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Discrete Cubane-like Bromide-Water Cluster Abolghasem Bakhoda, Hamid Reza Khavasi,* and Nasser Safari Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran 1983963113, Iran
bS Supporting Information ABSTRACT: A well-isolated unique discrete cubane-like dibromide-hexahydrate cluster in the solid phase has been observed as a pyridylphosphine iron(II) counteranion. The bromide-water cluster is stabilized and orderly arranged by hydrogen bonds which display high symmetry.
W
ater is the most extraordinary and essential components of all living organisms. In the past few dacades, considerable attention has been focused on the structural investigations of discrete water clusters, including theoretical and experimental studies.1 Water clusters (H2O)n, including tetramers,2 pentamers,3 hexamers,4 octamers,5 decamers,6 etc.,7 are known to exist as discrete cyclics, chains, tapes, cages, layers, and other supramolecular architectures.8 Interactions between aggregated water molecules and surrounding ions play a key role in the stabilizing of packings. Recently, Vittal and co-workers have found that the water cluster can be sustained by weak interactions with BF4- and ClO4-.9 However, in contrast to the presence of anions within crystal packings containing water aggregates, descrete inorganic anion-water clusters are rare, with the exception of [(NO3)4(H2O)6]4-,10 [Cl(H2O)4]-,11 and [Cl2(H2O)6]2-.12 To our knowledge, no structural report of a discrete dibromide-hexahydrate cluster has been published. We now report on the structural study of the cluster [Br2(H2O)6]2- (12-), as bis(tris(2-pyridylphosphine oxide))iron(II) (12þ), the counteranion. Slow evaporation of a methanolic solution of FeBr3 and tris(2-pyridyl)phosphine [P(2-py3)] in a 1:1 molar ratio afforded deep red crystals with the composition [Fe(PO(2-py)3)2]Br2 3 6H2O, as indicated by X-ray diffraction, TGA, 31P NMR, and elemental analysis. Single crystal X-ray diffraction analysis13 showed that the complex crystallizing in the trigonal space group C23i set as R3 throughout with Z = 3, so that one sixth of the cation, 12þ, is crystallographically independent together with one sixth of the anion, 12(one molecule of water and one third of a bromide ion) making up the asymmetric unit of the structure. A view of the 12þ and the atom labeling scheme used is shown in Figure 1. In the cation, the ligands are coordinated in a teripodal manner through the three pyridine N atoms. The three pyridine planes of each ligand are parallel to the P-Fe-P axis. The Fe-N(py) and bridgehead P-C(py) bond distances are 2.006(2) Å and 1.821(3) Å, respectively. The average FeN(py) bond length of this cation in [Fe(PO(2-py)3)2](NO3)2 reported by Murray and co-workers14 is 1.982(2) Å. The similar length of the Fe-N(py) bond in these cations provides some evidence for the presence of π-back-bonding, in comparison with [Fe(py)6]2þ, where the average of the Fe-N(py) length is 2.273 Å.15 The 31P{1H}NMR spectrum of the [Fe(PO(2r 2011 American Chemical Society
Figure 1. ORTEP diagram of the cation, 12þ, in [Fe(PO(2-py)3)2]Br2 3 6H2O with atom labeling and 30% thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Fe1-N1 = 2.007(3), P1-O1 = 1.428(15), P1-C1 = 1.821(3), C1-N1 = 1.363(4), N1-Fe1-N1a = 91.59(12), N1-Fe1-N1c = 180.00, N1-Fe1-N1d = 88.41(12), O1-P1-C1 = 117.68(10), C1-P1-C1a = 100.15(14), Fe1-N1-C1 = 122.1(2). Symmetry codes: (a) -Y, X - Y, Z; (b) -X þ Y, -X, Z; (c) -X, -Y, 1 - Z; (d) Y, -X þ Y, 1 - Z; (e) X - Y, X, 1 - Z.
py)3)2]Br2 3 6H2O in DMSO-d6 solution shows a single peak at -7.67 ppm. A view of 12- and the atom labeling scheme used is shown in Figure 2. The structure of 12- was found as the discrete [Br2(H2O)6]2- cubane-like cluster, in which the bromide ions occupy opposite vertices of the cube. The striking feature of this cluster is that every bromide anion connects with three water molecules and every water molecule is linked by two bromide anions and two H2O via hydrogen bonds. One hydrogen atom is along each edge Received: December 4, 2010 Revised: January 15, 2011 Published: January 28, 2011 933
dx.doi.org/10.1021/cg101613b | Cryst. Growth Des. 2011, 11, 933–935
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of the cube, so each bromide ion is involved in three hydrogen atoms. Each oxygen atom has two hydrogen bonds to an oxygen atom and a bromide ion and one hydrogen bond from an adjacent
oxygen atom on the same edge. There are two kinds of O-H 3 3 3 O and O-H 3 3 3 Br hydrogen bonds in this water cluster. The hydrogen bonded O 3 3 3 O separation is 2.879(7) Å, which is comparable to the 2.8345(11) Å reported by Curnow and co-workers for the [Cl2(H2O)6]2- cluster.12a The Br 3 3 3 O separation is 3.367(5) Å. The bond distances and angles of O-H 3 3 3 O, 2.05(6) Å and 168(7)°, and of O-H 3 3 3 Br, 2.66(7) Å and 154(7)°, are in accordance with strong/medium hydrogen bonds.16 These strengths of hydrogen bonding are confirmed by thermal analysis. The packing diagram of this structure is shown in Figure 3a and b in the b- and c-directions, respectively. As is clear from Figure 3, water clusters are well-trapped in isolated cavities surrounded by the six cations. There is some C(phenyl)-H 3 3 3 O(water) [H2 3 3 3 O2i = 2.41(5), C2 3 3 3 O2i = 3.256(6) Å, and C2-H2 3 3 3 O2i = 137.0(4)°, symmetry code: (i) Y, 1 - X þ Y, 1 - Z] weak interaction between 1- and surrounding 1þ moieties. The thermal stability of the bromide-water cluster in [Fe(PO(2-py)3)2]Br2 3 6H2O has been studied by thermogravimetric analysis (TGA). As shown on the TGA curve (Figure 4), the compound exhibits a first weight loss of 12.2% in the temperature range 278-365 °C corresponding to the loss of water molecules in the cluster (calculated weight loss 12.5%). This analysis confirms that there are six water molecules per formula unit, as expected from X-ray diffraction and elemental analysis data. The temperature
Figure 2. Cubane-like dibromide-hexahydrate cluster, 12-, in [Fe(PO(2-py)3)2]Br2 3 6H2O. Hydrogen bond distances (Å) and angles (deg): O2-H2B = 0.84(6), O2 3 3 3 O2b = 2.879(7), H2B 3 3 3 O2b = 2.05(6) and O2-H2B 3 3 3 O2b = 168(7), O2-H2C = 0.76(6), O2 3 3 3 Br1a = 3.367(5), H2C 3 3 3 Br1a = 2.66(7) and O2-H2B 3 3 3 Br1a = 154(7). Symmetry codes: (a) 2/3 - X, -2/3 - Y, 4/3 - Z; (b) -1/3 = X - Y, -2/3 þ X, 4/3 - Z; (c) 2/3 þ Y, 1/3 - X þ Y, 4/3 - Z; (d) 1 - X þ Y, -X, -Z; (e) -Y, -1 þ X - Y, Z.
Figure 3. Packing diagram of [Fe(PO(2-py)3)2]Br2 3 6H2O in the (a) b- and (b) c-directions. In part b, green and blue molecules show coplanar iron atoms. Water clusters and couner-cations are displayed in space-filling and ball-stick modes, respectively. 934
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(2) (a) Zuhayra, M.; Kampen, W. U.; Henze, E.; Soti, Z.; Zsolnai, L.; Huttner, G.; Oberdorfer, F. J. Am. Chem. Soc. 2006, 128, 424. (b) Ng, M. T.; Deivaraj, T. C.; Klooster, W. T.; McIntyre, G. J.; Vittal, J. J. Chem.—Eur. J. 2004, 10, 5853. (3) (a) Ma, B.-Q.; Sun, H.-L.; Gao, S. Chem. Commun. 2004, 2220. (b) Day, M. B.; Kirschner, K. N.; Shields, G. C. J. Phys. Chem. A 2005, 109, 6773. (4) (a) Ghosh, S. K.; Bharadwaj, P. K. Inorg. Chem. 2004, 43, 5180. (b) Moorthy, J. N.; Natarajan, R.; Venugopalan, P. Angew. Chem., Int. Ed. 2002, 41, 3417. (c) Wang, J.; Zheng, L.-L.; Li, C.-J.; Zheng, Y. Z.; Tong, M.-L. Cryst. Growth. Des. 2006, 6, 357. (d) Li, Y.; Jiang, L.; Feng, T.-B.; Lu, X.-L. Cryst. Growth. Des. 2008, 8, 3689. (5) (a) Ma, B.-Q.; Sun, H.-L.; Gao, S. Chem. Commun. 2005, 2336. (b) Atwood, J. L.; Barbour, L. J.; Ness, T. J.; Raston, C. L.; Raston, P. L. J. Am. Chem. Soc. 2001, 123, 7192. (c) Doedens, R. J.; Yohannes, E.; Khan, M. I. Chem. Commun. 2002, 62. (6) (a) Barbour, L. J.; Orr, G. W.; Atwood, J. L. Nature 1998, 393, 671. (b) Barbour, L. J.; Orr, G. W.; Atwood, J. L. Chem. Commun 2000, 859. (c) Yoshizawa, M.; Kusukawa, T.; Kawano, M.; Ohhara, T.; Tanaka, I.; Kurihara, K.; Niimura, N.; Fujita, M. J. Am. Chem. Soc. 2005, 127, 2798. (7) (a) Lakshminarayanan, P. S.; Suresh, E.; Ghosh, P. Angew. Chem., Int. Ed. 2006, 45, 3807. (b) Ma, B.-Q.; Sun, H.-L.; Gao, S. Angew. Chem., Int. Ed. 2004, 43, 1374. (c) Liu, Q. Y.; Xu, L. CrystEngComm 2005, 7, 87. (d) Neogi, S.; Savitha, G.; Bharadwaj, P. K. Inorg. Chem. 2004, 43, 3771. (e) Ghosh, S. K.; Bharadwaj, P. K. Angew. Chem., Int. Ed. 2004, 43, 3577. (f) Ghosh, S. K.; Ribas, J.; Fallah, M. S. E.; Bharadwaj, P. K. Inorg. Chem. 2005, 44, 3856. (g) Ghosh, S. K.; Ribas, J.; Fallah, M. S. E.; Bharadwaj, P. K. Inorg. Chem. 2004, 43, 6887. (8) (a) Infantes, L.; Motherwell, S. CrystEngComm 2002, 4, 454– 461. (b) Fayoz, J.; Infantes, L.; Cano, F. H. Cryst. Growth Des. 2005, 5, 191. (9) (a) Mir, M. H.; Vittal, J. J. Cryst. Growth. Des. 2008, 8, 1478. (b) Mir, M. H.; Vittal, J. J. Angew. Chem., Int. Ed. 2007, 46, 4925. (10) Liu, D.; Li, H.-X.; Ren, Z.-G.; Chen, Y.; Zhang, Y.; Lang, J.-P. Cryst. Growth Des. 2009, 9, 4562. (11) Custelcean, R.; Gorbunova, M. G. J. Am. Chem. Soc. 2005, 127, 16362. (12) (a) Butchard, J. R.; Curnow, O. J.; Garrett, D. J.; Maclagan, R. G. A. R. Angew. Chem., Int. Ed. 2006, 45, 7550. (b) Mascal, M.; Infantes, L.; Chisholm, J. Angew. Chem., Int. Ed. 2006, 45, 32. (c) Dalley, N. K.; Krakowiak, K. E.; Bradshaw, J. S.; Kou, X.; Izatt, R. M. J. Heterocycl. Chem. 1995, 32, 1201. (13) Crystallographic data and refinement parameters for 1: C30H36Br2Fe1N6O7P2, Mr = 870.24 g mol-1, trigonal, space group R3, a = 9.8606(11) Å, b = 9.8606(11) Å, c = 30.562(5) Å, V = 2573.5(6) Å3, Z = 3, F = 1.685 g cm-3, μ = 2.917 mm-1, T = 298(2) K, 2722 reflections collected, 1532 independent reflections (Rint = 0.0341), R1( I g 2σ(I)) = 0.0520, wR2 (I g 2σ(I)) = 0.1432, R1(all) = 0.0609, wR2(all) = 0.1514, residual electron density = 0.539 and -0.537 e 3 Å-3. (14) Anderson, P. A.; Astley, T.; Hitchman, M. A.; Keene, F. R.; Moubaraki, B.; Murray, K. S.; Skelton, B. W.; Tiekink, E. R. T.; Toftlund, H.; White, A. H. J. Chem. Soc., Dalton Trans. 2000, 3505. (15) Doedens, R. J.; Dahl, L. F. J. Am. Chem. Soc. 1966, 88, 4847. (16) (a) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48.(b) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University Press: Oxford, 1997. (c) Scheiner, S. Hydrogen Bonding. A theoretical Perspective; Oxford University Press: Oxford, 1997. (d) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond in Structural Chemistry and Biology; Oxford University Press: Oxford, 1999. (17) (a) Atwood, J. L.; Barbour, L. J.; Jerga, A.; Schottel, B. L. Science 2002, 298, 1000. (b) Atwood, J. L.; Barbour, L. J.; Jerga, A. Science 2002, 296, 2367. (c) Atwood, J. L.; Barbour, L. J.; Jerga, A. Angew. Chem., Int. Ed. 2004, 43, 2948. (d) Tian, L.; Vittal, J. J. Cryst. Growth Des. 2006, 6, 822.
Figure 4. Thermogram of [Fe(PO(2-py)3)2]Br2 3 6H2O showing TGA at the heating rate of 20 °C/min.
required for water molecules removal is well above 100 °C (more than 278 °C), suggesting that the hydrogen bonding that builds the bromide-water cluster must be of a significant strength and H2O molecules are strongly incorporated as a part of this cluster. Such observation of retaining very volatile liquids in the crystal packing has been reported previously.17 In summary, a discrete dibromide-hexahydrate water cluster has been trapped in the solid state structure as counteranion for bis(tris(2-pyridylphosphine oxide))iron(II) cation. This water cluster has a cubane-like structure in which the bromide anions occupy opposite corners. From thermal analysis, the temperature required for water molecules removal is more than 278 °C, which shows the hydrogen bonding that builds the bromide-water cluster is strongly incorporated as a part of this cluster. However, this study would certainly provide new insights into the properties of interaction of the aggregated water molecules and surrounding ions.
’ ASSOCIATED CONTENT
bS Supporting Information. Detailed synthesis of 1 (CCDC No. 789370) and full crystallographic data for 1. This material is available free of charge via the Internet at http://pubs.acs.org. ’ AUTHOR INFORMATION Corresponding Author
*Telephone: þ98 21 29903105. Fax: þ98 21 22431663. E-mail:
[email protected].
’ ACKNOWLEDGMENT We would like to thank the Graduate Study Councils of Shahid Beheshti University, G.C., for financial support. ’ REFERENCES (1) (a) Wang, X.; Lin, H.; Mu, B.; Tian, A.; Liu, G. Dalton Trans. 2010, 39, 6187. (b) Rasaiah, J. C.; Garde, S.; Hummer, G. Annu. Rev. Phys. Chem. 2008, 59, 713. (c) Blanton, W. B.; Gordon-Wylie, S. W.; Clark, G. R.; Jordan, K. D.; Wood, J. T.; Geiser, U.; Collins, T. J. J. Am. Chem. Soc. 1999, 121, 3551. (d) Beitone, L.; Huguenard, C.; Gunsmuller, A.; Henry, M.; Taulelle, F.; Luiseau, T.; Ferey, G. J. Am. Chem. Soc. 2003, 125, 9102. (e) Dai, F. N.; He, H. Y.; Sun, D. F. J. Am. Chem. Soc. 2008, 130, 14064. (f) Henry, M. ChemPhysChem 2002, 3, 607. (g) Jin, C.-M.; Zhu, Z.; Chen, Z.-F.; Hu, Y.-J.; Meng, X.-G. Cryst. Growth Des. 2010, 10, 2054. (h) Das, M. C.; Bharadwaj, P. K. Eur. J. Inorg. Chem. 2007, 1229. (i) Das, M. C.; Maity, S. B.; Bharadwaj, P. K. Curr. Opin. Solid State Mater. Sci. 2009, 13, 76. 935
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