Coordination-Induced Syntheses of Two Hybrid Framework Iodides: A

Jul 20, 2016 - To reveal the relationship between the photoemission behavior and structure of 1, single-crystal X-ray diffraction data of the same cry...
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Coordination-Induced Syntheses of Two Hybrid Framework Iodides: A Thermochromic Luminescent Thermometer Ren-Chun Zhang,† Jun-Jie Wang,† Jing-Chao Zhang,† Meng-Qi Wang,† Min Sun,† Feng Ding,† Dao-Jun Zhang,*,† and Yong-Lin An*,‡ †

Key Laboratory of New Optoelectronic Functional Materials (Henan Province), College of Chemistry and Chemical Engineering, Anyang Normal University, Anyang 455000, China ‡ College of Chemistry, Dalian University of Technology, Dalian 116024, China S Supporting Information *

ABSTRACT: Two new 3D hybrid framework iodides, Hmta[(Hmta)Ag4I4] (1; Hmta = hexamethylenetetramine) and [(Hmta)2Ag8I6]I2 (2), have been synthesized under solvothermal conditions. Compound 1 consists of a neutral 3D framework built up from alternation of the tetrahedral Ag4I4 unit and Hmta with dia-b topology. Compound 2 features a 3D cationic framework with flu topology, constructed by cationic [Ag8I6]2+ units linked with Hmta. Tetrahedral Hmta plays crucial structuredirecting roles in the formation of these 3D frameworks with high symmetry. The temperature-dependent photoluminescent measurement reveals luminescent thermochromism of the compounds, the emission maximum of which shows a gradual blue shift with increasing temperature. The results indicate that 1 is a promising wavelength- and intensity-dependent luminescent thermometer applicable in two different temperature ranges.

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INTRODUCTION Microporous materials with regular pore architectures are important in industrial technologies such as catalysis, sorption, and ion exchange.1 Since Martin and Zubieta advanced zeolitic framework metal halides in 1997,2 microporous metal halides have attracted increasing interest because of their diverse structures and fascinating properties, such as porosity, fluorescence, semiconductivity, nonlinear optical, thermochromism, photochromism, and effective visible optical catalytic properties.3−5 For the construction of novel microporous metal halides, the Ag−I system is of particular interest because of the diverse coordination styles of Ag+ (linear, trigonal, and tetrahedral geometry) as well as flexible linkage between AgIx units. From the structural point of view, the complicated condensation behaviors between primary AgIx units in combination with the high covalent feature of the Ag−I bond and possible existing Ag···Ag interactions promise to access diverse and stable open frameworks. The template method has been demonstrated as an effective approach toward the syntheses of porous materials.1,6 Recently, template syntheses of metal halides, © XXXX American Chemical Society

especially Ag−I compounds, have received considerable attention.7−10 Various guest cations such as quaternary ammonium, protonated organic amine, alkaline-metal cations, and metal complex cations were used as structure-directing agents (SDAs) and introduced into the synthesis systems, leading to the formation of diverse Ag−I compounds.4d,f,g,5c,8−10 However, only a limited number of 3D Ag−I-based frameworks have been synthesized up to now, although a number of templates with high symmetry were used.4d,g,5c,8g,10a−c This can be partially attributed to the unsuccessful structural information transfer from guest templates to host frameworks because of the lack of strong guest−host interactions and specific interaction sites. The interactions between guest templates and host frameworks are weak, such as electrostatic attraction, hydrogen-bonding, and space-filling effects. Therefore, the prediction and design syntheses of novel high-dimensional Ag−I-based frameworks are of great challenge. Received: April 21, 2016

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DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Calcd for 1 (C12H24N8Ag4I4): C, 11.39; H, 1.90; N, 8.86. Found: C,11.45; H, 2.10; N, 8.65. [(Hmta)2Ag8I6]I2 (2). The synthetic procedure of 2 was similar to that of 1, except that NH4I (0.069 mmol, 10.0 mg), Hmta (0.125 mmol, 14.0 mg), and 120 μL of methanol and 300 μL of acetonitrile as a mixed solvent were used and heated at 105 °C for 7 days. The products were washed with ethanol several times, and pale-yellow octahedral-shaped crystals were obtained in 16.2% yield based on AgI. EDS analysis on several crystals gave an average 1:1 Ag/I ratio approach. Elem anal. Calcd for 2 (C12H24N8Ag8I8): C, 6.25; H, 1.04; N, 4.86. Found: C, 6.40; H, 1.15; N, 4.68. Crystal Structure Determination. Crystallographic data collections were performed on a Bruker Smart APEX II diffractometer equipped with graphite-monochromitized Mo Kα radiation (λ = 0.71073 Å). Single-crystal data of 1 were collected at 120, 180, and 296 K, and 2 was measured at 100 and 296 K. The structures were solved by direct methods and refined by full-matrix least squares on F2 using SHELX-97.13 All non-H atomic positions were located on Fourier maps and refined anisotropically, while all of the H atoms were located at geometrically calculated positions and refined with the isotropic displacement parameter. Room temperature experimental crystallographic data are summarized in Table 1, while low-temperature crystallographic data are listed in Tables S1 and S2, and selected bond lengths and angles are listed in Table S3

Our recent work indicates that the incorporation of metal ions with tetrahedral coordination, such as Ge4+ or Sn4+ into complicated Cu−S systems, can induce the formation of novel frameworks with high symmetry and low framework density.11 Unlike guest templates, structural information on the tetrahedral metal cations can be transferred to the framework through direct covalent interactions. Inspired by structuredirecting roles of tetrahedral metal cations, we inferred that the incorporation of templates into Ag−I-based host frameworks by strong bonding interactions may access novel microporous materials. Hexamethylenetetramine (Hmta) is a rigid tetrahedral molecule with Td symmetry and shows a strong coordination affinity with transition-metal ions.12 In our continual efforts to construct novel Ag−I-based frameworks,10a,b we are especially interested in incorporating tetrahedral Hmta into the Ag−I system to construct highdimensional hybrid frameworks. In this contribution, we report the solvothermal syntheses, structures, and photoluminescent properties of two 3D hybrid framework iodides, Hmta[(Hmta)Ag4I4] and [(Hmta)2Ag8I6]I2, built up from high-symmetry Ag4I4 or [Ag8I6]2+ units interconnected with tetrahedral Hmta, respectively.

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Table 1. Crystal Data and Structure Refinement Details

EXPERIMENTAL SECTION

Materials and General Methods. All reagents were purchased from commercial sources and used without further purification. Energy-dispersive spectroscopy (EDS) was made on a JEOL JSM5600LV scanning electronic microscope. Elemental analysis (C, H, and N) was carried out on a Vario EL III elemental analyzer. Powder X-ray diffraction (PXRD) data were obtained using a UItima III diffractometer with Cu Kα radiation (λ = 1.5418 Å). The data were collected at room temperature with a step size of 0.02°, and the operating power was 40 kV/40 mA. The UV−vis spectra were measured at room temperature using a Shimadazu UV-2550 doublebeam, double monochromator−spectrophotometer, equipped with an integrating sphere at 296 K, and a BaSO4 plate was used as the reference. Thermogravimetric analysis (TGA) was carried out using a Mettler-Toledo Star analyzer under a flow of nitrogen (40 mL min−1) from 35 to 600 °C at a heating rate of 10 °C min−1. Photoluminescence spectra were recorded on an Edinburgh FLS-980 fluorescence spectrometer using single-photon-counting measurement. The excitation source was a 450 W xenon lamp. Emission spectra were corrected for detection and optical spectral response of the spectrofluorimeter, and excitation spectra were corrected for the spectral distribution of the lamp intensity using a photodiode reference detector. The emission lifetime of compound 1 was recorded with an nf920 ns flash lamp as the excitation source, and data were analyzed by exponential curve fitting. The quantum yield (QY) in the solid state was determined by an absolute method using an integrating sphere (150 mm diameter, Benflec coating) as the sample chamber. Temperature-dependent emission spectra of the compounds in the solid state were recorded on an Edinburgh FLS-980 fluorescence spectrometer, and the temperature was controlled with the help of a heating/cooling stage from an Oxford MercuryiTC temperature controller. Syntheses of Compounds 1 and 2. Hmta[(Hmta)Ag4I4] (1). AgI (0.025 mmol, 6.0 mg), NH4I (0.083 mmol, 12.0 mg), and Hmta (0.054 mmol, 6.0 mg) were placed in a Pyrex glass tube, and then 300 μL of methanol and 80 μL of N,N-dimethylformamide (DMF) as a mixed solvent were added. After the mixture was thoroughly stirred, the glass tube was sealed (reagents filled about 5% volume of the tube) under an air atmosphere, placed in a stainless steel autoclave, into which water as a media for heat transfer and press balance was added to 80% filling, and then heated at 85 °C for 4 days. The products were washed with ethanol several times, and colorless block crystals were obtained as a pure phase in 87.5% yield based on AgI. EDS analysis on several crystals gave an average 1:1 Ag/I ratio approach. Elem anal.

empirical formula fw temp/K cryst syst space group a/Å α/deg V/Å3 Z calcd density/Mg m−3 abs coeff/mm−1 F(000) 2θ(max)/deg index range

no. of collected/unique param rflns [R(int)] GOF on F2 final R indices [I > 2σ(I)] wR2 Δρmax, Δρmin/e Å−3

1

2

C12H24N8Ag4I4 1219.47 296 cubic F4̅3m 13.29350(10) 90.0 2349.19(3) 4 3.448 8.560 2208 51.06 −16 ≤ h ≤ 16 −15 ≤ h ≤ 16 −16 ≤ h ≤ 12 1603/260 0.0153 1.059 0.0097 0.0254 0.210, −0.302

C12H24N8Ag8I8 2158.55 296 cubic Fm3̅m 14.5614(4) 90.0 3087.5(2) 4 4.644 12.985 3808 50.0 −15 ≤ h ≤ 17 −17 ≤ h ≤ 17 −15 ≤ h ≤ 17 2415/176 0.0251 1.043 0.0855 0.2690 2.345, −2.794

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RESULTS AND DISCUSSION Synthesis Chemistry. The reaction of AgI, NH4I and Hmta under solvothermal conditions provides two new hybrid framework Ag−I compounds, 1 and 2. In the reactions, excessive NH4I as a mineralizer was used in the synthetic system, which can effectively increase the solubility of AgI and promote crystallization of the two compounds. It should be noted that the solvent systems and reaction temperature have a significant impact to the syntheses of these two compounds. In comparison, 1 is apt to form under more basic conditions and relatively low temperature. The introduction of a small amount of DMF is crucial for the synthesis of compound 1. Compound 2 can be synthesized in a relatively wide temperature range B

DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 1. The perspective view (at the 30% probability level) of the coordination environment for the cubane-like Ag4I4 (a) and Hmta (b) units in 1.

Figure 2. (a) Supertetrahedral cage a. (b) Supertetrahedral cage b.

between 80 and 105 °C, however, is frequently accompanied by an unknown white precipitation. The best synthesis temperature for 2 is 105 °C. Presumably, condensation of active building units and further crystallization can be effectively promoted under such a temperature. When the reaction temperature exceeds 105 °C, only brown precipitation on the inwall of the glass tube can be obtained. In addition, the amount of Hmta used can affect access of the pure phase of the compounds rather than change the formation between 1 and 2. The purity of 1 and 2 was confirmed by PXRD patterns (Figures S1 and S2). Crystal Structure. Single-crystal X-ray diffraction analysis reveals that compound 1 crystallizes in the space group F4̅3m and possesses the neutral hybrid 3D framework [(Hmta)Ag4I4], constructed from alternation of cubane-like Ag4I4 units and Hmta. As depicted in Figure 1, the cubane-like Ag4I4 unit with Td symmetry consists of a tetrahedron of four Ag+ ions, each face of which is capped by a μ3-I− ion. The adjacent Ag···Ag distance in the tetrahedron is 3.054 Å. Each Ag+ ion adopts a tetrahedral coordination geometry bonding to three neighboring I− ions and an Hmta ligand. The Ag−I and Ag−N bond lengths are 2.899 and 2.395 Å, respectively, which are consistent with those of reported cubane-like Ag4I4 clusters.5c,8f−h,9c,14 Although having different configurations, both of the cubanelike Ag4I4 clusters and adamantine-like Hmta molecules serve as tetrahedral building units and interconnect to each other to form a 3D framework with dia-b topology (Figure S3). Interestingly, there are two different supertetrahedral cages found in the framework. As shown in Figure 2, cage a is built

up from the tetrahedral arrangement of four Ag4I4 units linked by six Hmta molecules, while cage b is formed in reverse by the tetrahedral arrangement of four Hmta molecules bridged by six Ag4I4 units. Cage b represents a rare example of a supersupertetrahedron, denoted as the Tp,q cluster.15 It is comparable to the typical T2,2 cluster in zeolitic chalcogenides UCR-22, CPM-121, and CPM-122, in which four T2 clusters are arranged into a T2 supertetrahedron.15a,b It is worth noting that a discrete Hmta molecule is located in cage b. The discrete Hmta molecule is ordered, and its size and symmetry match well with those of the cavity. Compound 2 crystallizes in the cubic space group Fm3̅m and features a cationic hybrid framework, [(Hmta)2Ag8I6]2+, constructed from an unusual [Ag8I6]2+ cluster connected by Hmta, with disordered I− ions located in the channels as counterions. As shown in Figure 3, the cationic [Ag8I6]2+ cluster with Oh symmetry consists of a cubic array of eight Ag+ ions, each face of which is capped by an μ4-I− ion.16a The adjacent Ag···Ag distance of the cube is 2.761 Å. Such a distance is shorter than that found in compound 1, indicating significant d10−d10 interactions.16b Each Ag+ cation adopts tetrahedral coordination geometry bonding to three neighboring iodide anions and an N atom from an Hmta ligand. The Ag−I and Ag−N bond lengths are 2.834 and 2.490 Å, respectively. The cationic [Ag8I6]2+ clusters serving as 8-connected nodes interconnect with tetrahedral Hmta to generate an extended 3D cationic framework with a flu network (Figure S4). Particularly, the framework of compound 2 is cationic because of the connection between the cationic [Ag8I6]2+ clusters and neutral Hmta linker. It represents one of the rare hybrid 3D cationic C

DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX

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well as the frameworks. Such a structure-directing effect is significant because of the strong bonding interaction and directional feature of the coordination bond and is absolutely different from those of guest SDAs, which mainly depend on weak host−guest interactions, such as electrostatic attraction, hydrogen-bonding, and space-filling effects. Therefore, the syntheses of compounds 1 and 2 indicate that the incorporation of Hmta into the Ag−I system can not only increase the local symmetry of the framework but also induce high-symmetry Ag−I building units through the direct coordination bond to favor high-dimensional frameworks. This effect of the coordination bond is also reflected in some hybrid iodides containing the Dabco ligand, in which both of the N atoms reside at the C3 rotation axis of the molecule. For example, in the MTN-type zeolitic framework [Cu4I4(Dabco)2]n and cationic framework [Cu4I3(Dabco)2]I3,4a,b Dabco serves as a linear linker bridging Td- or Ohsymmetric Cu−I units into the high-symmetry framework, in which the C3 symmetry of the N atoms was transferred to the framework by the direct coordination bond, while in the silverrich iodide (DabcoH)2[(Dabco)2Ag14I16] and isostructural [Cu7I8(DabcoH)Dabco],10b,d Dabco dangling on the inorganic framework plays crucial structure-directing roles in the formation of C3-symmetric Cu/Ag−I building units through the coordination bond. Thus, the C3 symmetry of the N atoms can be readily transformed to the inorganic building units when the N atom occupies one coordination site of the tetrahedral cation. This structural information transfer by the coordination bond may provide new opportunities to the design syntheses of novel framework materials. Luminescence Properties. Both 1 and 2 show photoluminescence in the solid state at room temperature. The emission spectra are shown in Figure 5. Upon excitation

Figure 3. The perspective view (at the 30% probability level) of the coordination environment for the cationic [Ag8I6]2+ unit.

framework halides.4b,16c Recently, Xin et al. reported a new 3D cationic framework built up from the cationic [Cu8I6]2+ unit, which is isostructural to the [Ag8I6]2+ unit and serves as an 8conneted node. Unlike the [Ag8I6]2+ units in 2, these [Cu8I6]2+ units interconnected with linear bridging ligands (1,4diazabicyclo[2.2.2]octane, Dabco) to form a bcu topological structure.4b Structure-Directing Effect of Hmta. In these two structures, Hmta not only serves as ligand and structure building units but also plays crucial structure-directing roles in the formation of the high-symmetry Ag−I clusters and construction of the 3D frameworks. In comparison to simple tetrahedron TO4 (denoted as T1) in the zeolites, the adamantane-like Hmta molecule represents a higher level of tetrahedral unit (T2) resembling the core of supertetrahedral clusters (Figure 4), such as [Ge4S10]4− and [In4S10]10−, which are regular tetrahedrally shaped fragments of the cubic ZnStype lattice.17 It exhibits ideal Td symmetry and owns four N atoms with strong coordination ability.18 Because of its intrinsic rigidity, it can increase the local symmetry of the framework into which it was incorporated.19 For example, Hmta can decorate the tetrahedral sites to form a zeolite MTN topological metal−organic framework (MOF) with high symmetry.19d In compounds 1 and 2, Hmta resides on the 4̅3m sites in the cubic cell and decorates on the tetrahedral sites of the 3D framework with dia-b and flu topology, respectively, resulting in its high-symmetry imprinting on the frameworks. Particularly, each N atom in Hmta is located at the C3 rotation axis; when it occupies one tetrahedral site of a metal cation, the local symmetry of the N atom can be readily transferred to the cation or building unit because of direct coordination interactions. In compounds 1 and 2, C3 symmetry of the N atoms was successfully transferred to the Ag−I units as

Figure 5. Emission spectra of compounds 1 and 2.

Figure 4. (a) Typical T1 [GeS4]4− cluster. (b) Typical T2 [Ge4S10]2− cluster. (c) Tetrahedral coordination of the Hmta ligand. D

DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 6. (a) Temperature-dependent emission spectra of 1 from 120 to 400 K with an interval of 20 K excited at 333 nm. (b) CIE chromaticity diagram showing the temperature dependence of the (x, y) color coordinates of 1. (c) Temperature-dependent emission spectra of compound 2 from 80 to 340 K with an interval of 20 K excited at 330 nm. (d) CIE chromaticity diagram showing the temperature dependence of the (x, y) color coordinates of 2.

shift with increasing temperature. Upon an increase in the temperature from 80 to 350 K, the emission peak shifts from 675 to 620 nm accompanied by a decline of the emission intensity (Figures S7 and S8). The corresponding luminescence color changes from orange to pink and then blue, as shown in the CIE (x, y) chromaticity diagram at different temperatures. Luminescent thermochromism of copper halides has been reported for decades and has received intense interest recently;22,23 however, that of Ag−I compounds has rarely been documented.19a To the best of our knowledge, 1 and 2 represent the first 3D hybrid framework Ag−I compounds displaying luminescent thermochromism. Previously, Zink’s group found the luminescent thermochromism phenomenon of two isomers of Ag4I4(PPh3)4 clusters.20a Unlike the gradual blue shift of λmax found in 1, the emission maximum of Ag4I4(PPh3)4 clusters shows an obvious red shift as the temperature increases from 12 to 120 K; however, the mechanism of luminescent thermochromism and its relationship with the structure were not discussed. Very recently, a series of iodoargentates reported by Fu’s group showed interesting thermochromism,4g,5c,8h,i which was ascribed to the intermolecular charge transfer and affected by the electron affinity of the template cations. There is no direct relationship with the luminescence, and the effects of structural variations on the thermochromism were excluded in their systematic work. To reveal the relationship between the photoemission behavior and structure of 1, single-crystal X-ray diffraction data of the same crystal were collected at 120, 180, and 296 K (Table S1). Structure analyses indicate that no phase transition occurs at low temperature, and the PXRD pattern (Figure S9)

centered at 333 nm, 1 exhibits a strong photoluminescent emission band centered at 620 nm, while 2 exhibits a weak photoluminescent emission band centered at 596 nm when excited at 396 nm. The luminescent properties and mechanisms of the two compounds are similar to those of silver iodide compounds.9,10b The luminescence can be assigned to clustercentered emission, derived from halide-to-metal charge transfer (I → Ag) mixed with a Ag···Ag (4d → 5s) metal-centered excited state.9,10b,20 Fluorescence QY measurement indicates that the QYs of 1 and 2 are 18.5% and 0.5%, respectively. The low QY of 2 and its weak absorption at 396 nm in the UV−vis spectrum (Figure S5) may be the main reasons for its weak photoluminescent emission. The luminescence decay of 1 monitored at the emission band maximum (620 nm) indicates that it has an emission lifetime of 498 ns at room temperature (Figure S6). Interestingly, the temperature-dependent photoluminescent measurement indicated that 1 and 2 show luminescent thermochromism. The emission maximum of 1 exhibits a gradual blue shift from 730 to 600 nm as the temperature increases from 120 to 400 K (Figure 6a). The corresponding luminescence color changes from red to orange, yellow, and then white, as shown in the CIE (x, y) chromaticity diagram at different temperatures (Figure 6b). In addition, the emission intensity shows little change in the temperature range from 120 to 180 K and then progressively decreases as the temperature increases from 180 to 400 K, which can be ascribed to thermal activation of the nonradiative-decay pathways.21 2 exhibits luminescent thermochromism when excited at 330 nm (Figure 6c,d). Similar to 1, the emission peak exhibits a gradual blue E

DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 7. (a) Emission spectra of 1 recorded between 120 and 180 K (excited at 333 nm). (b) Temperature-dependent emission maximum and fitted curve at different temperatures from 120 to 180 K. (c) Emission spectra of 1 recorded between 200 and 300 K (excited at 333 nm). (d) Temperature-dependent intensity and fitted curve for 1 in the temperature range from 200 to 300 K.

temperature increases from 140 to 350 K. In contrast, the LE emission intensity decreases significantly. Therefore, the contribution from the HE emission gradually becomes remarkable to luminescent thermochromism as the temperature increaes, especially above 200 K. Such a mechanism for luminescent thermochromism is different from the mechanism originating from a single emission shift of compound 1, while is comparable to the coupling between the HE and LE emissions.23d,j Prompted by the unique temperature-dependent luminescent property of 1, we measured the emission spectra with a narrow interval (10 K; Figures S11−S13) to evaluate its potential as a luminescent thermometer. Our results reveal that the emission maximum of 1 exhibits a regular blue shift from 730 to 675 nm as the temperature increases from 120 to 180 K (Figure 7a), although the emission intensity shows negligible change. There is a good linear relationship between the maximum emission wavelength and temperature. This linear relationship can be fitted as a function of λmax = 839.5−0.925T (T = 903.23 − 1.07λmax) with a correlation coefficient of 0.9972, where λmax is the maximum emission wavelength (nm; Figure 7b). Calculations show that the corresponding wavelength shift per 1 K is 0.925 nm, indicating that λmax of this material is sensitive to the temperature in the range from 120 to 180 K. In contrast to most luminescent thermometers for temperature detection based on the intensity and/or decay time of the compounds,24 1 represents a rare wavelength-dependent luminescent thermometer.24c

of the sample after 400 K treatment and TGA (Figure S10) confirm the framework stability during the luminescent measurement, while structure analyses reveal that the Ag···Ag distance (3.054 Å at 296 K) is slightly shortened (3.024 Å at 120 K and 3.034 Å at 180 K; Table S3). Photoemission of the M4X4L4 (M = Cu, Ag) complexes, as calculated by DFT, was derived from the triplet cluster-centered excited state.20 Thus, the M···M interactions have a great impact on the luminescence of the clusters and particularly the low-energy (LE) emission band. As the Ag···Ag distance becomes shorter, the bonding character increases, the energy level is lowered, and thus the emission band shifts to a longer wavelength.23a,c,e,j Consequently, luminescent thermochromism of 1 can be ascribed to a slight contraction of the Ag···Ag distance at low temperature. For compound 2, low-temperature single-crystal X-ray diffraction reveals that no phase transition occurs at low temperature (Table S2), while the Ag···Ag distance (2.762 Å at 296 K) becomes shorter (2.722 Å at 100 K; Table S3). Similar to 1, the emission peak shift of 2 can be also ascribed to a slight contraction of the Ag···Ag distance. It should be noted that such a LE emission peak shift only partially contributes to luminescent thermochromism of compound 2 because of the presence of a high-energy (HE) emission band around 450− 500 nm. Below 140 K, luminescent thermochromism can be ascribed to the peak shift of the LE emission because of absolute predomination of the LE emission band. The emission intensity of the HE band shows a negligible change as the F

DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX

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It is also worth noting that the emission intensity decreases gradually as the temperature increases from 200 to 300 K, accompanied by a slight blue shift of λmax from 660 to 620 nm (Figure 7c). The linear relationship between the intensity and temperature can be fitted as a function of I = 2.05 × 106 − 5854.3T with a correlation coefficient of 0.9993 (Figure 7d). The emission intensity decreases on average by 0.66% per 1 K with increasing temperature from 200 to 300 K with 65.7% in total. Therefore, the emission intensity of compound 1 is sensitive to the temperature, suggesting that it can be used as an intensity-dependent luminescent thermometer. The relative sensitivity (Sr) is an important factor for the evaluation and comparison of the performances of thermometers.24a Following the definition, the maximum Sr of such an intensity-based thermometer is determined to be 1.98% at 300 K. It is slightly higher than the lanthanide−MOF luminescent thermometers ZJU-88⊃perylene (Sr = 1.28) and Eu0.0069Tb0.9931-DMBDC (DMBDC = 2, 5-dimethoxy-1, 4-benzenedicarboxylate; Sr = 1.15)25a,b but lower than Tb0.957Eu0.043cpda [cpda =5-(4carboxyphenyl)-2,6-pyridinedicarboxylate] with the highest Sr = 16%, which is a ratiometric and colorimetric luminescent thermometer applicable in a wide temperature range of 40−300 K.25c

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CONCLUSION

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (D.-J.Z.). *E-mail: [email protected] (Y.-L.A.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge support of this research by the National Natural Science Foundation of China (Grants 21301009, 21501006, and 21171028) and Science and Technology Department of Henan Province (Project 132102210446).

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REFERENCES

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Two new hybrid 3D framework iodides built up from different Ag−I units and Hmta have been synthesized under solvothermal conditions, and their structures and fluorescence properties were characterized. Hmta plays crucial structuredirecting roles in the formation of high-symmetry Ag−I units as well as 3D frameworks. Unlike guest templates, the structural information transformation of Hmta was realized through the direct coordination bond. Therefore, syntheses demonstrate the feasibility to access novel Ag−I-based framework materials by the incorporation of SDAs into the host framework and provide a new idea for the design and syntheses of other openframework materials. The temperature-dependent photoluminescent measurement indicated that 1 and 2 show luminescent thermochromism. They represent the first 3D hybrid framework Ag−I compounds displaying luminescent thermochromism. In addition, the results indicate 1 as a promising luminescent thermometer applicable in two different temperature ranges: a wavelength-dependent luminescent thermometer in the temperature range of 120−180 K and an intensitydependent luminescent thermometer between 200 and 300 K.

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00973. PXRD patterns, UV−vis absorption spectra, TGA curve, luminescent decay curves, temperature-dependent luminescent emission spectra, and corresponding λmax and Imax curves (PDF) X-ray crystallographic data in CIF format (CIF) X-ray crystallographic data in CIF format (CIF) X-ray crystallographic data in CIF format (CIF) X-ray crystallographic data in CIF format (CIF) X-ray crystallographic data in CIF format (CIF) G

DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.6b00973 Inorg. Chem. XXXX, XXX, XXX−XXX