Variable-temperature 31P Research Articles

Interionic bonding in aqueous phosphonium ionic liquid solutions exhibiting LCST behavior with high phase separation temperatures

Phosphonium-derived ionic liquids have emerged as a powerful class of thermoresponsive materials with sought after Lower Critical Solution Temperature (LCST) phase separation with applications across a broad range of fields. Herein, we report the spectroscopic examination of phosphonium salts bearing the general structure [X][P444n] wherein systematic structural variations were designed to gain a fundamental understanding behind the impact of alkyl chain length, anion size, and effective nuclear charge on their temperature-dependent phase separation behavior. Using variable temperature 1H, 31P, and 19F NMR, the bonding changes which drive LCST phase separation for the assembled thermoresponsive ILs were elucidated. For the first time, spectroscopic evidence revealed a delicate balance between the interdependence of alkyl chain length and anion size on phase separation that formed the basis of new LCST design principles.

Charge storage performance of a structurally flexible hybrid ionic liquid electrolyte

AbstractThe electrochemical and charge storage performance of a fluorine‐free structurally flexible hybrid pyrrolidinium‐based ionic liquid electrolyte (HILE) in a symmetric graphite‐based supercapacitor is thoroughly investigated. The HILE revealed thermal decomposition at above 230°C, a glass transition (Tg) temperature of below −70°C, and ionic conductivity of 0.16 mS cm−1 at 30°C. The chemical and electrochemical properties are investigated using a systematic variable temperature 1H and 31P NMR spectroscopy and diffusometry, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge‐discharge (GCD). The supercapacitor demonstrated a notable specific capacitance of 186 F g−1 at a scan rate of 1 mV s−1 and a specific capacitance of 122 F g−1 at a current density of 0.5 A g−1. The maximum energy density of 48.8 Wh kg−1, a power density of 450 W kg−1 at a current density of 0.5 A g−1, and a potential window of 4 V were obtained. Altogether, this study demonstrates that the new HILE can be used in symmetric graphite‐based supercapacitors over a wide potential window of 4 V and a temperature range from −20°C to 90°C.

Characterization of nanodisc-forming peptides for membrane protein studies

Lipid-bilayer nanodiscs provide a stable, native-like membrane environment for the functional and structural studies of membrane proteins and other membrane-binding molecules. Peptide-based nanodiscs having unique properties are developed for membrane protein studies and other biological applications. While the self-assembly process rendering the formation of peptide-nanodiscs is attractive, it is important to understand the stability and suitability of these nanodisc systems for membrane protein studies. In this study, we investigated the nanodiscs formation by the anti-inflammatory and tumor-suppressing peptide AEM28. AEM28 is a chimeric peptide containing a cationic-rich heparan sulfate proteoglycan- (HSPG)-binding domain from human apolipoprotein E (hapoE) (141–150) followed by the 18A peptide’s amino acid sequence. AEM28-based nanodiscs made with different types of lipids were characterized using various biophysical techniques and compared with the nanodiscs formed using 2F or 4F peptides. Variable temperature dynamic light-scattering and 31P NMR experiments indicated the fusion and size heterogeneity of nanodiscs at high temperatures. The suitability of AEM28 and Ac-18A-NH2- (2F-) based nanodiscs for studying membrane proteins is demonstrated by reconstituting and characterizing a drug-metabolizing enzyme, cytochrome-P450 (CYP450), or the redox complex CYP450-CYP450 reductase. AEM28 and 2F were also tested for their efficacies in solubilizing E. coli membranes to understand the possibility of using them for detergent-free membrane protein isolation. Our experimental results suggest that AEM28 nanodiscs are suitable for studying membrane proteins with a net positive charge, whereas 2F-based nanodiscs are compatible with any membrane proteins and their complexes irrespective of their charge. Furthermore, both peptides solubilized E. coli cell membranes, indicating their use in membrane protein isolation and other applications related to membrane solubilization.

Observation and Stereochemistry of Betaine Intermediates in the Reaction of Phosphonium Ylide Containing a Phosphaboratatriptycene Skeleton with Benzaldehyde.

Betaine intermediates, rather than the corresponding 1,2-oxaphosphetanes, were observed in the reaction of the phosphonium ylide containing a phosphaboratatriptycene skeleton with PhCHO in THF. Their chemical shifts were -4.56, -4.92, -7.32, and -11.1 ppm at -10 °C in variable temperature (VT) 31P{1H} NMR experiments. These signals were observed by the deprotonations of β-hydroxyalkylphosphonium salts with lithium hexamethyldisilazide (LiHMDS) and sodium hexamethyldisilazide (NaHMDS). Their signals were assigned to betaine lithium complexes and salt-free betaines, respectively. The betaine lithium complexes were thermodynamically stable even at 25 °C and were converted to β-hydroxyalkylphosphonium salts by protonation, whereas the salt-free betaines were unstable, providing the corresponding ethylphosphonium salt and PhCHO at 0 °C, instead of olefins and phosphine oxide. The potential structures of the betaine lithium complexes and salt-free betaines were investigated by optimizing the expected stereoisomers and estimating the phosphorus chemical shifts by density functional theory (DFT) calculations. The results indicated that the erythro-syn- and threo-syn-betaines were more stable than their anti-forms. Erythro-syn-betaines were the most thermodynamically stable among the expected stereoisomers in both lithium complexes and salt-free betaines. The estimated phosphorus-31 signals were in good agreement with those experimental values.

Spontaneous Decomposition of an Extraordinarily Twisted and Trans-Bent Fully-Phosphanyl-Substituted Digermene to an Unusual GeI Cluster.

Ditetrelenes R2 E=ER2 (E=Si, Ge, Sn, Pb) substituted by multiple N/P/O/S-donor groups are extremely rare due to their propensity to disaggregate into their tetrylene monomers R2 E. We report the synthesis of the first fully phosphanyl-substituted digermene {(Mes)2 P}2 Ge=Ge{P(Mes)2 }2 (3, Mes=2,4,6-Me3 C6 H2 ), which adopts a highly unusual structure in the solid state, that is both strongly trans-bent and highly twisted. Variable-temperature 31 P{1 H} NMR spectroscopy suggests that 3 persists in solution, but is subject to a dynamic equilibrium between two conformations, which have different geometries about the Ge=Ge bond (twisted/non-twisted) due to a difference in the nature of their π-stacking interactions. Compound 3 undergoes unprecedented, spontaneous decomposition in solution to give a unique GeI cluster {(Mes)2 P}4 Ge4 ⋅5 CyMe (7).

Rhodium disulfur and dioxygen complexes: examination of boron secondary coordination sphere effects

A series of diphosphine-ligated rhodium(III) η 2-peroxo and -persulfido compounds are targeted with one subset containing a boron-rich secondary coordination sphere (SCS). A systematic investigation using both experimental and theoretical methods has been performed to assess whether peripheral boranes can be used to engage with rhodium(III)-bound chalcogenides. For the model compound, [RhI(dnppe)2]BPh4 (dnppe = 1,2-bis(di-n-propylphosphino)ethane), adducts of the form [RhI(dnppe)2(η 2-Ch2)]BPh4 (Ch = O or S) were characterized. For the octaboranyl compound, [RhI(P2BCy 4)2]BPh4 (P2BCy 4 = 1,2-bis(di(3-dicyclohexylboranyl)propylphosphino)ethane), however, treatment with O2 resulted in SCS decomposition via B–O bond formation, while reaction with 0.25 equivs. S8 provided [RhI(P2BCy 4)2(η 2-S2)]BPh4, which, based on variable-temperature 31P NMR spectroscopic measurements, does not exhibit a B–S interaction. Using a compound with a single pendant borane as a model, potential energy surface (PES) scans suggest kinetic and thermodynamic feasibility of a B–O interaction with ΔG(B–O) = −2.5 kcal mol−1; a stationary point for the related B–S system was not located.

Observation of intermediates in reaction of non-stabilized phosphonium ylide containing phosphaboratatriptycene skeleton with PhCHO

The signals of intermediates in the reaction of non-stabilized phosphonium ylide containing a phosphaboratatriptycene skeleton with PhCHO were observed as broad singlets at around −4.56 ∼ −5.77 ppm between −50 °C and −10 °C by variable temperature (VT) 31P{1H} NMR spectroscopy. The signals assignable to the same intermediates were also observed from −90 °C to −10 °C in the deprotonation of the diastereomeric mixture of β-hydroxyalkylphosphonium salts containing a phosphaboratatriptycene skeleton with TMS2NNa by VT-31P{1H} NMR spectroscopy. The results strongly suggested that the observed phosphorus signals were not assigned to 1,2-oxaphosphetanes but betaine intermediates because the signals due to 1,2-oxaphosphetanes containing phosphaheteratriptycene skeletons with Group 14 and 15 elements were observed around −55.7 ∼ −82.8 ppm except for Bi.

Fluxionality in the Tropolone Hinokitiol Chelate.

Tropolonate complexes of Ru(II), Ru(III), and Os(II) with hinokitiol, also termed β-thuljaplicin, or 4-isopropyltropolone, readily formed by chloride and triarylphosphine substitution in RuCl2(PPh3)3 and MHCl(CO)(PR3)3 (M = Ru, R = Ph; M = Os, R = Ph and p-tolyl). The resulting colorful complexes have variable and strong charge transfer bands and also have a surprising combination of stereochemical selectivity and lability. For the Os(II) d6 examples, the tropolone chelate has a fluxionality with a barrier of only 90 kJ/mol for the R = aryl examples, as determined by variable-temperature 31P NMR. Chlorination with N-chlorosuccinimide results in MCl(CO)(hino)(PPh3)2 (M = Ru and Os). Together these results quantify the fluxionality of this important chelate which in turn has consequences for its biochemistry.

Di(hydroperoxy)cycloalkane Adducts of Triarylphosphine Oxides: A Comprehensive Study Including Solid-State Structures and Association in Solution.

Four new di(hydroperoxy)cycloalkane adducts (Ahn adducts) of p-Tol3PO (1) and o-Tol3PO (2), namely, p-Tol3PO·(HOO)2C(CH2)5 (3), o-Tol3PO·(HOO)2C(CH2)5 (4), p-Tol3PO·(HOO)2C(CH2)6 (5), and o-Tol3PO·(HOO)2C(CH2)6 (6), have been synthesized and fully characterized. Their single crystal X-ray structures have been determined and analyzed. The 31P NMR data are in accordance with hydrogen bonding of the di(hydroperoxy)alkanes to the P═O groups of the phosphine oxides. Due to their high solubility in organic solvents, natural abundance 17O NMR spectra of 1-6 could be recorded, providing the signals for the P═O groups and additionally the two different oxygen nuclei in the O-OH groups in the adducts 3-6. The association and mobility of 3-6 were explored by 1H DOSY (diffusion ordered spectroscopy) NMR, which indicated persistent hydrogen bonding of the adducts in solution. Competition experiments with phosphine oxides allowed ranking of the affinities of the di(hydroperoxy)cycloalkanes for the different phosphine oxide carriers. On the basis of variable temperature 31P NMR investigations, the Gibbs energies of activation ΔG‡ for the adduct dissociation processes of 3-6 at different temperatures, as well as the enthalpy ΔH‡ and entropy ΔS‡ of activation, have been determined. IR spectroscopy of 3-6 corroborated the hydrogen bonding, and in the Raman spectra, the ν(O-O) stretching bands have been identified, confirming the presence of peroxy groups in the solid materials. The high solubilities in selected organic solvents have been quantified.

Application of NMR Crystallography to Highly Disordered Templated Materials: Extensive Local Structural Disorder in the Gallophosphate GaPO-34A.

We present an NMR crystallographic investigation of two as-made forms of the recently characterized gallophosphate GaPO-34A, which has an unusual framework composition with a Ga:P ratio of 7:6 and contains both hydroxide and fluoride anions and either 1-methylimidazolium or pyridinium as the structure-directing agent. We combine previously reported X-ray crystallographic data with solid-state NMR spectroscopy and periodic density functional theory (DFT) calculations to show that the structure contains at least three distinct types of disorder (occupational, compositional, and dynamic). The occupational disorder arises from the presence of six anion sites per unit cell, but a total occupancy of five of these, leading to full occupancy of four sites and partial occupancy of the fifth and sixth (which are related by symmetry). The mixture of OH and F present leads to compositional disorder on the occupied anion sites, although the occupancy of some sites by F is calculated to be energetically unfavorable and signals relating to F on these sites are not observed by NMR spectroscopy, confirming that the compositional disorder is not random. Finally, a combination of high-field 71Ga NMR spectroscopy and variable-temperature 13C and 31P NMR experiments shows that the structure directing agents are dynamic on the microsecond time scale, which can be supported by averaging the 31P chemical shifts calculated with the SDA in different orientations. This demonstrates the value of an NMR crystallographic approach, particularly in the case of highly disordered crystalline materials, where the growth of large single crystals for conventional structure determination may not be possible owing to the extent of disorder present.

Versatile coordinative abilities of perhalophenyl-gold(I) fragments to Xantphos: Influence on the emissive properties

Reaction of perhalophenylgold(I) complexes [AuR(tht)] (R = C6Cl2F3, C6Cl5; tht = tetrahydrothiophene) with different number of equivalents of Xantphos (4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene) leads to discrete complexes in which the metal atom displays very different coordination environments. Thus, the ionic complex [Au(Xantphos)2][Au(C6Cl2F3)2] (1) or the neutral [Au(C6Cl5)(Xantphos)] (2) one are obtained when a 1:1 (Au:Xantphos) stoichiometry is used. However, similar compounds [Au2R2(μ-Xantphos)] (R = C6Cl2F3 (3); C6Cl5 (4)) are synthesized when the amount of gold is increased to a 2:1 ratio. The use of diphosphine Xantphos, which can act as bridging, chelate or even as mono-dentate ligand, together with the use of different perhalophenyl groups bonded to the gold(I) centres, allows the synthesis of cationic tetracoordinate gold(I) fragments (1), mononuclear (2) or dinuclear (3–4) dicoordinated gold(I) complexes. This structural diversity in the coordination arrangements as well as the different aryl groups present in the molecules directly affect their photophysical properties, giving rise to different luminescent emission energies ranging from 470 to 580 nm, and also to a different origin for the electronic transitions related to them such as 3IL (3) to 3MLCT (4) and also a mixture of them 3MLCT/3IL (1 and 2). The experimental photophysical results obtained for these gold(I) complexes were supported by DFT and TD-DFT calculations. On the other hand, the behaviour of these complexes in solution is different, losing their emissive properties for all complexes or displaying the co-existence of different structural arrangements in the case of complexes 1 and 2, as observed through variable-temperature 31P{1H} NMR experiments.

Dynamics of Cation-Induced Conformational Changes in Nanometer-Sized Uranyl Peroxide Clusters.

Conformational changes of the pyrophosphate (Pp)-functionalized uranyl peroxide nanocluster [(UO2)24(O2)24(P2O7)12]48- ({U24Pp12}), dissolved as a Li/Na salt, can be induced by the titration of alkali cations into solution. The most symmetric conformer of the molecule has idealized octahedral (Oh) molecular symmetry. One-dimensional 31P NMR experiments provide direct evidence that both K+ and Rb+ ions trigger an Oh-to-D4h conformational change within {U24Pp12}. Variable-temperature 31P NMR experiments conducted on partially titrated {U24Pp12} systems show an effect on the rates; increased activation enthalpy and entropy for the D4h-to-Oh transition is observed in the presence of Rb+ compared to K+. Two-dimensional, exchange spectroscopy 31P NMR revealed that magnetization transfer links chemically unique Pp bridges that are present in the D4h conformation and that this magnetization transfer occurs via a conformational rearrangement mechanism as the bridges interconvert between two symmetries. The interconversion is triggered by the departure and reentry of K (or Rb) cations out of and into the cavity of the cluster. This rearrangement allows Pp bridges to interconvert without the need to break bonds. Cs ions exhibit unique interactions with {U24Pp12} clusters and cause only minor changes in the solution 31P NMR signatures, suggesting that Oh symmetry is conserved. Single-crystal X-ray diffraction measurements reveal that the mixed Li/Na/Cs salt adopts D2h molecular symmetry, implying that while solvated, this cluster is in equilibrium with a more symmetric form. These results highlight the unusually flexible nature of the actinide-based {U24Pp12} and its sensitivity to countercations in solution.

P-Ge/Sn π Interactions Versus Arene···Ge/Sn Contacts for the Stabilization of Diphosphatetrylenes, (R2P)2E (E = Ge, Sn).

The diphosphatetrylenes {(Dipp)(R')P}2E [R' = Mes, E = Ge (1Ge), Sn (1Sn); R' = CH(SiMe3)2, E = Sn (2Sn)] have been isolated and characterized by multinuclear and variable temperature NMR spectroscopy and X-ray crystallography [Dipp = 2,6-iPr2C6H3, Mes = 2,4,6-Me3C6H2]. All three compounds crystallize as discrete monomers with two pyramidal phosphorus centers. However, variable-temperature 31P{1H} NMR spectroscopy indicates that both 1Ge and 2Sn are subject to dynamic exchange between this form and a form containing one planar and one pyramidal phosphorus center in solution. In contrast, 1Sn retains two pyramidal phosphorus centers in solution and exhibits no evidence for exchange with a form containing a planar phosphorus center. The related compound [{(Me3Si)2CH}2P]2Sn (3Sn) was isolated in very low yield and was shown by X-ray crystallography to possess one planar and one pyramidal phosphorus center in the solid state. DFT calculations reveal that the conformations of 1Ge, 1Sn, and 2Sn observed in the solid state are significantly stabilized by the delocalization of electron density from the aromatic rings into the vacant p-orbital at the tetrel center. Thus, for diphosphatetrylenes possessing aromatic substituents at phosphorus, stabilization may be achieved by two competing mechanisms: (i) planarization of one phosphorus center and consequent delocalization of the phosphorus lone pair into the vacant tetrel p-orbital or (ii) pyramidalization of both phosphorus centers and delocalization of aromatic π-electron density into the tetrel p-orbital. For 3Sn, which lacks aromatic groups, only the former stabilization mechanism is possible.

Electrochemical, Spectroelectrochemical, and Structural Studies of Mono- and Diphosphorylated Zinc Porphyrins and Their Self-Assemblies.

Three series of porphyrins containing a Zn(II) central metal ion and zero, one, or two phosphoryl groups at the meso-positions of the macrocycle were characterized as to their electrochemical, spectroscopic, and structural properties in nonaqueous media. The investigated compounds are represented as 5,15-bis(4'-R-phenyl)porphyrinatozinc, 10-(diethoxyphosphoryl)-5,15-bis(4'-R-phenyl)porphyrinatozinc, and 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-R-phenyl)porphyrinatozinc, where R = OMe, Me, H, or CN. Linear-free energy relationships are observed between the measured redox potentials at room temperature and the electronic nature of the substituents at the 5 and 15 meso-phenyl groups of the macrocycle. The mono- and bis-phosphoryl derivatives with two p-cyanophenyl substituents provide electrochemical evidence for aggregation at low temperature, a greater degree of aggregation being observed in the case of 5,15-bis(diethoxyphosphoryl)-10,20-bis(4'-cyanophenyl)porphyrinatozinc(II). This compound was characterized in further detail by variable-temperature 1H and 31P{1H} NMR spectroscopy in solution combined with single crystal X-ray analysis in the solid state. The data obtained from these measurements indicate that this porphyrin has a dimeric structure in CDCl3 at 223-323 K but forms a 2D polymeric network when it is crystallized from a CHCl3/MeOH mixture.

Softening the Donor-Set: From [Cu(P^P)(N^N)][PF6] to [Cu(P^P)(N^S)][PF6

We report the synthesis and characterization of [Cu(P^P)(N^S)][PF6] complexes with P^P = bis(2-(diphenylphosphino)phenyl) ether (POP) or 4,5-bis(diphenylphosphino)-9,9- dimethylxanthene (xantphos) and N^S = 2-(iso-propylthio)pyridine (iPrSpy) or 2-(tert-butylthio)pyridine (tBuSpy). The single crystal structures of [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] have been determined and confirm a distorted tetrahedral copper(I) centre and chelating P^P and N^S ligands in each complex. Variable temperature (VT) 1H and 31P{1H} NMR spectroscopy reveals dynamic behavior with motion of the POP backbone in [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] frozen out at 238 K. VT NMR spectroscopic data including EXSY peaks in the ROESY spectrum of [Cu(xantphos)(tBuSPy)][PF6] at 198 K reveal that two conformers exist in an approximate ratio of 5:1. Replacing bpy by the N^S ligands shifts the Cu+/Cu2+ oxidation to a higher potential. The copper(I) compounds are weak emitters in the solid state with PLQY values of <2%. These values are similar to those for [Cu(POP)(bpy)][PF6] and [Cu(xantphos)(bpy)][PF6] in the solid state.

Influence of Chain Length on the Structures and Dynamic Behavior of Alkyl-Tethered α,ω-Diphosphide Complexes of Lithium and Their Use in the Synthesis of P-Heterocyclic Stannylenes.

The alkyl-tethered α,ω-diphosphines (Dipp)PH(CH2) nPH(Dipp) ( n = 1 (3H), 2 (4H), 3 (5H), 4 (6H), and 5 (7H)) were prepared in good yield and characterized by multinuclear NMR spectroscopy [Dipp = 2,6- iPr2C6H3]. Treatment of 3H with 2 equiv of nBuLi and 2 equiv of TMEDA gives the diphosphide complex [CH2{P(Dipp)}2]Li2(TMEDA)2 (3Lia), which crystallizes as discrete monomers which do not exhibit temperature-dependent NMR behavior. Treatment of 4H-7H with 2 equiv of nBuLi in THF gives the diphosphides [[CH2{P(Dipp)}]2]2Li4(THF)2(OEt2)2 (4Li), [CH2{CH2P(Dipp)}2]Li2(THF)4 (5Li), [{CH2CH2P(Dipp)}2]Li2(THF)6 (6Li), and [CH2{CH2CH2P(Dipp)}2]2Li4(THF)6·PhMe (7Li) after crystallization. Compounds 4Li-7Li adopt either monomeric or dimeric structures in the solid state, depending on the length of the alkyl tether of the diphosphide ligand. In solution, compounds 4Li-7Li exhibit dynamic behavior: variable-temperature 31P{1H} and 7Li NMR spectroscopic studies indicate that this involves equilibria between monomeric and dimeric or higher oligomeric species with the nature of the equilibrium again depending on the length of the alkyl tether of the diphosphide ligand. The reactions between 3Li, 6Li, or 7Li and SnCl2 in THF give mixtures of products which could not be separated. In contrast, the reactions between 4Li or 5Li and 1 equiv of SnCl2 give the dimeric P-heterocyclic stannylenes [{CH2P(Dipp)}2Sn]2 (4Sn) and [CH2{CH2P(Dipp)}2Sn]2.1/2THF (5Sn), respectively. While compound 5Sn is isolated exclusively as the cis isomer, 4Sn is isolated as a mixture of cis and trans isomers in an approximate 5:1 ratio. The solid-state structures of trans-4Sn and cis-5Sn were obtained, and multinuclear NMR spectroscopy indicates that the dimeric structures of these compounds are maintained in solution. Compounds 4Sn and 5Sn represent the first P-heterocyclic stannylene dimers to be structurally characterized.

Unexpected effects of inorganic phosphate glass on crystallization and thermo-rheological behavior of polyethylene terephthalate

The effects of ultra-low glass transition temperature (Tg) phosphate glass (Pglass) on the thermal, morphological, rheological, mechanical, and crystallization properties of hybrid Pglass/poly(eththylene terephthalate)(PET) were investigated. Nano- and micro-scale distribution of the Pglass in the PET polymer matrix was observed. The polydispersed Pglass in the PET matrix functioned as a nucleation agent, resulting in increasing crystallization temperature. The Pglass in the PET matrix decreased the Tg, indicating a plasticizing effect of the Pglass in the hybrids that was confirmed by the significantly decreased complex viscosity of the PET matrix. In addition, with increasing temperature, a non-terminal behavior of the viscoelastic properties occurred due to the hybrid structural changes and improved miscibility of the hybrid components. Further, the obtained solid-state variable temperature 31P and 1H NMR spectroscopy results showed strong Pglass concentration dependency of the interactions at the PET-Pglass interface.

Coordination of Carbon Dioxide to the Lewis Acid Site of a Zinc‐Substituted Polyoxometalate and Formation of an Adduct Using a Polyoxometalate–2,4,6‐Trimethylpyridine Frustrated Lewis Pair

The coordination of CO2 to Lewis bases is well‐known; however, its binding to Lewis acids is much less common. The ligation of CO2 to a zinc‐substituted Wells–Dawson type polyoxometalate yielded [(n‐C8H17)4N]8[α2‐P2W17O61Zn(CO2)], which was studied by variable temperature 1H NMR, 13C NMR, and 31P NMR spectroscopy from room temperature to 201 K. The spectra were analyzed in consideration of predicted “end‐on” coordination, POM‐Zn‐O‐C‐O, and “side‐on” coordination where in addition an adjacent basic oxygen atom in the polyoxometalate binds the carbon atom of CO2. After adding 2,4,6‐trimethypyridine into the solution, a plausible adduct, POM‐CO2‐2,4,6‐trimethypyridine, was observed.

Mechanistic insights into the tropo-inversion of the biphenyl moiety in chiral bis-amido phosphites and in their palladium(ii) complexes.

Chiral bis-amido phosphites L1 and L2 containing a diaminobiphenyl unit and a chiral alkoxy group derived from either (-)-menthol or 3-acetoxy deoxycholic methyl ester have been synthesised. Both L1 and L2 react with PdCl2(NCPh)2 affording di- or mononuclear derivatives with formula trans-[Pd(μ-Cl)Cl(L)]2 (1a, L = L1; 1b, L = L2) or trans-PdCl2(L)2 (2a, L = L1; 2b, L = L2) depending on the Pd : L molar ratio. The crystal structure of (M,P)-1a confirms the trans arrangement of the ligand L1 and shows an unusual puckering of the Pd2(μ-Cl)2 core (θ 46°). Both the ligands L1 and L2 and their complexes (1 and 2) are fluxional in solution as a consequence of the tropo-inversion of the diaminobiphenyl unit. For L1, L2, 1a and 2a a combined study including variable temperature 31P{1H} NMR spectroscopy and line shape analysis, Eyring plots and DFT calculations have shed light on the mechanism of the tropo-inversion.

Revealing Local Dynamics of the Protonic Conductor CsH(PO3H) by Solid-State NMR Spectroscopy and First-Principles Calculations

A joint study incorporating multinuclear solid-state NMR spectroscopy and first-principles calculations has been performed to investigate the local structure and dynamics of the protonic conductor CsH(PO3H) in the paraelectric phase. The existence of the superprotonic phase (>137 °C) is clearly confirmed by NMR, in good agreement with the literature. The variable-temperature 1H, 2H, and 31P NMR data further reveal a distribution of motional correlation times, with isotropic rotation of the phosphite ion being observed below the superprotonic phase transition for a small but gradually increasing subset of anions. This isotropic rotation is associated with fast local protonic motion, with the distribution of correlation times being tentatively assigned to internal defects or surface adsorbed H2O. The phosphite ion dynamics of the majority slower subset of phosphite ions is quantified through analysis of variable-temperature 17O spectra recorded from 34 to 150 °C, by considering a model for the pseudo C3 rot...