SUI Yan, LUO Qiu-yan, LIN Wen-hua, WU Hong-qin

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SYNTHESIS, STRUCTURE AND SWITCHABLE DIELECTRIC PROPERTIES OF DIETHYLAMMONIUM HEXACHLOROSTANNATE(IV)

*SUI Yan1,2, LUO Qiu-yan1,2, LIN Wen-hua1, WU Hong-qin1

(1 .School of Chemistry and Chemical Engineering, Jinggangshan University, Ji’an, Jiangxi 343009, China;2 .Institure of Applied Chemistry, Jinggangshan University, Ji’an, Jiangxi 343009, China)

Diethylammonium hexachlorostannate(IV) [Et2NH2]+2[SnCl6]2-(1)was prepared and characterized by single-crystal X-ray diffraction, elemental analysis, DSC and temperature-dependent dielectric spectroscopy. The results indicated that compound 1 could undergo a reversible first-order phase transition over 370 K. Corresponding to this phase transition, compound 1 was foundfor the first timetoundergotransitions between high and low dielectric states, which indicates a new type of molecule-based material with high-temperature switchable dielectric property.

diethylammonium hexachlorostannate; phase transition; switchable dielectric; molecule-based

Introduction

Molecule-based dielectric switches, which could undergo transitions between high and low dielectric states at a phase transition temperature (c), are important materials applicable in data communication, signal processing and rewriteable optical data storage, etc[1-2]. For the past few decades, increasing research interest has been paid to the design and synthesis of molecule-based dielectric switches utilizing the rotation or orientation motions of polar molecules or ions[3-4], such as the molecular rotator-stator system of molecular gyroscopes[5-6],supramolecular rotators[7-9], metal-organic frameworks (MOFs)[10-11]and order-disorder molecular-ionic solid[12]. Although great progress has been made in designing sophisticated small molecular analogue machines, it still remains a great challenge in the synthesis of switchable molecular dielectrics. The synthesized switchable molecular dielectrics either suffer from lower phase transition temperature, or relatively small dielectric change between high and low dielectric states at present. As a result, practical applications of those materials are limited.

In this paper, we report a simple salt diethylammonium hexachlorostannate (IV) [Et2NH2]+2[SnCl6]2-(1), which can undergo reversible phase transitions and exhibit switchable dielectric property with high phase transition temperature up to over 370 K.

1 Experimental

1.1 Materials and Methods

All reagents were purchased from commercial sources and used as received. DSC measurement was performed by heating and cooling the samples in the temperature range of 295~424 K on PerkinElmer Diamond DSC instrument. The measurements were carried out under nitrogen at atmospheric pressure in aluminum crucibles with a heating rate of 5 K min-1. Complex dielectric permittivity was performed using automatic impedance TongHui 2828 Analyzer. The measuring AC voltage was 1 V.

1.2 Synthesis of Compound 1

Diethylamine (1.46 g, 20 mmol) aqueous solution neutralized to pH=2 by dilute hydrochloric acid was added into the solution of SnCl4·5H2O (3.50 g, 10 mmol) dissolved in dilute hydrochloric acid solution. The mixed solution was kept stirring and heating for about 0.5 h, then filtered and left to stand undisturbed. Upon slow evaporation at room temperature for several days, single crystals suitable to X-ray analysis were obtained.

1.3 X-ray Crystallographic Analysis

X-Ray diffraction experiment was carried out using a Rigaku Saturn 924 diffractometer with Mo-Ka radiation (λ= 0.71073?). Data processing including empirical absorption correction was performed using the crystalclear software package (Rigaku, 2005). The structure was solved using direct methods and successive Fourier difference synthesis (SHELXS-97), and refined using the full-matrix least-squares method on F2using the SHELXLTL software package (Sheldrick, 2008). Non-H atoms were refined anisotropically using all reflections with I > 2 s(I). H atoms on C atoms were placed in calculated positions and refined using ‘riding’ model and ammonium H atoms were obtained from the Q peaks in difference Fourier maps. Crystallographic data and details of the data collection and refinement are summarized in Table 1.

Table 1 Crystal data, data collection and refinement results for 1

R= Σ||o| - |c||/Σ|Fo|,2= [Σ(|o2| - |c2|)2/Σ(|Fo2|)2]1/2

2 Results and Discussion

2.1 Crystal Structure

The structure of diethylammonium hexachloros- tannate (IV) has been obtained from PXRD by others[13-14], but here we report its single crystal structure with high quality. The single crystal structure analysis revealed that compound 1 crystallized in centrosymmetric space group21/. The asymmetric unit contains one diethylammonium cation and one [SnCl3]-anion moiety (Fig.1). Sn atom lies in the symmetric center and adopts regular octahedron geometry coordinated by six Cl atoms. Selected bond lengths and angles were summarized in Table 2. Table 3 is the hydrogen bond parameters. The Sn-Cl bond lengths are almost the same to each other. Every hexahalogenostannate(IV) anion is hydrogen-bonded to four diethylammonium cations through six N-H…Cl hydrogen bonds, in which Cl1 and Cl2 shared the same hydrogen atom. The Sn atoms can be reduced as four-connected nodes, which are linked together through hydrogen bonds bridge into a square grid plane. In each square grid, two diethylammonium cations are above the plane and another two are below the plane (Fig.2).

Fig.1 The asymmetric unit of compound 1 (30% probability thermal ellipsoids)

Table 2 Selected bond length (nm) and angle (°) for (1)

Symmetry code: (i) ?+2, ?+2, ?+1.

Table 3 Selected hydrogen-bond parameters (nm, °)

Symmetry codes: (ii) ?x+3/2, y?1/2, ?z+3/2; (iii) x?1/2, ?y+3/2, z+1/2; (iv) ?x+1, ?y+1, ?z+1.

2.2 Thermal Analysis

The DSC measurement for 1 is performed in the temperature region of 295~424 K. The heating and cooling curves of 1 show one pair of reversible peaks, an exothermic peak at 360.9 K and an endothermic peak at 371.2 K (Fig. 3). These observed peaks represent a reversible phase transition with a thermal hysteresis of about 10 K. The sharp peaks reveal the discontinuous character of the phase transition, being indicative of a first-order phase transition[15].

Femperature/K

Fig.3 DSC measurement for compound 1

2.3 Dielectric Properties

As usual, phase transition is accompanied by an anomaly of the dielectric constant near the structural phase transition temperature. Figure 4 showed the temperature-dependent dielectric constant of compound 1 in powder pressed pellet in the temperature range of 360~425 K at the frequency of 1000 KHz. The dielectric constant sharply increased from ca. 7.0 to ca. 11.0 when the temperature was increased to about 395 K, and then remained almost unchanged; it was suddenly dropped from 11.0 to 6.7 when the temperature was decreased to ca. 396 K. The reversible dielectric anomaly indicated a reversible phase transition in this temperature range. Except for this anomaly, no obvious dielectric change was observed even down to 125 K. The obvious switchable dielectric property may be resulted from the order-disorder motions of diethylammonium groups.

Fig.4 Temperature dependence of dielectric constants of compound 1 (the measured frequency is fixed at 1000 KHz)

It should be noted that: (1) only one dielectric anomaly was found over the whole measurement temperature range; (2) the dielectric constant is kept almost unchanged respectively at high and low dielectric states; (3) the phase transition temperature is above room temperature and high enough. Although some molecule-based dielectric switches have been reported previously,[16-17]there are few examples like diethylammonium hexachlorostannate (IV) which could satisfied with these demands for practical applications.

3 Conclusions

In conclusion, diethylammonium hexachlorostan- nate (IV) [Et2NH2]+2[SnCl6]2-is found to be a new type of high-temperature switchable dielectric materials corresponding to the reversible first-order phase transition occurred over 370 K. Our findings indicate a new type of functional material with potential applications in molecular switches and electronic materials.

Supplementary Material

CCDC No. 993545 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge viaby emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK. Fax: C44 1223336033.

References：

[1] Koumura N, Zijlstra R W J, van Delden R A, et al. Light-driven monodirectional molecular rotor[J]. Nature, 1999, 401(6749): 152-155 .

[2] Simon P, Gogotsi Y. Materials for electrochemical capacitors[J]. Nature materials, 2008, 7(11): 845-854.

[3] Garcia-Garibay M A. Crystalline molecular machines: Encoding supramolecular dynamics into molecular structure[J]. Proceedings of the National Academy of Sciences of the United States of America, 2005, 102(31): 10771-10776.

[4] Kay E R, Leigh D A, Zerbetto F. Synthetic molecular motors and mechanical machines[J]. Angewandte Chemie International Edition, 2007, 46(1-2): 72-191.

[5] Kim Y, Kumar A,Ovchinnikov O,et al. First-order reversal curve probing of spatially resolved polarization switching dynamics in ferroelectric nanocapacitors[J]. ACS nano, 2011, 6(1): 491-500.

[6] Fu D W, Zhang W, Cai H L, et al. Supramolecular bola-like ferroelectric: 4-methoxyanilinium tetrafluorobo- rate-18-crown-6[J]. Journal of the American Chemical Society, 2011, 133(32): 12780-12786.

[7] Hoshino N, Takeda T, Akutagawa T. Multi-functional molecular rotators with dielectric, magnetic and optical responses[J]. RSC Advances, 2014, 4(2): 743-747.

[8] Akutagawa T, Koshinaka H, Sato D, et al. Ferroelectricity and polarity control in solid-state flip-flop supramole- cular rotators[J]. Nature materials, 2009, 8(4): 342-347.

[9] Sun Z, Wang X, Luo J, et al. Ferroelastic phase transition and switchable dielectric behavior associated with ordering of molecular motion in a perovskite-like architectured supramolecular cocrystal[J]. Journal of Materials Chemistry C, 2013, 1(14): 2561-2567.

[10] Zhang W, Ye H Y, Graf R, et al. Tunable and switchable dielectric constant in an amphidynamic crystal[J]. Journal of the American Chemical Society,2013,135(14): 5230- 5233.

[11] Vogelsberg C S, Garcia-Garibay M A. Crystalline molecular machines: function,phase order,dimensionality, and composition[J]. Chemical Society Reviews, 2012, 41(5): 1892-1910.

[12] Du Y, Hao H M, Zhang Q C, et al. An above-room- temperature switchable molecular dielectric with a large dielectric change between high and low dielectric states[J]. Science China Chemistry, 2013, 56(7): 917-922.

[13] Okuda T, Nakao M, Kawase M, et al. Molecular motion and phase transition in diethylammonium hexahalogeno- stannate(IV) complexes [(C2H5)2NH2]2Sn X6 (X = Cl and Br) studied by means of35Cl and81Br NQR and2H NMR[J]. Journal of molecular structure￡? 1995, 345: 181-188.

[14] Cameron T S, James M A, Knop O, et al. Bis(diethylam- monium) hexachlorostannate(IV), (Et2NH2)2SnCl6, and tris-(di-n-propylammonium)hexachlorostannate(IV) chloride, (n-Pr2NH2)3(SnCl6)Cl: crystal structure and hydrogen bonding [J], Canadian journal of chemistry, 1983, 61(9):2192-2198.

[15] Zhang W, Xiong R G. Ferroelectric metal-Corganic frameworks[J]. Chemical reviews, 2011, 112(2): 1163- 1195.

[16] Zhang W, Cai Y, Xiong R G, et al. Exceptional dielectric phase transitions in a perovskite-type cage compound[J]. Angewandte Chemie International Edition,2010,49(37). 6608-6610.

[17] Cui H B,Takahashi K,Okano Y, et al. Dielectric properties of porous molecular crystals that contain polar molecules[J]. Angewandte Chemie International Edition, 2005, 44(40): 6508-6512.

二乙胺六氯化錫（IV）的合成、結(jié)構(gòu)及介電開關(guān)特性

*隋 巖1,2，羅秋燕1,2，林文華1，吳紅勤1

( 1. 井岡山大學化學化工學院，江西，吉安 343009；2. 井岡山大學應(yīng)用化學研究所，江西，吉安 343009)

本研究合成了化合物二乙胺六氯化錫 [Et2NH2]+2[SnCl6]2-(1)并對其進行了單晶X-射線衍射， DSC以及變溫介電性能測試。研究結(jié)果表明，化合物1在高于370 K時發(fā)生了可逆一級相變，其相變過程與六氯化錫陰離子的各向同性旋轉(zhuǎn)以及二乙胺陽離子的180°翻轉(zhuǎn)運動有關(guān)。對應(yīng)于該相變過程，化合物1可以實現(xiàn)高低介電狀態(tài)轉(zhuǎn)換，因而有望成為一種新型的高溫分子基介電開關(guān)材料。

二乙胺六氯化錫；相變；介電開關(guān)；分子基

O614.43

A DOI:10.3969/J.issn.1674-8085.2015.06.008

1674-8085(2015)06-0036-05

O614.43

A

10.3969/j.issn.1674-8085.2015.06.008

2015-09-07;modified date:2015-10-10

This work was supported by National Natural Science Foundation of China (21361012); Science and Technology Supporting Project of Jiangxi Province (20133ACG70007); Young Scientist of Jiangxi Province(20144BCB23038); Education Department of Jiangxi Province (KJLD12034) and Innovation and Entrepreneurship Training Project for College Students of Jinggangshan University.

*SUI Yan(1974-), male, born in Changling County of Jilin Province, Professor, Ph.D., mainly engaged in organic synthesis and application (E-mail:ysui@163.com);

LUO Qiu-yan(1972-), female, born in Ji’an City of Jiangxi Province, senior experimentalist, mainly engaged in structural characterization and analysis, (E-mail:luoqy0407@126.com);

LIN Wen-hua(1992-), male, born in Zhangzhou City of Fujian Province, Student of College of Chemistry and Chemical Engineering of Jinggangshan University, (E-mail: 263128625@qq.com);

WU Hong-qin(1993-), female, born in Shangrao City of Jiangxi Province, Student of College of Chemistry and Chemical Engineering of Jinggangshan University, (E-mail: 492547454@qq.com).