Ultra-large Dielectric Relaxation and Self-Recovery Triggered by

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Ultra-large Dielectric Relaxation and Self-Recovery Triggered by Hydrogen-Bonded Polar Components Danli Hong, Yang-Hui Luo, Xiao-Tong He, Cong Wang, Jia-Ying Wang, Fang-Hui Chen, Hong-Shuai Wu, Chen Chen, and Bai-Wang Sun ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b18883 • Publication Date (Web): 30 Jan 2019 Downloaded from http://pubs.acs.org on February 2, 2019

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ACS Applied Materials & Interfaces

Ultra-large Dielectric Relaxation and Self-Recovery Triggered by Hydrogen-Bonded Polar Components

Dan-Li Hong, Yang-Hui Luo, * Xiao-Tong He, Cong Wang, Jia-Ying Wang, Fang-Hui Chen, Hong-Shuai Wu, Chen Chen and Bai-Wang Sun*

School of Chemistry and Chemical Engineering, Southeast University, Nanjing, 211189, P.R. China. E-mail: [email protected] (LYH); [email protected] (SBW).

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Abstract: The subtle integration of rotatable polar components into dielectric crystals can contribute significantly to the adjustable switch temperatures (Ts) and dielectric relaxation behaviors. Currently, one of the biggest challenges lies on design of the optimal polar components with moderate motion resistance in the crystalline system. Here in this work, we demonstrate that under the refrigerator condition, the rotatable hydrogen-bonded 1D cationic chains {[C2H6N5]+}n (C2H6N5 = 3,5-diamino-1,2,4-triazolinium) and 2D anionic layers {[(H2O)2•SO4]2-}n can be generated in organic salt 3 ([C2H6N5]2•[(H2O)2•SO4]). Compared with the non-hydrated precursor 2 ([C2H7N5]•[SO4]), the rotation of these 1D and 2D ionic species have triggered the reversibly phase transition and dielectric switching in 3. In addition, the much sluggish rotation of the 1D cationic chains from parallel to un-parallel stacking, and the counter-clockwise rotation of the 2D anionic layers than the reverse process, have induced the frequency-dependent dielectric response with a more highly adjustable heating Ts ↑ than the cooling Ts ↓. More importantly, 3 possess excellent self-recovery ability attributing to the highly dynamics character of the hydrogen-bonded ionic species. The strategy here can provide a fairly good model for designing the dielectric crystals with desired rotatable polar components.

Keywords: dielectric, rotatable polar components, reversibly phase transition, self-recovery, organic salt.

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INTRODUCTION Molecular crystals showing stimuli-responsive properties have become one of the hotspots in the solid-state chemistry/physics field during the past decade.1-5 In general, spatially resolved anisotropic local structural changes of the molecular crystals that emerged as responses to appropriate external stimuli (e.g., temperature, light radiation, press, guest molecules, and external force), can be accompanied by dramatical variations of the bulk physical/chemical properties (e.g., magnetization, polarity and luminescence) between at least two distinct states,6-10 as well as the significant morphological changes or even mechanical motion.11-15 As a consequence, these kinds of stimuli-responsive molecular crystals have shown potential to be applied in the fields of sensors, actuators, displays, information storages, signal processing, and varactors.16-20 Thus, subtle molecular design to control the assemble of crystals with desired stimuli-responsive performance are of significant importance for both fundamental aspects and potential applications. Switchable polarity, which refers to the redistribution of positive and negative charge centers upon external stimuli, has emerged as a striking member of the stimuli-responsive materials family in recent years.20-25 The switching of polarity in molecular crystals contributes to the reversibly transition of dielectric responses between high and low dielectric states (HDS and LDS), thus has the potential to be incorporated into modern electrical and electronic devices.26-29 Note that, remarkable bi-stability and ultra-large relaxation behaviors in the 3



vicinity of room temperature under ambient conditions, are highly desired for the above-mentioned purpose.30,

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To date, the most promising dielectric

relaxations behavior are mainly focused on inorganic materials (such as ceramics),32,

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and only a handful examples of organic-inorganic hybrid

materials have been reported.34-41 Du et al.39 have confined the polar trimethylammonium cations in the three-dimensional (3D) cage-like frameworks, and found that the dynamics of cations has regulated the phase-transition and dielectric relaxation behaviors of the 3D frameworks; Tang et al.40 have constructed a two-dimensional (2D) 2,5-pyrro-lidinedione-lithium(I) hybrid compound, and their have demonstrated that the twist motion of pyrrolidine ligand and order-disorder motion of counter ClO4− anions were responsible for the reversible phase transition and ultra-large (15K) dielectric relaxation behaviors; More recently, Du et al.41 further reduced the rotation resistance of trimethylammonium cations through replacement of the covalently-bonded framework by a flexible hydrogen-bonded supramolecular framework, which has induced the frequency-regulated dielectric switch with highly adjustable switch temperatures (Ts). It should be noted that, the rotatable polar components in all of the above-mentioned examples belong to the isolated ionic points, which were distributed discretely in the gaps of crystal skeletons. Then the questions arise: what will happen if the isolated ionic points are connected into multi-dimensional ionic species? Or even the crystal skeleton itself became rotatable? Obviously, highly adjustable Ts and ultra-large dielectric relaxation

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behaviors can be demonstrated.

Scheme 1. Schematic illustration of the thermal induced rotation of hydrogen ions (a) and non-hydrogen ions (b) in hydrogen-bonded anionic species. In our recent work,42 we have demonstrated that the in-situ 90 degree rotation of the phosphate ions ([H2PO4]-) in 2D hydrogen-bonded phosphate layers (Scheme 1a, and Figure S1), as well as the 90 degrees rotation of hydrogenbonded one-dimensional (1D) 3,5-diamino-1,2,4-triazolinium cation ([C2H6N5]+) chains, have resulted the reversible phase transition and unprecedented 40K wide dielectric relaxation behaviors near room temperature in organic salt [C2H6N5]·[H2PO4] (1). These encouraging results have inspired us to explore the influence of hydrogen-bonded ionic species in different forms on phase transition and dielectric relaxation behaviors, for the purpose of controlled synthesis and oriented dielectric properties. With the above-mentioned considerations in mind, we then performed co-crystallization of 3,5-diamino1,2,4-triazole with H2SO4 (see the experimental section). Note that, the separate [SO4]2- anions can’t be connected into the hydrogen-bonded ionic species as [H2PO4]- ions, unless the presence of double hydrogen-donor molecules (Scheme 1b). Hence, the searching for new crystallization strategies 5



to generate multi-dimensional hydrogen-bonded ionic species with nonhydrogen ions are highly desired. Under ambient conditions, the organic salt [C2H7N5]•[SO4] (2) without the formation of hydrogen-bonded ionic species was formed. While under refrigerator conditions, the hydrated organic salt [C2H6N5] 4•[(H2O)2•SO4]2 (3) with the formation of multi-dimensional hydrogen-bonded ionic species was obtained. As a consequence, 2 shows no obviously phase transition and dielectric response. On the contrary, 3 displays thermal induced reversibly phase transition and frequency-regulated dielectric switching between HDS and LDS, accompanied by frequency-tuned ultra-large dielectric relaxation width. The inherent switching mechanism of 3 was demonstrated by variable-temperature single-crystal analyses, variable-temperature-frequency dielectric measurements, as well as the molecular surfaces calculations (crystal voids, Hirshfeld surfaces, deformation charge density and electrostatic potential). More importantly, dehydration experiments revealed that 3 possess excellent self-recovery ability, the 3-dehydration species can completely recover into 3 in air within 2.5h.

RESULTS AND DISCUSSIONS Under ambient conditions, the co-crystallization of 3,5-diamino-1,2,4-triazole and H2SO4 give birth to column-shaped crystals of 2 ([C2H7N5]•[SO4]). The thermogravimetric analysis (TGA) shows that 2 can maintained to 180 ºC under a nitrogen atmosphere (Figure S2). Single-crystal X-ray diffraction at RT reveals that 2 crystallizes in monoclinic P21/c space group (Table S1) with the 6


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asymmetric unit (ASU) consists of an entire molecule of 3,5-diamino-1,2,4triazolinium cation ([C2H7N5]2+ and [SO4]2- anion, with all the nitrogen atoms on triazole moieties have been protonated) (Figure S3). In the crystal, each cation binds to five anions through N-H…O hydrogen bonding contacts (Figure 1a), and vice visa for each anion (Figure 1b), generating a complicated 3-D structure (Figure 1c). Note that, both the cations and anions in the crystal of 2 were separated without the formation of multi-dimensional hydrogen-bonded ionic species. In addition, the variable temperature single-crystal X-ray diffraction have demonstrated the almost identical crystal structure with that of 293 K (Table S1, Figure S3 and S4), suggesting the absence of phase transition. Hence, the searching for the effectively crystallization strategy to generate the desired multi-dimensional hydrogen-bonded ionic species with [SO4]2- anion was of urgent importance. After screened for several attempts, we found that the refrigerator conditions can meet this ambition. Where, the block-shaped hydrated crystals 3 (4[C2H6N5]4•[(H2O)2•SO4]2) was obtained. Single-crystal X-ray diffraction at RT reveals that 3 crystallizes in triclinic P-1 space group (Table S2) with the ASU consists of four molecules of 3,5-diamino-1,2,4-triazolinium cation ([C2H6N5]+), two [SO4]2- anions and four H2O molecules (Figure 1d). Note that, the introduction of double hydrogen-donor H2O molecules has resulted in the formation of multi-dimensional hydrogen-bonded ionic species. Where, the [C2H6N5]+ cations were connected into 1-D structures through moderate N7



Figure 1. Crystal structure of crystals 2 and 3. (a) and (b): the crystalline environment of [C2H7N5]2+ cation and [SO4]2- anion in 2; (c): the 3-D motif of crystal 2; (d) and (e): the ASU of 3-HDS and 3-LDS (the blue planes represent the fitting-plane of 1-D cationic chains, the dihedral angle and distance between them have been highlighted); (f): the 3-D stacking motif of the hydrogen-bonded 1-D cationic chains {[C2H6N5]+}n and 2-D anionic layers {[(H2O)2.SO4]2-}n in crystal 3; (g) the connecting style of the 1-D cationic chains; (h-k) comparison between the centroids…centroids (h and j) and edge…edge distances (i and k) of stacked1-D cationic chains at HDS (upper) and LDS (lower).

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H…N hydrogen bonding contacts (N…N distance of 3.069 Å) involving NH2 and triazole moieties along the crystallography a axis, resulting a 1-D hydrogenbonded cationic chains (Figure 1f and g). While the H2O molecules and [SO4]2anions were connected into 2-D hydrogen-bonded anionic layer via O-H…O hydrogen bonding contacts (Figure 1f and Figure 2). Note that, this 2-D layer was composed by [(H2O)2•SO4]2- units in a wavy manner which contribute to the rotation (Figure 2 and Figure S5). In the crystal, the 1-D cationic chains were stacked along the crystallography b axis, which were further supported by the 2-D anionic layers along the crystallography c axis into 3-D framework (Figure 1f and Figure S6). It should be stressed that, the adjacent 1-D cationic chains were un-parallel stacking with dihedral angle of 1.67 Å (Figure 1d), and the 2-D anionic layers were arranged in …A(-A)… manners (Figure 2 upper). TGA measurements revealed the removal of water molecules in 70-95 ºC range, and the residual species can be maintained to 250 ºC under a nitrogen atmosphere (Figure S2). The formation of multi-dimensional hydrogen-bonded ionic species in 3 has indicated the possibility of phase-transition, which was verified by the variabletemperature single-crystal X-ray diffractions. Upon cooling to 100K, the space group of 3 is still P-1, however, the unit cell parameters (Table S2) and crystal structures (Figure 1e) have changed dramatically. Compared with the crystal structure at 293K, the ASU at 100K has reduced in half with only one [SO4]2anion, two molecules of cation ([C2H6N5]+) and two molecules of H2O (Figure 9



Figure 2. (a): Comparison between the connecting motif of the 2-D anionic layers {[(H2O)2•SO4]2-}n at HDS (upper) and LDS (lower); (b) the rotation of the [(H2O)2•SO4]2- unit upon phase transition has been highlighted (the blue planes represent the fitting-plane of O-H…O hydrogen bonding plane). S6). In the crystal, the 1-D cationic chains, the 2-D anionic layers, as well as the 3-D stacking styles were retained. However, significant changes of the ionic clusters have been observed. For the 1-D cationic chains, the distance of NH…N hydrogen bonding contacts has decreased (Figure S7), and the adjacent 1-D chains has parallel stacking with plane…plane distances of 3.141 Å (Figure 1e), demonstrating the rotation of cationic chains accompanied by phase transition, which was similar to our previously results. More importantly, the stacking of 1-D cationic chains has become more compact with dramatical 10


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decrease in distance along the crystallography b and c axis. Where, the centroids…centroids and edge…edge distances of adjacent 1-D cationic chains have decreased upon cooling (Figure 1h-k), which was in accordance with the dramatical change of unit cell parameters (Table S2) and the calculated crystal voids (decreased from 142 Å3 to 62 Å3, Figure S8), demonstrating an interesting contraction phase transition. While for the 2-D anionic layers, both the [SO4]2- anion and H2O molecules have underwent about 120 ºC degree clockwise rotation upon cooling to 100K (Scheme 1b, Figure 2), which was accompanied by a decrease in O-H…O hydrogen bonding distances within the 2-D layers (Figure S9), demonstrating again the compact crystal stacking after phase transition. Note that, the compact stacking was at the expense of increasing in the distances between adjacent [ (H2O)2•SO4]2- units (Figure S5). The above crystal structural analysis has suggested the single-crystal-tosingle-crystal (SCSC) phase transition of crystal 3, which was further confirmed by the differential scanning calorimetry (DSC) measurements (Figure 3a). Upon cooling from room temperature, a sharp exothermic peak at around -25 ºC was observed, which can be assigned to the transformation from HDS to LDS, with un-parallel to parallel stacking rotation of the 1-D cationic chains and clockwise rotation of the 2-D anionic layers; while on the warming procedure, the sharp endothermic peak was appeared at around 5 ºC. Thus, a reversible phase transition with 30K wide large thermal hysteresis loop has been presented, suggesting that the LDS to HDS transformation, which corresponds to the

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breaking of a more compact crystal from parallel to un-parallel stacking rotation of the 1-D cationic chains, and counter-clockwise rotation of the 2-D anionic layers, were thermodynamics difficult than its reverse process. Thus, excellent dielectric switching properties with tunable dielectric relaxation behaviors can be expected with 3.

Figure 3. (a) DSC curves of 3 as measured in cooling−heating cycles; (b) and (c) comparison between the 3-D dnorm Hirshfeld surfaces, deformation charge density and electrostatic potential of [C2H6N5]+ cation and [SO4]2- anion at HDS (upper) and LDS (lower); (d) comparison between the 2-D fingerprint plots of [C2H6N5]+ cation at HDS (left) and LDS (right). The multi-dimensional hydrogen-bonded ionic species belongs to the polar components, and the rotation of them will certainly have a profound effect on the polarity of crystals. To demonstrate this, molecular surfaces calculations 12


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(Hirshfeld surfaces, deformation charge density and electrostatic potential) for 3,5-diamino-1,2,4-triazolinium cation ([C2H6N5]+) and [SO4]2- anion in 3 have been performed. For the cation, 3-D dnorm Hirshfeld surface (Figure 3b) and Deformation charge density calculations demonstrate the complete reverse of the positive and negative charge center (Figure 3b), which will lead to the complete reorientation of dipoles.42 In addition, partial of the positive electrostatic potential has shifted to the amino group upon HDS to LDS transition (Figure 3b), suggesting again the reorientation of dipoles on 1-D cationic chains. For the [SO4]2- anion, obviously changes between Hirshfeld surfaces, deformation charge density and electrostatic potential at different dielectric state also have been observed (Figure 3c), which will certainly contribute significant to the dielectric properties of 3. For comparison, the molecular surfaces calculations of 2 have been performed, results revealed that it seems impossible for the double protonated cation ([C2H7N5]2+) to have changeable deformation charge density and electrostatic potentials (Figure S10), which was further confirmed straightforward the formation of multidimensional hydrogen-bonded ionic species is the significant premise for the occurrence of phase transition and polarity switching for this kind of organic salts.

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Figure 4. (a) and (b): Real part of the dielectric constants of 3 depend on temperature at 1000 KHz and 500 Hz, respectively; (c)-(f): Comparison between the real (c and d) and imaginary (e and f) part of 3 upon cooling and heating under different frequency, respectively. The significant influence of the rotatable multi-dimensional hydrogen-bonded ionic species on the dielectric properties of crystal 3 has been demonstrated by the variable-temperature dielectric spectroscopy. Shown in Figure 4a was the variation of the real part (ε′) value at 500 Hz as a function of temperatures on cooling-warming cycles. Upon cooling, a rapid decrease of ε′ value from 256 at -32 ºC to 14 at -70 ºC, with cooling Ts ↓ = -46 ºC was observed, indicating a complete transformation from the HDS to the LDS. While on the warming runs, the ε′ value has shown a gradual increase of from 14 at -62 ºC to 328 at 10 ºC, with heating Ts ↑ = -26 ºC, corresponding to the complete LDS to HDS transition. Thus, a 20K wide hysteresis loop for the reversible HDS-LDS

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transformation was demonstrated. It should be stressed that, the dielectric responses of the LDS-HDS transition is relatively gradual and almost 1.3 times larger

than

its

reverse

process,

which

can

be

attributed

to

the

thermodynamically difficult rotation of both the 1-D cationic chains from parallel to un-parallel stacking, and the counter-clockwise rotation of the 2-D anionic layers in the highly compacted crystals. When at 1000 KHz, the ε′ - T curves have shown the similar profile as that at 500 Hz (Figure 4b). However, the switching process becomes more gradual, the Ts ↓ and Ts ↑ has shifted to -40 and -5 ºC, respectively. Thus, a frequencyregulated dielectric switch with highly adjustable Ts and relaxation width can be proposed. To verify this conclusion, the ε′ - T curves at 1, 5, 10 and 100 KHz have been recorded (Figure 4c and d). As we have expected, the gradualness was increased with the frequency, the Ts ↓ and Ts ↑ have measured to be -45 and -25 ºC, -45 and -20 ºC, -44 and -18 ºC, -43 and -15 ºC, respectively. Thus, the rarely documented frequency-dependent dielectric switching with highly adjustable Ts and hysteresis loop have been demonstrated. In addition, strong frequency dependence in imaginary part has also been demonstrated (Figure 4e and 4f). This phenomenon can’t be observed without the presence of rotatable

multi-dimensional

hydrogen-bonded

ionic

species,

as

the

thermodynamically difficult rotation of hydrogen-bonded ionic species (LDS-toHDS) have resulted in more highly adjustable Ts ↑ than its reverse process (Ts ↓, HDS-to-LDS). We can then conclude that the more thermodynamically

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difficult rotation of polar components, the more highly adjustable dielectric switch temperature and hysteresis loop, which are of practical importance for the controlled synthesis of materials with oriented dielectric properties.

Figure 5. Comparison of PXRD patterns (a) and TGA profiles (b) of 3 at different self-recovered state. From the above discussions, the water molecules have played the key role for the striking contrast between crystals 2 and 3, the dynamics of water was then deserved to be investigated. Upon heating under 100 ºC for 2h, the crystalline water has removed and the crystal lattice of 3 has been destructed (Figure 5a). The obtained 3-dehydrated species have shown highly “hungry” to water. It can absorb the equal amount water as the hydrated species from the air within 0.5 h (Figure 5b). Note that, at that time, the absorbed water was not fully integrated into the crystal lattice, as it can be completely removed before 78 ºC. To our surprise, the absorbed water molecules can be integrated into the crystal lattice progressively with prolonged exposure in air, and finally, the 3-dehydrated species can completely self-recovered into 3 with exposure for 16


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2.5h, as have been confirmed by the PXRD and TGA measurements (Figure 5a and 5b, Figure S11). These results have demonstrated the excellent selfrecovery ability of organic salt 3, which was further verified by the SEM (scanning electric microscopy) measurements (Figure 6). After dehydration, the lamellar samples of 3 were destructed into discrete pieces, upon exposure in air, the discrete pieces were merged into lamellar block progressively. After in air for 2.5h, it can completely recover into the initial state of 3 (Figure S12). We speculate that the formation of 2-D hydrated anionic layers contributes mainly to the self-recovery ability.

Figure 6. SEM images of 3-dehydrated species in air with different exposure times.

Conclusion In summary, through the refrigerator condition crystallization strategy, the multidimensional hydrogen-bonded ionic species have been generated in organic salt ([C2H6N5]2•[(H2O)2•SO4]). Compared with the non-hydrated precursor 17



([C2H7N5]•[SO4]),

the

rotatable

hydrogen-bonded

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1-D

cationic

chains

{[C2H6N5]+}n and 2-D anionic layers {[(H2O)2•SO4]2-}n have triggered reversibly phase transition and dielectric switching between HDS and LDS. Upon considering the rotation resistance for polar components in the more compact lattice, the parallel to un-parallel stacking rotation of the1-D cationic chains and the counter-clockwise rotation of the 2-D anionic layers are more sluggish than their reverse process, resulting a frequency-dependent dielectric response with a more highly adjustable LDS-to-HDS heating Ts ↑ than the HDS-to-LDS cooling Ts ↓. As a consequence, the dielectric relaxation width has been tuned from 20K to 35K. More importantly, the hydrated organic salt has shown excellent self-recovery ability, demonstrating the highly dynamics of the multidimensional hydrogen-bonded ionic species. These results can provide a fairly good model for designing the dielectric materials with desired rotatable polar components.

EXPERIMENTAL SECTION Materials. All syntheses were performed under ambient conditions and all the chemicals were of analytical grade and used without further purification. The aqueous solution (20 mL) containing 3, 5-diamino-1, 2, 4-triazole (C2H5N5, 0.99 g, 10 mmol) and H2SO4 was evaporated under ambient condition to afford colorless column-shaped crystals of 2 (yield 86%, based on 3, 5-diamino-1, 2, 4-triazole). While under refrigerator conditions, the block-shaped crystals of 3 were precipitated (yield 90%, based on 3, 5-diamino-1, 2, 4-triazole). 18


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Physical Measurements. High-temperature TGA measurements for 2 and 3 were performed using a Mettler-Toledo TGA/DSC STARe System at a heating rate of 10 K min-1 under an atmosphere of dry N2 flowing at 20 cm3min-1 over a range from 50 to 800 °C. LOW-temperature DSC measurements for 3 were measured on a PerkinElmer Diamond DSC under nitrogen at 0.1 MPa with a heating/cooling rate of 10 K min−1 in the temperature range -100 - 25 ºC. Dielectric constant was measured with a Tonghui TH2828A impedance analyzer over the frequency range from 0.5 kHz to 1 MHz with an applied electric field of 0.5 V in the temperature range -150 -25 ºC. The SEM images were recorded by using a Field emission scanning electron microscope (FESEM, HITACHI S-4800 20 kV). The PXRD measurements were performed on an Ultima IV diffractometer equipped with Cu Kα radiation (λ = 1.5418 Å) in the range 5-50°at room temperature. Molecular Hirshfeld surface calculations (Hirshfeld surfaces, deformation charge density and electrostatic potential) were performed by using the CrystalExplorer17 program.43 The single-crystal X-ray diffraction data for 2 and 3 were collected with a Bruker-AXS SMART APEXII diffractometer equipped with a CCD type area detector and Mo-Kα radiation (λ = 0.71073 Å) in ω-2θ scan mode. The diffraction data were corrected for Lorentz and polarization effects and for absorption by using the SADABS program. The structures were solved by direct methods, and the structure solution and refinement based on |F|2 were performed with the SHELX software. All non-hydrogen

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atoms were refined with anisotropic displacement parameters, whereas all hydrogen atoms were positioned geometrically and refined with isotropic displacement parameters according to the riding model. All geometrical calculations were performed with the SHELXL-2014 software.44 The crystal data and structure refinement parameters at different temperatures for 2 and 3 were summarized in table S1 and S2, respectively. CCDC 1556505 and 1854591-1854593 contain the supplementary crystallographic data of 2 and 3 at different temperatures. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. The rotation style of the hydrogen-bonded phosphate ions ([H2PO4]-), TGA plots, crystal data and structure refinement details, additional crystal structural analysis and molecular surfaces calculations for crystals 2 and 3.

AUTHOR INFORMATION Corresponding Author *[email protected] (Y.H. Luo)

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*[email protected] (B.W. Sun) Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by the Natural Science Foundation of China (Grant No. 21701023), Natural Science Foundation of Jiangsu Province (Grant No. BK20170660), “Perfect Young Scholars” Program of Southeast University and PAPD of Jiangsu Higher Education Institutions.

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