Syntheses, Characterization, and Luminescence Properties of Four

Article pubs.acs.org/crystal

Syntheses, Characterization, and Luminescence Properties of Four Metal−Organic Frameworks Based on a Linear-Shaped Rigid Pyridine Ligand Zemin Ju, Wei Yan, Xiangjing Gao, Zhenzhen Shi, Ting Wang, and Hegen Zheng* State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, P. R. China S Supporting Information *

ABSTRACT: Solvothermal syntheses in DMF (or DMA) and H2O afforded four novel metal−organic frameworks: {[Cd(DPBT) (BDC)]·2(H2O)}n (1), {[Zn2(DPBT)2(IPA)2]·2(DMA)}n (2), {[Co2(DPBT)2(BDC)2]·2(DMF)·5(H2O)}n (3), and {[Ni(DPBT)2(H2O)4]·(BDC)}n (4) (DPBT = 4,7di(4-pyridyl)-2,1,3-benzothiadiazole, BDC = 1,4-benzene dicarboxylate, IPA = isophthalic acid, DMA = N,Ndimethylacetamide, and DMF = N,N-dimethylformamide). X-ray analyses show that 1 and 3 show similar structures with the same building blocks and possess 3-dimensional 6connected pcu net. Compounds 1 and 3 are based on a 2fold interpenetrating network with solvent molecules located in the framework, whereas 3 is different in the absence of DMF solvent molecules. Compared with compounds 1 and 3, 4 is constructed under the same conditions except with metal ions and possesses a completely different structure type. Luminescence properties of 1 and 2 without any activation well-dispersed in common solvents have also been investigated systematically; the luminescence properties show different intensities depending on the nature of the solvents, especially for nitrobenzene (NB), which exhibits a significant quenching effect. Compound 2 possesses a layered structure; the distance between two parallel layers is big enough to allow small molecules to more easily move into the crystal skeleton and interact with each other. Thus, the luminescence responses of 2 were investigated for various nitro compounds. When the concentration of PA is up to 0.1 mM, the emission of 2 is completely quenched. These results show that compound 2 has great potential to be developed as the favorable sensor for highly selective detection of PA. Furthermore, the magnetic properties of compound 3 were investigated.

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INTRODUCTION

detect nitro compounds, metal ions, and so forth. Furthermore, different detection mechanisms have also been investigated.16,17 Most explosives contain nitro compounds, and picric acid (2,4,6-trinitrophenol, PA) is one of the most powerful explosives in its class.18,19 The explosive characteristics of PA were discovered early in our history. In 1885, experiments with PA were conducted in Lydd, England, and the English adopted it as an explosive material called “Lyddit” in 1888. It was used extensively in bombs and grenades during the World Wars and international terrorist attacks.20 In addition to using in explosives, PA is also widely used in medicine, leather, dye synthesis, and pesticides. Extensive use of PA not only causes health issues but also results in serious environmental pollution, such as soil and aquatic system problems.21,22 Hence, timely and effective detection of trace amounts of PA has become an urgent and arduous task for national governments. However, rapid and selective detection of trace amounts of PA from other

As porous materials, metal−organic frameworks (MOFs), formed by a self-assembled supramolecular network structure that consists of interactions between metal ions and organic ligands, have been a material of interest in academia over the past 20 years.1−3 The design and synthesis of MOFs has become a hot research topic in the field of organic and inorganic chemistry because of their mesh structure, uniform pores, tunable pore size, huge specific surface area, and unique properties in optical,4−6 solvatochromic,7,8 magnetic,9 porous materials,10,11 and so forth. Therein, potential application as fluorescent probes has attracted much attention.12−15 Compared with traditional luminescent materials, luminescent MOFs have shown promise in the following aspects: First, they possess properties of organic and inorganic materials, which gives birth to a variety of light-emitting properties. Second, synthesis of MOFs generally only requires mild conditions, such as solvothermal conditions. Finally, they can be rationally designed and functionalized at the molecular level. A variety of MOFs have been used as fluorescent probes to © XXXX American Chemical Society

Received: May 17, 2015 Revised: March 22, 2016

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DOI: 10.1021/acs.cgd.5b00681 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Figure 1. (a) Coordination environment of Cd(II) in 1. Symmetry codes: #1 x, y − 1, z; #2 x, y + 1, z; #3 x + 1/2, y, −z + 1; #4 −x, y, −z + 1/2; #5 x − 1/2, y, −z + 1. (b) Flat structure formed by Cd(II) and BDC. (c) View of the 3D network. (d) The 2-fold interpenetrating structure.

Figure 2. (a) Coordination environment of Zn(II) in 2. Symmetry codes: #1 −x + 1, −y + 1, −z + 1; #2 x − 1, y + 1, z; #3 −x + 1, −y + 1, −z; #4 x, y, z − 1. (b,c) Two kinds of channels in the flat structure formed by two ligands and Zn(II) viewed along the a and c axes. (d,e) Stacked graph of 2D layer structure of 2 viewed along the a and c axes.

compounds due to their short response time, high sensitivity, operability, ease of visualization, and affordability. In this paper, a rigid fluorescent ligand, 4,7-di(4-pyridyl)-2,1,3-benzothiadiazole, has been designed to assemble four MOFs with π-

nitro compounds is still a serious challenge. Currently, detection methods include precision apparatus and canines, which are complex, inconvenient, and expensive.23,24 However, fluorescent MOFs show great promise for detecting nitro B



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hydrogen bonding in the structure to yield a 3D network. There exist two free DMA molecules in the asymmetric unit, which are squeezed by PLATON. As shown in Figure 2b and c, there are two kinds of channels in each planar layer: one is formed by the second building units Zn2(COO)4 and the other is constituted by IPA ligands connecting Zn(II) ions. The presence of channels formed by the stacking of 2D layers in an AAA··· mode is one interesting structural feature of 2. Infinite one-dimensional channels are created along the aaxis when the parallel layers are accumulating (Figure 2d). Figure 2e shows the channels viewed along the c axis. The solvent-accessible volume of these channels, calculated with the PLATON program, is 458.2 Å3, or 19.3% of the total unit cell volume whose channels are occupied by many disordered DMA solvent molecules. Crystal Structure Description of 3. Compound 3 reveals a 3D structure and crystallizes in the orthorhombic crystal system of the Pcc2 group. As Figure 3a shows, the asymmetric

conjugated coligands BDC and IPA under solvothermal conditions, namely, {[Cd(DPBT) (BDC)]·2(H2O)}n (1), {[Zn2(DPBT)2(IPA)2]·2(DMA)}n (2), {[Co2(DPBT)2(BDC)2]·2(DMF)·5(H2O)}n (3), and {[Ni(DPBT)2(H2O)2]·(BDC) }n (4). Compounds 1 and 3 show similar structures with the same building blocks and possess 3dimesional (3D) 6-connected pcu net. However, compound 4 is a zero dimensional structure, and there exists one free nitrogen atom in the DPBT ligand. Compounds 1, 3, and 4 were constructed under the same conditions except for the metal ions; they possess different coordination modes and space structures, which indicates that syntheses of MOFs can be influenced by the nature of metal ions, such as electron configuration and orbits. The luminescence responses of 1 and 2 to various solvents were investigated. Furthermore, the luminescence responses of 2 to various nitro compounds were also investigated. These results show that 2 is an efficient fluorescence sensor for PA with high sensitivity and selectivity, and the quenching mechanism was further studied through theoretical calculations.

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RESULTS AND DISCUSSION Crystal Structure Description of 1. The single-crystal Xray diffraction study reveals that 1 crystallizes in orthorhombic space group Pcca and displays a 3D coordinate framework. In the asymmetric unit of 1 (Figure 1a), there exist one crystallographically identical Cd(II) center, one BDC ligand, one DPBT ligand, and two free water molecules. The Cd(II) center adopts a six-coordinated octahedron geometry (CdO4N2) by coordinating to four oxygen atoms from three BDC anions and two nitrogen atoms from two DPBT molecules. The Cd−N and Cd−O distances are in the ranges of 2.304(2)−2.334(2) Å and 2.273(2)−2.417(3) Å, respectively, which deviated from normal bond lengths found in other Cd compounds.25,26 In the BDC ligand, the two carboxylate groups display two different coordination modes: one adopts a bidentate chelating mode to link one Cd(II) ion and the other also adopts a bidentate bridging mode to combine two Cd(II) ions. Nitrogen atoms from DPBT ligands locate in the axis direction of the plane that formed by oxygen and Cd(II) atoms. In compound 1, two crystallographically equivalent Cd(II) cations prefer a square-pyramidal geometry, with four BDC molecules coordinated to the Cd(II) center, to form a Cd paddle wheel second building unit Cd2(COO)4 (SBU). The SBU is bridged by BDC ligands to form a 2D (4, 4) flat network with square grids (Figure 1b). DPBT ligands connect the adjacent 2D layers to form the 3D framework structure (Figure 1c). TOPOS software illustrates that 1 is a 6-connected node 3D network structure constructed by DPBT ligands and Cd(II) SBUs with the point symbol {412.63} and pcu topology type. As shown in Figure 1d, 1 reveals a 2-fold interpenetration architecture to reduce the nanosized void space (Figure 1d). Crystal Structure Description of 2. Compound 2 crystallizes in the triclinic crystal system of P1̅ space group. As shown in Figure 2a, the asymmetrical unit contains two crystallographically independent Zn(II) ions. Four oxygen atoms and two nitrogen atoms constitute a distorted octahedral geometry with the Zn(II) sites. Four oxygen atoms from three IPA ligands locate in the equatorial plane, whereas the axial positions consist of two nitrogen atoms from the DPBT ligand (Figure 2a). 2D planar layers, which are constructed by the two kinds of ligands coordinating to the Zn(II) ions, are held together by different types of π···π stacking interactions and

Figure 3. (a) Coordination environment of 3. Symmetry codes: #1 −x + 2, y, z + 1/2; #2 −x + 2, y, z − 1/2; #3 −x + 1, y, z − 1/2; #4 −x + 1, y, z +1/2; #5 x, y − 1, z; #6 x, y + 1, z. (b) Flat structure formed by SBUs and BDC. (c) The 3D framework of 3. (d) The 2-fold interpenetrating structure.

unit of 3 consists of two crystallographically identical Co(II) centers, two BDC ligands, two DPBT ligands, two free DMF molecules, and five solvent water molecules, of which some of the solvent molecules are squeezed by PLATON. The Co(II) center adopts a six-coordinated octahedral geometry (CoO4N2) by coordinating to four oxygen donors from three BDC anions and two nitrogen atoms from two DPBT molecules. The Co− O and Co−N distances are in the ranges of 1.999(3)−2.200(4) Å and 2.132(4)−2.169(4) Å, respectively, which are similar to the values found in other Co compounds.25−27 In compound 3, the binuclear SBUs Co2(COO)4 formed by two identical Co(II) centers connect with each other by BDC ligands to form a 2D layer composed of a 2:1 ratio of BDC and SBUs (Figure 3b). Similar to compound 1, the adjacent 2D layers are bridged BPDT ligands that form the 3D lattice structure (Figure 3c). Topologically, the Cd(II) ions can be considered as 6-connected nodes; thus, the whole framework of C



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Figure 4. (a) Coordination environment of 4. Symmetry codes: #1 −x + 2, −y + 1, −z; #2 −x + 1, −y, −z. (b) Schematic view of the packing structure.

Figure 5. (a,b) Emission spectra of compounds 1 and 2 in common solvents when excited at 357 and 364 nm, respectively. (c,d) Fluorescence intensities of compounds 1 and 2 in common solvents, respectively.

3 can be simplified as a common 6-connected pcu topology with a point symbol of {412.63}. Compound 3 exhibits a 2-fold interpenetration of architecture that is similar to 1 (Figure 3d). Crystal Structure Description of 4. Single-crystal X-ray diffraction analysis shows that compound 4 crystallizes in a monoclinic crystal system of the P21/c space group. The asymmetric unit contains one Ni(II), one free BDC ligand, two

DPBT ligands, and four coordinated water molecules. As Figure 4a shows, each Ni(II) sits in an octahedron that is constituted by two nitrogen atoms and four oxygen atoms from two DPBT ligands and four water molecules, respectively. The four oxygen atoms construct the equatorial plane, and two nitrogen atoms occupy the apical positions. The Ni−O bond lengths range from 2.0785(19) to 2.096(2) Å, and the Ni−N bond length is D



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Figure 6. (a) Percentage of fluorescence quenching of 2 obtained for six different nitro compounds (0.1 mM). (b) Fluorescence spectral changes with different concentrations of PA added to the emission. (c) Calculated HOMO and LUMO levels for nitro compounds. (d) X-ray powder diffraction of 2 under different conditions.

shown in Figure S3, upon excitation at 356 nm for 1 and 375 nm for 2, the maximum emission peaks of the compounds are observed at 464 and 513 nm, respectively. Compared with that of free DPBT ligand, the emission intensities of both compounds are much stronger; namely, the formation of MOFs enhances the fluorescence of the DPBT ligand, which is a typical instance of aggregation-induced emission (AIE).28 The emission peak of compound 1 is slightly blue shifted in comparison to that of the DPBT ligand (λem = 465 nm), which can be assigned to n−π* and/or π−π* transition.29,30 However, compound 2 is red-shifted 48 nm, which may be because of the contribution of ligand-to-metal charge transfer (LMCT).31 The differences in the peak positions of these compounds might be attributed to the differences in coordination environments and the metal centers. The fluorescence properties of compounds 1 and 2 were examined in liquid emulsions: ground single-crystalline powder samples of both compounds (1 mg) without any activation were dispersed in 3 mL of common organic solvents, which were treated by ultrasonication for 0.5 h, and then stable emulsions were obtained after standing for 3 days for applying to fluorescence analysis. DMF, DMA, methanol (MeOH), ethanol (EtOH), acetone, trichloromethane (TCM), dichloromethane (DCM), tetrahydrofuran (THF), acetonitrile, methylbenzene (MB), 1,4-dioxane, ethyl acetate (EA), hexane,

2.121(2) Å. These independent asymmetric units are tightly held together by π−π stacking interactions and O−H···O hydrogen bonding to generate a compact packing structure (Figure 4b). Compounds 1, 3, and 4 were constructed under the same conditions except for the metal ions, and they possess different coordination modes. Single crystal X-ray analyses reveal that 1 and 3 show similar structures with the same building blocks and possess 3D 6-connected pcu net. Compounds 1 and 3 are both based on a 2-fold interpenetrating network with solvent molecules located in the framework. Compound 3 possesses three more free water molecules and two more DMF molecules than those of 1. Furthermore, the eight oxygen atoms in the SBU of 1 are coplanar, which is different from that of 3, which are in two planes (Figures S1 and S2). However, compound 4 is zero dimensional structure, and there exists one free nitrogen atom in the DPBT ligand. These results indicate that syntheses of MOFs can be influenced by the nature of metal ions. Photofluorescent Properties. Because compounds 1 and 2 are constructed from Cd2+ and Zn2+ ions with d10 electron and a rigid fluorescent DPBT ligand, they are highly likely to exhibit potential photoluminescence (PL) properties. Thus, the PL properties of both compounds were examined. The spectra of single-crystalline powder samples of compounds 1−4 and the DPBT ligand were recorded at room temperature. As E



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mM. The emission of 1 almost completely disappeared when the concentration of PA was as low as 0.2 mM. However, the other five nitro compounds exhibit minor quenching effects on the fluorescence change of 1. Those results show that 1 can be applied to highly selectivity detect PA as an efficient fluorescence sensor. It is essential to investigate the mechanism of quenching to understand the origin of the high selectivity toward PA. When the MOFs are irradiated by light of certain wavelengths, an electron transfers from the ground state to an excited state, and then the excited electron returns to the ground state with fluorescence emission. Generally, the excited electron will possess a better driving force for electron transfer to electrondeficient analytes instead of relaxation to the ground state when the LUMOs of analytes lie at lower energies than the conduction band of a MOF, which leads to fluorescence quenching. As shown in Figure 6c, density functional theory at the B3LYP/6-31G* level was used to calculate molecular orbital energy calculations for electron-deficient nitro compounds. The low LUMO energy level is conducive to electron transfer from the excited state of MOFs to the electrondeficient analyte.35 Calculation results show that the LUMO energy of PA is lower than that of DPBT (Figure S18 and Table S3), and the other nitro compounds display higher LUMO energy values. Thus, among the six given nitro compounds, the quenching efficiency of PA is apparently larger than those of the others for both compounds at the same concentration, suggesting that the as-prepared compounds have great potential to be developed as favorable sensors for the detection of PA. The experimental results for PA agree well with the theoretical calculation LUMO energy levels with the maximum quenching response, but the order of the observed quenching efficiencies is not fully in accordance with the LUMO energies of the other nitro compounds. This indicates that photoinduced electron transfer is not the only mechanism for quenching. For the stabilities of the compounds in suspensions to be confirmed, with 2 as an example, the PXRD spectra of 2 were measured immersed in NB and 3.0 × 10−3 M PA solution (Figure 6d). The recorded patterns of diffraction peaks are the same as those of the simulated patterns and as-synthesized samples from single crystal structures, which indicate that the crystal framework is retained in the suspensions. The strong stability and emission of 2 in organic suspensions shows its potential to be utilized in liquid-phase fluorescence detection. In addition, we also investigated the emission decay lifetimes of both compounds. The curves (Figures S19 and S20) are best fit by biexponentials in emulsions. The emission decay lifetimes of compounds 1 and 2 are as follows: τ = 4.93 ns (χ2 = 1.113) for emulsion 1 and τ1 = 6.27 ns (69.35%) and τ2 = 2.83 ns (30.65%, χ2 = 0.995) for emulsion 2. The emission lifetime values of both compounds are up to nanoseconds, which indicate that both compounds can be used as fluorescence materials to detect PA and metal ions. Thermogravimetric Analyses and Powder X-ray Diffraction. The thermal behaviors of compounds 1−4 were investigated by TGA to understand the stability of the coordinated skeletons. As shown in Figure S21, because of the loss of the solvent water molecules and the collapse of the molecular skeleton, two weight losses are observed at approximately 120 and 460 °C, respectively, for compound 1. Compound 2 also shows two main steps of weight loss: one is observed from 150 to 250 °C resulting from the loss of solvent

ethylene glycol (EG), and nitrobenzene (NB) are used as solvents. As shown in Figure 5a and b, all of the PL spectra of both compounds exhibit ligand emissions with nearly the same broad maximum at 443 nm (λex = 357 nm for 1 and λex = 364 nm for 2) as those of the DPBT ligand (λmax = 440 nm, λex = 357 and 364 nm, respectively; Figure S4). It is interesting to note that the linker-centered emissions of 1 and 2 display different solvent-dependent fluorescence phenomena (Figure 5c,d). Compound 1 immersed in NB shows the weakest luminescent intensity, and when it is dispersed in EA, the spectrum exhibits enhancing behavior, which is the strongest emission. The fluorescence intensities of 2 immersed in EG, DCM, and MeOH are stronger than those in the other solvents, and in NB, the emission of 2 was completely quenched. In light of the volatility and toxicity of those solvents, the titration experiments were carried out with DMF suspensions. Detection of Nitro Compounds. In the 3D network of 2, the distance between two parallel layers is 9.43 Å, which makes it easier for small molecules to move into the crystal skeleton and interact with each other. Thus, the PL titration for 2 upon the addition of nitro compounds with 3.0 × 10−3 M to corresponding emulsions were also conducted in the following sensing experiments by the addition of PA, 2,4-dinitrotoluene (2,4-DNT), 4-nitrotoluene (4-NT), 1,4-dinitrobenzene (1,4DNB), nitrobenzene (NB), and 1,3-dinitrobenzene (1,3-DNB) to DMF emulsions. The PL intensity of 2 is quenched to different degrees by adding the six nitro compounds (Figure 6a). The most effective quencher is PA with a quenching percentage ((QP) = (I0 − I)/I0 × 100%, where I0 and I are the fluorescence intensities of the emulsions before and after exposure to the nitro compounds) of 99.7% when the concentration is up to 0.1 mM, far more than those of the other nitro compounds, which shows that 2 is an efficient fluorescence sensor for selective sensing PA. The sensing performances of 2 for nitro compounds were investigated by PL titration experiments. The addition of nitro compounds into DMF emulsions results in a fluorescence quenching effect (Figure 6b and Figures S5−9). The order of quenching efficiency is PA > 1,4-DNB > NB > 4-NT > 1,3DNB > 2,4-DNT. The highest fluorescence quenching percentage is PA, which quenches the emission by as much as 99.7% when the concentration reaches 0.1 mM. However, under the same concentration, other nitro compounds exhibit indistinct changes with a QP of 10.8% for 1,4-DNB and lower values for the other four nitro compounds. These results shows that 2 as a fluorescence sensor material has great potential to selective detect PA. The relationship between the fluorescence intensities and the concentration of PA can be fitted well with a first-order exponential equation,32 and a Ksv of 5.9 × 104 M−1 is observed for PA (R2 = 0.999, Figure S10). It is obvious that an upward and nonlinear curve appears with an increase in the PA concentration, suggesting that there is possibly simultaneous static and dynamic quenching in the process of fluorescence quenching.33As shown in Figure 6b, the fluorescence emission of the emulsion without PA is 443 nm. As the concentration of PA increased, the maximum emission of the emulsion gradually shifts, which may be due to fluorescence resonance energy transfer.34 The fluorescence responses of 1 to various nitro compounds were also investigated (Figures S11−17). Similar to 2,the incremental concentration of PA to 1 led to high and fast fluorescence quenching behavior with a QP of 74.3% at 0.1 F



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decreases and reaches 0.51 cm3 K mol−1 at 1.8 K, possibly owing to spin−orbital coupling and/or weak antiferromagnetic interactions. The magnetic data of the entire temperature range are fitted using the PHI program based on the [Co2(COO)4] unit37 with a fitted value g = 2.02, coupling constant J = −0.95, orbital reduction factor κ = 0.8, and λ = −178 cm−1 (Figure 7).

DMA molecules, and the other occurs after 370 °C, which is due to collapse of the molecular skeleton. There are three steps for compound 3; the former two steps of weight loss are in the ranges of 40−115 °C and 120−300 °C, which are attributed to the loss of the solvent water molecules and free DMF molecules. The final step is observed at higher than 350 °C, which results from the collapse of the molecular skeleton. There is only one weight loss for compound 4 in the range 460−500 °C, which results from collapse of the molecular skeleton. PXRD experiments for compounds 1−4 were carried out to confirm whether the crystal structures are truly representative of the bulk materials. As shown in Figures S22−25, the main peak positions of PXRD experiments agree well with those of the corresponding computer-simulated compounds, showing that the bulk crystal is homogeneous. Magnetic Properties. The magnetic measurements of sample 3 were performed on a SQUID magnetometer over the temperature range of 1.8−300 K under an applied field of 2000 Oe. The temperature dependence of magnetic susceptibility of 3 in the forms of χMT and χM versus T is displayed in Figure 7; the experimental χMT value of 6.07 cm3 K mol−1 at 300 K is greater than the theoretical value of 3.75 cm3 K mol−1 for two isolated high-spin Co(II) ions (g = 2 and S = 3/2) per formula due to the prominent orbital contribution arising from the 4T1g ground state of Co(II).36 Upon cooling, χMT continuously

Ĥ = Ĥ so + Ĥ ex + Ĥ zee Ĥ so = λκL̂ i ·Sî Ĥ ex = −2J ·S1̂ ·S2̂

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Ĥ zee = μgβ ·H ·S

CONCLUSIONS In summary, under solvothermal conditions, we successfully synthesized four new MOFs based on a fluorescent ligand. Under the same conditions with different metal ions, compounds 1, 3, and 4 possess different coordination modes and space structures. Compounds 1 and 3 show similar structures with the same building blocks and possess 3D 6connected pcu net. Furthermore, 1 and 3 are based on a 2-fold interpenetrating network with solvent molecules located in the frameworks. Compound 4 possesses zero dimensional structure, and there exists one free nitrogen atom in the DPBT ligand. Compound 2 possesses a layered structure. In the light of the layered structure for compound 2, it was tested for sensing nitro compounds, and showing selective PL quenching for PA compared to other nitro derivatives. Moreover, a magnetism study of compound 3 indicates that there are antiferromagnetic interactions between Co(II) atoms in this system.

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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.cgd.5b00681. Fluorescence responses of 2 toward DMF solutions of various nitro compounds, solid-state emission spectra, syntheses, crystal data, and structural refinement parameters of compounds 1−4, and PXRD and TGA data (PDF) Crystallographic information for compound 1 (CIF) Accession Codes

CCDC 1449467−1449470 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*Fax: 86-25-83314502. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by grants from the National Natural Science Foundation of China (21371092 and 91022011) and

Figure 7. (a) χMT versus T plot and (b) χM versus T plot for 3; the red lines are the best fit. G



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(32) Cho, W.; Lee, H. J.; Choi, G.; Choi, S.; Oh, M. J. Am. Chem. Soc. 2014, 136, 12201−12204. (33) Carboni, M.; Lin, Z.; Abney, C. W.; Zhang, T.; Lin, W. Chem. Eur. J. 2014, 20, 14965−14970. (34) Kong, L.; Wong, H. L.; Tam, A. Y.; Lam, W. H.; Wu, L.; Yam, V. W. ACS Appl. Mater. Interfaces 2014, 6, 1550−1562. (35) Sanchez, J. C.; Di Pasquale, A. G.; Rheingold, A. L.; Trogler, W. C. Chem. Mater. 2007, 19, 6459−5470. (36) Zhu, Y. Y.; Cui, C.; Zhang, Y. Q.; Jia, J. H.; Guo, X.; Gao, C.; Qian, K.; Jiang, S. D.; Wang, B. W.; Wang, Z. M.; Gao, S. Chem. Sci. 2013, 4, 1802−1806. (37) Chilton, N. F.; Anderson, R. P.; Turner, L. D.; Soncini, A.; Murray, K. S. J. Comput. Chem. 2013, 34, 1164−1175.

the National Basic Research Program of China (2010CB923303).

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