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Mar 6, 2017 - ABSTRACT: Humidity-induced single-crystal transformation was ob- served in the indium metal−organic polyhedra [In2(TCPB)2]·2H2O (In1)...
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Unusually Flexible Indium(III) Metal−Organic Polyhedra Materials for Detecting Trace Amounts of Water in Organic Solvents and High Proton Conductivity Xi Du, Ruiqing Fan,* Liangsheng Qiang, Yang Song, Kai Xing, Wei Chen, Ping Wang, and Yulin Yang* MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, P. R. China S Supporting Information *

ABSTRACT: Humidity-induced single-crystal transformation was observed in the indium metal−organic polyhedra [In2(TCPB)2]·2H2O (In1), where H3TCPB is 1,3,5-tri(4-carboxyphenoxy)benzene. When the humidity is above 58% relative humidity (RH) at room temperature, the neutral compound In1 could be successfully converted into the positively charged compound In1-H along with the color change from yellow to deep red, which also undergoes a reversible transformation into In1 driven by thermal dehydration. Notably, the color of In1 takes only 5 min to change under 58% RH at room temperature, which is much quicker than common desiccant bluestone. As the water content is increased from 0.0% to 0.2% in acetonitrile solvent, compound In1 exhibits rapid detection of trace amounts of water through turn-off luminescence sensing mechanism with a low detection limit of 2.95 × 10−4%. Because of the formation of extensive hydrogen-bonding network between the metal−organic polyhedra (MOPs) and surrounding guest OH− ions, compound In1-H, along with isostructural Ga1-H, displays excellent proton conductivity up to 2.84 × 10−4 and 2.26 × 10−4 S cm−1 at 298 K and 98% RH, respectively. Furthermore, the activation energies are found to be 0.28 eV for In1-H and 0.34 eV for Ga1-H. This method of incorporation of OH− ions to obtain high proton conductivity MOPs with low activation energy demonstrates the advantage of OH− ion conduction in the solid-state materials.

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INTRODUCTION Functional metal−organic polyhedra (MOPs) have been a frontier exploration field, appealing from catalysis,1 magnetism,2 photoluminescence,3 adsorption and separation,4 sensing,5 to biomembrane.6 Of particular interest are those showing solidstate phase dynamically altered by external stimuli, which is often associated with significant functional changes.7 With the in-depth scientific research, this stimuli−responsive dynamics, called “flexible crystals”, provides visual observation about the structural variation during the phase transitions and well illustrates the relationship between structure and property. The typical dynamic material involving the rupturing/reforming of covalent bonds, this configuration implies the possibility of applying a certain external stimulus to disturb the covalent connections to trigger the dynamics change, while retaining the integrity of the extended structures. A handful of reported compounds undergo external stimuli such as light,8 temperature variation,9 redox,10 anion exchange,11 and mechanochemical forces.12 Nevertheless, humidity-induced single-crystal transformation has rarely been described. Sensors and sensing have become an important and pervasive part of our society.13 Tremendous efforts are contributed to detect and control water content in organic solvents © 2017 American Chemical Society

qualitatively and quantitatively because the water molecule, for high-purity requirements or moisture-sensitive chemicals, oils, and petroleum products, is the common impure component.14 Nevertheless, the applied limitation of the traditional Karl Fischer titration method is requirement of specialized instruments and well-trained personnel.15 Beyond that, researching a feasible and accessible method for trace amounts of water detection ( 2σ(I)] R1a wR2b R indices (all data) R1 wR2 largest diff. peak and hole (e·Å−3) CCDC a

In1 C54H34In2O20 1232.45 hexagonal R3c̅ 11.296(2) 11.296(2) 76.07(2) 90.00 90.00 120.00 8406(3) 6 1.461 0.896 3696 1.61 to 27.05 −14 ≤ h ≤ 14 −13 ≤ k ≤ 13 −95 ≤ l ≤ 93 1984/0/116 0.997

In1-H C54H37In3O23 1398.25 hexagonal R3c̅ 11.4098(3) 11.4098(3) 78.8081(19) 90.00 90.00 120.00 8885.0(4) 6 1.561 1.234 4116 3.31 to 27.56 −12 ≤ h ≤ 14 −14 ≤ k ≤ 14 −102 ≤ l ≤ 89 2292/0/124 1.016

Ga1-H C54H37Ga3O23 1262.95 hexagonal R3c̅ 11.3253(3) 11.3253(3) 78.989(5) 90.00 90.00 120.00 8773.9(6) 6 1.427 1.449 3792 1.55 to 27.51 −14 ≤ h ≤ 13 −12 ≤ k ≤ 14 −102 ≤ l ≤ 73 2253/7/126 1.114

0.0565 0.2024

0.0614 0.2156

0.0870 0.2587

0.0667 0.2141 1.574 and −0.532 1516136

0.0747 0.2475 1.970 and −0.863 1516137

0.1079 0.2874 2.833 and −0.952 1516138

R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = [∑[w(F02 − Fc2)2]/∑[w(F02)2]]1/2.

3D frameworks.17 However, the proton concentration is inevitably reduced, because higher-dimensional structures require greater degree of ligand deprotonation. On the basis of this, we anticipate that discrete MOPs might provide an opportunity to decorate the entire surface through hydrogenbonding interaction to achieve a higher concentration of proton carriers, which is conducive to optimize the conduction path and better elucidate the underlying proton transport mecha-

nism.18 The chosen ligands are expected to possess the high density of oxygen atoms. Because these oxygen sites could offer extensive hydrogen bonding between the MOPs and surrounding guest molecules, it can function as an effective route for proton conduction. In addition, anion-conducting MOPs remain little-explored. Particularly, the OH− ion conductors have attracted increasing interest for the development of inexpensive and highly efficient alkaline fuel cells.19 3430

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Figure 1. (a) Crystal structure of In1. (b) C−H···O interactions in In1. (c) 2D layers of In1 in the ab plane through C−H···O interactions. (d) 3D supramolecular framework of In1. While it stirred for 30 min in air, it was transferred into a 20 mL Teflon-lined stainless steel autoclave and heated at 120 °C for 120 h. After it slowly cooled to room temperature, yellow block crystals of In1 were dried at room temperature (yield 76.2% based on H3TCPB). Anal. Calcd for [C54H30O18In2 (Mr: 1196.42)]: C, 54.21; H, 2.53%; found: C, 54.22; H, 2.54%. IR (KBr pellet, cm−1): 3058 (br, s), 1609 (vs), 1446 (s), 1412 (vs), 1272 (w), 1221 (s), 1124 (m), 1009 (m), 826 (w), 763 (m), 727 (w), 648 (m), 580 (w), 527 (w), 465 (m) (Figure S1 in the Supporting Information). Synthesis of Hydrated {[In3O(TCPB)2(H2O)3]OH}. When the humidity is above 58% RH at room temperature, the yellow crystals of In1 experienced a color change to deep red crystals of In1-H, which is demonstrated by single-crystal X-ray diffraction (yield 68.2% based on In(NO3)3). Anal. Calcd for [C54H37O23In3 (Mr: 1398.30)]: C, 46.38; H, 2.67%; found: C, 46.35; H, 2.69%. IR (KBr pellet, cm−1): 3409 (br, s), 1603 (vs), 1445 (s), 1408 (vs), 1265 (w), 1221 (s), 1123 (m), 1003 (m), 828 (w), 758 (m), 722 (w), 641 (m), 571 (w), 505 (w), 461 (m), 428 (w). Synthesis of Hydrated {[Ga3O(TCPB)2(H2O)3]OH}. The mixture of Ga(NO3)3 (0.0512 g) and 1,3,5-tri(4-carboxyphenoxy)benzene (0.0486 g) having the molar ratio of ∼2:1 is dissolved in CH3CN solvent (8 mL). While it stirred for 30 min in air, it was transferred into a 20 mL Teflon-lined stainless steel autoclave and heated at 120 °C for 120 h. After it slowly cooled to room temperature, deep yellow powders were obtained and subsequently immersed in water solvents with pH 3.2 by addition of NaOH to give deep red crystals of Ga1-H (yield 71.5% based on Ga(NO3)3). Anal. Calcd for [C54H37O23Ga3 (Mr: 1263.00)]: C, 51.35; H, 2.95%; found: C, 51.37; H, 2.96%. IR (KBr pellet, cm−1): 3423 (br, s), 1606 (vs), 1448 (s), 1404 (vs), 1273 (w), 1217 (s), 1125 (m), 1005 (m), 829 (w), 757 (m), 723 (w), 645 (m), 628 (w), 583 (w), 467 (m), 419 (w).

On the basis of the above consideration, herein, we choose multifunctional aromatic tricarboxylate ligand 1,3,5-tri(4carboxyphenoxy)benzene (H3TCPB) as an organic linkage unit to construct three novel compounds, namely, [In2(TCPB)2]·2H2O (In1), {[In3O(TCPB)2(H2O)3]OH} (In1-H), and {[Ga3O(TCPB)2(H2O)3]OH} (Ga1-H), noting that compounds In1-H and Ga1-H are isostructural. Yellow crystals of In1 undergo a humidity-induced structural transformation to yield a new species of deep red crystals In1-H, which also undergoes a reversible transformation into In1 driven by thermal dehydration. Such transformation is seldom observable by single-crystal X-ray diffraction studies, because In(III) metal salt is susceptible to hydrolysis, and the drastic structural changes could cause loss of crystallinity. Notably, the color of In1 takes only 5 min to change under relative humidity (RH) of 58% at room temperature, which is much quicker than a similar change in the common desiccant bluestone. Upon irradiation with UV light, In1 exhibits bright blue luminescence in organic solvents. When water content increased in the range from 0.0% to 0.2% in acetonitrile solvent, In1 could rapidly detect trace amounts of water through turn-off luminescence sensing mechanism with a low detection limit of 2.95 × 10−4% (Scheme 1). In addition, compounds In1-H and Ga1-H display excellent proton conductivity up to 2.84 × 10−4 and 2.26 × 10−4 S cm−1 at 298 K and 98% RH, respectively. Thus, we pay attention to investigate the relationship between structure and property to further elucidate the proton-conduction mechanism.

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RESULTS AND DISCUSSION Structural Description of [In2(TCPB)2]·2H2O. Singlecrystal X-ray diffraction analysis demonstrated that In1 has crystallized in the hexagonal crystal system with space group

EXPERIMENTAL SECTION

Synthesis of [In2(TCPB)2]·2H2O. A mixture of In(NO3)3 (0.0603 g) and 1,3,5-tri(4-carboxyphenoxy)benzene (H3TCPB) (0.0486 g) having the molar ratio of ∼2:1 is dissolved in CH3CN solvent (8 mL). 3431

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Figure 2. Compound In1−H showing (a) 1D chain through C−H···O interactions; (b) 2D layers through C−H···O interactions; (c) topological representation of 3D structure.

R3c̅ (Table 1). There is one-third of In(III) ion, one-third of TCPB3− anion, and one-third of free H2O molecule in the asymmetry unit. Using Addison’s model,20 the coordination geometry around the indiun atom in In1 (τ4 = 0.126) can be better described as a quadrilateral geometry by four bidentate carboxylic groups from two individual H3TCPB ligands (Figure 1a). The bond distances of In−O are 1.927 and 1.935 Å, all of which are similar to those reported for other In(III) ion compounds (Table S1 in the Supporting Information).21 Interestingly, the distance of adjacent In(III) ion is 3.328 Å, which is much smaller than the sum of the van der Waals radii for In (ca. 1.93 Å for In),22 indicating the existence of In···In interaction. Carefully observing the structure, there exists an extensive hydrogen-bonding network that helps connect adjacent discrete monomers to create a 3D supramolecular architecture (Figure 1). The mononuclear units are linked through C5−H5A···O3 hydrogen bonding to generate a 2D layer, of which the H···O distance is 2.657 Å (Table S2 in the Supporting Information). The 2D layers were further linked through C6−H6A···O3 hydrogen-bonding interaction (d(H6A···O3) = 2.985 Å), constructing a 3D supermolecular framework. Viewing the metal as node and the TCPB3− ligand as linker, the whole framework could be reduced to a six-connected pcu topological network (Figure S2 in the Supporting Information). The PLATON calculation23 shows the overall solvent-accessible

volume equal to 1777.3 Å3 per unit cell, which accounts for ∼21.1% of the cell volume of 8406.0 Å3. Structural Description of In3O(TCPB)2(H2O)3]OH} (In1H) and Ga3O(TCPB)2(H2O)3]OH} (Ga1-H). Considering that compounds In1-H and Ga1-H are isostructural, we choose In1H to represent the detailed structure. Compound In1-H has crystallized in the hexagonal space group R3̅c and displays a sixconnected 3D supramolecular network. In its asymmetric unit, there is one-half of In(III) ion, one-third of TCPB3− anion, one-sixth of μ3-O2− anion, and one-half of terminal water molecule with a positive formula of [In3O(TCPB)2(H2O)3]+. The framework is constructed from indium trimer, in which three indium cations are bonded to a central O2−, and each pair of indium sites is bridged by four oxygen atoms. The key feature is that each trimeric [In3O(RCO2)6(H2O)3]+ node has three open metal sites (one on each In) coordinated by a total of three water molecules (Figure S3 in the Supporting Information). As a result, the charge of the trimer is positive and balanced by OH−. With the help of hydrogen-bonding interactions, each trimer serves as a six-connected node, leading to the formation of a 3D pcu network (Figure 2). The overall channel value without solvent molecules is calculated as 1747.8 Å3, accounting for ∼19.7% of the total volume of 8885.0 Å3. Single-Crystal Structural Transformation. The original neutral compound [In2(TCPB)2]·2H2O (In1) could be successfully converted into the positively charged compound {[In3O(TCPB)2(H2O)3]OH} (In1-H) along with color change 3432

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Figure 3. Detailed structure change of In1 and In1-H involved in this structural transformation.

Figure 4. Comparison color change for In1 (first and second rows) and bluestone (third row) under different humidity atmosphere at room temperature.

from yellow to deep red via breakage/formation of chemical bonds in the presence of water. The optical band gaps are 3.32 eV for In1 and 2.96 eV for In1-H (Figure S4 in the Supporting Information), which is consistent with the crystal colors of yellow for In1 and deep red for In1-H. This structural transition provides us an excellent opportunity to explore the change in the crystal interior.24 As shown in Figure 3, the fourcoordinated tetrahedral geometry of In(III) cations in In1 change to the six-coordinated pentagonal bipyramid geometry

of In(III) cations in In1-H. When coordinated water molecules are added, the In−O bond distances of In1-H range from 2.027 to 2.247 Å, which are significantly longer than that of In1 (1.925 and 1.931 Å). The average In−O (water) bond distance in In1-H is 2.165 Å, much longer than that of the typical In−O bond (1.928 Å) in In1. Gallium element, however, has a higher acid character than indium element. It is relatively difficult to bond with oxygen atom. Fortunately, after immersion, the reaction powders of gallium compound with the same 3433

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Figure 5. (a) Luminescence intensity of In1 in different organic solvents. (b) Emission spectra of In1 in different organic solvents (λex = 365 nm). (c) Job’s plot of In1−water.

Compared with Common Desiccant Bluestone. As a representative of common desiccant, bluestone shows a capability to rapidly change color upon contact with water, while in the dry air, it might make a color change in a long time. In the same condition, In1 takes only a few minutes to achieve color change. To further obtain response time, we investigated the interaction time about color change between In1 and water, shown in Figure 4 compared with common desiccant bluestone. No obvious color change of In1 was observed within 15 min in dry air (15% RH). Notably, the color of In1 only takes 5 min to change under 58% RH at room temperature, which is much quicker than that of bluestone (taking 6 h to have obvious color change under the same condition, shown in Figure S7 in the Supporting Information). This indicates that the humidity-induced structural transformation is fast. We therefore reasoned that In1 may be as a new switch for sensing water. Detecting Trace Amounts of Water in Diverse Solvents. Simple, fast, and reliable sensors that can indicate trace amounts of water are of significance in the chemical industry.25 As shown in Figure 5, the luminescence intensities of In1 strongly depend on the solvents, particularly with regard to water, which shows the most significant “turn off” quenching effect by naked-eye observation, whereas other solvents show negligible effect on the luminescence intensities. Known as Job’s plot, is the most commonly applied method for the determination of stoichiometry of metal−ligand chemical entities.26 We keep initial concentrations of water and In1 at 10 μM and change the molar ratio of water (XM = [water]/ ([water] + [In1])) to obtain Job’s plot for the luminescence. The luminescence intensity reaches the maximum value when

condition of In1 in water solvent to adjust pH to 3.2 with an aqueous solution of NaOH; thus, we obtain the isostructural Ga1-H compound. This suggests that, for gallium and indium elements, the relative stabilities of the metal−oxygen bonds under water solvent condition with suitable pH value are finely balanced. The above structural transformation from In1 to In1H contains bond reformation and the change of coordination geometry of the metal center. Inspired by the color change from In1 to In1-H caused by the water molecule, we expected that In1 could be a visual water sensor. Notably, the reversibility of the structural transformation is achieved, as supported by thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD) analysis (Figures S5 and S6 in the Supporting Information). First, the solid sample of In1-H was heated at 180 °C under vacuum for 1 d for full activation to produce In1-H′. The weight loss of In1-H′ is ∼5.14% in comparison with that of In1-H, which can be attributed to the removal of guest solvent molecules in the channels, coordinated center oxygen atom, and water molecules on the framework. Subsequently, the TGA curve of In1-H′ shows one continuous weight loss step and starts to decompose at 292 °C upon further heating, which is similar to that of In1. In addition, acceptable matches in PXRD were observed between the experimental diffraction patterns for In1-H′ and In1, suggesting that In1-H′ possesses the original structure of In1 accompanying crystal parameters change. Consequently, the above findings clearly show that the structure of In1 is quite flexible and dynamic, because it undergoes a reversible structural transformation with significant crystal expansion and contraction driven by hydration and dehydration. 3434

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Figure 6. (a) Visual luminescence photos of In1 in acetonitrile with various water contents (v/v) under 365 nm UV light. (b) Luminescence spectra of In1 in acetonitrile solvent containing water content from 0.0 to 0.6%. (c) Luminescence intensity as a function of water content from 0.0 to 0.6% in acetonitrile solvent. (d) Fitting curve between luminescence intensity and water content from 0.0 to 0.2%.

Figure 7. Nyquist plots of the pellet sample. (a) Compound In1-H at 298 K and 98% RH, S = 1.135 cm2, L = 0.087 cm. (b) Compound Ga1-H at 298 K and 98% RH, S = 1.135 cm2, L = 0.126 cm.

the ratio of [water] to [water] + [In1] is ∼0.75, which suggests a 3:1 complex between [water] and [In1] has been formed. It matches with X-ray structural analysis. Meanwhile, the PXRD pattern of the sample after luminescence test is also matching with the PXRD pattern of In1-H (Figure S8 in the Supporting Information). The PXRD pattern measurement result demonstrates the stability of In1-H and further confirms structural transformation to support the Job’s plot and single-crystal X-ray diffraction analysis, which reveal that binding mode between water molecule and In1 follows a 3:1 stoichiometry. We therefore propose that organic molecules, for example, dimethyl sulfoxide, acetone, methanol, and so on, are insufficiently capable of coordinating with indium center due to the lack of

space for large solvent molecules to get close, whereas only the water molecule has the capability to arrive in the quite narrow space and coordinate with indium center. This result implies that In1 can be considered as a sensor for detecting water. Encouraged by this special luminescence property of In1 in organic solvents, we attempt to quantify detection of water molecules. Taking acetonitrile as an example, upon gradually increasing the water content in acetonitrile, the intensity of blue emission peak shows continuous decrease and ultimately reaches the equilibrium state (especially the luminescence intensity is directly proportional to the water content from 0.0% to 0.2%) shown in Figure 6. The detection limit for water molecule is calculated as 2.95 × 10−4% (v/v) (Table S3). The 3435

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Figure 8. Pellet sample of In1-H. (a) Nyquist plots under different RH conditions at 298 K. (b) Nyquist plots at different temperatures under 98% RH. (c) Arrhenius plot for proton conductivity. (d) Time-dependent proton conductivity at 298 K and 98% RH.

facilitates water molecule absorption to enhance the proton conductivity. Second, because of coordination activation effect, the coordinated water molecules in the trimeric metal cluster could promote mobile H+ proton. To further illustrate the proton conduction mechanism affected by the OH− ion and water molecule, we investigated the impedance values (under 98% RH at different temperatures). As shown in Figure 8b and Figure S12 in the Supporting Information, the proton conductivities of compounds increased from 2.84 × 10−4 S cm−1 at 298 K to 3.43 × 10−4 S cm−1 at 358 K for In1-H and from 2.26 × 10−4 S cm−1 at 298 K to 3.15 × 10−4 S cm−1 at 358 K for Ga1-H. As a function of temperature, the proton conductivity is derived from the Arrhenius equation as follows:

low detection limit demonstrates that In1 can act as an excellent sensor for the selective and sensitive detection of trace amounts of water. Proton Conduction. Considering water molecules in the framework and OH− ions in the channel, we seek to analyze the proton conductivity properties of the solid compounds In1-H and Ga1-H by the Nyquist plot of alternating current (A.C.) impedance spectroscopy. As shown in Figure 7, both compounds possess relatively high proton conductivities at 298 K and 98% RH. Because of bulk and grain boundary resistance, there is a semicircle in high-frequency region. At the same time, with the limited diffusion of mobile ions at the electrode−electrolyte interface, there is a tail in the lowfrequency region.27 The proton conductivities of compounds In1-H and Ga1-H reach 2.84 × 10−4 and 2.26× 10−4 S cm−1, respectively. The slight difference observed in the conductivity values of compounds In1-H and Ga1-H may be related to different metal ion in the unit cell. The IR and PXRD data of compounds In-H and Ga1-H before and after the proton conductivity are matched well (Figures S9 and S10 in the Supporting Information), which reveal the integrity of the framework during the test process. Similar to literature reports, the proton conductivities of these compounds depended much on humidity, which increased from 1.63 × 10−4 S cm−1 under 63% RH to 2.84 × 10−4 S cm−1 under 98% RH for In1-H and from 1.54 × 10−4 S cm−1 under 63% RH to 2.26 × 10−4 S cm−1 under 98% RH for Ga1-H at 298 K (Figure 8a and Figure S11 in the Supporting Information). Combining the structures of the compounds, the factor of humidity proves the importance of water molecule as proton carrier in proton conductivity.28 First, under the help of hydrogen-bonding interaction, the water affinity in the narrow channels of the framework is obviously improved, which

σ=

σ0 E exp − a T kT

The σ0 is representative of pre-exponential factor, the σ is representative of proton conductivity, the k is representative of Boltzmann constant, the T is representative of absolute temperature, and the Ea is representative of activation energy of proton hopping. According to Arrhenius plots [ln(σT) vs 1000 T−1] shown in Figure 8c and Figure S13 in the Supporting Information, the calculated Ea for the proton transfer is 0.28 eV for In1-H and 0.34 eV for Ga1-H. Similar to the Grotthuss mechanism (0.1−0.4 eV)29 observed for hydrated H3O+ ions, we speculate that the effective OH− ions transfer through hydrogen-bonding network from water molecule to cationic framework resulting in low activation energy (Figure 9 and Figure S14 in the Supporting Information). It is comparable to the hydrated OH− ions in liquid30 and indicates that the extended hydrogen-bonding network of OH− ions and water molecules enhances the proton 3436

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (Grant Nos. 21371040 and 21571042) and the National Key Basic Research Program of China (973 Program, No. 2013CB632900).

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Figure 9. Schematic representation of cationic framework with hydroxide anions inside the channel for efficient hydroxide ion conduction.

conductivity of the material. Importantly based on the timedependent conductivity measurement, there is no obvious loss in conductivity performance after 48 h (Figure 8d and Figure S15 in the Supporting Information).

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CONCLUSIONS In summary, we have developed an interesting structural transformation from the neutral compound (yellow) to the positively charged compound (deep red) by the naked eye observed. The color-switching abilities are attributed to humidity-induced changes in the metal coordination patterns and solvent molecules. The compound In1 could serve as an efficient sensor of trace amounts of water through turn-off luminescence sensing mechanism. The detection limit is as low as 2.95 × 10−4% with increasing water content in the range from 0.0% to 0.2%. Because of the formation of extensive hydrogen-bonding network between the MOPs and surrounding guest OH− ions, the compounds In1-H and Ga1-H show hydroxide conductivities of 2.84× 10−4 and 2.26 × 10−4 S cm−1 at 298 K and 98% RH. Furthermore, the activation energies are found to be 0.28 eV for In1-H and 0.34 eV for Ga1-H. This work provides a rare example of a proton-conductive MOPs with a well-illustrated proton-conduction mechanism and is a promising sensor for trace amounts of water for future application.

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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.6b02963. IR, PXRD, TGA, additional structures, and proton conductivity figures (PDF) Crystallographic data for In1 (CIF), In1-H (CIF), and Ga1-H (CIF) (ZIP)

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AUTHOR INFORMATION

Corresponding Authors

*Fax: +86−451−86413710. E-mail: [email protected]. (R.Q.F.) *E-mail: [email protected]. (Y.Y.) ORCID

Ruiqing Fan: 0000-0002-5461-9672 Wei Chen: 0000-0003-0647-6563 Yulin Yang: 0000-0002-2108-662X 3437

DOI: 10.1021/acs.inorgchem.6b02963 Inorg. Chem. 2017, 56, 3429−3439

Article

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DOI: 10.1021/acs.inorgchem.6b02963 Inorg. Chem. 2017, 56, 3429−3439