Silver Phosphate Crystal Growth by Screw Dislocation Driven of

Article pubs.acs.org/crystal

Silver Phosphate Crystal Growth by Screw Dislocation Driven of Dynamic-Template Jian-Dong Wang,† Jin-Ku Liu,*,† Chong-Xiao Luo,† Yi Lu,† and Xiao-Hong Yang‡ †

Key Laboratory for Advanced Materials, East China University of Science and Technology, Shanghai 200237, P.R. China Department of Chemistry, Chizhou University, Chizhou 247000, P.R. China

‡

ABSTRACT: An interesting route was developed for symmetrical structures of the silver phosphate (Ag3PO4) crystal with gyro shape. The Ag3PO4 crystal belongs to the cubic crystal system and revealed a screw dislocation in the {100} facets with helical growth along the epitaxial spin axis. In this reaction system, the acrylamide (AM) polymer monomer was used as a cooperation reagent. The Ag3PO4 crystal exhibits photooxidative capabilities for the polymerization to form polyacrylamide (PAM) under visible-light irradiation, and the energy released during this polymerization overcomes the surface energy required for creating screw dislocation forming hexagonal spin axes in three dimensions spontaneously. The investigated mechanism confirmed the driven role of dynamic-template, and the explored Ag3PO4 crystal control method could be used to synthesize other inorganic crystals.

1. INTRODUCTION

since the structures of organic molecules remain unchanged in the whole reaction. In this paper, the effect of Ag3PO4 to the photocatalytic polymerization reaction of acrylamide (CH2CHCONH2, AM) has been investigated, and the research result indicates that the photoproduction electronics in the Ag3PO4 microcrystal have a high activity. These photoproduction holes on the CB of Ag3PO4 can have a reaction with AM to form highly reactive radicals which can make the polymerization reaction happen between AM molecules, and then polyacrylamide (PAM) molecules were achieved. During the research, the polymerization reaction was carried out on the surface of Ag3PO4 crystal, therefore the change of energy caused by polymerization may influence the crystal growth and lead to a kind of Ag3PO4 crystal with a gyro shape being synthesized. On the basis of this study, a growth mechanism of Ag3PO4 crystal which synthesized by dynamic template method driven by screw dislocation was proposed.

As a visible light photocatalyst, the silver phosphate (Ag3PO4) crystal has recently attracted considerable attention, which exhibits extremely high photooxidative capabilities for organic dye decomposition under visible-light irradiation.1−6 Unfortunately, the conduction band (CB) position of Ag3PO4, which is lower than the potential of H+/H2O as a result of H2, cannot be reduced from H2O.7,8 Due to the above reason, the Ag3PO4 is only a semiphotocatalyst which can split H2O to O2 or degrade the organics by the photoproduction holes on the valence band (VB). The photoproduction electronics on the CB were always bonded by the sacrificial reagents, and studies about how to utilize those photoproduction electronics effectively are rare in recent years. So, confirming the photocatalytic activity of photoproduction electronics in the Ag3PO4 microcrystal is very meaningful in order to develop the photocatalystic application of the Ag3PO4 crystal. Synthesis of inorganic crystals with a specific size and morphology has recently attracted a lot of interest because of their potential in the design of new materials and devices as well as special applications.9−12 In particular, as a result of the organic molecule being a facile and effective template for control of crystal growth,13,14 there are a lot of methodologies for fabrication of inorganic crystals by template approaches, including the hard template method, soft template method,15,16 and the synergic template route.17−19 Recently, several mechanisms of control crystal morphology have emerged to explain the roles of different organic matter, such as small organic molecules,20,21 large organic molecules,22,23 and polymers.24,25 Only one specific kind of crystal morphology will be formed under the influence of one organic template, © 2013 American Chemical Society

2. EXPERIMENTAL SECTIONS The eggshell membrane was made from a fresh eggshell after removing the outer shell and washing with deionized water. Thereafter, it was fastened in a reactor to separate it into two horizontal compartments, into which 25 mL of 0.15 mol/L AgNO3 solution and 25 mL of 0.05 mol/L Na2HPO4 solution were added, respectively. The 0.025 g (i.e., 1 g/L) of AM was also added to both sides as a cooperative reagent. The system was kept at room temperature for 3, 6, 12, and 24 h, Received: June 29, 2013 Revised: October 2, 2013 Published: October 9, 2013 4837

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Figure 1. (a) SEM image and (b) XRD pattern of the Ag3PO4 crystal. Inset: schematic drawing of the crystal structure.

Figure 2. (a) FT-IR spectrum and (b) UV−vis spectrum of Ag3PO4 crystal. Inset: production mechanism of e-CB on the surface of the Ag3PO4 crystal.

3. RESULTS AND DISCUSSION 3.1. Morphology and Structure. The typical SEM image of the Ag3PO4 crystal synthesized by dynamic-template method showed in Figure 1a. The Ag3PO4 crystal possessed symmetrical and regular gyrolike morphology with an average length of 6 μm in the three axes. The crystal was constituted by a central part and six orthogonal protrusions whose tops were conelike and was 0.6 μm in diameter. The XRD pattern of Ag3PO4 crystal is shown in Figure 1b. The diffraction peaks were matched with the standard XRD data of the cubic-phase Ag3PO4 crystal (JCPDS file, no: 06-0505).26−28 The symmetric space type of the cubic phase Ag3PO4 crystal was P43n̅ . In the range of 2θ = 10−90°, no other peaks could be observed, which also confirmed that the product was exclusively a cubic phase Ag3PO4 crystal. From the polyhedron configuration of Ag3PO4 crystal consists of tetrahedral PO4 (P−O distance of 1.529 Å) and AgO4 (Ag−O distance of 2.314 Å), it is obvious that one PO4 tetrahedron and three tetrahedral AgO4 are combined with each other through the corner oxygen (inset of Figure 1b). 3.2. Optical Properties. The typical vibration peaks of the products in the FT-IR spectrum are shown in Figure 2a. It can be seen that the main bands of the spectrum are located at 2350, 1635, 1390, 1015, and 560 cm−1, which are assigned to water−phosphate hydrogen bonding, the water ν1(H−O−H) antisymmetric bending mode, ν2(PO43−) antisymmetric stretching mode, the ν3(PO43−) symmetric stretching mode, and the ν3(PO43−) in-phase P−O bonding, respectively.29 From analysis of the UV−vis spectrum (Figure 2b) of the Ag3PO4 microcrystal, it revealed that the absorptivity of products showed a trend to increase in the range of 200−520 nm and reached a peak at 510 nm, which belonged to the visible region (Figure 2b). The electrons on the VB of Ag3PO4 leaped into the CB after absorbing the energy from visible light, and the band gap was estimated to be 2.31 eV (inset of Figure 2b).

respectively. The obtained products were separated in a centrifuge with 1500 rpm, followed by the wash with deionized water and alcohol several times, respectively, until no Ag+ ions were detected. The clear products were collected and dried in a desiccator, the products with different morphologies were obtained. The polymerization of the AM reaction was performed in the same apparatus. Ten milliliters of reaction solution was separated from from apparatus to a centrifuge with 1500 rpm. The clear solution was analyzed by use of a gas chromatograph (Agilent 6890 series GC system). The 0.25 g Ag3PO4 crystals was added into 50 mL of 1 × 10−5 g/L Rhodamine B (RhB) solution and then exposed under sunlight. (The photodegradation reactions were measured between 11.00 am and 2.00 pm, and the temperature was about 25 °C.) The UV−vis absorption spectras of samples which were taken as the time changed were tested at room temperature on a UV-2450 (Shimadzu) spectrometer. The structures of Ag3PO4 crystal were characterized by X-ray powder diffraction (XRD) using a Shimadzu XD−3A diffractometer. X-ray photoelectron spectroscopy (XPS) (Shimadzu ESCA-3400, Mg Kα radiation) measurements were carried out so as to evaluate the surface electronic state and to analyze the surface atom of the sample. The microstructures and morphologies were analyzed with Philips S-4800 scan electron microscopy (SEM) and Hitachi-800 transmission electron microscopy (TEM). The optical properties of the products were studied by Fourier conversion infrared spectroscopy (FT-IR). UV−vis absorption spectra were investigated at room temperature by a UV-2450 (Shimadzu) spectrometer. The polymerization degree of PAM was determined by Perkin-Elmer-200 gel-permeation chromatography (GPC). 4838

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1s, and P 2p3/2 was recorded. The Ag 3d spectra of the products (a), characterized by the two spin−orbit components, Ag 3d5/2 and Ag 3d3/2, separated by 5.5 eV, exhibit two doublets, indicating that Ag is in a highly ionic Ag+ state. The position of the O 1s XPS peaks in the Ag3PO4 crystal (530.5 and 531.9 eV, Figure 4b) agree with the expected value for oxygen in the Ag3PO4 crystal. A shoulder peak showed a higher BE (531.9 eV) attributing to oxygen in the form of the −OH group. The energy of P agreed well with standard sample in the chemical state: Ag3PO4 (P 2p3/2 = 132.6, Figure 4c).1,30 3.4. Photocatalytic Properties. The photocatalytic efficiency of the Ag3PO4 crystals was showed in Figure 5.

However, the CB position of the Ag3PO4 crystal was lower than the electric potential of H+/H2O and which means the photoproduction holes on the CB of Ag3PO4 only can be used to split water to release O2. The photoproduction electronics needed acceptors to ensure the production of holes which can synthesize O2 from H2O or degrade organics under visible-light irradiation. 3.3. Composition Analysis. Energy dispersive X-ray spectrum (EDS) analysis performed on the Ag3PO4 crystal showed that the surface of the Ag3PO4 microcrystal was constituted by Ag, O, and P atoms with a ratio of 3:4:1, which was identical with the theoretical result (Figure 3). It indicated that the dynamic-template method could prepare a high purity of the cubic-phase Ag3PO4 crystal.

Figure 5. The photocatalytic efficiency of the Ag3PO4 crystals.

The 0.25 g of Ag3PO4 crystals was added into 50 mL of 1 × 10−5 g/L Rhodamine B (RhB) solution and then exposed under sunlight. (The photodegradation reactions were measured between 11.00 am and 2.00 pm, and the temperature was about 25 °C.) It can be clearly showed that the RhB dyes can be degraded completely in 15 min, which indicated the high photocatalytic activity of the Ag3PO4 crystals synthesized by a dynamic-template route.

Figure 3. Energy-disperse X-ray spectrum (EDS) taken on the selected area containing the Ag3PO4 crystal.

The X-ray photoelectron spectrum (XPS) also showed the presence of Ag, O, and P elements in the surface of the Ag3PO4 crystal (Figure 4). The binding energy of Ag 4d5/2, Ag 3d3/2, O

Figure 4. XPS spectra of Ag3PO4 crystal in several conditions: (a) Ag 4d5/2 and 3d3/2, (b) O 1s, and (c) P 2p3/2. 4839

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Figure 6. SEM images of Ag3PO4 crystal: (a) 1 g/L PAM as a template and (b) no reagent.

Figure 7. The SEM images of the observed Ag3PO4 crystal under different aging times: (a) 3, (b) 6, (c) 12, and (d) 24 h.

4. MECHANISM OF DYNAMIC TEMPLATE 4.1. Cooperation Reagents. Figure 6a showed the typical SEM images of the Ag3PO4 crystal, which were synthesized under same method with PAM as the template. The product possessed special coral-shaped cluster crystals. In the absence of organic reagents (as shown in Figure 6b), the Ag3PO4 crystal with perfect and regular dendritic crystals were grown in a large dimension. These results were quite different from the morphology of the Ag3PO4 crystal under the condition of AM as the template and indicated that the AM molecules had a very important effect for the formation of the Ag3PO4 crystal with a gyro shape. In the formation process of the Ag3PO4 crystal, not only did the AM molecules work as the template but also, more importantly, they could absorb photoproduction electronics on the CB of the Ag3PO4 crystal, which was produced by the electron transition after absorbing the energy from sunlight, and then transform into radicals which would react with other monomers in the system to form PAM. The heat released by the polymerization reaction promoted the helical growth of the Ag3PO4 crystal with the gyro shape driven

by the screw dislocation component of an axial dislocation along the six square {100} facets. On the other hand, the PAM cannot catch the photoproduction electronics and it is only a traditional organic template which will affect the growing of crystals by its functional groups and molecular structure. As the above reasons, the morphologies of Ag3PO4 crystals were totally different with AM or PAM as the template. 4.2. Growth Stages. The time-dependent crystal morphology evolution through interception of the intermediate products was performed at different crystal growth stages. The SEM images of the Ag3PO4 crystal were under a different aging time, as 3, 6, 12, and 24 h, respectively (Figure 7, panels a−d). As the crystal began to form, the size of the crystal nucleus is quite small and can be viewed as a spherelike shape from the whole region of the image (shown in Figure 7a). After aging 6 h, the crystal had an irregular morphology through further grow (Figure 7b). In Figure 7c, it can be observed obviously as the polyhedral shape of the Ag3PO4 crystal after 12 h. Figure 7d showed the complete and regular final morphology of the Ag3PO4 crystal with a gyro shape. 4840

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Figure 8. SEM images of observed Ag3PO4. (a) Prefect and (b) intermediate crystals.

4.3. Direction Growth. Through the comparison of the results of Figure 8 (panels a and b), it is revealed that the protrusions grown from the six faces of the cubic Ag3PO4 microcrystal. In accordance with past reports, these faces were all {100} facets, which had a high photocatalytic activity.3 The formation of the Ag3PO4 crystal with a gyro shape was caused by helical growth driven by the screw dislocation component of an axial dislocation along the six square {100} facets. 4.3. Dynamic Mechanism. In order to determine the activity of photoproduction electronics in the Ag3PO4 crystal, the AM molecules were added into the reaction system. The production rate of PAM under different polymerization times was determined by gas chromatography (Figure 9). The result

shown in Figure 7c, it can be clearly seen that the gyro structure of the Ag3PO4 crystal has formed, which was transformed from the cubic sharp, as shown in Figure 7b. The heat released by the polymerization reaction mainly caused the transformation of crystal’s sharp as mentioned above in the first 12 h. As the reaction progresses, the generation rate of the polymer was decreased sharply as the reduction of monomer’s amount, but the polymerization reaction still occurred in the system over 12 h. The heat released by the polymerization reaction promoted the helical growth of the Ag3PO4 crystal with the gyro shape driven by the screw dislocation component of an axial dislocation along the six square {100} facets. Table 1. Peak Molecular Weight Report RT

area

PMwt

Mw

Mn

Mw/Mn

22.723

97432.1

247949.9

429458.9

236815.5

1.8135

The polymerization degree of PAM can be determined by the molecular weight which was tested by the gel permeation chromatography (GPC, Perkin-Elmer-200). And the result showed in Figure 10 indicated that the average molecular weight of PAM was 236815.5, which means the average polymerization degree was about 3335.

Figure 9. The production rate of PAM under different polymerization times.

showed that the amount of PAM increased obviously with the change in reaction time. It was found that the generation rate of AM almost reached a peak after 12 h, and it increased very slowly in the next 24 h, which was in accordance with the mechanism of the chain polymerization reaction. Therefore, it can conclude that the most probable way of the primary radical generation in the reaction investigation was the AM activation by the photoproduction electronics on the CB of the Ag3PO4 crystal. The AM molecules could absorb photoproduction electronics on the CB of the Ag3PO4 crystal and then transform into radicals which would react with other monomers in the system to form PAM. This process was very interesting because the polymerization of AM was a chain reaction. In addition, the polymerization reaction does not finish at 12 h; it just slows down, which is in line with the mechanism of the polymerization reaction. In the first 12 h of the polymerization reaction, the monomer was activated and transferred into a radical rapidly due to its high concentration in the reaction system. As

Figure 10. GPC chromatogram of PAM products.

In accordance with the UV−vis spectra of AM and PAM, the two organic agents had the same functional groups and the same peak position of UV−vis absorption (Figure 11). The peak position at 195 nm indicated that AM and PAM had no response to visible light, which meant AM would not polymerize and convert into PAM even exposed under visible light. However, the morphologies of the Ag3PO4 crystal were quite different when AM, PAM, and no reagent were used as 4841

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Figure 11. The UV−vis spectra of AM and PAM. Figure 13. Growth schematic of the Ag3PO4 crystal by screw dislocation of the dynamic template.

templates, respectively. So, the reason for helical growth along the six square {100} facets was the energy change caused by polymerization reaction of AM, rather than the influence of the organic reagents’ polarity or organic functional groups. The reason for the helical growth epitaxial spin axis on the {100} facets of cubic phase Ag3PO4 crystal is proposed: The polymerization of AM is strongly exothermic. After the AM molecules transforming into AM radicals, the highly exothermic phase of AM radical propagation not only drives anisotropic growth but also causes the spontaneous formation of crystal due to the dislocation strain energy (Figure 12). Due to the

energy from sunlight, and AM molecules were transformed into AM radicals. (5) Ag3PO4 microcrystals kept adsorbing the AM molecules in the system. (6) The polymerization reaction of AM radicals happened with heat released. (7) Ag+ and PO43− ions gathered on the six {100} facets of Ag3PO4 microcrystals. (8) The heat released by the polymerization reaction promoted the helical growth of the Ag3PO4 crystal with a gyro shape driven by the screw dislocation component of an axial dislocation along the six square {100} facets. (9) Ag+ and PO43− ions gathered on the protrusions, which formed on the six {100} facets of Ag3PO4 microcrystals. (10) The protrusions kept growing until the gyro Ag3PO4 crystal was formed.

4. CONCLUSIONS In summary, the high activity of photoproduction electronics of the Ag3PO4 crystal was determined through the study of photooxidative capabilities of Ag3PO4 for the polymerization of AM under visible-light irradiation. Those photoproduction electronics on the CB of the Ag3PO4 crystal could act with AM molecules to form AM radicals with high activity, which would impel the polymerization of AM. Furthermore, with the polymerization on the surface of the Ag3PO4 microcrystal, the change of energy caused by the polymerization reaction would affect the crystal growth. By analysis of the experimental results, the growth mechanism of the gyro Ag3PO4 crystal is as follows: First, the crystal nuclei of the Ag3PO4 would keep growing until the cubic Ag3PO4 microcrystal with high activity and uniform morphology formed. Then, these cubic Ag3PO4 microcrystals began to gather AM molecules. The electrons on the VB of the Ag3PO4 crystal leapt into the CB, and finally into the AM molecules after absorbing the energy from visible light; after that, the AM molecules were transformed into radicals. The change of energy caused by the polymerization reaction among radicals promoted the helical growth epitaxial spin axis on the {100} facets of the cubic Ag3PO4 crystal.

Figure 12. Schematic representation of crystal growth due to a screw dislocation.

disruption of the perfect periodicity within the crystal lattice, there is a stress need for only one equation, as symmetry allows only one radial coordinate to be used:

τ=

−μb 2πr

(1)

where μ is the shear modulus, b is the Burgers vector, and r is a radial coordinate. As b increases, eventually the crystal contains enough strain energy. It explains why the Ag3PO4 crystal formed a small cubic shape at the intermediate stage, but it finally grew a complex shape after polymerization of the AM molecules. The growing process31−33 of the Ag3PO4 crystal with a gyro shape was shown in Figure 13: (1) The crystal nuclei of Ag3PO4 microcrystals were produced after the reaction between AgNO3 and NaH2PO4 in the solution. The crystal nuclei were not enough to gather the AM molecules. (2) Cubic phase Ag3PO4 microcrystals could be observed through continuous growth of the crystal nucleus. (3) Cubic phase Ag3PO4 microcrystals began to gather AM molecules. (4) The electrons on the VB of Ag3PO4 leaped into the CB after absorbing the

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. 4842

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(30) Buckley, J. J.; Lee, A. F.; Olivic, L.; Wilson, K. J. Mater. Chem. 2010, 20, 8056−8063. (31) Huang, F. Z.; Shen, Y. H.; Xie, A. J.; Yu, S. H.; Chen, L.; Zhang, B. C.; Chang, W. G. Cryst. Growth Des. 2009, 9, 722−727. (32) Cong, H. P.; Ren, X. C.; Yao, H. B.; Wang, P.; Colfen, H.; Yu, S. H. Adv. Mater. 2012, 24, 1309−1315. (33) Yan, B.; Guo, M. Inorg. Chim. Acta 2013, 399, 160−165.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grant 21341007 and 21071024), Fundamental Research Funds for the Central Universities (Grant 222201313005) and State Key Laboratory of Pollution Control and Resource Reuse Foundation (Grant PCRRF11019).

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REFERENCES

(1) Liu, J. K.; Luo, C. X.; Wang, J. D.; Yang, X. H.; Zhong, X. H. CrystEngComm 2012, 14, 8714−8721. (2) Bi, Y. P.; Hu, H. Y.; Ouyang, S. X.; Lu, G. X.; Cao, J. Y.; Ye, J. H. Chem. Commun. 2012, 48, 3748−3750. (3) Bi, Y. P.; Ouyang, S. X.; Umezawa, N.; Cao, J. Y.; Ye, J. H. J. Am. Chem. Soc. 2011, 133, 6490−6492. (4) Teng, W.; Li, X. Y.; Zhao, Q. D.; Zhao, J. J.; Zhang, D. K. Appl. Catal., B 2012, 125, 538−545. (5) Yang, X. F.; Cui, H. Y.; Li, Y.; Qin, J. L.; Zhang, R. X.; Tang, H. ACS Catal. 2013, 3, 363−369. (6) Yi, Z. G.; Ye, J. H.; Kikugawa, N.; Kako, T.; Ouyang, S. X.; Williams, H. S.; Yang, H.; Cao, W. J.; Li, Z. S.; Liu, Y.; Withers, R. L. Nat. Mater. 2010, 9, 559−564. (7) Dong, P. Y.; Wang, Y. H.; Li, H. H.; Li, H.; Ma, X . L.; Han, L. L. J. Mater. Chem. A 2013, 1, 4651−4656. (8) Elahifard, M. R.; Rahimnejad, S.; Haghighi, S.; Gholami, M. R. J. Am. Chem. Soc. 2007, 129, 9552−9553. (9) Arnold, I.; Pfeiffer, K.; Neupert, W.; Stuart, R. A.; Schagger, H. J. Biol. Chem. 1998, 17, 7170−7178. (10) Zhou, S. Q.; Wen, M.; Wang, N.; Wu, Q. S.; Wu, Q. N.; Cheng, L. Y. J. Mater. Chem. 2012, 22, 16858−16864. (11) Ni, Y. H.; Zhang, Y. M.; Hong, J. M. Cryst. Growth Des. 2011, 11, 2142−2148. (12) Du, W. M.; Zhu, J.; Li, S. X.; Qian, X. F. Cryst. Growth Des. 2008, 8, 2130−2136. (13) Gajjela, S. R.; Ananthanarayanan, K.; Yap, C.; Grätzel, M.; Balaya, P. Energy Environ. Sci. 2010, 3, 838−845. (14) Luo, C. X.; Liu, J. K.; Lu, Y.; Du, C. S. Mater. Sci. Eng., C 2012, 33, 680−684. (15) Tao, F.; Guan, M.; Jiang, Y.; Zhu, J.; Xu, Z.; Xue, Z. Adv. Mater. 2006, 18, 2161−2164. (16) Gartner, Z. J.; Brian, N. T.; Grubina, R.; Doyon, J. B.; Snyder, T. M.; Liu, D. R. Science 2004, 305, 1601−1605. (17) Lv, R.; Cao, C.; Zhai, H.; Wang, D.; Liu, S.; Zhu, H. Solid State Commun. 2004, 130, 241−245. (18) Sun, L. B.; Li, J. R.; Park, J. H.; Zhou, H. C. J. Am. Chem. Soc. 2012, 134, 126−129. (19) Gao, L.; Song, X. Mater. Chem. Phys. 2008, 110, 52−55. (20) Kong, Y.; Qiu, T.; Qiu, J. Appl. Surf. Sci. 2012, 34, 113−117. (21) Cheng, S.; Tarby, C. M.; Comer, D. D.; Williams, J. P.; Caporale, L. H.; Myers, P. L.; Boger, D. L. Bioorg. Med. Chem. 1996, 4, 727−737. (22) Rosei, F.; Schunack, M.; Jiang, P.; Gourdon, A.; Laegsgaard, E.; Stensgaard, I.; Joachim, C.; Besenbacher, F. Science 2002, 296, 328− 331. (23) Ogasawara, W.; Shenton, W.; Davis, S. A.; Mann, S. Chem. Mater. 2000, 12, 2835−2837. (24) Hernandez, B. A.; Chang, K. S.; Fisher, E. R.; Dorhout, P. K. Chem. Mater. 2002, 14, 480−482. (25) Ding, J. H.; Gin, D. L. Chem. Mater. 2000, 12, 22−24. (26) Wang, J.; Teng, F.; Chen, M. D.; Xu, J. J.; Song, Y. Q.; Zhou, X. L. CrystEngComm 2013, 15, 39−42. (27) Hu, H. Y.; Jiao, Z. B.; Yu, H. C.; Lu, G. X.; Ye, J. H.; Bi, Y. P. J. Mater. Chem. A 2013, 1, 2387−2390. (28) Liu, Y. P.; Fang, L.; Lu, H. D.; Liu, L. J.; Wang, H.; Hu, C. Z. Catal. Commun. 2012, 17, 200−204. (29) Kumar, S.; Surendar, T.; Baruah, A.; Shanker, V. J. Mater. Chem. A 2013, 1, 5333−5340. 4843

dx.doi.org/10.1021/cg4009812 | Cryst. Growth Des. 2013, 13, 4837−4843