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Article

Phase Transition and Switchable Dielectric Properties of a Three-Dimensional Hydrogen-Bonding Framework Based on Cobalt (Ⅲ), o-Bromoaniline, and 18-Crown-6

1
Chemistry and Chemical Engineering College, Xinjiang Agricultural University, Ürümqi 830052, China
2
College of Mechanical and Electrical Engineering, Xinjiang Agricultural University, Ürümqi 830052, China
3
Xinjiang Sub-Center, National Engineering Research Center of Novel Equipment for Polymer Processing, Guangzhou 510641, China
*
Authors to whom correspondence should be addressed.
Crystals 2024, 14(1), 87; https://doi.org/10.3390/cryst14010087
Submission received: 15 December 2023 / Revised: 11 January 2024 / Accepted: 11 January 2024 / Published: 16 January 2024
(This article belongs to the Section Crystal Engineering)

Abstract

:
The organic–inorganic hybrid compound, (o-BrAH)[H2Co(CN)6]0.5·(18-crown-6)0.5·H2O, was synthesized and characterized by variable-temperature X-ray diffraction, single-crystal diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and dielectric measurements. Single-crystal X-ray diffraction revealed a three-dimensional cage-like structure formed through the hydrogen bonds of cobalt hexacyanide, supermolecular cations, and water molecules. Temperature variation triggered an abrupt change in the cage structure and simultaneously caused dynamic oscillation of the supramolecules within the framework of [Co(CN)6]3, inducing a phase transition accompanied by a step-like change in the dielectric physical properties.

Graphical Abstract

1. Introduction

Molecular machines have attracted significant interest in the field of materials science owing to their wide application in sensors, gas storage, smart materials, and high-energy materials [1,2,3,4]. These molecular devices aim to convert energy into controllable movements in response to variations in temperature, pressure, light, electric or magnetic fields, and other external stimuli [5,6,7,8,9,10]. Among the family of molecular machines, solid molecular rotors, as components of artificial molecular machinery, have received much attention for their dynamic and physical properties [11,12,13,14].
Recent studies have reported the design of solid materials endowed with remarkable dynamics in their various components [15,16,17,18]. A class of materials that exhibit open-framework structures is the category of organic–inorganic hybrid supermolecular materials. These hybrids stand out for their diverse range of attributes compared to specific pure organic supermolecular compounds, such as optical, magnetic, ferroelectric, and dielectric properties while allowing easy structural tunability, excellent processability, non-toxicity, lightweight qualities, flexibility, and the occurrence of well-defined symmetry-breaking phase transitions [19,20,21,22,23].
Typically, electrical, magnetic, or optical responses tend to change abruptly close to the phase transition temperature. Organic–inorganic hybrids have emerged as favorable candidates for integrating phase transition properties with diverse switching response characteristics [24,25,26,27,28]. For responsive dielectrics, the dipolar orientation (e.g., order–disorder or melting/frozen-like transition) is the primary contributor to the dielectric constant. For example, polar molecules or functional groups often yield switchable dielectric constants, undergoing dielectric transitions between high and low dielectric states [29,30,31,32,33,34,35,36].
Xiong et al., presented a new organic–inorganic hybrid molecular ferroelectric, [cyclopentylammonium]2CdBr4(1), showing a moderate above-room-temperature TC of 340.3 K. The mechanism of the ferroelectric phase transition from Pnam to Pna21 in 1 is ascribed to the order–disorder transition of both the organic cations and inorganic anions [37,38]. Cyanogen metal complexes have a relatively stable thermal energy structure. If it is introduced into the molecular motor system, it will effectively improve the thermal stability of inorganic–organic hybrid functional materials [39,40,41,42,43]. One example is (DMA)2(H2O)[Co(CN)6] (DMA = dimethylammonium cation), with two-dimensional frameworks of the (H2O)[Co(CN)6] and (DMA)[Co(CN)6] components arranged alternately through hydrogen bonding [41]. The compound demonstrates how intermolecular interactions control crystal packing and influence the dynamics of the polar components, which are responsible for the switchable dielectric properties.
To design an organic–inorganic hybrid supermolecular rotor, it is necessary to select appropriate organic and inorganic components. Macrocyclic ligands such as crown ethers have been the subject of intense research for several decades owing to their superior selectivity in complexation with organic cations and metal ions [44,45,46]. Crown ether complexes can form non-covalent and hydrogen-bonded complexes with ammonium cations in both solution and solid states [47,48,49]. Typically, 18-crown-6 and its derivatives display the strongest affinities for organic ammonium cations (NH4+, RNH3+, R2NH2+, etc.) in a 1:1 stoichiometry, as observed in numerous studies. However, certain structurally characterized complexes of crown ethers with RNH3+ exhibit varying stoichiometries, as highlighted in specific studies [50,51].
In our previous work, we discovered that the protonated organic amine RNH3+ cation (R = organic group) can be easily anchored within the cavity of 18-crown-6 and act as a rotator or pendulator in the design of molecular machines. Such interactions can create effective structural polarizations, providing a novel way to reveal the structure–property relationship [52,53]. By using this method, several new crown ether clathrates, such as 3-methoxyanilinium-18-crown-6 bis(trifluoromethanesulfonyl)ammonium ([(3-methoxyanilinium)(18-crown-6)][trifluorosulfuric acid]) [54] and [15-crown-5][Y(NO3)2(H2O)5][NO3] [55] were synthesized with large dielectric anomalies at 260 K. These studies clearly show that different organic amines and anions have significant impacts on the phase transition temperatures and polarization intensity.
Building upon the insights from previous discoveries, we synthesized a new hybrid compound, (o-BrAH)[H2Co(CN)6]0.5·(18-crown-6)0.5·H2O (o-BrAH = o-bromoaniline), denoted as compound 1, exhibiting intricate cage-like hydrogen-bonded three-dimensional frameworks. Subsequently, the phase transition and switchable dielectric constant of 1 were verified using scanning calorimetry, single-crystal X-ray diffraction, and variable-temperature dielectric constant measurements. Our results showed that the dielectric transition of 1 originated mainly from the stretching deformation of the space between the cobalt atoms of the vertex of the cage-like structures.

2. Materials and Methods

2.1. Material and Instruments

All chemicals and solvents purchased from commercial sources were of analytical grade and were used directly without any further purification. Elemental (C, H, and N) analyses were performed using a Varo EL Elementar Analysen System GmbH (Hanau, Germany). Thermogravimetric (TG) and differential thermal analysis (DTA) were carried out by TA Q50 thermal analyzer (New Castle, DE, USA) in the temperature range of 300–860 K under a nitrogen atmosphere at a heating rate of 10 K min−1. Differential scanning calorimetry (DSC) measurements were carried out on a TA Q2000 (TA Instruments Inc., New Castle, DE, USA) for a single-crystal sample between 200 and 350 K at a temperature scanning rate of 10 K min−1. The excess heat capacity associated with the phase transition was evaluated by subtracting from the data the baseline representing the variation in the absence of the phase transitions. Infrared spectra (IR) were recorded on a Thermo Scientific Nicolet iS5 (Waltham, MA, USA) instrument at room temperature, within the range of 400–4000 cm−1. Powder X-ray diffraction (PXRD) data were collected on a BrukerD2 PHASER powder diffractometer operating at 40 kV and 30 mA using Cu Kα radiation with λ = 1.5418 Å for 2θ of 5 to 50°. The crystal and copper wire were stuck together with silver glue to form the corresponding capacitor structure. The dielectric permittivity was measured using a TH2828A precision LCR meter in the temperature range of 150–295 K at frequencies ranging from 500 Hz to 1 MHz. The commonly used equipment for testing dielectric constant is the TH2828A precision LCR instrument. Select a single crystal with complete structure, apply uniform silver glue on both sides of the single crystal, and then connect the copper wire with the silver glue. The other end of the copper wire is connected to both sides of the small circuit board to form a capacitor structure, and then, connect the small circuit board to the dielectric device. In the range of temperature 150–295K at frequencies ranging from 500 Hz to 1 MHz, a better curve of dielectric constant change is obtained through the gradual change of temperature and frequency.

2.2. Preparation of (o-BrAH)[H2Co(CN)6]0.5·(18-Crown-6)0.5·H2O (1)

Compound 1 was obtained by slow evaporation of methanol solution. As shown in Scheme 1, three clean beakers were prepared and 10 mL of methanol was added, and 0.76 mmol (130.73 mg) o-bromoaniline, 0.76 mmol (200.00 mg) 18-crown-6, and 0.76 mmol (166.13 mg) cobalt cyanide H3[Co(CN)6] were added, respectively. First, o-bromoaniline was fully mixed with 18-crown-6 methanol solution. Then, the methanol solution of cobalt cyanide H3[Co(CN)6] was carefully added in a dropwise manner to make the mixed solution fully mixed. The mixed solution (30 mL) was evaporated at room temperature for one week to obtain yellow crystals. The yield of the product is about 67%.
The analytical calculated composition for C15H22BrN4O4Co0.5 was as follows: C, 41.73%; H, 5.14%; N, 12.98%. The actual found composition was C, 41.51%; H, 5.31%; N, 12.76%.

2.3. Crystal Structure Determination

Single-crystal X-ray diffraction experiments at 100 K and 296 K were conducted using a Bruker Smart ApexⅡ single-crystal diffractometer with Mo Kα radiation (λ = 0.71073 Å). Data reduction and absorption correction were carried out using SAINT and SADABS software packages, respectively. The crystal structures at different temperatures were resolved via direct methods using the SHELXL-97 software package. Non-H atoms were refined anisotropically, and all H atoms were generated geometrically and refined by using a “riding” model with Uiso = 1.2 Ueq(c). Details of data collection, structure refinement, and crystallography are summarized in Table 1.

3. Results and Discussion

3.1. Spectral Properties

Each component showed the characteristic IR stretches of the individual component of the molecule (Figure S1). The IR spectra of 1 contained the characteristic peaks of 18-crown-6 molecules at 835, 955, and 1089 cm−1, corresponding to the specific –O–C–C– structural unit. The strong broad band from 3541 cm−1 to 2643 cm−1 indicated the intermolecular N–H···O hydrogen bonding interactions between the N atom of the protonated –NH2 group and the O atoms of 18-crown-6. The series of characteristic peaks at 1599, 1563, 1348, 1300, and 1250 cm−1 were assigned to the skeletal vibrations of the aromatic rings. The sharp peaks within the 2175–2050 cm−1 range were characteristic of the stretching vibrations of the –C≡N bond of the [Co(CN)6]3 anion. Overall, the IR spectra analysis revealed the successful incorporation of the three effective constituents (18-crown-6, o-bromoanilinium, and [Co(CN)6]3 anion) in compound 1.

3.2. TG and DSC Analysis

In order to explore potential crystal phase transitions within compound 1 triggered by external temperature variations, we conducted sequential heating and cooling cycles between 200 and 290 K. As shown in Figure 1, an endothermic peak occurred during the heating process at a temperature of approximately 265 K, attributed to Tc. The phases below and above Tc were labeled as LTP (low-temperature phase) and RTP (room-temperature phase), respectively, for ease of reference.
During the cooling process, the corresponding exothermic peak shifted to a lower temperature of about 255 K. The appearance of a well-defined reversible anomaly and a large thermal hysteresis (10 K) suggested that the transition was first order. The transition enthalpy (ΔH) of the endothermic process was estimated to be 1.63 kJ mol−1, corresponding to an entropy change (ΔS) of 6.17 J mol−1 K−1. The calculation of the ratio of geometrically distinguishable orientations, represented as N, was performed using the Boltzmann equation (ΔS = RlnN), with R denoting the gas constant. The resulting value for N was 2.1, surpassing two, indicating an order–disorder mechanism rather than a displacive mechanism [56].
Thermogravimetric (TG) and differential thermal analyses (DTA) were performed in an N2 atmosphere from 300 to 860 K at a heating rate of 10 K min−1. The DTA curve showed a weak endothermic peak at 382 K (Figure S2), which corresponded to the melting point of 1. The TG curve revealed three primary weight-loss regions. Compound 1 maintained an ordered structure up to 382 K. Within the range of 382 to 429 K, the TG of compound 1 indicated an initial weight loss of 4.31% (calculated at 4.17%), attributed to the loss of a single free water molecule. The second sharp weight loss of nearly 70.31% was observed within the range of 429–519 K, where the decomposition of the supramolecular cation (o-BrAH)(18-crown-6)0.5 occurred. The third weight-loss step of 25.38% (calculated at 25.14%) involved the [H2Co(CN)6]0.5 anion. Overall, the DSC and TG analyses demonstrated the relatively good thermal stability of 1.

3.3. XRD Analysis

The phase purity of compound 1 was determined using X-ray powder diffraction (XRD). Comparison between the peak positions in both the experimental and simulated XRD patterns indicated good agreement (Figure 2). This result confirmed the successful acquisition of compound 1 in a pure crystalline phase. The difference in the intensity was attributed to the preferred orientation of the powder sample.

3.4. Description of Crystal Structure

To understand the origin of the reversible phase transition of compound 1, variable-temperature single-crystal X-ray structural analyses were performed at 100 K (LTP) and 296 K (RTP). The (o-BrAH)[H2Co(CN)6]0.5·(18-crown-6)0.5·H2O(1) structure crystallized in a centrosymmetric triclinic crystal system with space group P-1 (No. 2) at both LTP and RTP, indicating the existence of reversible iso-symmetric structural phase transitions. The complete crystallographic data and their collection and refinement are presented in Table 1.
Considering the minor alterations in cell parameters observed between LTP and RTP, it implies that factors beyond the phase transition, such as the presence of a distorted octahedral cation or molecular frame motion, could be contributing to this phenomenon.
The asymmetric units of the LTP and RTP of compound 1 comprised one o-BrAH cation, one-half of the 18-crown-6 molecule, and one-half of the [H2Co(CN)6] anion (Figure 3a,b). Figure 3 shows that the atomic temperature factor increased, indicating heightened thermal vibrations across all atoms as the temperature was increased from LTP to RTP. In addition, the thermal ellipsoids of the C, N, and O atoms of the 18-crown-6 molecule and o-BrAH cations showed significant changes from LTP to RTP. Such thermal ellipsoid changes can be attributed to the intermolecular oscillation or motion of the supramolecular cation (o-BrAH)(18-crown-6) upon heating, leading to detectable heat changes in compound 1.
In Figure 4, the cell of compound 1 contains two [H2Co(CN)6] anions and two supramolecular cations (o-BrAH)(18-crown-6). During the process from low temperature to room temperature, the distance between the two cobalt atoms and the planes of the two crown ethers increases from 11.508 A to 11.556 A and 8.138 A to 8.288 A, respectively. This is mainly due to the thermal expansion of molecules.
The change in supramolecular cations between the two phases is crucial for determining the origin of the structural phase transition. The most striking structural feature in the LTP and RTP is the tripolymer supramolecular cation structure (o-BrAH)2(18-crown-6) with two o-BrAH cations and one 18-crown-6 molecule connected through N–H···O hydrogen-bonding interactions. The oxygen atoms of 18-crown-6 are displaced above (O1, O2, O3) and below (O1i, O2i, O3i) the median plane of the ring, resulting in two completely parallel triangular planes.
The N atom of the o-BrAH cation is positioned in the perching configuration rather than the nesting configuration, resting at distances of 1.309 Å (LTP) and 1.422 Å (RTP) above the optimal plane formed by the O atoms of the 18-crown-6. Six hydrogen bondings exist between the O atoms of 18-crown-6 and the N atoms of the o-BrAH cation, where the short distance of N–H···O signifies strong interactions in the range of 2.832–3.188 Å at 100 K, and 2.844–3.220 Å at 296 K. In addition, the aromatic ring of the o-BrAH cation forms smaller dihedral angles to the O atom plane of the 18-crown-6 molecule, measuring 38.14° (LTP) and 40.83°(RTP) (Figure S3). This dihedral angle underwent a significant change with the temperature increase, suggesting that the angular change in the intermolecular oscillation of the supramolecular cation can affect the structural phase transition of 1.
To determine the coordination configuration of the Co ions, we analyzed the structures of the metal complexes at different temperatures. The Co–C bond lengths were in the range of 1.902–1.909 Å (LTP) and 1.901–1.911 Å (RTP), and the Co–C–N angles were from 178.84 to 179.64° (LTP) and 178.18 to 179.45° (RTP), generally close to 180°. Through all its six CN groups, two CN groups connected to two protons to form the new coordinating C–N–H+ group.
Because of the hydrogen protons, each water molecule formed three different types of hydrogen bonds: O–H···O, O–H···N, and N–H···O, forming connections with surrounding water molecules and two [H2Co(CN)6] anions (Figure 5a). The hydrogen bond lengths were 2.489 Å (LTP) and 2.479 Å (RTP) for O–H···O, 2.744 Å (LTP) and 2.715 Å (RTP) for O–H···N, and 2.704 Å (LTP) and 2.732 Å (RTP) for N–H···O (Table S1). This result indicated that, compared to the alterations in the Co–C bonds of the [H2Co(CN)6] anion, the hydrogen bond lengths underwent notable changes with the temperature increase.
The two [H2Co(CN)6] anions established connections with two adjacent water molecules through the interaction of N–H···O and O–H···N hydrogen bonds, forming a one-dimensional chain structure that extended along the a-axis direction (Figure 5b). The Co–Co distances, bridged by the CN groups and water molecules in adjacent [H2Co(CN)6] anions, ranged from 8.566 Å (LTP) to 8.724 Å (RTP) with the temperature changes. These changes in the hydrogen bond lengths and Co–Co distances clearly indicated that the molecular interaction was related to the phase transition and the corresponding changes in physical properties.
The two water molecules in the one-dimensional chain structure were connected to each other through O–H···O hydrogen bonds, creating a two-dimensional layered structure in the ab plane (Figure 6a), providing sufficient space for the (o-BrAH)2(18-crown-6) cation interpenetration. The interlayer distances between the averaged planes were 11.508 Å at LTP (Figure 6b) and 11.556 Å at RTP, indicating a significant distance elongation with increasing temperature.
The two protonated 2-bromoanilines in the dimer structure interacted with the crown ether molecules through N–H···O hydrogen bonds (Figure 7c). Complex 1 exhibited a three-dimensional supermolecular architecture, which can be visualized as connected dimer and 2D layer structures in the ab plane through N–H···N hydrogen-bond interactions between the remaining –C≡N ligand of the [H2Co(CN)6] anion and the –NH3+ group of the (o-BrAH)2(18-crown-6) cation (Figure 7a and Figure S4). A new type of framework was formed inside the crystal, in which the Co atoms were positioned in its vertices, presenting a hexahedral cage-like structure (Figure 7b). Notably, the supramolecular cation (o-BrAH)2(18-crown-6) occupied the space within the hexahedral cage-like structure, resulting in the formation of a novel filling arrangement (Figure 7d and Figure S5).
The most notable feature of the three-dimensional cage-like structure was the parallelepiped structure consisting of the eight cobalt (III) ions from the [H2Co(CN)6] anions (Figure 8). In LTP, the non-bonding angle values of the central Co···Co···Co atoms were 97.871°, 118.856°, and 100.254°, respectively. However, in the RTP, the non-bonding angle in the same position as the parallelepiped exhibited a notable change at temperature increments of 84.009°, 91.674°, and 106.350°.
By comparing the distances of adjacent Co···Co atoms in the two LTP and RTP structures, the adjacent Co···Co distances of 12.823 Å and 13.253 Å along the b- and a-axis orientation in the LTP structure resembled those of 12.860 Å and 13.210 Å for the RTP structure. In contrast, the adjacent Co···Co distance of 13.067 Å along the c-axis orientation in the LTP structure was determined to be longer than that in the RTP structure (11.556 Å), representing a significant change of 11.56%. These results suggested that the transformation of the parallelepiped structure along the c-axis through temperature changes caused structural phase transitions and dielectric anomalies.

3.5. Dielectric Properties

Various physical property anomalies change sharply near the phase transition temperature, and the degree of change is related to the characteristics of the phase transitions. The temperature- and frequency-dependent dielectric constants are effective indicators of the structural phase transitions. In the mechanism of the phase transition confirmed by DSC and the low- and room-temperature X-ray results mentioned above, compound 1 was presumed to exhibit a dielectric anomaly response triggered by changes in the temperature and electric field frequency.
Dielectric measurements were performed along each axis of compound 1 after pasting the crystal with elargol-conducting glue, over the frequency range of 500 Hz to 1 MHz upon cooling and within the temperature range of 150 K to 295 K. Figure 9 shows the changes in the real part of the temperature-dependent dielectric constant upon cooling. As the temperature decreased, distinct anomalies emerged around 265 K, aligning with the findings from the DSC results.
The real part of the dielectric constant showed strong temperature dependency under an applied electric field. Throughout the cooling process, the real parts of compound 1’s dielectric constant stayed steady at around 2.5. Between 150 K and 260 K at LTP, it exhibited a substantial increase up to approximately 16 near 265 K across all frequencies. It maintained this level until experiencing a notable temperature escalation to 295 K.
The results indicated that the dielectric constants could switch between high and low states, exhibiting two-phase transitions. These transitions allowed for tuning between two different states during the cooling processes. Furthermore, the independence of the dielectric constant from the frequency in the temperature range of 150–295 K indicated the absence of molecular motor rotation in the crystal.
Such temperature-triggered switching dielectric behavior is related to the intermolecular oscillation of the supramolecular cation (o-BrAH)(18-crown-6). At higher temperatures, the thermal vibrations of the atoms are intensified. The adjacent Co–Co distances of the parallelepiped in the crystal space varied between RTP and LTP, indicating notable deformation of the parallelepiped. As a result, the thermally activated intermolecular oscillation of the supramolecular cation and the deformation of the parallelepiped lead to dielectric anomalies.

4. Conclusions

In summary, we present a novel organic–inorganic hybrid compound, (o-BrAH)[H2Co(CN)6]0.5·(18-crown-6)0.5·H2O (1), with a three-dimensional hydrogen-bonding cage-like structure. The integration of low- and room-temperature structural analyses, DSC measurements, and dielectric measurements successfully showcased compound 1 as a new switchable molecular dielectric material. This material exhibits reversible structural phase transitions at 265 K and can be tuned to two distinct dielectric states by varying the temperature. Different temperature structure analyses revealed that the structural phase transition and dielectric anomaly were related to the intermolecular oscillation of the supramolecular cation and deformation of the parallelepiped structure at the eight cobalt (III) centers in the [H2Co(CN)6] anion. The switchable nature of the dielectric constant in 1 enhances the diversity of responsive dielectric materials within its family.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/cryst14010087/s1, Figure S1: IR spectrum of compound 1; Figure S2: TG and DTA curves of compound 1; Table S1: Hydrogen bond N–H···O geometry (Å, °) for compound 1; Figure S3: Swing diagram of crown ether cation complex o-BrAH of compound 1 at room and low temperature; Figure S4: ac planar graph of compound 1; Figure S5: bc planar graph of compound 1.

Author Contributions

Conceptualization, Z.-Q.L. and Y.L.; methodology, H.-Z.H.; software, N.W.; validation, H.-Z.H.; formal analysis, Y.-B.Y.; investigation, H.-Z.H. and A.A.; resources, Z.-Q.L.; data curation, H.-Z.H.; writing—original draft preparation, Y.L.; writing—review and editing, Z.-Q.L.; project administration, Z.-Q.L.; funding acquisition, Z.-Q.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the General Program of Natural Science Foundation of Xinjiang Uygur Autonomous Region (Grant No.2022D02A76); Key Research and Development Projects of the Xinjiang Uygur Autonomous Region (Grant No. 20220264-3); the Key R&D Plan Project in Xinjiang Autonomous Region (2022B02033-3, 2022B02049-3); the National Natural Science Foundation of China (Grant No. 21561030); the Xinjiang “Tianshan talent plan” project (Grant No. 2021061); and the Open Research Fund of Xinjiang Key Laboratory of Agricultural Chemistry and Biomaterials (KF202206).

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Scheme 1. Synthesis of compound 1.
Scheme 1. Synthesis of compound 1.
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Figure 1. DSC curves for compound 1 during the heating process.
Figure 1. DSC curves for compound 1 during the heating process.
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Figure 2. Experimental XRD pattern (a) and simulated pattern (b) of compound 1.
Figure 2. Experimental XRD pattern (a) and simulated pattern (b) of compound 1.
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Figure 3. Molecular structure of compound 1 at different temperatures: (a) asymmetric unit at 100 K, (b) asymmetric unit at 296 K.
Figure 3. Molecular structure of compound 1 at different temperatures: (a) asymmetric unit at 100 K, (b) asymmetric unit at 296 K.
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Figure 4. The change of the cell at different temperatures: (a) at 100 K (b) at 296 K.
Figure 4. The change of the cell at different temperatures: (a) at 100 K (b) at 296 K.
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Figure 5. (a) Molecular structure of water and cobalt cyanide anions; (b) N–H···O hydrogen bonds formed between cobalt cyanide anions and O atoms in adjacent water molecules.
Figure 5. (a) Molecular structure of water and cobalt cyanide anions; (b) N–H···O hydrogen bonds formed between cobalt cyanide anions and O atoms in adjacent water molecules.
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Figure 6. (a) Two-dimensional layered structure of compound 1. (b) Distance between cobalt atoms in adjacent layers.
Figure 6. (a) Two-dimensional layered structure of compound 1. (b) Distance between cobalt atoms in adjacent layers.
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Figure 7. (a) Two-dimensional layered structure formed by (18-crown-6)(o-BrAH) and [Co(CN)6] through hydrogen bonds. (b) Three-dimensional cage-like construction formed by 2D layered structure and two water molecules. (c) Dimeric structure of (18-crown-6)(o-BrAH)2. (d) Cage-like clathrate hydrate structure filled with the dimer.
Figure 7. (a) Two-dimensional layered structure formed by (18-crown-6)(o-BrAH) and [Co(CN)6] through hydrogen bonds. (b) Three-dimensional cage-like construction formed by 2D layered structure and two water molecules. (c) Dimeric structure of (18-crown-6)(o-BrAH)2. (d) Cage-like clathrate hydrate structure filled with the dimer.
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Figure 8. Three-dimensional cage-like construction at (a) 100 K and (b) 296 K.
Figure 8. Three-dimensional cage-like construction at (a) 100 K and (b) 296 K.
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Figure 9. Anisotropic dielectric constants of 1 along the c-axis at 500 Hz to 1 MHz upon cooling.
Figure 9. Anisotropic dielectric constants of 1 along the c-axis at 500 Hz to 1 MHz upon cooling.
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Table 1. Crystallographic data for compound 1.
Table 1. Crystallographic data for compound 1.
Temperature100 K296 K
Chemical formulaC15H22BrN4O4Co0.5C15H22BrN4O4Co0.5
Formula weight431.73431.73
Crystal size (mm3)0.22 × 0.20 × 0.180.22 × 0.20 × 0.18
Crystal systemTriclinicTriclinic
Space groupP-1P-1
a (Å)8.566(3)8.724(3)
b (Å)9.831(4)9.687(3)
c (Å)11.508(4)11.556(4)
α (°)75.764(4)77.799(4)
β (°)79.755(4)78.954(4)
γ (°)88.092(4)88.451(4)
V3)924.3(6)936.8(5)
Z11
Dcalc (g cm−1)1.5491.529
F (000)440440
μ (mm−1)2.6832.647
Measured 2θ range (°)0.980–25.2420.898–25.242
Rint0.04890.0700
R (I > 2(I)) [a]0.05790.0947
WR (all data) [b]0.13430.1918
GOF1.0881.054
CCDC23131242313125
[ a ] : R = ( F o F c ) / F o
[ b ] : R w 2 = w ( F o 2 F c 2 ) 2 / w ( F o 2 ) 2
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Hu, H.-Z.; Yan, Y.-B.; Wang, N.; Adila, A.; Liu, Y.; Liu, Z.-Q. Phase Transition and Switchable Dielectric Properties of a Three-Dimensional Hydrogen-Bonding Framework Based on Cobalt (Ⅲ), o-Bromoaniline, and 18-Crown-6. Crystals 2024, 14, 87. https://doi.org/10.3390/cryst14010087

AMA Style

Hu H-Z, Yan Y-B, Wang N, Adila A, Liu Y, Liu Z-Q. Phase Transition and Switchable Dielectric Properties of a Three-Dimensional Hydrogen-Bonding Framework Based on Cobalt (Ⅲ), o-Bromoaniline, and 18-Crown-6. Crystals. 2024; 14(1):87. https://doi.org/10.3390/cryst14010087

Chicago/Turabian Style

Hu, Hong-Zhi, Yi-Bo Yan, Na Wang, Abuduheni Adila, Yang Liu, and Zun-Qi Liu. 2024. "Phase Transition and Switchable Dielectric Properties of a Three-Dimensional Hydrogen-Bonding Framework Based on Cobalt (Ⅲ), o-Bromoaniline, and 18-Crown-6" Crystals 14, no. 1: 87. https://doi.org/10.3390/cryst14010087

APA Style

Hu, H. -Z., Yan, Y. -B., Wang, N., Adila, A., Liu, Y., & Liu, Z. -Q. (2024). Phase Transition and Switchable Dielectric Properties of a Three-Dimensional Hydrogen-Bonding Framework Based on Cobalt (Ⅲ), o-Bromoaniline, and 18-Crown-6. Crystals, 14(1), 87. https://doi.org/10.3390/cryst14010087

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