133Cs Nuclear Magnetic Resonance Research Articles

Anion and cation dynamics in a carbon-substituted cesium closo-hydroborate CsCB11H12: 1H and 133Cs NMR studies

Cesium monocarba-hydroborate CsCB11H12 belongs to the family of alkali-metal closo- hydroborate salts which are considered as promising solid electrolytes for battery applications. To study the dynamical properties of this compound at the microscopic level, we have measured the 1H and 133Cs nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over the temperature range of 80–434 K. Our measurements have revealed a coexistence of two types of reorientational jump processes of the complex [CB11H12]− anions. For the faster of these processes characterized by the average activation energy of 310 meV, the anion reorientations are not “frozen” at the NMR frequency scale down to 120 K. The behavior of the 133Cs NMR line width in CsCB11H12 is consistent with the onset of long-range diffusive motion of Cs+ ions at the frequency scale of ∼104 s−1 above 340 K, and the distinct effects of the diffusive Cs+ jumps on both the 1H and 133Cs spin-lattice relaxation rates become observable above 380 K.

Effect of aliovalent bismuth substitution on structure and optical properties of CsSnBr3

Aliovalent substitution of the B component in ABX3 metal halides has often been proposed to modify the band gap and thus the photovoltaic properties, but details about the resulting structure have remained largely unknown. Here, we examine these effects in Bi-substituted CsSnBr3. Powder X-ray diffraction (XRD) and solid-state 119Sn, 133Cs and 209Bi nuclear magnetic resonance (NMR) spectroscopy were carried out to infer how Bi substitution changes the structure of these compounds. The cubic perovskite structure is preserved upon Bi-substitution, but with disorder in the B site occurring at the atomic level. Bi atoms are randomly distributed as they substitute for Sn atoms with no evidence of Bi segregation. The absorption edge in the optical spectra shifts from 1.8 to 1.2 eV upon Bi-substitution, maintaining a direct band gap according to electronic structure calculations. It is shown that Bi-substitution improves resistance to degradation by inhibiting the oxidation of Sn.

Solvent effects on the interaction between alkali metal cations and 1,3-Diisopropoxycalix [4] arenecrown-6: Nuclear magnetic resonance spectroscopy and Independent Gradient Model Non-Covalent interactions analysis

The combination of 1,3-Diisopropoxycalix [4] arenecrown-6 (BPC6) and alkali metal ions were studied in different solvents by 1H and 133Cs Nuclear magnetic resonance (NMR) spectra, gmx_MMPBSA, and Independent Gradient Model (IGM) non-covalent interactions analysis based on Molecular Dynamics (MD) Simulations. The binding energy of BPC6·M+ complex follows the order: BPC6·Cs+ > BPC6·Rb+ > BPC6·K+ in CHCl3, which is completely reverse to that in vacuum. In addition, the coordination properties depend on solvent polarity: In the low polarity solvent such as CHCl3, all the oxygens in crown ether chain of BPC6 are involved in the coordination with Cs+ ions. By comparison, in the high polarity solvents such as CH3CN and CH3OH, the number of oxygens participates in the complexation decreases, and the cation-π interaction areas of complexes are also reduced. That is because the contribution of electrostatic interactions in complexation is weakened by solvent effect. The cation-π interaction plays a very important role in selectivity among alkali metal cations and coordination stability of BPC6·M+ complex in different solvents.

Combined Brønsted Base-Promoted CO2 Fixation into Benzylic C-H Bonds of Alkylarenes.

Interest in developing methods for direct CO2 fixation into readily available unfunctionalized C-H bonds in organic substances has recently surged. In contrast to the well-studied carboxylations of alkynyl C(sp)-H and aromatic C(sp2)-H bonds, carboxylation of benzylic C(sp3)-H bonds to produce 2-arylacetic acids is limited to photoirradiation reactions and continues to be a challenging issue because of the low chemical reactivity. We herein describe that a combined Brønsted base (i.e., LiO-t-Bu/CsF and LiOCEt3/CsF) achieves benzylic carboxylation of electron-deficient, -neutral, and -rich alkylarenes and enables various functionalities, including fragile ones such as bromide, alkene, alkyne, and carbonyl moieties. Dicarboxylation at the benzylic position is also established. Cs-alkoxide generated in situ acts as a reactive base, as demonstrated in experiments with independently prepared CsO-t-Bu and by 133Cs nuclear magnetic resonance studies.

Diffusion NMR-based comparison of electrostatic influences of DNA on various monovalent cations

Counterions are important constituents for the structure and function of nucleic acids. Using 7Li and 133Cs nuclear magnetic resonance (NMR) spectroscopy, we investigated how ionic radii affect the behavior of counterions around DNA through diffusion measurements of Li+ and Cs+ ions around a 15-bp DNA duplex. Together with our previous data on 23Na+ and 15NH4+ ions around the same DNA under the same conditions, we were able to compare the dynamics of four different monovalent ions around DNA. From the apparent diffusion coefficients at varied concentrations of DNA, we determined the diffusion coefficients of these cations inside and outside the ion atmosphere around DNA (Db and Df, respectively). We also analyzed ionic competition with K+ ions for the ion atmosphere and assessed the relative affinities of these cations for DNA. Interestingly, all cations (i.e., Li+, Na+, NH4+, and Cs+) analyzed by diffusion NMR spectroscopy exhibited nearly identical Db/Df ratios despite the differences in their ionic radii, relative affinities, and diffusion coefficients. These results, along with the theoretical relationship between diffusion and entropy, suggest that the entropy change due to the release of counterions from the ion atmosphere around DNA is also similar regardless of the monovalent ion types. These findings and the experimental diffusion data on the monovalent ions are useful for examination of computational models for electrostatic interactions or ion solvation.

Orbital ordering and fluctuations in a kagome superconductor CsV3Sb5

Recently, competing electronic instabilities, including superconductivity and density-wave-like order, have been discovered in vanadium-based kagome metals AV3Sb5 (A = K, Rb, Cs) with a nontrivial band topology. This finding stimulates considerable interest to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state. Here, we performed 51V and 133Cs nuclear magnetic resonance (NMR) measurements on a CsV3Sb5 single crystal to clarify the nature of density-wave-like transition in these kagome superconductors. A first-order structural transition is unambiguously revealed below Ts ∼ 94 K by observing the sudden splitting of Knight shift in 51V NMR spectrum. Moreover, combined with 133Cs NMR spectrum, the present result confirms a three-dimensional structural modulation. By further analyzing the anisotropy of Knight shift and 1/T1T at 51V nuclei, we proposed that the orbital order is the primary electronic order induced by the first-order structural transition, which is supported by further analysis on electric field gradient at 51V nuclei. In addition, the evidence for possible orbital fluctuations is also revealed above Ts. The present work sheds light on a rich orbital physics in kagome superconductors AV3Sb5.

Exploring Structural Nuances in Germanium Halide Perovskites Using Solid-State 73Ge and 133Cs NMR Spectroscopy.

Metal halide perovskites remain top candidates for higher-performance photovoltaic devices, but concerns about leading lead-based materials remain. Ge perovskites remain understudied for use in solar cells compared to their Sn-based counterparts. In this work, we undertake a combined 73Ge and 133Cs solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and density functional theory (DFT) study of the bulk CsGeX3 (X = Cl, Br, or I) series. We show how seemingly small structural variations within germanium halide perovskites have major effects on their 73Ge and 133Cs NMR signatures and reveal a near-cubic phase at room temperature for CsGeCl3 with severe local Ge polyhedral distortion. Quantum chemical computations are effective at predicting the structural impact on NMR parameters for 73Ge and 133Cs. This study demonstrates the value of a combined solid-state NMR and DFT approach for investigating promising materials for energy applications, providing information that is out of reach with conventional characterization methods, and adds the challenging 73Ge nucleus to the NMR toolkit.

Two-dimensional spin dynamics in the itinerant antiferromagnet CsCo[formula omitted]Se[formula omitted] revealed by  133Cs-NMR measurements

In this paper, 133Cs nuclear magnetic resonance (NMR) measurements have been performed to investigate the magnetic properties of an A-type antiferromagnet CsCo2Se2. The field-sweeping NMR spectra become broadened mainly due to the internal magnetic field attributed to antiferromagnetic ordering. Both T-dependence of Knight shift 133K and T divided spin-lattice relaxation rate 1/T1T provide clear evidences for the antiferromagnetic transition at ∼ 70 K. 1/T1T exhibits a Curie–Weiss T-dependence down to 80 K, suggesting the development of antiferromagnetic spin fluctuations with decreasing temperature. The linear-relationship between T1T-T suggests that antiferromagnetic spin fluctuations are two-dimensional in the paramagnetic state.

Keggin-Type Mixed Polyoxomolybdates Catalyzed Cyclohexanone Oxidation by Hydrogen Peroxide: In Situ IR Pyridine Adsorption

Homogenous cyclohexanone oxidation was catalyzed by a series of Keggin-type polyoxometalates as formula H3PMo12O40, Cs3PMo12O40, CsSnPMo12O40, Cs2Sn0.5PMo12O40 and HSnPMo12O40 using hydrogen peroxide H2O2 (30%), without solvent. The following reaction products, adipic, glutaric and succinic acids, butane-1,3-diol and e-caprolactone were identified and quantified by high-performance liquid chromatography (HPLC). The catalysts were prepared and characterized by Fourier transform infrared spectroscopy (FTIR), chemical analysis (ICP), 31P and 133Cs nuclear magnetic resonance spectroscopies and in situ FTIR of pyridine adsorption. The presence of both BrOnsted and Lewis acid sites was evidenced for CsSnPMo12O40, Cs2Sn0.5PMo12O40 and HSnPMo12O40. Among them, HSnPMo12O40 exhibited total conversion with adipic acid, as major product (60% of yield).

Nuclear magnetic resonance study of anion and cation dynamics in CsSiH3

In order to study the dynamical properties of cesium silanide CsSiH3, we have measured the 1H and 133Cs nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates in this compound over the temperature range of 5–354 K. The results of the 1H NMR measurements indicate that [SiH3]‒ anions in CsSiH3 retain unusually high reorientational mobility down to low temperatures. In particular, a significant narrowing of the proton NMR spectrum due to [SiH3]‒ reorientations is observed in the range ∼ 10–14 K. The order-disorder (β→α) phase transition accompanied by the strong acceleration of [SiH3]‒ reorientations and by the change in the reorientational mechanism is observed above 200 K; according to the 1H spin-lattice relaxation data, this transition appears to be gradual. For the high-temperature disordered α-phase, the activation energy for [SiH3]‒ reorientations is found to be 41(4) meV. The 133Cs NMR results are consistent with the onset of diffusive motion of Cs+ cations at the frequency scale of ∼104 s−1 above 300 K.

Electronic and relativistic contributions to ion-pairing in polyoxometalate model systems.

Ion pairs and solubility related to ion-pairing in water influence many processes in nature and in synthesis including efficient drug delivery, contaminant transport in the environment, and self-assembly of materials in water. Ion pairs are difficult to observe spectroscopically because they generally do not persist unless extreme solution conditions are applied. Here we demonstrate two advanced techniques coupled with computational studies that quantify the persistence of ion pairs in simple solutions and offer explanations for observed solubility trends. The system of study, ([(CH3)4N]+,Cs)8[M6O19] (M = Nb,Ta), is a set of unique polyoxometalate salts whose water solubility increases with increasing ion-pairing, contrary to most ionic salts. The techniques employed to characterize Cs+ association with [M6O19]8- and related clusters in simple aqueous media are 133Cs NMR (nuclear magnetic resonance) quadrupolar relaxation rate and PDF (pair distribution function) from X-ray scattering. The NMR measurements consistently showed more extensive ion-pairing of Cs+ with the Ta-analogue than the Nb-analogue, although the electrostatics of the ions should be identical. Computational studies also ascertained more persistent Cs+-[Ta6O19] ion pairs than Cs+-[Nb6O19] ion pairs, and bond energy decomposition analyses determined relativistic effects to be the differentiating factor between the two. These distinctions are likely responsible for many of the unexplained differences between aqueous Nb and Ta chemistry, while they are so similar in the solid state. The X-ray scattering studies show atomic level detail of this ion association that has not been prior observed, enabling confidence in our structures for calculations of Cs-cluster association energies. Moreover, detailed NMR studies allow quantification of the number of Cs+ associated with a single [Nb6O19]8- or [Ta6O19]8- anion which agrees with the PDF analyses.

In situ7Li and 133Cs nuclear magnetic resonance investigations on the role of Cs+ additive in lithium-metal deposition process

Cesium ion (Cs+) has been reported to be an effective electrolyte additive to suppress Li dendrite growth which prevents the application of lithium (Li) metal as an anode for rechargeable Li batteries. In this work, we investigated the effect of Cs+ additive on Li depositions using quantitative in situ7Li and 133Cs nuclear magnetic resonance (NMR) with planar symmetric Li cells. It's found that the addition of Cs+ can significantly enhance both the formation of well aligned Li nanorods and reversibility of the Li electrode. In situ133Cs NMR directly confirms that Cs+ migrates to Li electrode to form a positively charged electrostatic shield during the charging process. Much more electrochemical “active” Li was found in Li films deposited with Cs+ additive, while more electrochemical “dead” and thicker Li rods were identified in Li films deposited without Cs+. Combining the in situ and the previous ex-situ results, a Li deposition model has been proposed to explain these observations.

NMR of 133Cs+ in stretched hydrogels: One-dimensional, z- and NOESY spectra, and probing the ion’s environment in erythrocytes

133Cs nuclear magnetic resonance (NMR) spectroscopy was conducted on 133Cs+ in gelatin hydrogels that were either relaxed or stretched. Stretching generated a septet from this spin-7/2 nucleus, and its nuclear magnetic relaxation was studied via z-spectra, and two-dimensional nuclear Overhauser (NOESY) spectroscopy. Various spectral features were well simulated by using Mathematica and the software package SpinDynamica. Spectra of CsCl in suspensions of human erythrocytes embedded in gelatin gel showed separation of the resonances from the cation inside and outside the cells. Upon stretching the sample, the extracellular 133Cs+ signal split into a septet, while the intracellular peak was unchanged, revealing different alignment/ordering properties of the environment inside and around the cells. Differential interference contrast light microscopy confirmed that the cells were stretched when the overall sample was elongated. Analysis of the various spectral features of 133Cs+ reported here opens up applications of this K+ congener for studies of cation-handling by metabolically-active cells and tissues in aligned states.

The interaction of sterically stabilized magnetic nanoparticles with fresh human red blood cells.

Sterically stabilized superparamagnetic iron oxide nanoparticles (SPIONs) were incubated with fresh human erythrocytes (red blood cells [RBCs]) to explore their potential application as magnetic resonance imaging contrast agents. The chemical shift and linewidth of 133Cs+ resonances from inside and outside the RBCs in 133Cs nuclear magnetic resonance spectra were monitored as a function of time. Thus, we investigated whether SPIONs of two different core sizes and with three different types of polymeric stabilizers entered metabolically active RBCs, consuming glucose at 37°C. The SPIONs broadened the extracellular 133Cs+ nuclear magnetic resonance, and brought about a small change in its chemical shift to a higher frequency; while the intracellular resonance remained unchanged in both amplitude and chemical shift. This situation pertained over incubation times of up to 90 minutes. If the SPIONs had entered the RBCs, the intracellular resonance would have become broader and possibly even shifted. Therefore, we concluded that our SPIONs did not enter the RBCs. In addition, the T2 relaxivity of the small and large particles was 368 and 953 mM−1 s−1, respectively (three and nine times that of the most effective commercially available samples). This suggests that these new SPIONs will provide a superior performance to any others reported thus far as magnetic resonance imaging contrast agents.

Phonon-Modulated Magnetic Interactions and Spin Tomonaga-Luttinger Liquid in the p-Orbital Antiferromagnet CsO2.

The magnetic response of antiferromagnetic CsO2, coming from the p-orbital S=1/2 spins of anionic O2(-) molecules, is followed by 133Cs nuclear magnetic resonance across the structural phase transition occurring at T(s1)=61  K on cooling. Above T(s1), where spins form a square magnetic lattice, we observe a huge, nonmonotonic temperature dependence of the exchange coupling originating from thermal librations of O2(-) molecules. Below T(s1), where antiferromagnetic spin chains are formed as a result of p-orbital ordering, we observe a spin Tomonaga-Luttinger-liquid behavior of spin dynamics. These two interesting phenomena, which provide rare simple manifestations of the coupling between spin, lattice, and orbital degrees of freedom, establish CsO2 as a model system for molecular solids.

133Cs Nuclear Magnetic Resonance Relaxometry as a Probe of the Mobility of Cesium Cations Confined within Dense Clay Sediments

133Cs nuclear magnetic resonance is used to quantify the mobility of cesium counterions confined within the interlamellar space of synthetic Hectorite clay under controlled hydration conditions. The degree of lamellae ordering within the macroscopic clay sediment is determined by analyzing the variation of the 133Cs NMR spectra as a function of the sample orientation in the static magnetic field. Furthermore, a detailed analysis of the 133Cs NMR spectra allows one to determine the order of magnitude of the quadrupolar and heteronuclear dipolar couplings monitoring the NMR relaxation of the cesium cations confined within clay sediments. Finally, a lower limit to the average residence time of the cesium cations within the clay interlamellar space is determined by using 133Cs NMR relaxation measurements under spin-locking conditions.

2H and 133Cs nuclear magnetic resonance study of Cs3D(SO4)2 single crystals in laboratory and rotating frames

To understand the physical properties of Cs3D(SO4)2 single crystals, in which deuterium replaces hydrogen, the temperature dependence of the NMR spectrum and the spin–lattice relaxation times in the laboratory frame, T1, and in the rotating frame, T1ρ, for 2H and 133Cs are investigated using Fourier transform nuclear magnetic resonance spectrometry. Our results for the 2H and 133Cs relaxation times provide no evidence of a phase transition. The strong temperature dependence of the 2H resonance lines is associated with deformation of the H(SO4)2− tetrahedra. Further, T1 and T1ρ for the 2H and 133Cs nuclei are governed by different mechanisms, which we discuss in terms of fast and slow motion.

Properties of Cs-intercalated single wall carbon nanotubes investigated by 133Cs Nuclear Magnetic resonance

In the present study, we investigated Cs-intercalated single wall carbon nanotubes (SWCNTs) using 133Cs Nuclear Magnetic resonance. We show that there are two types of Cs cations depending on the insertion level. Indeed, at low concentrations, Static spectra analysis shows that the Cs(α)+ species are fully ionized, i.e. α equal ca.1, while at higher concentrations a second paramagnetically shifted line appears, indicating the formation of Cs(β)+ ions with β<α∼+1. At low concentrations and low temperatures the Cs(α)+ ions exhibit a weak hyperfine coupling to the SWCNT conduction electrons, whereas, at higher temperatures, a thermally activated slow-motion diffusion process of the Cs(α)+ ions occurs along the interstitial channels present within the carbon nanotube bundles. At high concentrations, the Cs(β)+ ions seem to occupy well defined positions relative to the carbon lattice. As a matter of fact, the Korringa relaxation behavior suggests a strong hyperfine coupling between Cs nuclei and conduction electrons in the carbon nanotubes and a partial charge transfer, which suggest a plausible Cs(6s)–C(2p) hybridization.

1H and 133Cs nuclear magnetic resonance study of the NH4 and Cs occupation rates of mixed (NH4)2−xCsxZnCl4 (x = 0, 1, and 2) crystals

The NMR spectra and the spin–lattice relaxation times, T1, of the 1H and 133Cs nuclei in (NH4)2−xCsxZnCl4 (x=0, 1, and 2) single crystals were determined by using NMR spectroscopy. We investigated the crystallographic structures of these crystals by determining the NH4 and Cs occupation probabilities of the two cationic sites. Our NMR experimental results confirm that in (NH4)2ZnCl4 there are two crystallographically inequivalent NH4 groups, NH4(1) and NH4(2), occupying the A1 and A2 sites, and that in Cs2ZnCl4 there are two crystallographically inequivalent Cs ions, Cs(1) and Cs(2), occupying the A1 and A2 sites. Both types of NH4 ions and both types of Cs ions are found in mixed NH4CsZnCl4 crystals; the occupation rates of the two different sites are 1 and 1 for Cs(1) and Cs(2), respectively, and 1 and 1 for NH4(1) and NH4(2), respectively.

Nuclear Magnetic Resonance Relaxation Study of the Phase Transitions of Rb2CuCl4·2H2O and Cs2MnCl4·2H2O Single Crystals

The physical properties and phase transitions of Rb2CuCl4·2H2O and Cs2MnCl4·2H2O crystals were investigated by performing 85Rb, 87Rb, and 133Cs nuclear magnetic resonance relaxation analyses. The temperature dependences of the spectra and the spin–lattice relaxation times T 1 near T C are related to changes in the symmetry of the octahedrons consisting of four Cl− ions and two water molecules around Rb+ or Cs+; the forms of these octahedrons are disrupted by the loss of H2O. The difference between the relaxation times of the two crystals is possibly due to the difference between the electron structures of the Cu and Mn ions. Cu2+ has nine valence electrons in its 3d orbital, whereas Mn2+ has five valence electrons in its 3d orbital.