DOI: 10.1021/cg9004483
(AEDPH3) 3 (ureaH) 3 (H2O): A Novel Organic Supramolecular Plaster with Gas Adsorption Performance
2009, Vol. 9 3835–3839
Shuo-ping Chen, Le Hu, Xue-jia Hu, Yi-xuan Yuan, Ling-ling Pan, and Liang-jie Yuan* College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P. R. China Received April 22, 2009; Revised Manuscript Received June 30, 2009
ABSTRACT: A novel supramolecular plaster, namely (AEDPH3) 3 (ureaH) 3 (H2O) (1), is synthesized and characterized by infrared spectrum (IR), thermogravimetric analysis (TGA), elemental analysis (EA), single-crystal X-ray diffraction (SCD), and powder X-ray diffraction (PXRD). The supramolecular plaster is an organic acid-base compound that shows a 3D hydrogenbonded supramolecular network with extended 1D channels. It is simple to synthesize and process and shows good mechanical properties similar to the gypsum-based plaster. Moreover, it has nice gas adsorption performance. Inorganic gelling materials, including plaster1 and cement,2 are widely used in our life. The interactions among the components in these materials are electrovalent bonds. On the other hand, the hydrogen bond is important in designing and obtaining novel structures.3 Hydrogen-bonded assembly of organic molecules has been well-developed in recent years because of exquisite architectures and potential interesting functions.4 As an attempt at combining the gelling materials and organic supramolecular compounds, we focused on the construction of small organic molecules via hydrogen bond to novel supramolecular gelling materials as plaster. Among diverse organic supramolecular building blocks, 1-aminoethylidenediphosphonic acid ((CH3)C(PO3H2)2(NH2), AEDPH4) is found to be an excellent precursor for constructing novel supramolecular gelling materials with good mechanical performance.5 The first supramolecular plaster based on an organic acid-base compound, namely (AEDPH3) 3 (1,2,4-tzH) 3 (H2O) (2) (1,2,4-tz=1,2,4-triazole), has been reported as our recent work.6 This supramolecular plaster has good mechanical properties similar to the general gypsum plaster, as well as excellent sterilizing performance. To reduce the cost and design more similar organic supramolecular gelling materials with the help of crystal engineering, we chose urea as the base component to replace 1,2,4-tz. Another novel supramolecular plaster constructed by AEDPH4, urea, and water is successfully synthesized and reported herein (see Figure 1). This supramolecular plaster also has nice mechanical properties similar to the general gypsum plaster. In addition, because of its special crystal structure, the supramolecular plaster has good gas adsorption performance. The supramolecular plaster is simple to synthesize and process at room temperature and atmospheric pressure. (1) Milling: a mixture of 1-aminoethylidenedisphosphonic acid (AEDPH4) and urea with a 1:1 mol ratio was grinded at room temperature, gaining a kind of white powder. (2) Figuration: With strong agitation, distilled water with 0.75 amount (mass ratio) to the mixture was added. At this time, the mixture was a kind of milky suspension, which could be poured in a mold to shape into any forms. (3) Induration: After the distilled water had been added for 30 s, the suspension began to coagulate. It would indurate gradually in the following 60 s and finally turn into a hard and pure white solid. Compared with the plaster constructed by calcium sulfate, the surface of the supramolecular plaster is glossier and has a kind of ivory luster. By this manner, the supramolecular plaster could be made into arts (see Experimental Section and Figure 2). *Corresponding author. E-mail:
[email protected]. Tel: þ86-27-87218264. Fax: þ86-27-8721-8264. r 2009 American Chemical Society
To get the accurate structure of the supramolecular plaster, we obtained a colorless single crystal constructed by AEDPH4 and urea by slow evaporation (see Experimental Section). X-ray crystallographic analysis shows that the crystal is a new organic acid-base compound, namely (AEDPH3) 3 (ureaH) 3 (H2O) (1). Combined with the result of X-ray powder diffraction of the supramolecular plaster, it is proved that the structure of the plaster is the same as 1 (see Figure 3). In the supramolecular plaster, i.e., (AEDPH3) 3 (ureaH) 3 (H2O), each AEDPH4 molecule deprotonates one proton and transfers a proton to the amino-nitrogen atom, turning to AEDPH3- anion itself. Meanwhile, the oxygen atom of the urea molecule is protonated, forming an ureaHþ cation. In addition, there is one lattice water molecule in each asymmetric unit of the plaster (see Figure 1). As shown in Figure 4b, the AEDPH3- anions in supramolecular plaster form a stable two-dimensional (2D) supramolecular network. First, two AEDPH3- anions are self-assembled to form a dimer via strong hydrogen bond O1-H1 3 3 3 O3#10 (2.527(6) A˚) with a cyclic motif R22(8). Second, neighboring dimers are linked together and turn into a one-dimensional (1D) linear supramolecular chain with a R22(12) motif, which is formed by hydrogen bond N1-H1B 3 3 3 O2#7 (2.792(6)A˚). Third, hydrogen bond O4-H4 3 3 3 O2#9 (2.588(6) A˚) connects adjacent 1D chains, forming another R22(12) motif and extending the 1D chains to a 2D zigzag supramolecular layer. In addition, the amino of AEDPH3- anion remains two H(N1), forming hydrogen bonds close to O5 and O3, generating another R22(8) motif (N1H1A 3 3 3 O5#6=2.756(7) A˚, N1-H1C 3 3 3 O3#6 = 2.760(6) A˚), which helps to stabilize the 2D supramolecular network. Meanwhile, the ureaHþ cations and water molecules are connected each other with a cyclic motif R32(10), generating a 1D linear supramolecular chain along a axis (N3H3B 3 3 3 O1W#2, 2.903(9) A˚; N3-H3A 3 3 3 O1W#3, 3.021(9) A˚; N2-H2D 3 3 3 O7#5, 3.215(9) A˚) (see Figure 4a). The (ureaHþ 3 H2O)n supramolecular chain connects neighboring (AEDPH3-)n 2D supramolecular layers by various O-H 3 3 3 O and N-H 3 3 3 O hydrogen bonds (O7-H7 3 3 3 O5#1, 2.897(8) A˚; N2H2E 3 3 3 O6#4, 2.441(7) A˚; O1W-H2W1 3 3 3 O4#8, 3.149(7) A˚; O1W-H2W1 3 3 3 O6#8, 2.863(9) A˚; O1W-H1W1 3 3 3 O1#3, 2.955(8) A˚), forming a stable 3D sandwich-type supramolecular network (see Figure 4c). This supramolecular network is porous with extended 1D channels. There are mainly two kinds of 1D channels which are both constructed by a pair of parallel (ureaHþ 3 H2O)n supramolecular chains and (AEDPH3-)n supramolecular layers. The biggest one is with large aperture of ca. 10 3.5 A˚, whereas the aperture of the smaller one is ca. 4 2 A˚. The effective free volume of the supramolecular plaster is calculated by PLATON8 Published on Web 07/09/2009
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Figure 1. Formation and components of the supramolecular plaster: The Oak Ridge Thermal Ellipsoid Plot (ORTEP) of the unsymmetrical unit of the supramolecular plaster with thermal ellipsoids at the 30% probability.
analysis as being 9.1%, which indicates that this supramolecular plaster probably has good gas adsorption performance (see Figure 7a). As shown in Table 1, it can be observed that this supramolecular plaster is a kind of brittle material with high modulus. Compared with gypsum plaster for building purposes (bending strength g1.8 MPa, compressive strength g2.9 MPa),9 the bending strength of the supramolecular plaster is relatively weak, but its compressive strength is equal to the gypsum plaster. Moreover, its density (1.55 g/cm3) is smaller than that of general gypsum plaster (2.60-2.75 g/cm3). Therefore, this supramolecular plaster can replace the general gypsum plaster and be used in carving, building, painting and coating. By doping or improving the machining method, the mechanical properties of this supramolecular plaster may be enhanced to a large extent. Figure 5 shows the IR spectrum of the supramolecular plaster. The broad peak centered at 3439 cm-1 can be due to the stretching vibrations of H2O and the hydroxyl group of the ureaHþ ion. The corresponding bending vibration bands are located in 1665 and 1624 cm-1. There are a series of peaks in the region of 1250-1027 cm-1, which can be attributed to the P-O stretching vibrations of the AEDPH3- ion. The peak in 926 cm-1 is assigned to νs (PO3). The result of thermogravimetric analysis (TGA) of the supramolecular plaster is given in Figure 6. The supramolecular plaster can be stable up to 97 °C in air (the slightly weight loss below 97 °C is probably a result of adsorbent water molecules), above which the supramolecular plaster begins to decompose until 735 °C. The final product in 1000 °C is maybe 0.5P2O3, with a total weight loss of 80.58% (calcd 80.74%). The exploration of new crystalline porous materials is of current interest, many inorganic salts or metal-organic framework (MOF)10 are prove to be excellent porous materials for gasstorage and catalysis. On the other hand, acid-base compounds constructed via hydrogen-bonded assembly of small organic molecules have displayed novel supramolecular architectures11 and potential applications in molecular recognition,12 optics,13 and biomaterials.14 However, it has not been reported before for their ability of gas adsorption. Because the supramolecular plaster has porous supramolecular network, it is expected to have good gas adsorption ability. Figure 7b shows the isotherms of H2 adsorption/desorption cycle of the supramolecular plaster. It can be observed that at 77 K, the supramolecular plaster can absorb quite a large amount of hydrogen of 0.562 wt % if the hydrogen pressure is 1.2 MPa (62.5 cm3/g for standard temperature and pressure), moreover, it can desorb all of the hydrogen with the reduction of the pressure. At 1 atm and 77 K, the supramolecular plaster can take up 0.26 wt % H2, which is comparable to that found in metal-organic compound [RhCl2(Hhmp)(hmp)]2 (0.30 wt % H2 at 1 atm and 77 K).10i In conclusion, we have synthesized and characterized the first supramolecular plaster with good gas adsorption performance, namely (AEDPH3) 3 (ureaH) 3 (H2O) (1), which shows a 3D hydrogen-bonded supramolecular network with extended 1D channels. This supramolecular plaster is simple to synthesize and
process at room temperature, and shows good mechanical properties similar to the gypsum based plaster. Its porous supramolecular network plays a crucial role for its gas adsorption performance. Thus, it can be expected that the supramolecular plaster can be used for building, painting, coating and carving. Moreover, because of its gas adsorption performance, the supramolecular plaster can be used as a kind of special coating to adsorb toxic gas or store useful gas like H2. Combined with the bactericidal supramolecular plaster (AEDPH3) 3 (1,2,4-tzH) 3 (H2O) (2) reported previously,6 it is testified that supramolecular plasters based on hydrogen-bonded assembly of small molecules have good mechanical properties as well. In addition, the structures of these supramolecular plasters can be modified and functions can be changed by varying the choice of organic components. Therefore, this kind of supramolecular plasters shows a promising future. Current work is underway to investigate other properties and surface modifications of this supramolecular material as well as to design and synthesize more similar organic supramolecular gelling materials with desirable physical properties and other significant functions.
Experimental Section. General Materials and Measurements. The AEDPH4 was prepared according to the U.S. Patent
4239695.15 The urea (99% purity) was purchased from Chongqing Chemical Reagent Co.,Ltd. The elemental analysis data (C, H, N) were obtained from a Perkin-Elmer 240B elemental analyzer. IR spectra were recorded as KBr pellets at a range of 400-4000 cm-1 on a Nicolet 5700 FT-IR spectrometer with a spectral resolution of 4.00 cm-1. Thermogravimetric analysis (TGA) was carried out with a NETZSCH STA 449C at a heating rate of 10 K/min in air. The powder X-ray diffraction pattern (PXRD) of the supramolecular plaster products was obtained with a Shimadzu XRD-6000 diffractometer with Cu KR radiation (λ=1.54056 A˚) at 40 kV and 40 mA at the scan speed of 4°/min (2θ). The isotherms of H2 adsorption/desorption cycle of the supramolecular plaster were measured by a PCT measuring system.
Special Examples for the Synthesis of the Supramolecular Plaster. (1) A mixture of 30.75 g AEDPH4 (0.15 mol) and 9 g urea (0.15 mol) was grinded in a muller for 30 s. Then, 30 mL of distilled water was added to the mixture with a strong agitation to form a suspension. The suspension was poured in 0.5 1 10 cm and 222 cm molds quickly and completely coagulated after 90 s. The samples produced with this method were preserved in the laboratory condition for 2 h. After this period, they were demolded and deposited in room temperature for 7 days, and then tested for flexion and compression. (2) A mixture of 92.25 g of AEDPH4 (0.45 mol) and 27 g of urea (0.45 mol) was grinded in a muller for 30 s. Then, 90 mL of distilled water was added to the mixture with strong agitation to form suspension. The suspension was poured in a chook shaped mold immediately. It was preserved in the laboratory condition for 2 h and then demolded. A chook shaped statue
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Figure 3. PXRD pattern of the supramolecular plaster and PXRD pattern of compound 1, which is calculated by the single-crystal data.
Figure 2. (a) Some bricks of the supramolecular plaster. (b) Some statues that are made by the supramolecular plaster: left, a snake; middle, a chook; right, a pig. (c) The supramolecular plaster serving as chalk.
constructed by the supramolecular plaster was obtained in this method. Synthesis of (AEDPH3) 3 (ureaH) 3 (H2O) (1). A mixture of 0.2050 g of AEDPH4 (1 mmol), 0.0601 g of urea (1 mmol) and 10 mL of distilled water was vaporized in a beaker for 20 days at room temperature. Colorless crystals for single-crystal diffraction analysis were obtained. Yield: 50% (based on AEDPH4). Elemental anal. Found (%): C, 12.69; H,
Figure 4. Structure of the supramolecular plaster: (a) 1D supramolecular chain constructed by ureaHþ 3 cations and water molecules; (b) 2D supramolecular layer constructed by AEDPH3- anions; (c) 3D sandwich typed supramolecular network of the supramolecular plaster. Green, AEDPH3- anions; blue, ureaHþ cations. Dashed lines represent hydrogen bonds.
5.32; N, 14.80. Calcd for C3H15N3O8P2: C, 12.73; H, 5.34; N, 14.83. X-ray Crystallographic Analysis. Crystallographic measurement of compound 1 was manipulated on a Bruker SMART
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Table 1. Mechanical Properties and Concreting Times of the Supramolecular Plaster content bending strength (MPa) bending modulus (MPa) compressive strength (MPa) compressive modulus (MPa) Mohs’ scale initial concreting time (s) final concreting time (s)
supramolecular plaster 0.99 492.69 4.09 519.33 2 30 90
Figure 5. IR spectrum of the supramolecular plaster.
Figure 7. (a) Space-filling view of the supramolecular plaster showing the 1D channels. (b) Isotherms of the H2 adsorption/desorption cycle of the supramolecular plaster at 77 K.
Figure 6. Thermogravimetric (TG) curve and differential thermogravimetric (DTG) curve of the supramolecular plaster in air. Solid line, TG curve; dotted line, DTG curve.
CCD area-detector diffractometer. The structure was analyzed at room temperature using graphite monochromated Mo KR radiation (λ=0.71073 A˚) and by direct methods using SHELXS97 program.16 Non-hydrogen atoms were refined with anisotropic thermal parameters by full-matrix least-squares calculations on F2 using SHELXL-97. Hydrogen atoms were directly obtained from Difference Fourier Maps. Crystal data of 1 (C3H15N3O8P2): Mw = 283.12, T = 298(2) K, triclinic, space group P1, a=5.496(2) A˚, b=9.048(2) A˚, c=12.673(3) A˚, R= 83.611(4)°, β = 82.503(4)°, γ=77.561(4)°, V=607.9(2) A˚3, Z= 2, Dcalcd =1.547 g cm-3, μ=0.389 mm-1, R1 =0.0877, wR2 = 0.2244 (all data), GOF = 1.143. Crystallographic data (excluding structure factors) have been deposited with the Cambridge Crystallographic Centre as Supplementary Publication No. CCDC 704883. Measurements of the Mechanical Properties. The bending strength, compressive strength, bending modulus and compressive
modulus were measured by a WDW-20 universal material testing machine. The tests of bending strength and bending modulus were carried out on the samples of dimensions 0.5110 cm. The tests of compressive strength and compressive modulus were carried out on the samples of dimensions 2 2 2 cm. All tests were carried out in a laboratory condition at 20 ( 2 °C and around 65% relative humidity. Each of the results given in Table 1 represents the average measurement performed on three samples of the same composition. Acknowledgment. This work was supported by grants of the National Nature Science Foundation of China (20671074). We are thankful to Prof. Jin-ping Zhou, Prof. Li-di Wu, Dr. Lei Xie, Dr. Yu-lan Liu, Miss Shu-qin Xu, Miss Jin-hua Feng, Dr. Qiao-yun Liu, and Mr. Zhong-jing Li for helpful discussions. Supporting Information Available: Table S-1, hydrogen-bond distances and angles of the supramolecular plaster (PDF); CIF file of compound 1. This material is available free of charge via the Internet at http://pubs.acs.org.
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