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Hydrothermal synthesis and structure of ASU-14 topological framework by using ethylenediamine as a structure-directing agent
Microporous and Mesoporous Materials 70 (2004) 1–6 www.elsevier.com/locate/micromeso
Hydrothermal synthesis and structure of ASU-14 topological framework by using ethylenediamine as a structure-directing agent Yan Xu, Masaru Ogura, Tatsuya Okubo
*
Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan Received 10 October 2003; received in revised form 22 December 2003; accepted 22 December 2003
Abstract A new germanate with interesting three-dimensional channels, [(H2 en)2 (en)][Ge9 O18 (OH)4 ] (en ¼ ethylenediamine), was synthesized from an aqueous solution containing GeO2 , pyridine, phosphate, hydrofluoric acid and en as a structure-directing agent (SDA). The colorless block-shaped crystals were obtained, and characterized by scanning electron microscopy, thermogravimetric analysis and X-ray powder diffraction analysis. The structure was determined by single crystal diffraction to be monoclinic, space b ¼ 10:167ð2Þ A, c ¼ 13:032ð3Þ A, and b ¼ 90:11(3), and Z ¼ 2, V ¼ 1320:1ð5Þ A 3 , R1 ¼ 0:0600 for group P21 /n, a ¼ 9:963ð2Þ A, the reflections with I > 2rðIÞ and wR ¼ 0:1583. The three-dimensional structure has the same topological framework as the reported germanate ASU-14, which was originally synthesized with piperazine as an SDA, and is built up by GeO4 tetrahedra, GeO5 square pyramid and GeO6 octahedra, connected to form interesting 10-membered rings along the crystallographic a-axis. 2004 Elsevier Inc. All rights reserved. Keywords: Microporous germanate; 10-membered ring; 3-membered ring; Structure
1. Introduction Great efforts have been made to synthesize new openframeworks with either pure tetrahedral or mixed polyhedral microporous materials due to their widespread application in adsorption, ion-exchange, catalysis and radioactive waste remediation [1]. It is, therefore, vital to design novel porous materials with different structural characteristics. As open-framework building elements, not only silicon and aluminium, but also boron, gallium, phosphorus and transition metals have been used to make new three-dimensional materials. Germanium is the closest analogue to silicon, and is very interesting as a building element to form open-frameworks in zeolite chemistry. In the early 1990s, Xu et al. reported the possibilities of synthesizing some organically templated open-framework germanates by hydrothermal methods [2–5]. More recently, the research efforts have been continued with the synthesis and *
Corresponding author. Tel.: +81-3-5841-7348; fax: +81-3-58003806. E-mail address: [email protected] (T. Okubo). 1387-1811/$ - see front matter 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2003.12.015
characterization of several new types of germanate frameworks [6–18]. Germanium can adopt large Ge/O radius ratios to build polyhedra with coordinations of four (GeO4 , tetrahedron), five (GeO5 , square pyramidal or trigonal bipyramidal) and six (GeO6 , octahedron). A three-dimensional germanate can be built up by a single tetrahedral type or a combination of different polyhedral types. In germanates, the Ge–O bond distances are sig for nificantly longer than Si–O in silicates (about 1.76 A for Si–O), and the Ge–O–Ge angles Ge–O and 1.61 A are less than those for Si–O–Si (about 130 for Ge–O– Ge angles, and 140 for Si–O–Si angles). Therefore, the flexibility of the polyhedral structure for germanium allows the formation of various open-framework structures with an extra-large pore, which exhibit 24-membered ring channels, such as FDU-4 [19] and ASU-16 [20]. In particular, germanates exhibit a great possibility for the formation of 3-membered rings [21–24], which are postulated to be important with respect to form open-framework architectures [25]. We report herein the hydrothermal synthesis and structural determination of a new germanate [(H2 en)2 (en)][Ge9 O18 (OH)4 ], obtained with ethylenediamine(en)
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Y. Xu et al. / Microporous and Mesoporous Materials 70 (2004) 1–6
from a pyridine/water mixture as solvent. The use of this organic structure-directing agent (SDA) had been previously reported in the synthesis of [(H2 en)4 ][Ge18 O38 (OH)4 ] 2H2 O in pure aqueous medium [4].
2. Experimental 2.1. Synthesis The pyramidal colorless crystals of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] (average sizes: 0.12 mm · 0.09 mm · 0.08 mm) were prepared by a hydrothermal method from an organic rich solution consisting of GeO2 , ethylenediamine, HF, pyridine and H2 O in a molar ratio of 1:16:2:53:67. GeO2 (0.17 g) was added to a mixture of pyridine (4.56 g), ethylenediamine (1.25 g) and water (1.50 g). Thereafter, this gel was stirred to get a clear solution. Finally, 47% HF (0.10 g) was added. The solution was crystallized at 170 C for 10 days in a 25 ml Teflon-lined autoclave. The product was washed with de-ionized water and ethanol, dried at room temperature for 24 h. A product (0.112 g) yield of 51% based on GeO2 was obtained. 2.2. Characterization X-ray powder diffraction analysis was performed on an M03X-HF (MAC Science), with CuKa radiation at 40 kV and 20 mA at a scanning rate of 4/min by a step of 0.02. Thermogravimetric (TG) analysis of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] was carried out in O2 /He atmosphere on a Thenmoplus TG 8120 instrument (Rigaku) from 25 to 750 C and at a heating rate of 10/min. Single crystal X-ray diffraction data were collected at )60 C, on a Rigaku Mercury-CCD, using graphite monochromatized MoKa radiation (k ¼ 0:71073 A) from a rotation anode generator. A total of 10 312 reflections were collected in the region 3:26 < h < 28:10 from a crystal with the size 0.062 mm · 0.053 mm · 0.034 mm, of which 3017 were unique. The space group was determined to be P21 /n by the analysis of systematic absences and intensity distribution of all reflections (0 k 0, k ¼ 2n). An empirical absorption correction was applied. The structure solution and refinement were carried out using a SHELX97 program [26,27].
3. Results and discussion 3.1. Structure solution This structure was solved in the space group P21 /n by using direct methods, and the topology of the final
structure was confirmed to be 21 /n symmetry. The five unique germanium atoms were first revealed, and the remaining O, N and C atoms were found from successive Fourier map analysis. H atoms bonded to C and N atoms were introduced at calculated positions and treated as riding, while the H atom for (O–H) was located from difference maps at the final stages of the refinement. The final refinement including anisotropic thermal parameters of all non-hydrogen atoms converted to R1 ¼ 0:0600 and wR2 ¼ 0:1580. The highest 3 , and 0.77 A from Ge3. The crystal data peak is 1.57 e/A and results from the structural refinement are given in Table 1. The atomic coordinates and the thermal displacement parameters are presented in Table 2. 3.2. Structure description The title compound, [(H2 en)2 (en)][Ge9 O18 (OH)4 ], has the same framework topology as ASU-14([Ge9 O18 (OH)4 ] 2H2 ppz 0.5H2 O) [9], UCSB-40 and UCSB-41 ([Ge9 O18 (OH)4 ] 2[NH3 (CH2 )3 NH3 ] H2 O) [12], which is constructed from the structural building unit [Ge9 O22 OH]4 (shown in Fig. 1). The core of the structural building unit possesses a symmetry center and is composed of nine germanium centers, 22 oxygen atoms, and four hydroxide units. In [(H2 en)2 (en)][Ge9 O18 (OH)4 ], there are five unique germanium sites. Ge1 and Ge5 have regular tetrahedral coordination, while Ge3 and Ge4 are coordinated by four oxygen atoms and one dangling hydroxyl group. Ge2 is located at the inversion center, which is constrained by this symmetry, coordi-
Table 1 Crystal data and details of the structure for [(H2 en)2 (en)][Ge9 O18 (OH)4 ] Empirical formula Formula weight Crystal system Space group a, b, c (A)
C6 H32 Ge6 N6 O22 1193.69 Monoclinic P21 /n 9.963(2), 10.167(2), 13.032(3) 90.11(3) 1320.1(5) 2 3.003 1148 10.203 0.062 · 0.053 · 0.034 )60 3.26, 28.10 103 112, 3017, 0.0244 3011 0.0600, 0.1577, 1.144 1.573, )1.116
b () 3 ) V (A Z D (calc) (g/cm3 ) F ð0 0 0Þ l (MoKa) (mm1 ) Crystal size (mm) Temperature (C) h min–max () Total, unique data, R(int) Observed data [I > 2rðIÞ] R1 , wR2 , S Minimum and maximum 3 ) residual density (e/A P P P P 1=2 R1 ¼ kFo j jFc k= jFo j, wR2 ¼ f ½wðjFo j2 jFc j2 Þ2 = ½wðjFo j2 Þ2 g 2 2 2 2 2 and w ¼ 1=½r ðFo Þ þ ð0:0680P Þ þ 19:7686 where P ¼ ½ðFo Þ þ 2Fc =3; 3 , and 0.77 A from Ge3. the highest peak is 1.57 e/A
Y. Xu et al. / Microporous and Mesoporous Materials 70 (2004) 1–6
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Table 2 Final coordinates and equivalent isotropic displacement of the non-hydrogen atoms for [(H2 en)2 (en)][Ge9 O18 (OH)4 ] Atom
x
y
z
Ueq
Ge1 Ge2 Ge3 Ge4 Ge5 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 C1 N1 C2 N2 N3 C3
0.12003(11) 0.0000 )0.16167(11) 0.16567(11) )0.13193(11) )0.0120(6) 0.1454(7) 0.1171(8) 0.2091(8) 0.0214(7) )0.0272(8) )0.2824(8) 0.2104(7) )0.2122(7) )0.2350(7) 0.1693(8) 0.0603(16) 0.069(3) 0.0171(13) )0.1104(14) 0.0417(17) )0.0327(14)
0.65601(11) 0.5000 0.62140(11) 0.35961(11) 0.32352(11) 0.5671(7) 0.3981(7) 0.6385(7) 0.7424(8) 0.2866(8) 0.6852(8) 0.6718(8) 0.5049(7) 0.4485(8) 0.7159(8) 0.7725(9) 0.0447(16) 0.040(3) 0.9796(15) 0.9041(15) 0.6929(13) 0.5649(8)
0.27266(9) 0.5000 0.27499(8) 0.32956(8) 0.33043(8) 0.3636(5) 0.4582(5) 0.5406(5) 0.1704(6) 0.2760(6) 0.2031(7) 0.1769(6) 0.2604(6) 0.2650(6) 0.3721(5) 0.3686(5) 0.5112(14) 0.626(3) )0.0534(6) )0.0586(16) )0.0010(18) )0.0136(19)
0.0290(3) 0.0249(3) 0.0291(3) 0.0273(2) 0.0274(2) 0.0243(15) 0.0267(16) 0.0322(17) 0.0365(18) 0.0330(18) 0.038(2) 0.0343(18) 0.0320(17) 0.0359(19) 0.039(2) 0.039(2) 0.064(4) 0.176(9) 0.162(10) 0.266(11) 0.131(7) 0.131(8)
Fig. 1. The structure building unit of [(H2 en)2 (en)][Ge9 O18 (OH)4 ]. Open circles: H-atoms.
nated by six oxygen atoms (octahedral coordination), and linked to two Ge4 units. Compared to [Ge9 O18 Zn3 (OH)4 ] 3(en) [28], there are no zinc atoms present in the primary building unit; however, the symmetry (Monoclinic P) is the same.
Neighboring structural building units of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] are linked through bridging oxygen atoms to form an open-framework with the interesting three-dimensional channels. There are 10-membered ring channels, extending along the crystallographic aaxis, as shown in Fig. 2. Every 10-membered ring is being surrounded by four 3-membered rings, which are further surrounded by 10-membered rings. The approximate diameter of the narrowest cross-section of There are also 810-membered ring channels is 7.1 A. membered and 7-membered ring channels extended along the crystallographic [0 0 1] and [0 )1 1] directions (see Figs. 3 and 4). In [(H2 en)2 (en)][Ge9 O18 (OH)4 ], the symmetry of the inorganic framework is determined completely, by ordered diprotonated ethylenediamine cations and one molecule and all of organic SDAs are located at the inversion centers of the unit cell. In this germanate the inversion center of the lattice is in agreement with the molecular symmetry (inversion center) of each individual ethylenediamine cation and molecule. The structure of ethylenediamine can be easily understood from the symmetry consideration as shown in Fig. 5. In some synthesis of germanates, the condensation of the inorganic framework around the organic guest molecule is dictated by the molecular symmetry of organic molecules. Organic guest molecules exert SDA effects by using N–H O type hydrogen bonding. There exist two types of diprotonated ethylenediamine organic cations and one type organic molecule. The type I ethylenediamine cations are located in the 10-membered ring channels along the crystallographic a-axis. The type II
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Fig. 2. The three-dimensional framework along the a-axis in [(H2 en)2 (en)][Ge9 O18 (OH)4 ].
Fig. 4. The 7-membered ring channels along the [0 )1 1] direction in [(H2 en)2 (en)][Ge9 O18 (OH)4 ].
Fig. 3. The 8-membered ring channels along c-axis in [(H2 en)2 (en)][Ge9 O18 (OH)4 ].
ethylenediamine cations are located in the 8-membered ring channels along [0 1 0] and [1 1 0]. Both types of ethylenediamine cations and molecule form hydrogen bonds with oxygen atoms of the inorganic framework. for type I, The shortest N O distances are 2.69(2) A for type II. The type II ethylenediamine and 2.73(2) A cations also form hydrogen bonds with the amine molecule. The shortest N N distances between two amine cations are 2.73(2) A. Selected framework bond distances and angles are given in Table 3. The Ge–O bonds for the tetrahedral germanium centers range from 1.725(8) to 1.788(7) A, which are similar to those reported for the modification
The Ge–O bonds for five-coorof GeO2 (1.741(3) A). dinated and six-coordinated germanium centers are and 1.863(7)–1.907(6) A, respec1.748(8)–1.990(7) A, tively. The oxygen atoms O10 and O11 are terminal and correspond to hydroxyl groups. The two Ge–O(H) bond which are similar distances are 1.778(8) and 1.789(8) A, to the distances between Ge and bridging oxygen atoms. The O–Ge–O angles, 102.5(4)–113.2(4), are within the expected range for the tetrahedral geometry. However, the wide variation (from 91.4(3) to 134.0(4)) for Ge– O–Ge is in agreement with those reported for other germanates. Thermal analysis of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] in O2 /He atmosphere revealed total weight loss of 18.3% till 700 C. Calculated weight losses for combustion of the organic templates plus loss of OH (18.3%) are in excellent agreement with the TG experimental result. [(H2 en)2 (en)][Ge9 O18 (OH)4 ] is closely related to the recently reported germanate open-framework materials ASU-14 reported by Li et al. [9]. If the SDA piperazine
Y. Xu et al. / Microporous and Mesoporous Materials 70 (2004) 1–6
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in the ASU-14 is replaced by ethylenediamine, the germanate [(H2 en)2 (en)][Ge9 O18 (OH)4 ] is formed. Compared with ASU-14, the pore size of the 10-membered rings channel is a little smaller for the present germanate, due to the different size of the SDA. The solvent plays a crucial role in the synthesis of openframework germanates. The title compound and the earlier mentioned [(H2 en)4 ][Ge18 O38 (OH)4 ] 2H2 O [4] have different topologies, although the same SDA was used in the syntheses. Additionally, ASU-14 with the same framework topology as our material was obtained using a different SDA, but the same solvent of pyridine/ water mixture. 4. Conclusion In conclusion, we have reported a simple, high-yield and pure phase synthesis of an open-framework germanate, [(H2 en)2 (en)][Ge9 O18 (OH)4 ], which is characterized by a low framework density and the interesting 10-membered ring channels. The three-dimensional structure possessing the same topological framework as ASU-14 is built up by GeO4 tetrahedra, GeO5 square pyramids and GeO6 octahedra, connected to form interesting 10-membered rings along the crystallographic a-axis. The synthesis of [(H2 en)2 (en)]- [Ge9 O18 (OH)4 ] has demonstrated that the solvent plays an important role, and the different open-frameworks can be formed using different solvents with the same SDA. Acknowledgements Fig. 5. Three crystallographically unique ethylenediamine cations in [(H2 en)2 (en)][Ge9 O18 (OH)4 ] (A: symmetry center).
This work was supported by the Japan Society for the Promotion of Science (JSPS). The authors thank Dr.
Table 3 and angles () for [(H2 en)2 (en)][Ge9 O18 (OH)4 ] Selected framework bond distances (A) Ge1–O6 Ge1–O8 Ge1–O11 Ge1–O4 Ge1–O1 Ge4–O4b Ge4–O2 Ge4–O5 Ge4–O8 N3–C3
1.748(8) 1.786(7) 1.789(8) 1.824(8) 1.989(7) 1.726(8) 1.734(6) 1.760(7) 1.789(7) 1.507(14)
O5–Ge5–O7e Ge3–O1–Ge1
102.5(4) 91.4(3)
)x, 1 y, 1 z. )x þ 1=2, y 1=2, )z þ 1=2. c )x, )y, 1 z. d )x, 2 y, )z. e )x 1=2, y 1=2, )z þ 1=2. f )x, 1 y, )z. a
b
Ge2–O2 Ge2–O2a Ge2–O3 Ge2–O3a Ge2–O1 Ge2–O1a Ge5–O9 Ge5–O5 Ge5–O3a Ge5–O7e
1.863(7) 1.863(7) 1.902(7) 1.902(7) 1.908(6) 1.908(6) 1.727(8) 1.727(7) 1.731(7) 1.765(8)
Ge3–O10 Ge3–O6 Ge3–O7 Ge3–O9 Ge3–O1 C1–N1 C1–C1c C2–N2 C2–C2d C3–C3f
1.778(8) 1.764(8) 1.827(7) 1.833(8) 1.964(6) 1.48(4) 1.54(3) 1.486(15) 1.493(15) 1.513(16)
O9–Ge5–O7e Ge2–O1–Ge3
113.2(4) 134.0(4)
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Kazuhiro Uehara, Dr. Shirou Hikichi and Prof. Noritaka Mizuno for the collection of the single crystal diffraction data, and Dr. S.P. Elangovan for the English correction. References [1] A.K. Cheetham, G. Ferey, T. Loiseau, Angew. Chem., Int. Ed. 38 (1999) 3268. [2] J. Cheng, R. Xu, J. Chem. Soc. Chem. Commun. (1991) 483. [3] J. Cheng, R. Xu, G.J. Yang, Chem. Soc., Dalton. Trans. (1991) 1537. [4] R.H Jones, J. Chen, J.M. Thomas, A. George, M.B. Hursthouse, R. Xu, S. Li, Y. Lu, G. Yang, Chem. Mater. 4 (1992) 808. [5] S. Li, R. Xu, Y. Lu, Y. Xu, in: R. von Ballmoos, J.B. Higgins, M.M.J. Treacy (Eds.), Proceedings of the 9th International Zeolite Conference, Montreal, Butterworth-Heinemann, Boston, MA, 1992, p. 345. [6] C. Cascales, E. Gutierrez-Puebla, M.A. Monge, C. Ruız-Valero, Angew. Chem., Int. Ed. 37 (1998) 129. [7] H. Li, M. Eddaoudi, D.A. Richardson, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 8567. [8] H. Li, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 10569. [9] H. Li, M. Eddouadi, O.M. Yaghi, Angew. Chem., Int. Ed. 38 (1999) 653. [10] M. O’Keeffe, O.M. Yaghi, Chem. Eur. J. 5 (1999) 2796. [11] P. Feng, X. Bu, G.D. Stucky, Chem. Mater. 11 (1999) 3025.
[12] X. Bu, P. Feng, G.D. Stucky, Chem. Mater. 12 (2000) 1505. [13] T. Conradsson, M.S. Dadachov, X.D. Zou, Micropor. Mesopor. Mater. 41 (2000) 183. [14] T. Conradsson, X. Zou, M.S. Dadachov, Inorg. Chem. 39 (2000) 1716. [15] C. Cascales, E. Gutierrez-Puebla, M. Iglesias, M.A. Monge, C. Ruız-Valero, N. Snejko, Chem. Commun. (2000) 2145. [16] M.E. Medina, M. Iglesia, M.A. Monge, E. Gutierrez-Puebla, Chem. Commun. (2001) 2548. [17] C. Cascales, B. Gomez-Lor, E. Gutierrez-Puebla, M. Iglesias, M.A. Monge, C. Ruiz-Valero, N. Snejko, Chem. Mater. 14 (2002) 677. [18] L. Beitone, T. Loiseau, G. Ferey, Inorg. Chem 41 (2002) 3962. [19] Y. Zhou, H. Zhu, Z. Chen, M. Chen, Y. Xu, H. Zhang, D. Zhao, Angew. Chem., Int. Ed. 40 (2001) 2166. [20] J. Plevert, T.M. Gentz, A. Laine, H. Li, V.G. Young, O.M. Yaghi, M. O’Keeffe, J. Am. Chem. Soc. 123 (2001) 12706. [21] X. Bu, P. Feng, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 11204. [22] Y. Xu, W. Fan, N. Chino, K. Uehara, S. Hikichi, N. Mizuno, M. Ogura, T. Okubo, Chem. Lett. 33 (2004) 74. [23] R.J. Francis, A.J. Jacobson, Chem. Mater. 13 (2001) 4676. [24] H. Li, M. Eddaoudi, J. Plevert, M. O’Keeffe, O.M. Yaghi, J Am. Chem. Soc. 122 (2000) 12409. [25] G.O. Brunner, W.M. Meier, Nature 337 (1989) 146. [26] G.M. Sheldrick, SHELXS-Program for Solution of Crystal Structure, University of G€ ottingen, Germany, 1997. [27] G.M. Sheldrick, SHELXS-Program for Refinement of Crystal Structure, University of G€ ottingen, Germany, 1997. [28] X. Bu, P. Feng, G.D. Stucky, Chem. Mater. 12 (2000) 1811.
Hydrothermal synthesis and structure of ASU-14 topological framework by using ethylenediamine as a structure-directing agent Yan Xu, Masaru Ogura, Tatsuya Okubo
*
Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan Received 10 October 2003; received in revised form 22 December 2003; accepted 22 December 2003
Abstract A new germanate with interesting three-dimensional channels, [(H2 en)2 (en)][Ge9 O18 (OH)4 ] (en ¼ ethylenediamine), was synthesized from an aqueous solution containing GeO2 , pyridine, phosphate, hydrofluoric acid and en as a structure-directing agent (SDA). The colorless block-shaped crystals were obtained, and characterized by scanning electron microscopy, thermogravimetric analysis and X-ray powder diffraction analysis. The structure was determined by single crystal diffraction to be monoclinic, space b ¼ 10:167ð2Þ A, c ¼ 13:032ð3Þ A, and b ¼ 90:11(3), and Z ¼ 2, V ¼ 1320:1ð5Þ A 3 , R1 ¼ 0:0600 for group P21 /n, a ¼ 9:963ð2Þ A, the reflections with I > 2rðIÞ and wR ¼ 0:1583. The three-dimensional structure has the same topological framework as the reported germanate ASU-14, which was originally synthesized with piperazine as an SDA, and is built up by GeO4 tetrahedra, GeO5 square pyramid and GeO6 octahedra, connected to form interesting 10-membered rings along the crystallographic a-axis. 2004 Elsevier Inc. All rights reserved. Keywords: Microporous germanate; 10-membered ring; 3-membered ring; Structure
1. Introduction Great efforts have been made to synthesize new openframeworks with either pure tetrahedral or mixed polyhedral microporous materials due to their widespread application in adsorption, ion-exchange, catalysis and radioactive waste remediation [1]. It is, therefore, vital to design novel porous materials with different structural characteristics. As open-framework building elements, not only silicon and aluminium, but also boron, gallium, phosphorus and transition metals have been used to make new three-dimensional materials. Germanium is the closest analogue to silicon, and is very interesting as a building element to form open-frameworks in zeolite chemistry. In the early 1990s, Xu et al. reported the possibilities of synthesizing some organically templated open-framework germanates by hydrothermal methods [2–5]. More recently, the research efforts have been continued with the synthesis and *
Corresponding author. Tel.: +81-3-5841-7348; fax: +81-3-58003806. E-mail address: [email protected] (T. Okubo). 1387-1811/$ - see front matter 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2003.12.015
characterization of several new types of germanate frameworks [6–18]. Germanium can adopt large Ge/O radius ratios to build polyhedra with coordinations of four (GeO4 , tetrahedron), five (GeO5 , square pyramidal or trigonal bipyramidal) and six (GeO6 , octahedron). A three-dimensional germanate can be built up by a single tetrahedral type or a combination of different polyhedral types. In germanates, the Ge–O bond distances are sig for nificantly longer than Si–O in silicates (about 1.76 A for Si–O), and the Ge–O–Ge angles Ge–O and 1.61 A are less than those for Si–O–Si (about 130 for Ge–O– Ge angles, and 140 for Si–O–Si angles). Therefore, the flexibility of the polyhedral structure for germanium allows the formation of various open-framework structures with an extra-large pore, which exhibit 24-membered ring channels, such as FDU-4 [19] and ASU-16 [20]. In particular, germanates exhibit a great possibility for the formation of 3-membered rings [21–24], which are postulated to be important with respect to form open-framework architectures [25]. We report herein the hydrothermal synthesis and structural determination of a new germanate [(H2 en)2 (en)][Ge9 O18 (OH)4 ], obtained with ethylenediamine(en)
2
Y. Xu et al. / Microporous and Mesoporous Materials 70 (2004) 1–6
from a pyridine/water mixture as solvent. The use of this organic structure-directing agent (SDA) had been previously reported in the synthesis of [(H2 en)4 ][Ge18 O38 (OH)4 ] 2H2 O in pure aqueous medium [4].
2. Experimental 2.1. Synthesis The pyramidal colorless crystals of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] (average sizes: 0.12 mm · 0.09 mm · 0.08 mm) were prepared by a hydrothermal method from an organic rich solution consisting of GeO2 , ethylenediamine, HF, pyridine and H2 O in a molar ratio of 1:16:2:53:67. GeO2 (0.17 g) was added to a mixture of pyridine (4.56 g), ethylenediamine (1.25 g) and water (1.50 g). Thereafter, this gel was stirred to get a clear solution. Finally, 47% HF (0.10 g) was added. The solution was crystallized at 170 C for 10 days in a 25 ml Teflon-lined autoclave. The product was washed with de-ionized water and ethanol, dried at room temperature for 24 h. A product (0.112 g) yield of 51% based on GeO2 was obtained. 2.2. Characterization X-ray powder diffraction analysis was performed on an M03X-HF (MAC Science), with CuKa radiation at 40 kV and 20 mA at a scanning rate of 4/min by a step of 0.02. Thermogravimetric (TG) analysis of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] was carried out in O2 /He atmosphere on a Thenmoplus TG 8120 instrument (Rigaku) from 25 to 750 C and at a heating rate of 10/min. Single crystal X-ray diffraction data were collected at )60 C, on a Rigaku Mercury-CCD, using graphite monochromatized MoKa radiation (k ¼ 0:71073 A) from a rotation anode generator. A total of 10 312 reflections were collected in the region 3:26 < h < 28:10 from a crystal with the size 0.062 mm · 0.053 mm · 0.034 mm, of which 3017 were unique. The space group was determined to be P21 /n by the analysis of systematic absences and intensity distribution of all reflections (0 k 0, k ¼ 2n). An empirical absorption correction was applied. The structure solution and refinement were carried out using a SHELX97 program [26,27].
3. Results and discussion 3.1. Structure solution This structure was solved in the space group P21 /n by using direct methods, and the topology of the final
structure was confirmed to be 21 /n symmetry. The five unique germanium atoms were first revealed, and the remaining O, N and C atoms were found from successive Fourier map analysis. H atoms bonded to C and N atoms were introduced at calculated positions and treated as riding, while the H atom for (O–H) was located from difference maps at the final stages of the refinement. The final refinement including anisotropic thermal parameters of all non-hydrogen atoms converted to R1 ¼ 0:0600 and wR2 ¼ 0:1580. The highest 3 , and 0.77 A from Ge3. The crystal data peak is 1.57 e/A and results from the structural refinement are given in Table 1. The atomic coordinates and the thermal displacement parameters are presented in Table 2. 3.2. Structure description The title compound, [(H2 en)2 (en)][Ge9 O18 (OH)4 ], has the same framework topology as ASU-14([Ge9 O18 (OH)4 ] 2H2 ppz 0.5H2 O) [9], UCSB-40 and UCSB-41 ([Ge9 O18 (OH)4 ] 2[NH3 (CH2 )3 NH3 ] H2 O) [12], which is constructed from the structural building unit [Ge9 O22 OH]4 (shown in Fig. 1). The core of the structural building unit possesses a symmetry center and is composed of nine germanium centers, 22 oxygen atoms, and four hydroxide units. In [(H2 en)2 (en)][Ge9 O18 (OH)4 ], there are five unique germanium sites. Ge1 and Ge5 have regular tetrahedral coordination, while Ge3 and Ge4 are coordinated by four oxygen atoms and one dangling hydroxyl group. Ge2 is located at the inversion center, which is constrained by this symmetry, coordi-
Table 1 Crystal data and details of the structure for [(H2 en)2 (en)][Ge9 O18 (OH)4 ] Empirical formula Formula weight Crystal system Space group a, b, c (A)
C6 H32 Ge6 N6 O22 1193.69 Monoclinic P21 /n 9.963(2), 10.167(2), 13.032(3) 90.11(3) 1320.1(5) 2 3.003 1148 10.203 0.062 · 0.053 · 0.034 )60 3.26, 28.10 103 112, 3017, 0.0244 3011 0.0600, 0.1577, 1.144 1.573, )1.116
b () 3 ) V (A Z D (calc) (g/cm3 ) F ð0 0 0Þ l (MoKa) (mm1 ) Crystal size (mm) Temperature (C) h min–max () Total, unique data, R(int) Observed data [I > 2rðIÞ] R1 , wR2 , S Minimum and maximum 3 ) residual density (e/A P P P P 1=2 R1 ¼ kFo j jFc k= jFo j, wR2 ¼ f ½wðjFo j2 jFc j2 Þ2 = ½wðjFo j2 Þ2 g 2 2 2 2 2 and w ¼ 1=½r ðFo Þ þ ð0:0680P Þ þ 19:7686 where P ¼ ½ðFo Þ þ 2Fc =3; 3 , and 0.77 A from Ge3. the highest peak is 1.57 e/A
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Table 2 Final coordinates and equivalent isotropic displacement of the non-hydrogen atoms for [(H2 en)2 (en)][Ge9 O18 (OH)4 ] Atom
x
y
z
Ueq
Ge1 Ge2 Ge3 Ge4 Ge5 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 C1 N1 C2 N2 N3 C3
0.12003(11) 0.0000 )0.16167(11) 0.16567(11) )0.13193(11) )0.0120(6) 0.1454(7) 0.1171(8) 0.2091(8) 0.0214(7) )0.0272(8) )0.2824(8) 0.2104(7) )0.2122(7) )0.2350(7) 0.1693(8) 0.0603(16) 0.069(3) 0.0171(13) )0.1104(14) 0.0417(17) )0.0327(14)
0.65601(11) 0.5000 0.62140(11) 0.35961(11) 0.32352(11) 0.5671(7) 0.3981(7) 0.6385(7) 0.7424(8) 0.2866(8) 0.6852(8) 0.6718(8) 0.5049(7) 0.4485(8) 0.7159(8) 0.7725(9) 0.0447(16) 0.040(3) 0.9796(15) 0.9041(15) 0.6929(13) 0.5649(8)
0.27266(9) 0.5000 0.27499(8) 0.32956(8) 0.33043(8) 0.3636(5) 0.4582(5) 0.5406(5) 0.1704(6) 0.2760(6) 0.2031(7) 0.1769(6) 0.2604(6) 0.2650(6) 0.3721(5) 0.3686(5) 0.5112(14) 0.626(3) )0.0534(6) )0.0586(16) )0.0010(18) )0.0136(19)
0.0290(3) 0.0249(3) 0.0291(3) 0.0273(2) 0.0274(2) 0.0243(15) 0.0267(16) 0.0322(17) 0.0365(18) 0.0330(18) 0.038(2) 0.0343(18) 0.0320(17) 0.0359(19) 0.039(2) 0.039(2) 0.064(4) 0.176(9) 0.162(10) 0.266(11) 0.131(7) 0.131(8)
Fig. 1. The structure building unit of [(H2 en)2 (en)][Ge9 O18 (OH)4 ]. Open circles: H-atoms.
nated by six oxygen atoms (octahedral coordination), and linked to two Ge4 units. Compared to [Ge9 O18 Zn3 (OH)4 ] 3(en) [28], there are no zinc atoms present in the primary building unit; however, the symmetry (Monoclinic P) is the same.
Neighboring structural building units of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] are linked through bridging oxygen atoms to form an open-framework with the interesting three-dimensional channels. There are 10-membered ring channels, extending along the crystallographic aaxis, as shown in Fig. 2. Every 10-membered ring is being surrounded by four 3-membered rings, which are further surrounded by 10-membered rings. The approximate diameter of the narrowest cross-section of There are also 810-membered ring channels is 7.1 A. membered and 7-membered ring channels extended along the crystallographic [0 0 1] and [0 )1 1] directions (see Figs. 3 and 4). In [(H2 en)2 (en)][Ge9 O18 (OH)4 ], the symmetry of the inorganic framework is determined completely, by ordered diprotonated ethylenediamine cations and one molecule and all of organic SDAs are located at the inversion centers of the unit cell. In this germanate the inversion center of the lattice is in agreement with the molecular symmetry (inversion center) of each individual ethylenediamine cation and molecule. The structure of ethylenediamine can be easily understood from the symmetry consideration as shown in Fig. 5. In some synthesis of germanates, the condensation of the inorganic framework around the organic guest molecule is dictated by the molecular symmetry of organic molecules. Organic guest molecules exert SDA effects by using N–H O type hydrogen bonding. There exist two types of diprotonated ethylenediamine organic cations and one type organic molecule. The type I ethylenediamine cations are located in the 10-membered ring channels along the crystallographic a-axis. The type II
4
Y. Xu et al. / Microporous and Mesoporous Materials 70 (2004) 1–6
Fig. 2. The three-dimensional framework along the a-axis in [(H2 en)2 (en)][Ge9 O18 (OH)4 ].
Fig. 4. The 7-membered ring channels along the [0 )1 1] direction in [(H2 en)2 (en)][Ge9 O18 (OH)4 ].
Fig. 3. The 8-membered ring channels along c-axis in [(H2 en)2 (en)][Ge9 O18 (OH)4 ].
ethylenediamine cations are located in the 8-membered ring channels along [0 1 0] and [1 1 0]. Both types of ethylenediamine cations and molecule form hydrogen bonds with oxygen atoms of the inorganic framework. for type I, The shortest N O distances are 2.69(2) A for type II. The type II ethylenediamine and 2.73(2) A cations also form hydrogen bonds with the amine molecule. The shortest N N distances between two amine cations are 2.73(2) A. Selected framework bond distances and angles are given in Table 3. The Ge–O bonds for the tetrahedral germanium centers range from 1.725(8) to 1.788(7) A, which are similar to those reported for the modification
The Ge–O bonds for five-coorof GeO2 (1.741(3) A). dinated and six-coordinated germanium centers are and 1.863(7)–1.907(6) A, respec1.748(8)–1.990(7) A, tively. The oxygen atoms O10 and O11 are terminal and correspond to hydroxyl groups. The two Ge–O(H) bond which are similar distances are 1.778(8) and 1.789(8) A, to the distances between Ge and bridging oxygen atoms. The O–Ge–O angles, 102.5(4)–113.2(4), are within the expected range for the tetrahedral geometry. However, the wide variation (from 91.4(3) to 134.0(4)) for Ge– O–Ge is in agreement with those reported for other germanates. Thermal analysis of [(H2 en)2 (en)][Ge9 O18 (OH)4 ] in O2 /He atmosphere revealed total weight loss of 18.3% till 700 C. Calculated weight losses for combustion of the organic templates plus loss of OH (18.3%) are in excellent agreement with the TG experimental result. [(H2 en)2 (en)][Ge9 O18 (OH)4 ] is closely related to the recently reported germanate open-framework materials ASU-14 reported by Li et al. [9]. If the SDA piperazine
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in the ASU-14 is replaced by ethylenediamine, the germanate [(H2 en)2 (en)][Ge9 O18 (OH)4 ] is formed. Compared with ASU-14, the pore size of the 10-membered rings channel is a little smaller for the present germanate, due to the different size of the SDA. The solvent plays a crucial role in the synthesis of openframework germanates. The title compound and the earlier mentioned [(H2 en)4 ][Ge18 O38 (OH)4 ] 2H2 O [4] have different topologies, although the same SDA was used in the syntheses. Additionally, ASU-14 with the same framework topology as our material was obtained using a different SDA, but the same solvent of pyridine/ water mixture. 4. Conclusion In conclusion, we have reported a simple, high-yield and pure phase synthesis of an open-framework germanate, [(H2 en)2 (en)][Ge9 O18 (OH)4 ], which is characterized by a low framework density and the interesting 10-membered ring channels. The three-dimensional structure possessing the same topological framework as ASU-14 is built up by GeO4 tetrahedra, GeO5 square pyramids and GeO6 octahedra, connected to form interesting 10-membered rings along the crystallographic a-axis. The synthesis of [(H2 en)2 (en)]- [Ge9 O18 (OH)4 ] has demonstrated that the solvent plays an important role, and the different open-frameworks can be formed using different solvents with the same SDA. Acknowledgements Fig. 5. Three crystallographically unique ethylenediamine cations in [(H2 en)2 (en)][Ge9 O18 (OH)4 ] (A: symmetry center).
This work was supported by the Japan Society for the Promotion of Science (JSPS). The authors thank Dr.
Table 3 and angles () for [(H2 en)2 (en)][Ge9 O18 (OH)4 ] Selected framework bond distances (A) Ge1–O6 Ge1–O8 Ge1–O11 Ge1–O4 Ge1–O1 Ge4–O4b Ge4–O2 Ge4–O5 Ge4–O8 N3–C3
1.748(8) 1.786(7) 1.789(8) 1.824(8) 1.989(7) 1.726(8) 1.734(6) 1.760(7) 1.789(7) 1.507(14)
O5–Ge5–O7e Ge3–O1–Ge1
102.5(4) 91.4(3)
)x, 1 y, 1 z. )x þ 1=2, y 1=2, )z þ 1=2. c )x, )y, 1 z. d )x, 2 y, )z. e )x 1=2, y 1=2, )z þ 1=2. f )x, 1 y, )z. a
b
Ge2–O2 Ge2–O2a Ge2–O3 Ge2–O3a Ge2–O1 Ge2–O1a Ge5–O9 Ge5–O5 Ge5–O3a Ge5–O7e
1.863(7) 1.863(7) 1.902(7) 1.902(7) 1.908(6) 1.908(6) 1.727(8) 1.727(7) 1.731(7) 1.765(8)
Ge3–O10 Ge3–O6 Ge3–O7 Ge3–O9 Ge3–O1 C1–N1 C1–C1c C2–N2 C2–C2d C3–C3f
1.778(8) 1.764(8) 1.827(7) 1.833(8) 1.964(6) 1.48(4) 1.54(3) 1.486(15) 1.493(15) 1.513(16)
O9–Ge5–O7e Ge2–O1–Ge3
113.2(4) 134.0(4)
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