange approaches we have thus synthesized, alkene-coordinated structures, 1–viii {(NH ₄ ) ₄₂ [Mo ₁₃₂ O ₃₇₂ (L) ₃₀ (H _ii O) ₇₂ ]} (L = (1) acrylic acid, (2) crotonic acid, (iii) methacrylic acrid, (4) tiglic acid, (5) 3-butenoic acrid, (6) four-pentenoic acid, (vii) 5-hexenoic acid, and (viii) sorbic acid), which offer new internal surface properties and are utilised to homogeneously encapsulate and stabilise brusque chain thiols, preventing their evaporation in an aqueous environment.

Results and discussion

Synthetic strategy

Ii approaches for the synthesis of one–8 were employed here: direct and ligand exchange syntheses. Firstly, 1 was obtained via a direct synthesis arroyo where the final product is synthesised from readily available starting materials. Adapting the long-established procedure for the straight synthesis of {Mo ₁₃₂ (OAc) ₃₀ }^{half dozen} by replacing the acetate-containing reagents (acetic acid and ammonium acetate) with ammonia solution and an excess of acrylic acrid, the ammonium common salt of 1 was obtained. 1 could besides be obtained by ligand-exchange syntheses from a pre-assembled {Mo ₁₃₂ } complex, such equally {Mo ₁₃₂ (OAc) ₃₀ } or {Mo ₁₃₂ (SO _four ) ₃₀ }. Use of the {Mo ₁₃₂ (OAc) _xxx } or {Mo ₁₃₂ (SO ₄ ) ₃₀ } precursors resulted in faster, higher-yielding product formation (4 days) than in the direct synthesis (7 days), while the {Mo ₁₃₂ (SO ₄ ) ₃₀ } ligand exchange method produced crystals of the greatest quality for XRD study. Ligand commutation from {Mo ₁₃₂ (So ₄ ) _xxx } produced a further seven alkenyl-{Mo ₁₃₂ } products, two–8, which were non isolable via straight methods.

Structural assay

The directly synthesised single crystal 10-ray construction of 1 (Fig. 2a), exhibits an R [3 with combining macron] space group and confirms the expected presence of the spherical {Mo ₁₃₂ } framework. Additionally, 30 acrylate ligands are coordinated at the {Mo ₂ } linkers, with their tails facing towards the core of the Keplerate. The electron density map of one (Fig. 2b) highlights that the distribution of electron density of the ligand tails between two positions, due to rotation, is approximately equal. The ligand tails create an internal cavity which is approximately 12 Å in diameter, with an overall book of approximately 905 Å ⁱⁱⁱ . The internal cavities are not unoccupied, every bit indicated past the observed remainder electron density peaks; however, this cannot be definitively refined every bit specific counterions or solvent molecules.


	Fig. two (a) Combined ball-and-stick and space-filling model of ane, (b) second electron density map of 1, (c) combined ball-and-stick and infinite-filling model of two, and (d) 2D electron density map of 2. For (a) and (c) 1 pentagonal and 5 associated {Mo _two } linker-blazon units have been removed for simplicity. The green sphere highlights the inner cavities of 1 and two. The electron density maps testify the approximately even distribution between the two positions of the ligand tails, equally highlighted by the light-green/ruddy bonds shown in the insets. For two, there is a clear distinction between the ligand tail positions and the remaining unassigned electron density of the internal crenel. The region of low electron density between the ligand tails and internal cavity in ii is partially highlighted by the dark ruby-red box in (d) and represents a hydrophobic region inside the cavity with reduced water molecule occupancy. Cantlet fundamental: Mo; blue, O; red, C; yellow, and H; greyness.

Full structural analysis of two and 5 confirmed that the {Mo ₁₃₂ } framework is retained upon the ligand commutation synthesis. Coordinated alkene ligands, crotonic acid (two) and 3-butenoic acid (five) are constitute at the {Mo ₂ } linker-type positions. The ligand tails hang towards the middle of the structures, resulting in hydrophobic inner cavities of approximately 10 Å diameter, with a volume of approximately 523 Å ³ (Fig. 2c). The cavity volumes for both are significantly lower than that for one due to the longer concatenation length of the ligands used here. For 2 and 5, there is a distinct area of low electron density betwixt the positions of the ligand tails and the electron density of the central crenel, caused by electrostatic interactions between the terminal protons of the ligand tails and the solvent water molecules (Fig. 2d and S28†). The shorter length of the ligands in 1 in comparing to those coordinated in 2 and 5 (approximately 4.four Å vs. 5.5 Å) and the subsequently lower clustering of ligand tails towards the center of the cavity reduces this region of low electron density in the acrylate-coordinated structure.

For the remaining structures, the {Mo ₁₃₂ } framework was initially confirmed using Ten-ray diffraction past comparison of the unit cell dimensions of the single crystals. The UV-Vis spectra for all structures contained a wide peak with λ _max at approximately 450 nm, due to the presence of reduced Mo ⁵ centers, as expected for {Mo ₁₃₂ } structures (Fig. S3†). For 2–8, IR spectroscopy was utilized to confirm the complete replacement of sulphate ligands by the alkene ligands had occurred, with the absence of the typical triplet pattern, due to the splitting of the ν _iii stretching mode of coordinated sulphate ligands, betwixt 1040–1200 cm ^−one (Fig. S2†). The observations established in XRD and IR studies are farther facilitated past elemental analyses (Table S2†) and NMR spectroscopy solution studies, every bit will be discussed herein.

NMR solution studies

Solutions of ane–8 in D ₂ O (5 mM) were prepared for NMR study. For 1–8, the data obtained from these measurements follows a like full general trend therefore, to simplify the presentation of results, but the NMR data for v will be discussed in detail here, as information technology produced clear and well-defined peaks in the resulting spectra. Extensive data and analyses for the remaining structures is presented in the ESI.†¹³

Measurements were carried out by dissolving crystalline samples of 1–8 in D ₂ O, withal, culling approaches can exist applied with amorphous material which gives broadly similar results. For example, using {Mo ₁₃₂ (SO ₄ ) ₃₀ }, which is ¹ H and ^thirteen C silent, we tin can directly discover the result of ligand coordination by addition of the advisable alkene to the solution. The primary divergence in using this approach is that the number of coordinated ligands is lower here than using pure product crystals, due to the lower number of ligands added overall. The {Mo ₁₃₂ (OAc) ₃₀ } structure tin also be used in this way; however, the presence of NMR agile nuclei can obscure analyses.

The porous nature of the {Mo ₁₃₂ } construction facilitates partial ligand exchange with the solvent arrangement (D _ii O), providing the ligands are sufficiently labile, upon crystal dissolution. The resulting solution therefore is expected to contain signals representing coordinated ligands and resonances for gratuitous ligand species. Critically, encapsulation in the negatively charged and electron dense {Mo ₁₃₂ } construction leads to a separation of these peaks for a single ligand species which exists in two singled-out domains.^fourteen,15 In this regard, the ¹ H NMR of five (Fig. three), contains three small precipitous resonances for the free iii-butenoic acid ligand: CH ₂ (i) δ 3.2 ppm, CH ₂ (β,γ) δ 5.3 ppm, and CH(α) δ half dozen.0 ppm, and 3 corresponding broad peaks for the coordinated 3-butenoic acid ligands: CH ₃ (i′) δ 1.9 ppm, CH ₂ (β′,γ′) δ three.7 ppm, and CH(α′) δ 4.9 ppm, representing upfield peak shifts of Δδ −one.9 ppm, −1.vi ppm and −1.i ppm, respectively. The simultaneous presence of two sets of distinct peaks indicates that the commutation process is dull on the NMR timescale, with fast exchange regimes expected to result in a single peak set. Boosted peaks at δ 4.viii ppm and δ vii.4 ppm arise from solvent water and NH _iv ⁺ cation species, respectively.


	Fig. three (a) ^ane H NMR spectrum of 5, overlaid on the ⁱ H DOSY NMR spectrum of v (units for diffusion coefficient, D: ×10 ^−nine m ² s ⁻¹ ). The ruddy box (marked 1.) highlights the diffusion coefficient of the encapsulated 3-butenoic acid ligands whilst the blue box (marked ii.) highlights those signals arising from the solvated free ligands. (b) ^thirteen C DEPTQ NMR spectrum of 5 for unambiguity in the assignment of carbon and proton nuclei for all ligands, a unlike labelling convention has been used for the carbon nuclei.

Farther NMR studies were utilised to validate the above observations. ¹³ C NMR measurements of 5 (Fig. S31e†) followed a similar trend to the ^ane H NMR measurements. The carbon nuclei have been assigned sequentially, I–IV for five, from the carboxylate carbon, to differentiate the discussion of these nuclei from the proton assignments. Precipitous peaks assigned to the carbon nuclei of the free, solvated ligands are observed at δ 179 ppm [–COO ⁻ (I)], δ 130 ppm [–CH(3)], δ 118 ppm [–CH ₂ (IV)], and δ 41 ppm [–CH ₂ (II)]. Broad peaks are also observed at the aforementioned positions as the abrupt peaks, attributed to the coordination of the ligands within the {Mo ₁₃₂ } structure, see Fig. S31e† for expanded spectra. Diffusion-Ordered Spectroscopy (DOSY) NMR has been employed to constitute diffusion coefficients of the ligand species, which are inversely related to molecular size. The spectrum for v confirmed the presence of two distinct signals originating from free and encapsulated species, equally shown in Fig. 3a. The wide peaks possess diffusion coefficients in the range of 110–115 pm ² s ⁻¹ , whereas the free solvated ligand peaks, have higher diffusion coefficients in the range of 700–740 pm ² s ⁻¹ due to the sometime's coordination to the very large {Mo ₁₃₂ } framework. The diffusion coefficients of the broad peaks chronicle to a hydrodynamic radius of ∼22 Å, which is consistent with the inner cavity of {Mo ₁₃₂ } which has a crystallographic outer bore of (∼32 Å) and with previously reported values,¹⁶ indicating that these peaks originate from internally bound ligands, while a big departure in the two diffusion coefficients obtained point 2 distinct domains for the ligands – coordinated inside the framework and costless, solvated pocket-size molecules outside the Keplerate sphere.

Thiol uptake studies

The encapsulation of guest species within a suitable host provides a potential environment to protect against mechanical stress, temperature changes, reduction and oxidation. The use of porous materials to encapsulate guest species has been applied to diverse host classes such as extended arrays (MOFs,¹⁷ zeolites^eighteen), mesoporous materials,¹⁹ porous liquids,²⁰ and organic materials.^21–23 Whilst organic systems are unremarkably studied using solution land methods, for inorganic hosts, heterogenous mixtures are more widely used to course the host–invitee complex, with production analyses typically performed on the resulting solid fabric. Previous studies have utilised {Mo ₁₃₂ } frameworks, with alternative ligands, as hosts, for example to uptake alcohols using {Mo ₁₃₂ } decorated with propionate ligands.⁴ Here, nosotros sought to use the {Mo ₁₃₂ } alkene-containing structures to promote the homogeneous uptake of volatile organic species from aqueous solution, resulting in a stable host–guest circuitous which protects confronting guest evaporation at elevated temperatures.

Short-concatenation alkyl thiols (R–SH), are volatile species which are structurally analogous to alcohols, with –SH replacing the hydroxyl grouping. The large size of the sulfur atom makes it more polarizable than oxygen, while the reduced electronegativity of sulphur results in weaker hydrogen and intermolecular bonding, compared to the coordinating alcohols, equally reflected in the lower boiling points of the thiol species. Alkyl thiols are also of interest for their potential to undergo thiol-ene type reactions with the alkene functional grouping of the coordinated ligand species.²⁴ To explore the uptake of alkyl thiols, we utilized alkenyl appended Keplerates 1–8 to facilitate the uptake of a series of alkyl thiols from aqueous solutions. For all measurements, solutions of {Mo ₁₃₂ (SO _four ) ₃₀ } in D ₂ O (5 mM) were prepared in NMR tubes, followed by addition of excess ligand and invitee. Observations will be described in item for NMR interpretation using the 3-butenoic acrid ligand, as described for 5 above, although comparison studies betoken the trends observed are applicable to all ligands used in 1–viii.

Two sets of alkyl thiol isomers, with maximum chain lengths of 3–4 carbons were selected as guests to monitor their interaction with the {Mo ₁₃₂ } host. Propanethiol and butanethiol differ only by their carbon chains and their branched isomers were selected to monitor whatsoever structural effects on uptake capacities. Explicitly, the isomers used in this written report are ane-propanethiol (A), 2-propanethiol (B), 1-butanethiol (C), ii-butanethiol (D), 2-methyl-1-propanethiol (E), and 2-methyl-2-propanethiol (F). For brevity we will focus on invitee C as the benchmark for these studies.

Initially, 60 equivalents of the thiol guests were added to a solution of {Mo ₁₃₂ (SO _four ) ₃₀ } containing alkene ligands (too 60 equivalents) in D ₂ O, at room temperature. Add-on of the thiol species under these weather condition resulted in their immediate uptake, as indicated by the presence of broadened peaks appearing betwixt δ −0.6 ppm and 0.0 ppm, displacing internal solvent molecules, in improver to solvated thiol peaks (δ 0.9–1.6 ppm) (Fig. 4). To confirm that the origin of the broad peaks is from the encapsulation of the thiol species, additional NMR experiments were performed which could exist interpreted in a similar manner to those which were used for the previously described structural characterizations, namely ¹³ C, DEPTQ, HSQC, and DOSY spectra (Fig. S56, S57 and S59†).


	Fig. iv Comparison of {Mo ₁₃₂ (So ₄ ) _thirty } with added 3-butenoic acid ligands and one-butanethiol guests (C) prior to and mail service heating to lxx °C for 6 and 60 h. The peaks associated with the solvated ane-butanethiol guest (blue box) significantly reduce subsequently six h until no indicate is observed afterwards 60 h. In contrast, the resonances arising from encapsulated i-butanethiol (red box) remain largely unchanged after the same period.

Analysis of the extent of encapsulation could exist adamant by utilise of a methanesulfonic acrid external reference (Table S6†). The data obtained indicates that the extent of encapsulation is dominated past steric crowding of the key cavity of {Mo ₁₃₂ }, with longer ligand alkyl tails resulting in decreased uptake of the thiol guests. Additionally, the bulkier 2-methyl-2-propanethiol species (F) is broadly prevented from entering the inner crenel due to its large size in comparing to the {Mo ₁₃₂ } pore, which restricts internal access. To confirm that the addition of the thiol guests does not result in thiol oxidation and replacement of the previously coordinated alkene ligands, a comparing of the peak intensities for the alkene ligands prior to and following the improver of thiol guest was carried out. Fig. S58† shows that there is no pregnant decrease in the integral of the encapsulated alkene ligands or increase in the peak height for the solvated alkene ligands, as would be anticipated upon their replacement, indicating that the thiol species are independent within the fundamental cavity of the {Mo ₁₃₂ } structure.

Previous analogous encapsulation studies have utilised elevated temperatures to promote increased guest encapsulation and a similar investigation was applied hither.²⁵ Upon heating samples to 70 °C, during NMR analysis, an increment in the ratio of the encapsulated thiol species was coupled with a corresponding increase in the ratio of the free thiol species, with these initial changes attributed to the improved solubilities of the thiol species at elevated temperature. Continuous heating of the sample at 70 °C leads to a pregnant decrease in the peak intensity of the signals attributed to the complimentary thiol species afterwards a period of 6 h with well-nigh no free thiol remaining after a period of heating of lx h (Fig. 4). This behavior is reflected in the ⁱ H and ¹³ C NMR spectra of guest C in D ₂ O (Fig. S60a–f and S61†), with no additional peaks, representing side-products, being observed in whatsoever spectra. Similar measurements carried out using a J-Young'southward tap NMR tube led to no pregnant change in the observed meridian heights even subsequently twoscore h at elevated temperature, with subsequent heating of the sample for 20 h without a cap resulting in a loss of most of the NMR bespeak (Fig. S63†). These results signal that heating of the 1-butanethiol in D _ii O results in the loss of the species by evaporation.

The changes observed for the complimentary solvated thiol species are not reflected in the peak intensities of the signals attributed to the encapsulated species, even after elevating the temperature to 95 °C for sixty min (Fig. S64†). This is confirmed using HSQC before and after heating, with simply the loss of signals related to the free thiol species observed (Fig. S62†). This indicates that the clustering of the thiol species within the {Mo ₁₃₂ } cavity structure results in effective thermal insulation, preventing evaporation of fifty-fifty the most volatile encapsulated thiol species (E, b.p. = 70 °C) from occurring. Additionally, the initially established equilibrium, with free thiol and encapsulated thiol co-existing, is non re-established after heating due to the preferential clustering of the hydrophobic thiol species within the hydrophobic cavity.

Comparison of uptake in the organization described above with simply {Mo ₁₃₂ (SO _iv ) ₃₀ }, and {Mo ₁₃₂ (And so ₄ ) ₃₀ } + 60 acetate ligands, was performed. The resulting NMR spectra showed no uptake of any of the thiol species (Fig. S52c and d† for guest C), with peaks present for the free thiol guests just, except for minimal uptake of B and D with added acetate ligands. Upon increasing the number of equivalents of acetate added, from 60 to ninety and 120 equivalents, broadened peaks were observed, as described with alkene ligands, with reduced peak intensity here. By measuring the number of coordinated alkene or acetate ligands in each scenario, an understanding of this behavior tin can be derived. With threescore equivalents of ligand added, for iii-butenoic acrid, the number of coordinated ligands is approximately 26 (with 34 solvated free ligands), while, for acetate, the number of coordinated ligands is approximately 13 (with 50 solvated free ligands). Increasing the number of equivalents of acetate added results in xv coordinated ligands with 90 equivalents and 16 coordinated ligands with 120 equivalents added (Tabular array 1). Therefore, the inner surface of {Mo ₁₃₂ } with added alkene ligands is decorated with a much higher number of ligands than for the same conditions with acetate, resulting in a cavity surface with increased hydrophobicity, due to the hydrophobic alkyl/alkene tails. This hydrophobic grapheme enables the encapsulation of the primarily hydrophobic thiol guests at comparably lower concentrations of alkene in comparison to the acetate ligands. This encapsulation behaviour is not observed at all with just the hydrophilic {Mo ₁₃₂ (SO _four ) ₃₀ } structure, with no added hydrophobic components (acetate ligands or the ligands used for one–viii), (Fig. S52c†) due to the hydrophilic nature of the internal crenel promoted by the coordinated sulphate ligands, further confirming the role of the hydrophobic interaction in facilitating uptake.

Tabular array i Comparison of the extent of ligand coordination with 60, 90, and 120 equivalents of either acetate or iii-butenoic acrid ligands added. The resonances attributed to encapsulated i-butanethiol (C) are highlighted by the carmine boxes

Conclusions and future work

Keplerate POMs, based on the {Mo ₁₃₂ } framework, have been appended with alkenyl carboxylate ligands, through ligand exchange from {Mo ₁₃₂ (SO ₄ ) ₃₀ } creating an electron rich hydrophobic cavity measuring up to 12 Å in diameter. X-ray and NMR studies have demonstrated that alkenyl carboxylate uptake is higher than for acetate ligands creating a more than hydrophobic crenel than previously observed. Brusk concatenation alkyl thiol uptake within the Keplerate cavity in aqueous media was demonstrated by NMR studies and shown to provide boosted thermal insulation to the guest thiols, potentially allowing for novel higher temperature reactivity in hereafter work.

Conflicts of interest

The authors declare no competing financial interests.

Acknowledgements

This work was supported by the EPSRC grants (No. EP/J015156/1; EP/L023652/1; EP/I033459/1; EP/K023004/1), LC thank you the ERC for an Advanced Grant (ERC-ADG, 670467 SMART-POM). We thank the Diamond Light Source for time on Beamline I19, under the proposal MT18953. Nosotros would similar to give thanks Dr Nancy Watfa for aid with the NMR.

Notes and references

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