A Tetrahedral Water Tetramer in a Zeolite-like Metal-Organic Framework Constructed from {(H3O)2[Fe6O{(OCH2)3CCH3}4Cl6]‚4H2O} Guoqing Jiang, Junfeng Bai,* Hang Xing, Yizhi Li, and Xiaozeng You The State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing 210093, People’s Republic of China
CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 6 1264-1266
ReceiVed January 20, 2006; ReVised Manuscript ReceiVed March 28, 2006
ABSTRACT: For the first time, a tetrahedral water tetramer was observed in a zeolite-like metal-organic framework constructed from {(H3O)2[Fe6O{(OCH2)3CCH3}4Cl6]‚4H2O}, in which the host plays an important role in stabilization of this unstable species predicted by theoretical calculations. Water clusters are bridges between a single water molecule and liquid water or ice. Exploration of their possible structures and stabilities in different environments is quite crucial to understanding the nature of water-water interactions in liquid water or ice and its role in biological and chemical processes.1,2 Recent years have witnessed the rapid and intense studies of small water clusters3 from the theoretical4,5 and experimental aspects.2,6-8 Among them, the water tetramer is of particular interest.9 Their configurations have been predicted by ab initio electronic structure calculations (Chart 1),10 and some of them have been characterized by far-infrared vibration-rotation tunneling spectroscopy11 or found in different crystal hosts.3,12 However, until now, crystallographic observation and analysis of a tetrahedral water tetramer has not been possible due to its instability. Here we report a tetrahedral water tetramer in the solid-state structure of a three-dimensional (3D) supramolecular polymer of (H3O)2[Fe6O{(OCH2)3CCH3}4 Cl6]‚4H2O (1). Complex 1 was prepared by the reaction of [Fe3O(O2CCH2OPh)6(py)3]Cl in acetonitrile and H3thme (H3thme ) 1,1,1-tris(hydroxymethyl)ethane). After the sample was stirred for about 24 h, the mixture was filtered, and crystals were obtained by diffusion ethyl ether into the filtrate.13 Single-crystal structure analysis14 at 293 K revealed that the structure of the cluster core is similar to those reported.15 This compound crystallizes in a highly symmetric space group of the cubic system, namely, P4h3n. The hexametalate core exhibits six Fe(III) centers in an octahedral coordination sphere, consisting of one µ6-oxo ligand, four alkoxo bridges, and a terminal chloride (Figure 1). The central µ6-O is approximately in the center of an octahedron formed by six Fe(III) atoms. This OFe 6 aggregate is further encapsulated by a hydrophobic shell of four fully deprotonated, facially coordinated CH3C(CH2O)33- entities (Figure 1) and six terminal chlorides. Unusually, the charge balance is provided by two H3O+ ions. Interestingly, this molecular cluster {Fe6} further links each other into a zeolite-like framework by three C-H‚‚‚Cl hydrogen-bond interactions (Figure 2). The structure can be described as a fusion of two “3:3” assemblies: (1) Each [Fe6O{(OCH2)3CCH3}4Cl6]2core provides three donor hydrogens from C7 of a coordinated CH3C(CH2O)33- entity to three chlorine atoms (Cl2) from three adjacent [Fe6O{(OCH2)3CCH3}4Cl6]2- cores in which the distances of three C7‚‚‚Cl2, and three H7A‚‚‚Cl2 and the angles of three C7-H7A‚‚‚Cl2 are the same and the values are 3.573 Å, 2.619 Å, and 176.80°, respectively (Figure 3). It is noteworthy that the linear bonds C-H‚‚‚Cl (176.80°) are close to 180°, and the structural significance is that the dipole-monopole and dipole-dipole contribution to electrostatic energy is a maximum at 180° and zero at 90°.16 Therefore, it is a very strong C-H‚‚‚Cl hydrogen bond. (2) The three Cl2 atoms which are opposite to C7 in [Fe6O{(OCH2)3CCH3}4Cl6]2- cores as three acceptors of hydrogen bonds accept hydrogen atoms (H7) from three adjacent [Fe6O{(OCH2)3* To whom correspondence
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Figure 1. The structure of complex 1. Color code: Fe blue; O red; C gray; Cl green; H black (left); I displays the structure of facially coordinated tripodal ligands (H3thme) (right).
Chart 1.
Calculated Configuration of Cyclic Water Tetramer
CCH3}4Cl6]2- cores (Figure 3). The space-filling diagrams of the complex are shown in Figure 2, which was formed by propagating [Fe6O{(OCH2)3CCH3}4Cl6]2- cores from H7 and Cl2 (propagated angle: Fe1-Cl2‚‚‚H7 138.2°), and the [Fe6O{(OCH2)3CCH3}4Cl6]2- units have been incorporated into a self-assembled superstructure with three different types of channels viewed from three different directions. The channel (I) is a one-dimensional (1D) rectangular channel with an inner size of 4.6 × 6.0 Å2 in terms of apparent cross section on the projected plane. Meanwhile, both the channel (II) and channel (III) are 1D columns possessing internal surfaces of a minimum diameter of 7.6 and 8.8 Å, respectively. These channels are filled with H3O+ ions and disordered H2O molecules, which constitute 42.8% of the unit cell volume. If the [Fe6O{(OCH2)3CCH3}4-Cl6]2- core is symbolized as an elongated tetrahedron, the whole structure can be summarized in Scheme 1. A large tetrahedron made up of four such elongated tetrahedrons with a water tetramer in the center is formed, and such tetrahedrons are linked further to each other via hydrogen-bond interactions between the Cl2 atoms in each face and C7 atom in the apex to form 3D network (Scheme 1, top). Additionally, if this elongated tetrahedron, the [Fe6O{(OCH2)3CCH3}4-Cl6]2- core, is further
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Figure 2. The space filling diagram of complex 1, viewed along [001], [100], or [010]. All solvate molecules have been omitted for clarity. Bottom: dimensions of three channels.
Scheme 1. Pictograms of Structural Motifs in the Supramolecular Coordination Networks of 1 with the Tetrahedron (top) and Dot-Linked Representation (middle) and the Simplified Modes (bottom)a
Figure 3. C-H‚‚‚Cl hydrogen interactions of 1 shown in perspective (the stereo molecules are shown in blue, green, and red, and hydrogen bonds interactions in dashed lines).
Figure 4. Packing diagram of the tetrahedral water cluster and its neighboring environment in complex 1. a
simplified into two dots (Scheme 1, bottom) in which one is C7 and the other is the center of three Cl2 atoms, an open-framework structure with three different types of channels can be observed (Scheme 1, middle). It is noteworthy that the complex 1 belongs to the rare metal-organic open frameworks with a zeolite-like structure formed by weak interactions, and this zeolite-like metalorganic open framework is almost stable to 160 °C.
Color code: O red; C black; Cl green; C-H‚‚‚Cl pink.
The most striking feature is that an unprecedented tetrahedral water cluster exists in supramolecular channel (I). The coordination environment of it is shown in Figure 4, in which the hydrogen atoms of each water molecule are disordered. This tetrahedral water cluster is a regular tetrahedron with edge lengths of 3.43 (2) Å that is a slight lengthening of the (O‚‚‚O) bonds and significantly longer
1266 Crystal Growth & Design, Vol. 6, No. 6, 2006 than 2.78 Å estimated in the udud water tetramer of (D2O)11 in the gas phase, as well as longer than other tetrameric clusters reported previously.12 Theoretical predictions show that the “cage” structure is only a minimum on the ASP-P surface but is not present on the ASP-NB surface. This structure collapses to the (udud) structure in the MP2 optimizations and is probably not minima on the ASP-NB potential energy surface.10a,10b Rationally, the formation of an unstable cage water tetramer in 1 may be ascribed to the stablization of the zeolite-like metal-organic open framework. In conclusion, for the first time, an unstable tetrahedral water tetramer was observed in a zeolite-like metal-organic framework of complex 1. This framework plays an important role in stabilization of the tetrahedral water tetramer. Structural characterization of it may be helpful to our understanding of water-related species in biological and chemical processes. Acknowledgment. This work is supported by Talent Development Foundation of Nanjing University, Twenty-one Century Talent Foundation of the Ministry of Education, Foundation for the Returnee of the Ministry of Education, Measurement Foundation of Nanjing University, and National Natural Science Foundation of China (No. 20301010). Supporting Information Available: Experimental procedures for X-ray crystallography, physical measurements, and TGA; figures of TGA and X-ray powder diffraction; tables of crystallographic data interatomic distances and angles for 1. This material is available free of charge via the Internet at http://pubs.acs.org.
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Communications (10) (a) Gregory, J. K.; Clary, D. C. J. Phys. Chem. 1996, 100, 18014. (b) Udalde, J. M.; Alkorta, I.; Elguero, J. Angew. Chem., Int. Ed. 2000, 39, 717. (c) Owicki, J. C.; Shipman, L. L.; Scheraga, H. A. J. Phys. Chem. 1975, 79, 1794. (d) Lentz, B. R.; Scheraga, H. A. J. Chem. Phys. 1973, 58, 5296. (e) Bene, J. D.; Pople, J. A. J. Chem. Phys. 1970, 52, 4858. (f) Radhakrishnan, T. P.; Herndon, W. C. J. Phys. Chem. 1991, 95, 10609. (g) Dykstra, C. J. Chem. Phys. 1989, 91, 6472. (11) Cruzan, J. D.; Braly, L. B.; Liu, K.; Brown, M. G.; Loeser, J. G.; Saykally, R. J. Science 1996, 271, 59. (12) Chacko, K. K.; Saenger, W. J. Am. Chem. Soc. 1981, 103, 1708. Zabel, V.; Saenger, W.; Mason, S. A. J. Am. Chem. Soc. 1986, 108, 3664. Stephens, F. C.; Vagg, R. S. Inorg. Chim. Acta 1982, 57, 43. Xu, J.; Radkov, E.; Ziegler, M.; Raymond, K. N. Inorg. Chem. 2000, 39, 4156. Favas, M. C.; Kepert, D. L.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1980, 454. Supriya, S.; Das, S. K. New J. Chem. 2003, 27, 1568. Long, L.-S.; Wu, Y.-R.; Huang, R.-B.; Zheng, L.-Z. Inorg. Chem. 2004, 43, 3798. Zuhayra, M.; Kampen, W. U.; Henze, E.; Soti, Z.; Zsolnai, L.; Huttner, G. Oberdorfer, F. J. Am. Chem. Soc. 2006, 128, 424. (13) Synthesis of [Fe3O(O2CCH2OPh)6(py)3]Cl. Phenoxyacetic acid (4.636 g, 30.5 mmol) was dissolved in pyridine (20 mL) and FeCl3‚6H2O (1.604 g, 4.20 mmol) was added to it in small portions with stirring. Thirty minutes later, the solvent was removed under vacuo to give a brown oil. Addition of EtOH (50 mL) to this brown oil led to the final product of [Fe3O(O2CCH2OPh)6(py)3]Cl. It was collected by filtration, washed with EtOH/Et2O, and dried in vacuo. The yield was ∼60%. Anal. Calcd for C63H57O19N3Fe3Cl: C, 55.51%; H, 4.21%; N, 3.08%. Found: C, 55.61%; H, 4.17%; N, 3.15%. IR data (cm-1): 3421 (w), 1626 (vs), 1605 (s), 1495 (s), 1448 (vs), 1425 (s), 1384 (s), 1333 (m), 1301 (m), 1261 (m), 1216 (s), 1173 (w), 1085 (m), 1069 (m), 1043 (w), 1015 (w), 786 (w), 756 (s), 690 (s), 621 (w), 599 (w), 562 (w), 430 (w). Synthesis of (H3O)2[Fe6O{(OCH2)3CCH3}4Cl6]‚4H2O (1). Complex 1 was prepared by the reaction of [Fe3O(O2CCH2OPh)6(py)3]‚Cl (0.241 g, 0.2 mmol) in acetonitrile (10 mL) and H3thme (0.047 g, 0.2 mmol). After this mixture was stirred about 24 h, it was filtered. Single crystals were obtained by diffusion of ethyl ether into the filtrate. The yield was 15%. Anal. Calcd for C20H50O19Cl6Fe6: C, 21.03%; H, 4.68%. Found: C, 20.93%; H, 4.60%. CCDC 295164 (for 1) contains the supplementary Crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccde.cam.ac.uk/data request/cif. (14) Crystal data for 0.33 × 0.28 × 0.28 mm, cubic, space group P4h3n, a ) 21.6868 Å, R ) 90°, V ) 10199.7 Å3, Z ) 4, F ) 1.513 g/cm3, M ) 2285.14, µ(Mo KR) ) 2.033 mm-1. Of the 3341 symmetry independent reflections (1.88° < θ < 25.99°), 2519 reflections are observed (I > 2σ(I)). On the basis of all these data and 162 refined parameters, R1 ) 0.0598, wR2 ) 0.0979, and GOF on F2 of 1.012 were obtained; residual electron density: 0.420 and -1.352 eÅ-3. (15) (a) Cornia, A.; Gatteschi, D.; Hegetschweiler, K.; Hausherr-Primo, L.; Gramlich, V. Inorg. Chem. 1996, 35, 4414. (b) Hegetschweiler, K.; Schmalle, H.; Streit, H. M.; Schneider, W. Inorg. Chem. 1990, 29, 3625. (c) Hegetschweiler, K.; Schmalle, H. W.; Streit, H. M.; Gramlich, V.; Hund, H.-U.; Erni, I. Inorg. Chem. 1992, 31, 1299. (d) Finn, R. C.; Zubieta, J. J. Cluster Sci. 2000, 11, 461. (16) (a)Allen, F. H.; Howard, J. A. K.; Hoy, V. J.; Desiraju, G. R.; Reddy, D. S.; Wilson, C. C. J. Am. Chem. Soc. 1996, 118. 4081. (b) Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441.
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