NMR Spin-lattice Relaxation Times Research Articles

Dynamics of Novel Zinc Ion Electrolytes

Zinc ion batteries are a niche alternative for battery applications. Their implementation is however afflicted by several factors, one of which is the need for more efficient electrolytes. Deep eutectic solvent (DES) electrolytes based on ZnCl2salt offer many attributes including, including improved stability and reduced dendrite formation. In this work we will present a molecular level understanding of the ion dynamics in electrolyte mixtures based on ZnCl2 and various co-solvents including organic carbonates and water. Focus is on the ion dynamics as interrogated by 1H NMR spin-lattice relaxation times (T1 ) combined with ionic conductivity, viscosity and density measurements. As shown in Figure 1, preliminary T1 results infers multiple ionic coordinated species with varying rates of mobilities that are co-solvent dependent. Additionally, data shows selective interaction sites between the hydrogen bond donors and acceptors, as well as the co-solvents. Figure 1. 1H T1 for the null and AcN co-solvent mixtures of (a) 1ZnCl2:4EtG and (b) 1ChCl:1ZnCl2:6EtG. Figure 1

Ion transport in non-aqueous electrolyte mixtures of zinc chloride deep eutectic solvent (DES) and molecular solvents

The ion dynamics of null solvents 1ZnCl2:4EtG and 1ChCl:1ZnCl2:6EtG incorporating 1M water, propylene carbonate (PC) or acetonitrile (AcN) were investigated using 1H NMR spectra and spin-lattice relaxation time (T1) measurements combined with ionic conductivity, density, and viscosity, all as a function of temperature. Results show that the inclusion of all co-solvents increased the available free volume of the mixtures and followed the trend H2O ≤ PC < AcN. 1H NMR spectra and T1 inferred the presence of multiple ionic species with varying rates of mobilities. These dynamic heterogeneities were displayed by the broad T1 minima – especially for the 1ZnCl2:4EtG mixtures – and asymmetrically broadened linewidths. T1 results also revealed selective interaction sites between the hydrogen bond donors and acceptors, as well as with the co-solvents.

An NMR study of hexamethylbenzene (HMB) incorporated in 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) framework

Molecular motion of hexamethylbenzene (HMB) incorporated in 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) was investigated by 1H NMR spin-lattice relaxation time T1 measurements. In the porous space of one-dimensional (1D) CLPOT nanochannels, HMB molecules reorientate more freely compared to bulk HMB crystals. With low concentrations x < 0.5 of CLPOT-(HMB)x, the distribution of HMB seems to be quite inhomogeneous in 1D nanochannel. The activation energy of the in-plane reorientation of HMB is 5 kJ mol−1 due to the interaction with nanochannel-wall and 10 - 18 kJ mol−1 depending on the separation distance when the interaction between the adjacent HMB molecules determines the activation energy.

Temperature symmetry breaking and properties of lead-free organic-inorganic hybrids: bismuth(III) iodide and antimony(III) iodide: (S(CH3)3)3[Bi2I9] and (S(CH3)3)3[Sb2I9

We have synthesized and characterized two novel lead-free organic-inorganic hybrid crystals: (S(CH3)3)3[Bi2I9] (TBI) and (S(CH3)3)3[Sb2I9] (TSI). Thermal DSC, TG, and DTA analyses indicate structural phase transitions (PTs) in both compounds; TBI undergoes two structural phase transitions at 314.2/314.8 K (cooling/heating) and at 181.5 K of first (I ↔ II) and second order (II ↔ III), respectively. The crystal structures of TBI are refined for phases I (325 K), II (200 K) and III (100 K). TBI exhibits ferroelastic properties since both PTs are accompanied by a change in the symmetry of crystals: P63/mmc → C2/c (I → II) and C2/c → P1̄ (II → III). The presence of a ferroelastic domain structure has been confirmed by optical observations. In turn, TSI also reveals two PTs: I ↔ II (at 303.9/304.1 K) and II ↔ III (212.9/221.4 K). To compare and obtain insight into the mechanism of the PTs of TBI, we have carried out temperature dependent single crystal X-ray diffraction studies. Additionally, to confirm the change in the dynamical states of molecules in PTs, dielectric measurements have been carried out between 100 K and 400 K in the frequency range of 200 Hz to 2 MHz. Moreover, the measurements of the 1H NMR spin-lattice relaxation time, T1, and a second moment, M2, of the 1H NMR line have been undertaken in the temperature range between 100 and 300 K.

Reorientation of DABCO (1,4-diazabicyclo[2.2.2]octane) in hydrogen-bonded 1:2 molecular complexes DABCO-2(SBA) with substituted benzoic acids SBA

The molecular complexes of DABCO-2(SBA) with substituted benzoic acids SBA, which have the hydrogen-bonded trimeric unit, were prepared to investigate the DABCO reorientation in the trimeric unit. By the analysis of the temperature dependence of 1H NMR spin-lattice relaxation time, the correlation time of the DABCO reorientation was determined as a function of the temperature. It is suggested that a change of potential energy of the reorientation is caused with increasing rate of reorientation resulting in a structure change of the trimeric unit to a centrosymmetric structure. The correlation between the activation energy of the DABCO reorientation and the bond nature of the hydrogen bond involved in the trimeric unit is also discussed.

Molecular interaction and partitioning in α-keratin using 1H NMR spin-lattice (T1) relaxation times.

The interactions between small molecules and keratins are poorly understood. In this paper, a nuclear magnetic resonance method is presented to measure changes in the 1H T1 relaxation times of small molecules in human hair keratin to quantify their interaction with the fibre. Two populations of small-molecule compounds were identified with distinct relaxation times, demonstrating the partitioning of the compounds into different keratin environments. The changes in relaxation time for solvent in hair compared with bulk solvent were shown to be related to the molecular weight (MW) and the partition coefficient, LogP, of the solvent investigated. Compounds with low MWs and high hydrophilicities had greater reductions in their T1 relaxation times and therefore experienced increased interactions with the hair fibre. The relative population sizes were also calculated. This is a significant step towards modelling the behaviour of small molecules in keratinous materials and other large insoluble fibrous proteins.

In memoriam: John R. Mallard (1927-2021).

In memoriam: John R. Mallard (1927-2021).

Calixarene-Based lead receptors: an NMR, DFT and X-Ray synergetic approach

ABSTRACT The conformational changes of the homooxa adamantyl ketones 1 and 2, as well as of the calix[4]arene analogue derivative 3, all in the cone conformation, upon Pb2+ complexation were investigated by 1H, 13C, 207Pb NMR and proton spin-lattice relaxation times (T 1) experiments. The X-ray crystal structures of ketones 1 and 3 were determined. The inclusion of an acetonitrile molecule in the hydrophobic cavity of the ligands was observed in the solid state. In solution, inclusion was observed only in the case of Pb2+ ⊂ ketone 3 complex. DFT calculations were also performed to complement the NMR conformational analysis and to bring further insights to the cation complexation. The data confirmed the formation of 1:1 complexes between Pb2+ and the ligands, and that the cation is located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. In general, the ligand conformations became closer to a regular cone upon complexation, with the binding models found for the three ketones through the NMR studies corroborated by the DFT calculations.

Effect of methylene chain length of perovskite-type layered [NH3(CH2) n NH3]ZnCl4 (n = 2, 3, and 4) crystals on thermodynamic properties, structural geometry, and molecular dynamics.

The structure of organic–inorganic perovskite [NH3(CH2)4NH3]ZnCl4 was determined; the lattice constants with monoclinic structure were determined to be a = 7.2527 Å, b = 8.1101 Å, c = 10.3842 Å, and β = 80.3436°. The crystal was almost thermally stable up to approximately 560 K. The endothermic peaks at 481 K and 506 K were assigned to the phase transition of the material. In addition, the structural characteristics and molecular dynamics of the cation were studied via magic angle spinning nuclear magnetic resonance experiments. Based on the results, the effects of the length of the CH2 group in the cation of the [NH3(CH2)nNH3]ZnCl4 (n = 2, 3, and 4) crystals were considered. Regardless of whether n was even or odd, the differences in the thermal and physical properties were minimal. Moreover, a difference in molecular motion relative to the length of the cation was observed only at high temperatures. These results provide useful information about the thermal stability and molecular dynamics of [NH3(CH2)nNH3]ZnCl4 crystals and are expected to facilitate potential applications of such compounds in supercapacitors, batteries, and fuel cells.

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study.

Titanium dioxide (TiO2) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO2 influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO2 were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO2 enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T1 results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T1 values and large capillary pores with long T1 values. During early hydration times, TiO2 is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO2 appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.

Phase transitions and properties of 0D hybrid iodoantimonate(III) and iodobismuthate(III) semiconducting ferroics: [C(NH2)3]3Bi2I9 and [C(NH2)3]3Sb2I9

• The guanidinium derivatives, [C(NH 2 ) 3 ] 3 Bi 2 I 9 (GBI) and [C(NH 2 ) 3 ] 3 Sb 2 I 9 (GSI), as the promising compounds for a possible application in photovoltaics. • Optical, dielectric and UV–Vis results of studies on GBI and GSI. • Ferroelastic properties of [C(NH 2 ) 3 ] 3 Bi 2 I 9 (GBI) and [C(NH 2 ) 3 ] 3 Sb 2 I 9 (GSI). The guanidinium derivatives [C(NH 2 ) 3 ] 3 Bi 2 I 9 (GBI) and [C(NH 2 ) 3 ] 3 Sb 2 I 9 (GSI) are promising compounds from the viewpoint of their electrooptical and semiconducting properties. In this paper we present the optical, dielectric, UV–Vis, Raman and 1 H NMR (spin-lattice relaxation time, T 1 , and second moment, M 2 ) results of studies on GBI and GSI. The temperature and frequency dependent ac conductivity of GBI and GSI has been analyzed in terms of the Jonscher relationship. The parameters for the ac conductivity have been estimated. The UV–Vis spectra have been analyzed for GBI and GSI and the respective calculations regarding the band gap have been carried out. GBI and GSI reveal the semiconducting properties in their high temperature phases ( σ ac in the range 10 –5 – 10 –7 S/m). 1 H NMR studies indicate the key role of the guanidium cation dynamics in the phase transitions mechanisms.

Chain-folded lamellar structure and dynamics of the crystalline fraction of Bombyx mori silk fibroin and of (Ala-Gly-Ser-Gly-Ala-Gly)n model peptides

Solid-state NMR is a powerful analytical technique to determine the composite structure of Bombyx mori silk fibroin (SF). In our previous paper, we proposed a lamellar structure for Ala-Gly copolypeptides as a model of the crystalline fraction in Silk II. In this paper, the structure and dynamics of the crystalline fraction and of a better mimic of the crystalline fraction, (Ala-Gly-Ser-Gly-Ala-Gly)n (n = 2–5, 8), and 13C selectively labeled [3-13C]Ala-(AGSGAG)5 in Silk II forms, were studied using structural and dynamical analyses of the Ala Cβ peaks in 13C cross polarization/ magic angle spinning NMR and 13C solid-state spin-lattice relaxation time (T1) measurements, respectively. Like Ala-Gly copolypeptides, these materials have lamellar structures with two kinds of Ala residues in β-sheet, A and B, plus one distorted β-turn, t, formed by repetitive folding using β-turns every eighth amino acid in an antipolar arrangement. However, because of the presence of Ser residues at every sixth residue in (AGSGAG)n, the T1 values and mobilities of B decreased significantly. We conclude that the Ser hydroxyls hydrogen bond to adjacent lamellar layers and fix them together in a similar way to Velcro®.

Temperature-Stimulus Responsive Ferroelastic Molecular–Ionic Crystal: (C8H20N)[BF4

Molecular–ionic crystals, which are built of organic cations and discrete anionic components with AMX4 stoichiometry, easily induce structural order–disorder transitions. These phenomena can generate interesting ferroic properties. Herein, we have synthesized and characterized a novel AMX4-type crystal, (C8H20N)[BF4] (1). Thermal analysis, (DSC, TGA) indicates one structural phase transition (PT) at 257/259 K (cooling/heating, I ↔ II). The structure of 1 has been solved at two temperatures, 120 and 298 K, with single-crystal X-ray diffraction. The high-temperature phase I (1-HT) shows a tetragonal structure with the space group I4/mmm, whereas the low-temperature phase II (1-LT) is monoclinic with the space group P21/a. The PT belongs, thus, to the improper ferroelastic species 4/mmmF2/m with a 4-fold multiplication of the unit cell. All four possible ferroelastic domains of phase II have been identified in polarized light microscopy. The monoclinic deformation has been shown to give rise to a characteristic parquet-like texture preserving integrity of 1. The molecular mechanism of PT involving changes in the cationic and anionic dynamics has been postulated based on measurements of the 1H and 19F NMR spin–lattice relaxation times, T1, and second-moment, M2, and of the dielectric responses. The ac and dc conductivity measurements have been used to determine the transport properties of the charge carriers in 1. The intrinsic features of molecular–ionic crystals, such as the dynamics of molecular motions, structural instability with a lattice-symmetry change, formation of domain patterns, etc., provide a crystal with unique ferroelastic properties. This type of crystal may be useful as an functional material.

Reorientation Times for Solid-State Electrolyte Solvents and Electrolytes from NMR Spin-Lattice Relaxation Studies.

Ionic and molecular plastic crystals have been studied recently as solid electrolytes or solvents, but the specific role of molecular reorientation has not been clarified. We use NMR spin-lattice relaxation times (T1 minima) to compare the time scale for magnetic fluctuations in a plastic crystal solvent to the molecular reorientation times, as established by dielectric spectroscopy. We focus on a mixture of succinonitrile and glutaronitrile, in which the rotationally disordered phase is stabilized against crystallization. Reorientation times can then be studied over 13 orders of magnitude, down to the glass transition temperature at 144 K. For each nucleus, 1H and 13C, the most probable magnetic fluctuation time is found to be slightly shorter than the reorientation time, but with practically indistinguishable temperature dependence. This facilitates investigation of the relation of solvent reorientation to ion conductivity relaxation times in ionic conducting systems in which the conductivity swamps the dielectric signature of solvent reorientation.

Effect of Noncovalent Dispersion of Poly(Ethylene Oxide) in Columnar Polyether-Based Discotic Liquid Crystal on the Ionic Conductivity and Dynamics of Lithium Ions

The ionic conductivity of an electrolyte is represented by a product of carrier density, charge (electric), and ionic mobility. The overall goal of this study was to provide an insight into the influence of lithium ion conductivity and dynamic when a continuous discotic liquid crystal (DLC) matrix of hexaazatrinapthylene-polyether, HATN-TEG-1, is doped with a small amount of polyethylene oxide (PEO, 5% of MW 8000). The favorable non-covalent interactions between PEO and the DLC triethylene glycol side-chains is supported by the maintenance of the mesophase. The lithium ionic conductivity of HATN-TEG-1 was found to be 1.1 × 10−6 S cm−1, which is better than the corresponding HATN-TEG-1-5%PEO-8000 with a value of 6.06 × 10−7 S cm−1. These results are further supported by the dynamics of the lithium ions in HATN-TEG-1 and HATN-TEG-1-5%PEO-8000 as characterized by 7Li, and 1H NMR spin-lattice relaxation time and self-diffusion coefficient measurements. Though the additional PEO was found to increase the ion carriers, the significant lowering of the ionic conductivity may be attributed to the more pronounced decrease of the mobility of the ionic part when the HATN-TEG-1 matrix is dispersed with PEO. This finding indicates that the doping of 5% PEO onto the matrix of HATN-TEG-1 DLC has an adverse effect on both its diffusion rate and ion conductivity.

23Na nuclear magnetic resonance study of yNa2S + (1 − y)[xSiS2 + (1 − x)PS5/2] glassy solid electrolytes

23Na NMR spin lattice relaxation times, T1, and central linewidths were obtained for yNa2S + (1 − y)[xSiS2 + (1 − x)PS5/2] glassy solid electrolytes for two series of glasses, y = 0.5 and 0.67, and x = 0.1, 0.3, 0.5, 0.7, and 0.9. No pronounced mixed glass former effect in the activation energy was observed within experimental uncertainty for either series of glasses. Energy barriers to sodium motion were calculated using the Anderson-Stuart model for the y = 0.67 sample, and the results suggested that the energy barriers as a function of composition are strongly influenced by the dielectric constant of these glasses. DC Na+ ion conductivity values calculated using NMR-derived correlation times, an available Na+ ion site coordination number in the range z = 3–4, and an energy cutoff determined from the critical percolation threshold, were in agreement with the increasing trend in the experimental values for the y = 0.67 glasses. Using the same model, the conductivity values were calculated for the y = 0.50 glasses, which have as yet to be measured, and these revealed a decreasing conductivity as x increased. Sodium NMR second moment studies showed that the cation spatial arrangement followed a homogeneous distribution for y = 0.50 and 0.67 samples over most of the composition range, but deviated significantly away from this above a sodium concentration of 1.85 × 1028 m-3, suggesting a tendency for sodium to cluster under these conditions.

Symmetry breaking structural phase transitions, dielectric properties and molecular motions of formamidinium cations in 1D and 2D hybrid compounds: (NH2CHNH2)3[Bi2Cl9] and (NH2CHNH2)3[Bi2Br9

Two organic-inorganic hybrid halobismuthates(iii), (NH2CHNH2)3[Bi2Cl9] (FBC) and (NH2CHNH2)3[Bi2Br9] (FBB), have been prepared with their structures revealed by single-crystal X-ray diffraction at various temperatures. FBC is characterized by one-dimensional (1D) [Bi2Cl9]3-∞ anionic chains built by edge-sharing BiCl6 octahedra, whereas FBB adopts a layer structure (2D) [Bi2Br9]3-∞. Both materials were found to exhibit a rich polymorphism in the solid state. FBC undergoes two reversible phase transitions (PTs) at 218/220 K and at 123/126 K (cooling/heating), respectively, whereas for FBB also two PTs occur close together at 196/199 K and at 190/188 K. Dielectric response around the PT temperatures of FBC and FBB reflects high disorder of dipolar groups over the high temperature phases. The 'order-disorder' mechanism of these PTs is assigned to the dynamics of formamidinium cations. FBB is considered as a ferroic material exhibiting ferroelastic domains below 196 K. The molecular motions of organic cations in a wide temperature range were studied by means of 1H NMR (spin-lattice relaxation time). Presented findings will provide a new method to explore organic-inorganic multifunctional PT materials.

Supercooling and Nucleation of Fatty Acids: Influence of Thermal History on the Behavior of the Liquid Phase.

Saturated fatty acids are an exceptionally important class of liquids, used in many consumer products and suggested as phase change materials (PCMs) for thermal energy storage, in part because they crystallize with minimal supercooling. Here we investigate fatty acid nucleation to understand why crystallization is so facile, as a step toward identifying potential mechanisms for the suppression of supercooling in other PCMs. We find that fatty acid supercooling can be induced only if the liquid is first heated above a material-dependent threshold temperature. NMR spin-lattice relaxation time studies show that the average mobility of the alkyl chains in the fatty acids increases more rapidly with temperature above the supercooling threshold temperature, and NMR T1 hysteresis also sets in at that temperature. Measurements of the real portion of the dielectric constant as a function of temperature show that a liquid fatty acid heated far above its melting point behaves with an apparent temperature upon cooling that is higher than the actual temperature, when compared to its behavior at the same temperature upon heating. Our results suggest that molecular clusters in the liquid fatty acids break apart when the liquids are heated above their threshold temperature and do not immediately re-form on cooling. The breakup of clusters leads to an increase in the mobility of the fatty acid molecules. Because the clusters do not re-form quickly on subsequent cooling, nucleation does not occur, and substantial supercooling results.

Hybrid organic-inorganic bismuth(III)-based material [4-NH2C5H4NH]7[BiCl6]2Cl. Crystal structure, dielectric properties and molecular motions of 4-aminopyridinium cations

4-aminopyridinium analogue, [4-NH2PyH]7[BiCl6]2Cl, has been synthesized and characterized by single-crystal X-ray diffraction at 100 K, calorimetric, dilatometric and dielectric studies. The crystal structure is centrosymmetric with the monoclinic space group, P21/n. It consists of two discrete [BiCl6]3- octahedra, one loose Cl− anion and seven, partially disordered, 4-aminopyridinium cations. The compound reveals a reversible first-order phase transition (I→II) at 305/304 K of the ‘order-disorder’ type. The dielectric studies disclosed a relaxation process in the kilohertz frequency region, assigned to the dynamics of organic cations, described well by the Cole-Cole relation. The 1H NMR spin–lattice relaxation time measurements indicate a complex cations motion over the Phase II. The possible mechanism of the I → II phase transition in [4-NH2PyH]7[BiCl6]2Cl is discussed.

Optorelaxers: Achieving real-time control of NMR relaxation

We present an approach to increase the detection sensitivity of NMR by shortening the spin-lattice relaxation time using transient paramagnetic species created by light irradiation of “optorelaxer” molecules. In the ultimate implementation of this concept, not yet realized here, these transient species are absent during the detection period, thereby avoiding the loss of spectral resolution caused by inhomogeneous broadening from paramagnetic species. Real-time control of NMR relaxation by visible light is demonstrated with Fe(II)(ptz)6(BF4)2, (ptz = 1-propyltetrazole), abbreviated FePTZ. Illumination of FePTZ at 30 K results in a decrease of the 1H NMR spin-lattice relaxation time T1 due to formation of a high spin photoexcited state. The 1H NMR of polystyrene containing a low concentration of FePTZ molecules shows a similar reduction in T1, establishing that FePTZ can act as an optorelaxer for the protons of a matrix. Numerical modeling of the spin-diffusion processes from the protons in a FePTZ core to those in a shell of polystyrene accounts for the observed T1 effects under both dark and light conditions. Additionally, 1H MAS (magic-angle spinning) NMR results for pure FePTZ provide information on the isotropic and anisotropic portions of the electron-nuclear hyperfine interactions.