Spin-lattice Relaxation Time T1ρ Research Articles

Crystal structure, structural geometry, and molecular motion of organic–inorganic perovskite [N(CH3)4]2MnCl4 crystals at phases I, II, and III

Various aspects of the new development of organic-inorganic hybrid [N(CH3)4]2MnCl4 single crystals have been discussed. The phase transition temperatures were determined to be 268 K (TC2) and 291 K (TC1), and the thermodynamic stability was maintained at temperatures up to 669 K. The crystal structures at 250 K (phase III), 275 K (phase II), and 300 K (phase I) are monoclinic, orthorhombic, and orthorhombic, respectively. Notably, while the 1H and 13C chemical shifts gradually changed near TC1 and TC2, the 14N resonance frequency exhibited a split in the number of signals near TC1. Furthermore, the shorter spin-lattice relaxation time T1ρ of 1H than that of 13C suggests facile energy transfer for1H. Additionally, analysing the temperature dependencies of T1ρ for 13C revealed that the activation energy Ea in phase I is approximately five times greater than those in phases III and II. The high Ea observed in phase I primarily stems from the collective motion of the N(CH3)4 group, which contrasts with the considerable freedom observed for the CH3 group in phases III and II. These distinctive physical properties suggest potential applications for [N(CH3)4]2MnCl4 as an organic‒inorganic hybrid material.

Crystal structures, phase transitions, thermodynamics, and molecular dynamics of organic–inorganic hybrid crystal [NH(CH3)3]2ZnCl4

Understanding the physical properties of organic–inorganic hybrid [NH(CH3)3]2ZnCl4 is necessary for its potential application in batteries and fuel cells due to its environmentally-friendly, and highly stable character. Here, we determine its overall properties in detail, such as its orthorhombic crystal structure, and phase transition temperatures associated with five different phases. Structural geometry was studied by the chemical shifts caused by the local field around 1H. No changes were observed for the environment around 1H for CH3, whereas the 1H chemical shifts around NH in the cation were shown due to the change in the hydrogen bond N‒H···Cl. This is related to the change in Cl around Zn in the anion. In addition, the coordination geometry of 14N and 1H around 13C exhibited increased symmetry at high temperatures. Finally, we were able to understand its molecular dynamics by the significant change with temperature observed from the spin–lattice relaxation time T1ρ values, which represent the energy transfer for the 1H and 13C atoms of the cation. The activation energies obtained from the T1ρ results were 3–4 times large at phase I (> 348 K) than at phase V and IV (< 286 K). The relaxations show that the energy barriers in phases IV and V are related to the reorientation of methyl groups around the triple symmetry axis, while the reorientation of methyl groups of the cation in phase I is related to as a whole.

Analysis of the Structure, Thermal, and Molecular Dynamics of Organic-Inorganic Hybrid Crystal at Phases IV, III, II, and I: [NH2(CH3)2]2CdBr4.

A comprehensive understanding of the physicochemical properties of organic-inorganic hybrids is essential for their solid-state lighting applications. Therefore, a single crystal of [NH2(CH3)2]2CdBr4 was grown; the crystal structure was monoclinic, and the phase transition temperatures for the four phases IV, III, II, and I were 383 K (TC1), 417 K (TC2), and 427 K (TC3). Furthermore, the chemical shifts caused by the local field around 1H, 13C, 14N, and 113Cd changed continuously with temperature, especially near TC1, indicating that the local environment changes with temperature. Owing to the large change in 113Cd chemical shifts, the coordination geometry of Br around Cd in the CdBr4 tetrahedra changes near TC1. Therefore, it is proposed that Br plays a significant role in the N-H···Br hydrogen bond. Finally, the spin-lattice relaxation time T1ρ, representing the energy transfer around the 1H and 13C atoms of the cation, changed significantly with temperature. The activation energies obtained from the T1ρ results were two times larger at high temperatures than at low temperatures. This study provides an understanding of the fundamental properties of organic-inorganic hybrid compounds to broaden their applications.

Investigating the physicochemical properties, structural attributes, and molecular dynamics of organic–inorganic hybrid [NH3(CH2)2NH3]2CdBr4·2Br crystals

An in-depth understanding of the physicochemical properties of the organic–inorganic hybrid [NH3(CH2)2NH3]2CdBr6 whose structure corresponds to the formulation [NH3(CH2)2NH3]2CdBr4· 2Br is essential for its application in batteries, supercapacitors, and fuel cells. Therefore, this study aimed to determine the crystal structure, phase transition, structural geometry, and molecular dynamics of these complexes. Considering its importance, a single crystal of [NH3(CH2)2NH3]2CdBr6 was grown; the crystal structure was found to be monoclinic. The phase transition temperatures were determined to be 443, 487, 517, and 529 K, and the crystal was thermally stable up to 580 K. Furthermore, the 1H, 13C, 14N, and 113Cd NMR chemical shifts caused by the local field surrounding the resonating nucleus of the cation and anion varied with increasing temperature, along with the surrounding environments of their atoms. In addition, 1H spin–lattice relaxation time T1ρ and 13C T1ρ, which represent the energy transfer around the 1H and 13C atoms of the cation, respectively, varied significantly with temperature. Consequently, changes in the coordination geometry of Br around Cd in the CdBr6 anion and the coordination environment around N (in the cation) were associated with changes in the N–H···Br hydrogen bond. The structural geometry revealed critical information regarding their basic mechanism of organic–inorganic hybrid compounds.

Structural geometry and molecular dynamics of hybrid organic–inorganic [NH3(CH2)6NH3]CdCl4 crystals close to phase transition temperatures

Organic–inorganic hybrid perovskites are highly promising for application in various electrochemical devices, such as batteries and fuel cells. The physical properties of crystals of the organic–inorganic hybrid perovskite [NH3(CH2)6NH3]CdCl4 are important for their future application. Therefore, these crystals were grown and their phase transition temperatures TC1 = 337 K and TC2 = 472 K were determined using powder X-ray diffraction and differential scanning calorimetry. We observed that the crystallographic surroundings of 1H and 13C in the cation near TC1 did not show significant changes, whereas those of 113Cd in the anion changed significantly. The change in the coordination geometry of C1 around Cd near TC1 changed the N–H···Cl bond by connecting with the 1H of NH3. The nuclear magnetic resonance spin-lattice relaxation time T1ρ suggested that the 1H energy transfer processes in phases III and II were easier, whereas the 13C energy transfer processes were easier in phase III than in phase II. The results of the current study for [NH3(CH2)nNH3]CdCl4 (n = 6) were compared with those for n = 2, 3, 4, and 5 obtained from previous studies. The features of the length of CH2 and even–odd number of carbons in the diammonium chain are expected to facilitate potential applications in the future.

Crystal growth, phase transition, and nuclear magnetic resonance of organic-inorganic hybrid perovskite NH2(CH3)2CdCl3.

Understanding the physicochemical properties of organic-inorganic hybrid materials is essential to promote their applications. In this study, a single crystal of NH2(CH3)2CdCl3 was grown, and it exhibited a monoclinic structure. Its phase transition temperatures were 460 and 470 K, and it showed sufficient thermal stability. The changes in the NMR chemical shifts of each atom in the crystal with increasing temperature were determined; the chemical shift of 1H of NH2 in the NH2(CH3)2 cation changed with temperature, which was correlated to the changes in the chemical shift of 14N in NH2. The change in 113Cd chemical shifts indicate the change of six Cl atoms around Cd in CdCl6. Therefore, the change in the coordination geometry of CdCl6 is attributed to the change in the N-H⋯Cl hydrogen bond between the NH2(CH3)2 cation and CdCl6 anion. In addition, the 13C activation energies Ea obtained from the spin-lattice relaxation time T1ρ values are smaller than those of the 1H Ea values, suggesting that is free compared to 1H in the cation. We believe that this study furthers our fundamental understanding of organic-inorganic hybrid materials to promote their practical solar cell applications.

Structural Characterization and Dynamics of a Layered 2D Perovskite [NH3(CH2)5NH3]MnCl4 Crystal near Phase Transition Temperature

[NH3(CH2)5NH3]MnCl4 crystals are grown via slow evaporation, and the crystal undergoes a phase transition at 298 K (TC) according to differential scanning calorimetry, and the structures determined via X-ray diffraction at 173 and 333 K are orthorhombic systems in the space group Imma. These results differed slightly from those previously reported, and the reasons for this are analyzed. The thermal stability is relatively high, with a thermal decomposition temperature of approximately 570 K. The 1H spin-lattice relaxation times t1ρ exhibited very large variations, as indicated by the large thermal displacement around the 1H atoms, suggesting energy transfer at ~TC, even if no structural changes occurred. The influences of the chemical shifts of 1H of NH3 and short t1ρ of C1 adjacent to NH3 in cation are insignificant, indicating a minor change in the N−H⋯Cl hydrogen bond related to the coordination geometry of the MnCl6 octahedron. These properties will be make it a potential application for eco-friendly solar cells.

Dynamic motions of organic cation in organic–inorganic hybrid 1,4-butanediammonium tetrabromocuprate (II) crystal by solid-state nuclear magnetic resonance spectroscopy

The organic–inorganic hybrid perovskite [NH3(CH2)4NH3]CuBr4 is an important material for light-emitting and photovoltaic devices. In the present study, the thermal behavior, physicochemical properties, and structural geometries were investigated. Thermogravimetric analysis revealed thermal stability of the compound up to ∼490 K. Moreover, changes were observed in the nuclear magnetic resonance chemical shifts for 1H and 14N in the NH3 group bonded at both ends of the organic chain and for 13C in the CH2-b close to the NH3, which were related to the changes in the N–H•••Br hydrogen bonds. The molecular dynamics were analyzed in terms of the spin–lattice relaxation time T1ρ. The 13C T1ρ value for CH2-b was smaller than that of CH2-a because CH2-b was close to the NH3 group of the organic chain and formed an N–H•••Br hydrogen bond of the CuBr4 inorganic chain. Furthermore, the T1ρ value was smaller when 1H and 13C were located near the paramagnetic Cu2+ ion than when they were far away from the Cu2+ ion. Thus, [NH3(CH2)4NH3]CuBr4 crystal has good applicability because the T1ρ value is nearly constant with temperature.

Physicochemical properties of the cation in organic–inorganic perovskite [NH3(CH2)4(NH3)]ZnBr4 crystals investigated using 1H and 13C nuclear magnetic resonance relaxation

Despite having a wide range of applications as an organic–inorganic hybrid perovskite, detailed studies of the physical properties and structural dynamics of [NH3(CH2)4NH3]ZnBr4 crystals have not been published to date. This work investigates the structural properties of these crystals using X-ray diffraction, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The crystal structure was orthorhombic, and the phase-transition temperatures were 354, 434, and 514 ​K. In addition, the physicochemical properties of the cations in this crystal were investigated using 1H and 13C nuclear magnetic resonance (NMR) relaxation. The structural environments of 1H and 13C as evaluated by chemical shifts in the [NH3(CH2)4(NH3)] cation did not change significantly with increasing temperature. The spin-lattice relaxation times T1ρ for 1H were dependent on temperature change, but the T1ρ for 13C located in the center of the N–C–C–C–C–N bond was nearly independent of temperature. We compared [NH3(CH2)3NH3]ZnBr4 crystals previously reported and the [NH3(CH2)4(NH3)]ZnBr4 crystals prepared herein.

Thermodynamic Property and Solid-State Molecular Dynamics of Cs2MnBr4·2H2O Crystal

The lattice constants of Cs2MnBr4·2H2O crystals grown by the slow evaporation method were determined by X-ray diffraction. The thermal stability of Cs2MnBr4·2H2O was investigated as a function of its H2O content, and an endothermic peak at 378 K (= Tp) obtained by differential scanning calorimetry (DSC) was related to the loss of 2H2O. Thermogravimetric analysis (TGA) and DSC results revealed that Cs2MnBr4·2H2O was transformed to Cs2MnBr4 at temperatures above the TP. In addition, from 133Cs magic angle spinning nuclear magnetic resonance (MAS NMR) results, one Cs site was observed at temperatures below the TP and two Cs sites above it. The change of the spin–lattice relaxation time T1ρ near TP is related to variations in the symmetry of the octahedral Cs+ environment consisting of four Br− ions and two water molecules, upon the loss of H2O.

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.

Structures, local symmetries, and paramagnetic effects in Cs2Zn1-yCuyCl4 (y = 0, 0.3, 0.5, 0.7, and 1) mixed crystals by solid-state NMR

The effects of the partial replacement of Zn2+ ions with paramagnetic Cu2+ ions on Cs2Zn1-yCuyCl4 (y = 0, 0.3, 0.5, 0.7, and 1) crystals are discussed through MAS NMR. Here, five crystals are grown, and their structures are defined through X-ray diffraction. The local-structure environments for crystallographically inequivalent Cs(1) and Cs(2) sites surrounded by Cl− ions are discussed due to the differences in the chemical shifts and spin-lattice relaxation times T1ρ in the rotating frame of 133Cs. The results show that the structures, chemical shifts, and T1ρ with y = 0.3 and 0.5 are similar to those with y = 0, whereas those with y = 0.7 are similar to those with y = 1. In the case of y = 0.7, the signal at 848.54 ppm is obtained in addition to signals obtained from Cs(1) and Cs(2) site. The 133Cs T1ρ has small values according to the paramagnetic ions and these values are inversely proportional to the square of the hyperfine coupling strength.

Structural dynamics of CH3NH3+ and PbBr3\u2212 in tetragonal and cubic phases of CH3NH3PbBr3 hybrid perovskite by nuclear magnetic resonance

Understanding the structural dynamics of lead-halide perovskites is essential for their advanced use as photovoltaics.Here, the structural dynamics of the CH3NH3 cation and PbBr6 octahedra in the perovskite CH3NH3PbBr3 were studied via nuclear magnetic resonance (NMR) to determine the mechanism of the transition from the tetragonal to cubic phase. The chemical shifts were obtained by 1H, 13C, and 207Pb magic angle spinning NMR and 14N static NMR. The chemical shifts of the 1H nuclei in CH3 and NH3 remained constant with increasing temperature, whereas those of the 13C and 207Pb nuclei varied near the phase transition temperature (TC = 236 K), indicating that the structural environments of 13C and 207Pb change near TC. The spin–lattice relaxation time T1ρ values for 1H, 13C, and 207Pb nuclei increased with increasing temperature and did not exhibit an abrupt change near TC. In addition, the two lines in the 14N NMR spectra superposed into one line near TC, indicating the occurrence of a phase transition to a cubic phase with higher symmetry than tetragonal. Consequently, the main factor causing the phase transition from the tetragonal to cubic phase near TC is a change in the surroundings of the 207Pb nuclei in the PbBr6 octahedra and of the C–N groups in the CH3NH3 cations.

Thermodynamic, Physical, and Structural Characteristics in Layered Hybrid Type (C2H5NH3)2MCl4 (M = 59Co, 63Cu, 65Zn, and 113Cd) Crystals.

The thermal, physical, and molecular dynamics of layered hybrid type (C2H5NH3)2MCl4 (M = 59Co, 63Cu, 65Zn, and 113Cd) crystals were investigated by thermogravimetric analysis (TGA) and magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The temperatures of the onset of partial thermal decomposition were found to depend on the identity of M. In addition, the Bloembergen–Purcell–Pound curves for the 1H spin-lattice relaxation time T1ρ in the rotating frames of CH3CH2 and NH3, and for the 13C T1ρ of CH3 and CH2 were shown to exhibit minima as a function of the inverse temperature. These results confirmed the rotational motion of 1H and 13C in the C2H5NH3 cation. Finally, the T1ρ values and activation energies Ea obtained from the 1H measurements for the H‒Cl···M (M = Zn and Cd) bond in the absence of paramagnetic ions were larger than those obtained for the H‒Cl···M (M = Co and Cu) bond in the presence of paramagnetic ions. Moreover, the Ea value for 13C, which is distant from the M ions, was found to decrease upon increasing the mass of the M ion, unlike in the case of the Ea values for 1H.

Effects of paramagnetic interactions by the partial replacement of Zn2+ ions with Cu2+ ions in lead-free zinc-based perovskite (MA)2ZnCl4 crystal by MAS NMR

The growths, structures, phase transition temperatures, and molecular dynamics of mixed (MA)2Zn1-xCuxCl4 (x=0, 0.3, 0.5, 0.7, and 1) crystals were investigated to understand the effect of the random presence of paramagnetic Cu2+. In addition, the spin-lattice relaxation time T1ρ in the rotating frame by the magic angle spinning nuclear magnetic resonance (MAS NMR) method was obtained for 1H and 13C nuclei to understand the molecular dynamics for varying amounts of Cu2+ ions. The structure and phase transition temperature for the case where x=0.3 was similar to those for x=0, whereas those of x=0.5 and 0.7 were similar to those for x=1. Although the crystal structures and phase transition temperatures were similar for x (=0 and 0.3), and x (=0.5, 0.7, and 1), the molecular motions of 1H and 13C for x=0.3 differed from those for x=0, 0.5, 0.7, and 1. We compared the activation energies Ea by the molecular motions for 1H and 13C, based on the T1ρ. The Cu2+ presence for x=0.3 in the mixed structure indicates any differences in the Ea for 1H and 13C, and the replacement of Zn2+ ions by Cu2+ ions for x=0.3 was strongly affected by the molecular motions.

Interpretation of the crystal growth, phase transition, and molecular dynamics of [N(CH3)4]2ZnBr4 crystals by replacing partially the Zn2+ ions with Co2+ ions

The effects on the physical properties of [N(CH3)4]2Zn1-xCoxBr4 (x = 0, 0.5, 0.7, and 1) crystal due to the partial substitution of Zn2+ ions with paramagnetic Co2+ ions were discussed. The crystal structures and phase transition temperature (287 K) of layered perovskite-type [N(CH3)4]2Zn1-xCoxBr4 were nearly unaffected by the partial doping of Co2+ ions, as revealed by X-ray diffraction and differential scanning calorimetry experiments. The environments surrounding the 1H and 13C in [N(CH3)4]2Zn1-xCoxBr4 mixed systems were determined from the chemical shifts and the spin-lattice relaxation time T1ρ of 1H magic angle spinning nuclear magnetic resonance (MAS NMR) and 13C cross-polarization (CP)/MAS NMR. The molecular motions by the T1ρ for 13C nuclei were nearly unaffected when Zn2+ ions were substituted with Co2+ ions, whereas those for 1H nuclei were influenced by doping Co2+ ions. A comparison of the molecular dynamics of TMA-Zn1-xCoxBr4 studied in this paper with the previously reported TMA-Zn1-xCoxCl4 was made to understand the effects of Cl and Br ions.

Thermal and structural properties, and molecular dynamics in organic-inorganic hybrid perovskite (C2H5NH3)2ZnCl4.

The thermal and structural properties and molecular dynamics of layered perovskite-type (C2H5NH3)2ZnCl4 are investigated by differential scanning calorimetry, thermogravimetric analysis, and magic angle spinning nuclear magnetic resonance spectroscopy. The thermal properties and phase transitions are studied. Additionally, the Bloembergen–Purcell–Pound (BPP) curves for the 1H spin–lattice relaxation time T1ρ in the C2H5NH3 cation and for the 13C T1ρ in C2H5 are shown to have minima as a function of inverse temperature. This observation implies that these curves represent the rotational motions of 1H and 13C in the C2H5NH3 cation. The activation energies for 1H and 13C in the C2H5NH3 cation are obtained; the molecular motion of 1H is enhanced at the C-end and N-end of the organic cation, and that at the carbons of the main chain is not as free as that for protons at the C-end and N-end.

Molecular dynamics of cations and anions by 1H MAS NMR, 13C CP/MAS NMR, 14N NMR, and 113Cd NMR in hybrid organic-inorganic (CH3NH3)2CdBr4

The local structure of (CH3NH3)2CdBr4 as a function of temperature was investigated by 1H MAS NMR, 13C CP/MAS NMR, 14N NMR, and 113Cd NMR, with emphasis on the role of the CH3NH3+ cation and CdBr42− anion. The chemically and physically inequivalent CH3NH3+ groups, CH3(1) and CH3(2), NH3(1) and NH3(2), were clearly distinguished by 13C CP/MAS NMR and 14N NMR spectra. In addition, to obtain detailed information on the dynamics of the crystal, the spin-lattice relaxation times T1ρ of 1H and 13C and the spin-lattice relaxation time T1 of 113Cd were measured. The T1ρ of 13C showed a minimum and is governed by the tumbling motion of the CH3 groups, indicating that the 1H and 13C atoms in the CH3NH3+ groups exhibit high mobility at high temperatures. The spin-lattice relaxation time thus provides insight into the rates of cation reorientation at high temperatures.

Cation dynamics by 1H and 13C MAS NMR in hybrid organic-inorganic (CH3CH2NH3)2CuCl4.

To understand the dynamics of the cation in layered perovskite-type (CH3CH2NH3)2CuCl4, the temperature-dependent chemical shifts and spin–lattice relaxation times T1ρ in the rotating frame have been measured using 1H magic angle spinning nuclear magnetic resonance (MAS NMR) and 13C cross-polarization (CP)/MAS NMR techniques. Each proton and carbon in the (CH3CH2NH3)+ cation is distinguished in MAS NMR spectra. The Bloembergen–Purcell–Pound (BPP) curves for 1H T1ρ in CH3CH2 and NH3, and for the 13C T1ρ in CH3 and CH2 are revealed to have minima at low temperatures. This implies that the curves represent the CH3 and NH3+ rotational motions. The amplitude of the cationic motion is enhanced at the C-end, that is, the N-end of the organic cation is fixed to the inorganic layer through N–H⋯Cl hydrogen bonds, and T1ρ becomes short with larger-amplitude molecular motions.

Chemical shift and spin–lattice relaxation time for two crystallographically inequivalent 133Cs sites in Cs2BBr4 (B=57Co, 63Cu, and 65Zn) using magic-angle spinning nuclear magnetic resonance

The structural geometry around the 133Cs nuclei in Cs2BBr4 (B = 57Co, 63Cu, and 65Zn) was investigated by examining the chemical shifts and spin–lattice relaxation times in a rotating frame. Two crystallographically inequivalent Cs(1) and Cs(2) sites were differentiated. The spin–lattice relaxation times T1ρ of 133Cs nuclei in three crystals were measured to obtain detailed information about their structural dynamics. Cs(1) surrounded by eleven bromide ions was found to have a longer relaxation time than Cs(2) surrounded by nine bromide ions. The nuclear magnetic resonance (NMR) results were compared to previously reported results for Cs2BCl4. The halogen species in Cs2BX4 (X = Br, Cl) was not found to influence the relaxation time, whereas the B metal ion (B = Co, Cu, and Zn) was found to alter the relaxation time mechanism.