Thermally Induced Reversible Double Phase Transitions in an

An organic−inorganic hybrid iodoplumbate crystal (C4H12NPbI3, TMAPbI3) can ... Our results indicate that there is an existence of a transitional str...
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Thermally Induced Reversible Double Phase Transitions in an Organic−Inorganic Hybrid Iodoplumbate C4H12NPbI3 with Symmetry Breaking Guangfeng Liu,† Jie Liu,§ Zhihua Sun,‡ Zhenyi Zhang,# Lei Chang,† Junling Wang,† Xutang Tao,§ and Qichun Zhang*,†,⊥ †

School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China ‡ Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China # Bruker Scientific Technology Co. Ltd, Beijing 100081, China ⊥ Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore §

S Supporting Information *

ABSTRACT: A one-dimensional (1D) organic−inorganic hybrid iodoplumbate crystal (1, C4H12NPbI3, TMAPbI3) can undergo two reversible phase transitions as the temperature decreases. Its dynamic phase-transition behaviors were carefully studied by dielectric measurements, thermal analysis, and variable-temperature crystallographic studies. These results indicate that the phase transitions possess a disorder−order feature with a noncentrosymmetrical intermediate phase structure. Due to the existence of the ordered motion and reorientation of the C4H12N+ cation, 1 undergoes two phase transitions: the first one from space group P63/m at room temperature to Pm at 163 K with symmetry breaking, and the second one from space group Pm at 163 K to P61 at 142 K with partial symmetry restoration. Our results indicate that there is an existence of a transitional structure with a low symmetry space group during the disorder−order-type phase transitions, which can provide us valuable information to deeply understand the disorder−order phase transition in organic−inorganic hybrids.

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architectures.3b,5 However, although the dielectric anomaly and ferroelectric phenomenon have been reported in one-dimensional (1D) iodoplumbate hybrids,6 there are almost no reports about the solid-state phase transitions with an accurate analysis of crystal structures in this system, which makes it impossible to deeply understand the interactions between organic and inorganic components. Recently, switchable dielectric compounds7 have attracted wide research interests due to their possible applications in data communication, signal processing, thermoelectricity, and storage.8 Though great progress has been achieved in exploring and designing related materials, the key knowledge regarding the intrinsic motions of dipole moments induced by structural changes is still not sufficient. Moreover, the study of reversible solid-state phase transitions in artificial crystals can provide many opportunities to explore rotational, translational, or

INTRODUCTION Solid-state phase transitions, including polymorphism, play a key role in modern crystal chemistry.1 Understanding and controlling phase transitions should be very helpful to successfully prepare novel compounds with specific chemical and physical properties.2 This is particularly important to the research on iodoplumbate-based organic−inorganic hybrids because different spatial arrangements of inorganic components could lead to various electrical properties ranging from insulators to semiconductors.3 For example, the phase transitions of three-dimensional (3D) perovskite iodoplumbates, including methylammonium lead iodide (MAPbI3) and formamidinium lead iodide (FAPbI3), have been extensively studied because of their promising applications in photovoltaic and light emitting devices.3a,4 Meanwhile, photoluminescence and thermochromic phenomena have also been investigated in solid-state phase transitions of two-dimensional (2D) iodoplumbate hybrids, where PbI6 octahedral units could assemble into layered perovskite sheets from “natural quantum-well” © XXXX American Chemical Society

Received: May 10, 2016

A

DOI: 10.1021/acs.inorgchem.6b01143 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry reorientation behaviors of the moiety in crystalline materials.9 Meanwhile, pure inorganic or organic switchable dielectric compounds have existed for a long time, and only recently has a lot of effort been put forth to develop new inorganic−organic hybrids because there are many desirable features arising from the interactions between inorganic constituents and organic units.10 Obviously, structurally well-defined inorganic−organic hybrids should give us better insight into these interactions. However, the phase-transition research with an accurate analysis of solid-phase structures on 1D iodoplumbate hybrids for the switchable dielectric is still in its infancy, although the ferroelectric behavior has been observed in 3D perovskite hybrids MAPbI3.11 Such gaps strongly encourage us to investigate the solid-state phase transition of 1D iodoplumbate materials. Although the 1D iodoplumbate tetramethylammonium triiodolead(II) (C4H12NPbI3, TMAPbI3, 1) can be obtained through traditional complicated organic syntheses,12 in this research, we utilized a simple one-step approach (an in situ Nalkylation reaction13 to prepare compound 1). The as-prepared material possesses a 1D chain architecture constructed by PbI6 octahedrons and exhibits two reversible phase transitions due to the molecular motion of tetramethylammonium cationic moiety (C4H12N+). During the phase transitions, the cation acts as a rotator, while the PbI3− anion behaves as the stator-like part. More importantly, an interesting intermediate phase of C4H12NPbI3 was discovered, suggesting that a low symmetry transitional structure exists in the disorder−order phase transition.

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Table 1. Crystallographic Data and Structure Refinement Parameters of Three Phases of 1 phase

RTP (C4H12NPbI3)

ITP (C4H12NPbI3)

LTP (C4H12NPbI3)

T (K) formula weight space group Z a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) ρ calcd (g/cm3) R (int) R1 [I > 2σ(I)] wR2 [I > 2σ(I)] GOF

293 662.04 P63/m 2 9.798(3) 9.798(3) 7.953(3) 90 90 120 661.2 (5) 3.325 0.0486 0.0304 0.0780 0.943

163 662.04 Pm 2 9.6621(16) 15.840(3) 9.6626(16) 90 119.980(2) 90 1281.0(4) 3.433 0.0491 0.0664 0.1816 1.036

110 662.04 P61 6 9.616(3) 9.616(3) 23.734(6) 90 90 120 1900.5(11) 3.471 0.0622 0.0509 0.1404 1.006

for the ITP and LTP structures should be C4H12NPbI3. Moreover, there are no obvious N−H vibration peaks in the FT-IR spectrum of 1 (Figure S2), which further confirms that they should tetramethylammonium cations rather than trimethylamine cations in the RTP structure. Therefore, we believe that the automatically calculated formula as C3H9NPbI3 is not correct. Thus, we chose C4H12NPbI3 as the reported formula for the RTP structure. This B-level alert should be a result of the serious disorder of tetramethylammonium cations. The possible pseudo/new space group P63/mmc is also suggested by ADDSYM in the checkCIF report of the RTP structure. However, when we checked the ADDSYM through the program PLATON, two cases existed: (1) if ADDSYM was searched as chemical type I, there was no obvious space group change needed/suggested; and (2) if it was checked as chemical type N and Pb, space group P63/mmc and P6/mmm were suggested, respectively. Although we tried several times to change the space group from P63/m to P63/mmc, the entire structure became a mess when refined, which may result from the disorder of carbon atoms. A similar phenomenon was also reported by Contreras et al.12 Therefore, we believe that the real space group of RTP is P63/m, and the space group P63/mmc should a pseudo space group. Thermal Measurement. Under a nitrogen atmosphere, differential scanning calorimetry (DSC) was conducted in aluminum crucibles with heating and cooling rates of 10 K min−1 from 110 to 240 K. Thermogravimetric and differential scanning calorimetry synergetic tests (TGA-DSC) for 1 were carried out on a TGA/DSC/1600HT analyzer (METTLER TOLEDO Instruments). The sample was placed in an Al2O3 crucible and heated at a rate of 10 K min−1 from room temperature to 850 K under flowing nitrogen gas. Dielectric Constants Measurement. In the temperature-dependent dielectric constants experiments, powder samples and single-crystal samples of 1 were covered by a silver conductive paste on the surfaces as the electrodes. Complex dielectric permittivities (ε = ε′ − iε″) were measured using a TH2828A impedance analyzer at frequencies of 500 kHz and 1 MHz with an applied electric field of 0.5 V. Low-Temperature SHG Measurements. SHG measurements were performed using a Q-switched Nd:YAG laser beam (λ = 1064 nm, 5 ns pulse duration, 10 Hz repetition rate). The low temperature (160 K) was achieved using a Linkam stage.

EXPERIMENTAL SECTION

Materials and Methods. All starting materials are analytical grade and were directly used as received. To prepare compound 1, HI (≥40%, 1 mL), melamine (0.5 mmol, 63 mg), PbI2 (0.5 mmol, 231 mg), and CH3OH (4 mL) were mixed in a Teflon-lined autoclave (25 mL) and heated at 120 °C for 4 days. After being slowly cooled to room temperature at the speed of 10 K h−1, 1 was harvested as yellow prismatic crystals in 73% yield (based on PbI2). Powder X-ray Diffraction. The phase purity and identity of 1 were performed at room temperature on a power X-ray diffractometer (PXRD) equipped with Cu Kα radiation (λ = 1.54056 Å) in the 2θ range of 9−50° with scanning speed of 0.2 s/step and a step size of 0.02°. IR Spectroscopy. A Thermo-Nicolet Nexus 670 spectrometer has been used to record the attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR) of a powder sample of 1 in the range of 700−4000 cm−1 at room temperature. Variable-Temperature Single-Crystal X-ray Diffraction. Single-crystal X-ray data for a prism shape single-crystal of 1 (0.21 × 0.29 × 0.49 mm) was collected using graphite-monochromated and 0.5 mm mono cap-collimated Mo Kα radiation (λ = 0.71073 Å) with the ω scan method. The data reduction and cell refinement were processed with the SAINT program of the APEX2 software. The SADABS program for area detector was applied for multiscan absorption corrections. The structure was solved by the direct method and refined by the full-matrix least-squares method on F2 (SHELX-97).14 All nonH atoms were refined anisotropically. Hydrogen atoms were placed in idealized positions and included as riding with Uiso (H) = 1.2 Ueq (C). Crystallographic data and structure refinement of the low-temperature phase (LTP at 110 K), intermediate-temperature phase (ITP at 163 K), and room-temperature phase (RTP at 293 K) are provided in Table 1. Additional information in the form of CIF files has also been supplied as Supporting Information. For the RTP structure, the calculated and reported molecular weights have a difference of 15.03 in the checkCIF report because the formula is automatically calculated as C3H9NPbI3, while the formula calculation from the single-crystal of 1

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RESULTS AND DISCUSSION Usually, N-alkylated iodoplumbates are synthesized from the reaction between organic amines, PbI2, and alkyl iodides under an alkaline condition, whereas alkyl iodides are obtained from the reaction between alcohols and HI under acidic conditions. B

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two endothermic peaks at 153.6 and 176.4 K on heating. The exothermic and endothermic anomalies represent that the thermal hysteresis in the first-phase transition is about 11 K, and that of the second one is about 7 K. The relatively wide thermal hysteresis strongly suggests that these phase transitions possess the first-order phase transition feature,16 although the latent heat of the phase changes was small. These results further prove that an intermediate phase existed in the temperature range from 142 to 176 K, and the ordered low-temperature structure of 1 changed to the disordered room-temperature phase through this intermediate phase. For convenience, we name the phase below 142 K as the LTP, the phase from the temperature range between 142 to 176 K as the ITP, and the phase above 177 K as the RTP. The TGA-DSC curve of 1 shows no remarkable weight loss and no thermal anomaly before 629 K (Figure S3), demonstrating that 1 is stable over the temperature ranging from 300 to 620 K. It is well-known that materials with the ABX3 formula can adopt different crystal structures depending on the sizes of the A cation and the corner-sharing BX6 octahedron. An empirical r +r index named the Goldschmit tolerance factor (t = 2 A(r +Xr ) )

In this research, we chose another effective one-step approach to form compound 1, namely, in situ N-alkylation of organic amines with alcohols under solvothermal conditions13 followed by the formation of N-alkylated iodoplumbate. During the reaction, nitrogen-rich melamines were decomposed and reacted with MeOH to form the tetramethylammonium cations in the presence of HI, which helps the self-assembly of PbI3− anions (Scheme S1). The identity and purity of the as-obtained crystals were confirmed by PXRD (Figure S1) and FT-IR spectra (Figure S2). The PXRD results matched well with the calculated pattern based on the structure of 1 at roomtemperature. Note that there are no obvious N−H vibration peaks in the IR spectrum, which proved that the N-alkylation process did happen and that the tetramethylammonium (C4H12N+) cations were formed from the reaction between melamine and methanol. Figure 1 presents the shape of the

B

X

can be used to predict which structure is preferentially adopted, where rA, rB, and rX are the radii of the A cation, B cation, and X anion, respectively.17 The inorganic−organic hybrid halide materials tend to form an orthorhombic structure when t < 0.8, a cubic phase when 0.8 < t < 1, and a hexagonal structure when t > 1.18 For the target compound 1, C4H12NPbI3 (TMAPbI3), the radius of organic cation C4H12N+ is obviously bigger than that of CH3NH3+ in MAPbI3 and HC(NH3)2+ in FAPbI3. Although it is difficult to determine the exact size of C4H12N+ cations in the hybrids resulting from the nonspherical geometry and the rotation of these organic cations, the tolerance factor (t ≈ 1.1) can be qualitatively calculated according to the typical crystal ionic radius of C4H12N+, Pb2+, and I− (Table S1),19 suggesting that the crystal structure of 1 should possess the hexagonal feature. The variable-temperature X-ray single-crystal diffraction experiments were carried out at 293 (RTP), 163 (ITP) and 110 K (LTP) (Table 1). The results at 293 K reveal that 1 crystallized in the centrosymmetric space group P63/m and point group of 6/m with cell parameters of a = 9.798(3) Å, c = 7.953(3) Å, and V = 661.2 (5) Å3; the unit cell parameters are consistent with the previous report.12 As shown in Figure 3a, the asymmetric unit of RTP consists of a lead atom on a 6-fold screw axis and an iodine atom occupying a mirror plane. As for the structure of LTP, it still belongs to a hexagonal system, while the space group and point group change into chiral P61 and 6, respectively, with the detailed cell parameters a = 9.616(3) Å, c = 23.734(6) Å, and V = 1900.5(11) Å3. The asymmetric unit of LTP contains a PbI3− unit and a C4H12N+ unit (Figure 3c), which makes the c-axis length and the unit cell volume almost three times larger than those of RTP. Figures 3d and f display the C4H12N+ cation and the adjacent PbnI3n−n anionic 1D chain in the RTP and LTP structures. The C4H12N+ cation in the RTP is seriously disordered (every C atom locates three possible sites), and the bond length of all Pb−I bonds in the PbI6 octahedron equal 3.234 Å, which leads to a crystallographic m mirror plane and an inversion center in the structure. Meanwhile, for the LTP structure, the disordered C4H12N+ cation is totally frozen out and becomes well-ordered, while Pb−I bonds are anisotropic and have six different bond lengths, which makes the previous m mirror plane and the

Figure 1. Photo of single crystals of 1 and the predicted crystal morphology based on the BFDH method.

yellow prismatic crystals of 1 and its morphology deduced from the Bravais−Friedel Donnay−Harker (BFDH) method15 according to the room-temperature structure data. It can be concluded that the developed facets of the as-grown crystals are {1010̅ }, which is almost consistent with the BFDH results. It is well-known that DSC measurements can be used to effectively detect phase transitions and confirm the existence of heat anomaly. The heating−cooling cycle DSC measurements over the temperature range of 125 to 200 K were carried out on the polycrystalline sample of 1, and the corresponding results are shown in Figure 2. The DSC curve clearly indicates that 1 underwent two reversible phase transitions with two exothermic peaks at 169.2 and 142.6 K upon cooling and

Figure 2. DSC curves of 1 with a rate of 10 K min−1 in a heating− cooling cycle. C

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Figure 3. (a−c) Asymmetric units of the structures of three phases with 50% probability ellipsoids. (d−f) C4H12N+ cation and the adjacent PbnI3n−n anionic 1D chain in the RTP, ITP, and LTP structures. Color scheme: Pb (II), orange; I, purple; C, black; N, blue. H atoms are omitted for clarity.

inversion center disappear. It should be noted that the LTP structure exhibits the C···I weak bonds (i.e., C3···I1 = 3.68 Å in Figure 3f and C4···I3 = 3.639 Å in Figure S4), which are absent in the RTP structure. The C···I interactions link C4H12N+ cations and PbnI3n−n anions together, which forms the weakinteraction networks between inorganic units and organic components. We believe that such weak interactions are very important to lock the C4H12N+ cations at the LTP. It is highly desirable to obtain the intermediate structure of ITP during the transformation from LTP to RTP because this structure can provide a deep understanding of phase transitions with important information. According to the traditional phasetransition theory, the ITP structure usually adopts a supergroup of LTP,20 i.e., the ITP structure should be determined with higher symmetry operations in the hexagonal system. However, we tried to solve the structure with hexagonal models but always failed. The reasonable structure with the acceptable values of R, wR, and S could be obtained using only the space group Pm. The detailed cell parameters of ITP structure are as follows: a = 9.662(1), b = 15.840(2), and c = 9.663(2) Å and β = 119.980(2) and V = 1281.0 (4) Å3, showing that the ITP structure belongs to the Pm space group but almost possess a hexagonal feature. The pseudocharacteristic of the hexagonal lattice might come from the following reason: the heavy atoms in the structure can satisfy such symmetry, while the counter organic cations do not have that symmetry. The asymmetric unit of ITP with a 50% probability ellipsoid is shown in Figure 3b. There are two crystallographically independent Pb atoms in the slightly distorted octahedral coordination environment arising from the disappearance of the screw and rotoinversion axis (Figure 3e). Although all cationic moieties become more ordered in the ITP than those in the RTP, their thermal ellipsoids are still relatively larger than those of LTP, which suggests the disorder-half-disorder-order feature in the phase transition. Moreover, the noncentrosymmetrical feature of the ITP structure was further confirmed by the results of secondharmonic generation (SHG) experiments, which were obtained from the powder samples of 1 at 160 K. The obvious SHG signals demonstrate its nonlinear optical (NLO) behavior (Figure 4), which indicates that the ITP has a noncentrosymmetrical feature.

Figure 4. SHG oscilloscope traces of the sample of 1 at 160 K.

The space group and symmetric elements are listed as follows: P63/m with the symmetric elements (E, C2, S6, i, σh) for the RTP structure, Pm with symmetric elements (E, σh) for the ITP lattice, and P61 with symmetric elements (E, C2, C3, C6) for the LTP arrangement. A symmetry-breaking phenomenon occurs during the transition from RTP to ITP, although the space group Pm is not the maximal nonisomorphic subgroup of P63/m. The change of nonclassical symmetry during the transition process clearly shows the absence of a group-subgroup relationship in the two structures based on the Curie symmetry principle. The symmetric operation changes during the double phase transitions, depicted in Figure 5 as the following: from RTP to ITP, all symmetry axes and the inversion center disappear, but the mirror plane still remains; from ITP to RTP, the mirror plane disappears but the 21-fold, 31-fold, and 61-fold screw axes appear. Therefore, it is difficult to describe the phase transition using the classical Aizu notion. However, the symmetry is partly restored through the transition from ITP to LTP due to the pseudohexagonal characteristic of the ITP crystal lattices. These results indicate that a transitional structure with a low symmetry space group can exist in the disorder−order-type phase transitions. The packing patterns are shown in Figure 6. The typical perovskite cages that exist in the MAPbI3 and FAPbI3 structures are not found in 1, resulting from the larger ionic radius of D

DOI: 10.1021/acs.inorgchem.6b01143 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. Spatial symmetry operation changes of 1 during the double phase transitions.

using the powder sample of 1 are shown in Figure S6. The real parts of the dielectric constant display obvious anomalies with the bump-like shape at around the second Tc point (ITP-RTP) on all testing frequencies. The imaginary part of the dielectric constant also displays the bump-like changes on the 100 and 500 kHz and 1 MHz frequencies near the ITP-RTP phasetransition point. However, we did not find the dielectric anomalies at around the first Tc point in both the real and imaginary part curves. Figure 7 shows that the temperature-

Figure 6. Unit cells and packing patterns of three phase structures of 1. (a) View of the RTP and LTP structures along the c axis and the ITP structure along the b axis. (b) View of the RTP, ITP, and LTP structures along the a axis. Color scheme: Pb (II), orange; I, purple; C, black; N, blue. H atoms are omitted for clarity. Figure 7. Temperature-dependent dielectric constants of 1 measured at frequencies of 500 kHz and 1 MHz along the a-axis direction.

C4H12N+ (Table S1). Meanwhile, the 1D infinite chain structures are formed based on the corner-sharing PbI6 octahedrons in all three structures (Figure 6b). When the structures of these three phases are compared, the related disorder−order feature of the phase transitions can be clearly observed: the C4H12N+ cation moiety acts as a rotator, while the PbnI3n−n anionic 1D chains behave as the stator-like parts during the thermally induced phase transition. Moreover, the structure changes of the three phases are small, but the variations of unit cells are obvious: the ratios of the c-axis length of the LTP to the b-axis length of the ITP to the c-axis length of the RTP ≈ 3:2:1. The variable-temperature reduced unit cell data of 1 from SCXRD (Figure S5) showed the same proportional relationships of the length of the axis and further confirmed the existence of the ITP over the temperature range from 140 to 180 K. Usually, the physical properties of materials often exhibit drastic anomalies when approaching a phase-transition critical temperature (Tc), and the variable magnitude of the properties will prove the characteristics of phase transition. For example, the permittivity change usually reaches a related large value with orders of magnitude of enhancement during a ferroelectric phase transition, while no or only small dielectric anomalies occur in the process of some nonferroelectric disorder−order phase transitions. The temperature-dependent dielectric constant, including the real part (ε′) and the imaginary part (ε″), taken at fixed frequencies of 5, 10, 50, 100, and 500 kHz and 1 MHz over the temperature range from 120 to 200 K

dependent complex dielectric measurements of the singlecrystal sample of 1 along the a-axis direction at fixed frequencies of 500 kHz and 1 MHz over the temperature range from 120 to 200 K. The results clearly show the appearance of two small “step-like” anomalies at around about 154.8 and 172.6 K, which is consistent with the DSC results and indicates that the phase transitions do not belong to the ferroelectric-type phase transitions. However, the related anomalies are still not found in the imaginary part curves of the single-crystal dielectric measurements (Figure S7). All results suggest that only small or no dielectric changes can be found in all dielectric measurements, which may result from the fact that the reorientation of C4H12N+ cations is just involved with a small displacement during the phase transitions (Figure 6).21

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CONCLUSIONS In summary, the present work has reported the thermally induced reversible double phase transitions in the organic− inorganic hybrid iodoplumbate C4H12NPbI3 1. The crystals of 1 obtained under a solvothermal condition possess 1D chain architecture containing PbI6 octahedrons. DSC results reveal that C4H12NPbI3 undergoes two switchable phase transitions around 154 and 176 K. The crystal structures of C4H12NPbI3 determined at 293, 163, and 110 K by variable-temperature E

DOI: 10.1021/acs.inorgchem.6b01143 Inorg. Chem. XXXX, XXX, XXX−XXX

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(7) (a) Zhang, W.; Cai, Y.; Xiong, R.-G.; Yoshikawa, H.; Awaga, K. Angew. Chem., Int. Ed. 2010, 49, 6608−6610. (b) Zhang, W.; Ye, H.-Y.; Graf, R.; Spiess, H. W.; Yao, Y.-F.; Zhu, R.-Q.; Xiong, R.-G. J. Am. Chem. Soc. 2013, 135, 5230−5233. (c) Zhao, X.-H.; Huang, X.-C.; Zhang, S.-L.; Shao, D.; Wei, H.-Y.; Wang, X.-Y. J. Am. Chem. Soc. 2013, 135, 16006−16009. (d) Du, Z.-Y.; Xu, T.-T.; Huang, B.; Su, Y.-J.; Xue, W.; He, C.-T.; Zhang, W.-X.; Chen, X.-M. Angew. Chem., Int. Ed. 2015, 54, 914−918. (e) Shang, R.; Wang, Z.-M.; Gao, S. Angew. Chem., Int. Ed. 2015, 54, 2534−2537. (f) Shi, C.; Zhang, X.; Cai, Y.; Yao, Y.-F.; Zhang, W. Angew. Chem., Int. Ed. 2015, 54, 6206−6210. (g) Shi, C.; Yu, C.-H.; Zhang, W. Angew. Chem., Int. Ed. 2016, 55, 5798−5802. (8) (a) Salinga, M.; Wuttig, M. Science 2011, 332, 543−544. (b) Lencer, D.; Salinga, M.; Wuttig, M. Adv. Mater. 2011, 23, 2030− 2058. (9) (a) Lemouchi, C.; Vogelsberg, C. S.; Zorina, L.; Simonov, S.; Batail, P.; Brown, S.; Garcia-Garibay, M. A. J. Am. Chem. Soc. 2011, 133, 6371−6379. (b) Sun, Z.; Luo, J.; Zhang, S.; Ji, C.; Zhou, L.; Li, S.; Deng, F.; Hong, M. Adv. Mater. 2013, 25, 4159−4163. (10) (a) Sun, Z.; Luo, J.; Chen, T.; Li, L.; Xiong, R.-G.; Tong, M.-L.; Hong, M. Adv. Funct. Mater. 2012, 22, 4855−4861. (b) Ye, H.-Y.; Li, S.-H.; Zhang, Y.; Zhou, L.; Deng, F.; Xiong, R.-G. J. Am. Chem. Soc. 2014, 136, 10033−10040. (11) Filippetti, A.; Delugas, P.; Saba, M. I.; Mattoni, A. J. Phys. Chem. Lett. 2015, 6, 4909−4915. (12) Contreras, J. G.; Seguel, G. V.; Ungerer, B.; Maier, W. F.; Hollander, F. J. J. Mol. Struct. 1983, 102, 295−304. (13) (a) Zhang, Z.-J.; Xiang, S.-C.; Guo, G.-C.; Xu, G.; Wang, M.-S.; Zou, J.-P.; Guo, S.-P.; Huang, J.-S. Angew. Chem., Int. Ed. 2008, 47, 4149−4152. (b) Feng, D.-Q.; Zhou, X.-P.; Zheng, J.; Chen, G.-h.; Huang, X.-C.; Li, D. Dalton Trans. 2012, 41, 4255−4261. (14) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (15) Donnay, G. D. H.; Harker, D. Am. Mineral. 1937, 22, 446−467. (16) Fu, D.-W.; Zhang, W.; Cai, H.-L.; Ge, J.-Z.; Zhang, Y.; Xiong, R.-G. Adv. Mater. 2011, 23, 5658−5662. (17) Goldschmidt, V. M. Naturwissenschaften 1926, 14, 477−485. (18) Li, Z.; Yang, M.; Park, J.-S.; Wei, S.-H.; Berry, J. J.; Zhu, K. Chem. Mater. 2016, 28, 284−292. (19) (a) McCleskey, E. W.; Almers, W. Proc. Natl. Acad. Sci. U. S. A. 1985, 82, 7149−7153. (b) Palomo, J.; Pintauro, P. N. J. Membr. Sci. 2003, 215, 103−114. (c) Garde, S.; Hummer, G.; Paulaitis, M. E. J. Chem. Phys. 1998, 108, 1552−1561. (d) Shannon, R. D. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751−767. (20) Izyumov, Y. A.; Syromyatnikov, V. N. Phase transitions and crystal symmetry; Kluwer Academic Publishers: Dordrecht, 1990. (21) Fu, D.-W.; Song, Y.-M.; Wang, G.-X.; Ye, Q.; Xiong, R.-G. J. Am. Chem. Soc. 2007, 129, 5346−5347.

single crystal X-ray diffraction reveal that the compound went through two structure phase transitions, including one transition from RTP (P63/m) to ITP (Pm) with symmetry breaking and another transition from ITP to LTP (P61) with partial symmetry restoration. In addition, the temperaturedependent dielectric constant measurements also exhibit the obvious anomalies around the phase-transition critical temperatures. All results indicate the existence of the transitional structure in the disorder−order transformation processes.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01143. Reaction mechanism (Scheme S1), spectra and additional data (Figures S1−S7), and ionic radius and tolerance factor data (Table S1) (PDF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*Email: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS G.F.L. thanks Prof. Dr. Paul Boyle and Dr. Babu Varghese for helpful discussion. Q.Z. acknowledges financial support from AcRF Tier 1 (Grants RG133/14 and RG 13/15) and Tier 2 (Grant ARC 2/13) from MOE.

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DOI: 10.1021/acs.inorgchem.6b01143 Inorg. Chem. XXXX, XXX, XXX−XXX