Interplay of Hydrogen Bonds in Assembling (4,4)-Coordination Networks: Transformations from Open to Interpenetrated Networks via Anion Exchange Madhushree Sarkar and Kumar Biradha* Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India
CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 8 1742-1745
ReceiVed April 13, 2006; ReVised Manuscript ReceiVed June 8, 2006
ABSTRACT: Open (4,4)-coordination networks were shown to assemble via N-H‚‚‚O hydrogen bonds in two different ways: the usual offset packing via β-sheet hydrogen bonds and an unprecedented trigonal packing. Both of the structures have continuous channels that are occupied by guest molecules (nitrobenzene or EtOH and H2O) which account for 37% or 28% of the crystal volume. Interestingly, these complexes have shown an ability to exchange ClO4- with PF6- ions and transform into the doubly interpenetrated varieties. The construction of well-defined architectures with exotic geometries is of importance for a variety of functional properties ranging from nanotechnology to biology.1 An intriguing approach for such architectures is a thorough understanding of the various intermolecular interactions of organic functional groups in different environments.2 For a better understanding of the precession of recognition of various functional groups, it is important to design systems which have multiple functional groups. On the other hand, many (4,4)-coordination networks have been designed to date, but studies on assembling these networks via hydrogen bonds are relatively rare.3 Accordingly, 1 is our choice of a ligand for
designing 3D architectures by assembly of 2D coordination networks via N-H‚‚‚O hydrogen bonds. The ligand 1 contains two pyridine moieties for the formation of coordination networks, a butyl moiety for providing the flexibility, and two amide moieties for the formation of the N-H‚‚‚O hydrogen-bonded synthon I (β-sheet pattern) or II. Recently we and others have shown the utility of this type of ligand in the construction of coordination networks.3b,4 Here, we present our studies on reactions of 1 with Cu(ClO4)2 which resulted in two types of complexes with two different solvent systems: in one complex the (4,4)-network assembles in the usual offset fashion but via synthon I and also includes nitrobenzene as a guest molecule, while in the other the (4,4)-network assembles in an unprecedented trigonal fashion via synthon II. Further, both of the structures have shown an excellent ability to transform into 2-fold inclined interpenetrated networks upon exchange of ClO4with PF6-. The reaction of 1 with Cu(ClO4)2 in a water-EtOH-nitrobenzene solvent system resulted in crystals of the complex {(Cu(1)2* To whom correspondence should be addressed. Fax: +91-3222282252. Tel: +91-3222-283346. E-mail:
[email protected].
(H2O)2)‚2(ClO4)‚3(nitrobenzene)}n (2). An X-ray structure analysis reveals that the complex 2 contains a (4,4)-coordination network and includes three nitrobenzene molecules per metal atom (Figure 1).5 The Cu(II) atom in 2 has a distorted-octahedral geometry, as four units of 1 occupy the equatorial positions (Cu-N: 2.035(5), 2.052(5) Å) and two H2O molecules occupy the axial positions (Cu-O: 2.425(7), 2.583(7) Å). The (4,4)-network has elliptical cavities with a short axis of 18.6 Å and a long axis of 30.8 Å (Figure 1a). Within the network the metal atoms are separated by ligands at a distance of 18 Å. Interestingly, the butyl chain does not adopt an all-anti geometry but adopts a gauche-anti-gauche geometry and also the ligand is partially disordered, which has been modeled. The layers pack on each other via β-sheet hydrogen bonds (N-H‚‚‚O: 2.861(8) Å, 162°; 3.14(1) Å; 3.21(1) Å) in an offset fashion with the interlayer distance of 4.45 Å. The water molecules on Cu(II) hydrogen-bond to ClO4- ions (O-H‚‚‚O: 2.93(1) Å; 2.97(1) Å; 2.93(3) Å; 2.90(2) Å) (Figure 1c). The packing of the layers generates two types of continuous channels, large and small, which are occupied by nitrobenzene molecules (36% of the unit cell volume) and ClO4- anions, respectively. TGA shows the loss (29.3%) of three nitrobenzene molecules from 65 to 130 °C and the loss (3.8%) of coordinated water from 130 to 257 °C. Complex 2 exhibited selectivity in the complete exchange of nitrobenzene molecules with other aromatic guest molecules without altering the crystal structure.6 The reaction of 1 with Cu(ClO4)2 in EtOH and water, without nitrobenzene, resulted in the crystals of another complex, {(Cu(1)2(H2O)2)‚2(ClO4)‚(EtOH)(H2O)}n (3). The X-ray analysis of 3 reveals that it also contains an open (4,4)-network and the coordination environment of Cu(II) is a distorted octahedron (Cu-N: 2.052(8) Å; 2.017(11) Å; 2.034(10) Å; 2.051(10) Å) (Cu-O: 2.494(9) Å; 2.380(8) Å).7 Unlike the above structure, here the (4,4)-network is constituted by two crystallographically independent ligands which have different geometries of the butyl groups: one has a gauche-anti-gauche conformation, and the other has an all-gauche conformation (Figure 2). Interestingly, only one of the four amide groups in the structure engages in amide to hydrogen bonds via synthon II (N-H‚‚‚O: 2.93(2) Å, 167°). The N-H groups of the remaining three amides do not hydrogenbond to the amide CdO: two hydrogen-bond to perchlorates (N-H‚‚‚O: 2.94(2) Å, 151°; 2.99(2) Å, 162°) and one hydrogenbonds to a H2O molecule (N-H‚‚‚O: 3.10(4) Å, 147°). The layers have elliptical cavities, similar to those of 2, with long and short axis lengths of 31 and 18 Å, respectively, and pack in a trigonal fashion along the z axis, crystallizing in the P31 space group, such that there is continuous channel formation (Figure 2a). The channels are occupied by water and EtOH molecules which are accounted for the 28% of the crystal volume (Figure 2b). Each layer repeats for every three layers with the interlayer repeat distance of 4 Å. Further, each loop of (4,4)-net is connected to that of the neighboring layer by six hydrogen bonds (Figure 2c). Two are
10.1021/cg060216y CCC: $33.50 © 2006 American Chemical Society Published on Web 06/27/2006
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Figure 1. Illustrations for the crystal structure of 2: (a) space-filling representation of the (4,4) layer (red, O; blue, N, turquoise, H; gray, C); (b) β-sheet hydrogen bond pattern; (c) packing of (4,4)-layers (view along the b axis), with alternate layers shown in either green or magenta and nitrobenzene and ClO4- ions represented in space-filling mode; (d) disorder of the ligand.
Figure 2. Illustrations for the crystal structure of 3: (a) trigonal packing of the (4,4)-networks, with three networks shown in three different colors (view along the c axis); (b) space-filling representation of the channels; (c) top view of hydrogen bonds observed between the layers; (d) side view of hydrogen bonds observed between the layers. For (c) and (d), Cu(II) atoms that are connected by 1 are joined for the sake of clarity.
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Figure 3. Illustrations for the crystal structure of complex 4: (a) doubly interpenetrated (4,4)-networks (view along the c axis); (b) side view of the hydrogen bonds between four networks along (c axis) the walls of the channels.
formed between amide groups (N-H‚‚‚O), and four are formed between Cu-OH2 and CdO of the amide (O-H‚‚‚O: 2.82(1) Å; 2.79(1) Å). Generally, (4,4)-coordination networks of 4,4′-bipyridine analogues are known to form only three packing patterns: slippedslipped, slipped-offset, and offset-offset. To our knowledge, this is the first time such a trigonal and chiral packing has been observed for (4,4)-coordination networks. Remarkably, both of the above complexes have shown an excellent ability to exchange ClO4- ions with PF6- ions when placed in an aqueous solution with an excess of NH4PF6.8 The crystals dissolved and resulted in crystals of a new complex, {(Cu(1)2(H2O)2)‚2PF6}n (4), from both complexes 2 and 3. X-ray analysis of the crystals of 4 reveals that the compound crystallizes in the acentric space group I4h, which is different from the case for the above two structures.9 However, this complex is also composed of (4,4)-layers similar to those of parent complexes. Further, the coordination environment of the Cu atom remains unaltered (Cu-N: 2.033(4) Å; 2.064(4) Å) (Cu-O: 2.455(4) Å). In the asymmetric unit Cu(II) is present with 0.50 occupancy but only two PF6- ions, each with 0.25 occupancy, could be located. Elemental analysis and IR spectra confirmed the complete exchange of ClO4-.10 The major difference from the above two complexes is that the (4,4)-layers are not open but are doubly interpenetrated in an inclined mode (Figure 3). This structure is strikingingly similar to that of {Zn(4,4′-bipyridine)2(2H2O)(SiF6)}n, as both are doubly interpenetrated in an inclined mode and the channels are occupied by anions.11 However, the present structure differs from the above structure, as it crystallizes in the acentric space group I4h, whereas the Zn(II)-4,4-bipyridine species crystallizes in the centric space group P4/ncc. In 4, the interpenetrated networks are hydrogen-bonded to each other via synthon II (N-H‚‚‚O: 2.886(5) Å, 154°) and also via a O-H‚‚‚O hydrogen bond between Cu-OH2 and CdO of the amide (O-H‚‚‚O: 2.811(5) Å). One N-H of the amide is not involved in hydrogen bond formation with O or N atoms but points into the channel and may be engaged in forming N-H‚‚‚F interactions with PF6-anions. In conclusion, here we have shown that (4,4)-coordination networks formed by ligand 1 and Cu(II) have an ability to assemble via hydrogen bonds in three ways: offset and trigonal open networks and perpendicular doubly interpenetrated networks. The offset assembly occurred via synthon I, while the other two assemblies occurred via synthon II. The formation of complex 4 from both 2 and 3 upon anion exchange represents the greater template effect of the PF6- anion compared to that of the ClO4-
anion. We note that two out of the three complexes reported here crystallized in chiral/acentric space groups. Acknowledgment. We gratefully acknowledge financial support from the Department of Science and Technology (DST, No. SR/S1/OC-36/2002) and the DST-FIST for single-crystal X-ray facilities. M.S. thanks the CSIR for a research fellowship. Supporting Information Available: Text, tables, figures, and CIF files giving details of the synthesis, IR, powder X-ray, and TGA spectra, and crystallographic data for 2-4 and IR and powder spectra and elemental analysis data for guest exchange (removal) reactions with 2. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Lehn, J. M. Supramolecular Chemistry: Concepts and PerspectiVes; VCH: Weinheim, Germany, 1995. (b) Desiraju, G. R. Crystal Engineering: The Design of Organic Solids; Elsevier: Amsterdam, 1989. (c) Atwood, J. L.; Davies, J. E. D.; MacNicol, D. D.; Vo˜gtle, F., ComprehensiVe Supramolecular Chemistry; Pergamon: Oxford, U.K., 1996. (d) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University Press: New York, 1997. (e) Batten, S. R.; Murray, K. S. Coord. Chem. ReV. 2003, 246, 103. (f) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629. (g) Imai, H.; Inoue, K.; Kikuchi, K.; Yoshida, Y.; Ito, M.; Sunahara, T.; Onaka, S. Angew. Chem., Int. Ed. 2004, 43, 5618. (h) Sharma, C. V. K. Cryst. Growth Des. 2002, 2, 465. (2) (a) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (b) Aakero¨y, C. B. Acta Crystallogr, 1997, B53, 569. (c) Aoyama, Y. Top. Curr. Chem. 1998, 198, 131. (d) Zaworotko, M. J. Chem. Commun. 2001, 1. (e) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334. (f) Ockwig, N. W.; DelgadoFriedrichs, O.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2005, 38, 176. (g) Aakero¨y, C. B.; Beatty, A. M.; Helfrich, B. A. Angew. Chem., Int. Ed. 2001, 40, 3240. (h) Desiraju, G. R. Acc. Chem. Res. 2002, 35, 565. (i) Biradha, K. CrystEngComm 2003, 5, 274. (j) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460. (k) Fujita, M.; Kwon, Y. J.; Washizu S.; Ogura, K. J. Am. Chem. Soc. 1994, 116, 1151. (l) Papaefstathiou, G. S.; Milios, C.; MacGillivray, L. R. Microporous Mesoporous Mater. 2004, 71, 11. (3) (a) Uemura, K.; Kitagawa, S.; Fukui, K.; Saito, K., J. Am. Chem. Soc. 2004, 126, 3817. (b) Sarkar, M.; Biradha, K. Chem. Commun. 2005, 2229. (4) (a) Sarkar, M.; Biradha, K. Cryst. Growth Des. 2006, 6, 202. (b) Sarkar, M.; Biradha, K. Eur. J. Inorg. Chem. 2006, 531. (c) Muthu, S.; Yip, J. H. K.; Vittal, J. J. Dalton Trans. 2001, 3577. (d) Muthu, S.; Yip, J. H. K.; Vittal, J. J. Dalton Trans. 2002, 4561. (e) Ge, C.H.; Zhang, X.-D.; Zhang, P.; Guan, W.; Guo, F.; Liu, Q.-T. Polyhedron 2003, 22, 3493.
Communications (5) Single-crystal data were collected on a Bruker-Nonius Mach3 CAD4 X-ray diffractometer that uses graphite-monochromated Mo KR radiation (µ ) 0.710 73 Å) by the ω-scan method. The structures were solved by direct methods and refined by least-squares methods on F2 using SHELX-97. Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were fixed at calculated positions and refined using a riding model. Crystal data for 2: orthorhombic, Pbcn, a ) 18.567(4) Å, b ) 9.934(2) Å, c ) 30.764(6) Å, V ) 5674(2) Å3, Z ) 4, Dc ) 1.480 g cm-3, 2777 reflections out of 4535 unique reflections with I > 2σ(I), 1.72 < θ < 24.96°, final R factors R1 ) 0.0839, wR2 ) 0.1669. One nitrobenzene molecule exhibited disorder, which has been modeled and refined. Anal. Calcd: C, 47.48; H, 4.35; N, 12.18. Found: C, 47.43; H, 4.11; N, 11.83. (6) The complete exchange of nitrobenzene by anisole or p-xylene without alteration of the crystal structure was observed by IR and powder patterns. Elemental analysis suggests that there are two anisole or one and a half p-xylene molecules per Cu(II). However, similar reactions with benzonitrile or chlorobenzene were unsuccessful. Further guest removal of 2 resulted in different powder X-ray patterns, indicating the changes in the structure. The guest removed sample of 2 failed to readsorb the nitrobenzene. See the Supporting Information for spectra. (7) Crystal data for 3: hexagonal, P31, a ) 17.943(3) Å, b ) 17.943(3) Å, c ) 13.252(3) Å, V ) 3694.9(10) Å3, Z ) 3, Dc ) 1.293 g cm-3, 3752 reflections out of 4684 unique reflections with I > 2σ(I), 1.31 < θ < 24.96°, final R factors R1 ) 0.0767, wR2 ) 0.1895. The presence of one EtOH and one water molecule per Cu(II) was
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(8)
(9)
(10)
(11)
evidenced by elemental and TGA analysis. However, in the X-ray study the O atoms of water and ethanol were located and refined, but not the carbon atoms of the EtOH. The Flack parameter is 0.09(3), Anal. Calcd: C, 42.56; H, 5.00; N, 11.68. Found: C, 42.49; H, 4.93; N, 11.05. Recently some other coordination networks were shown to undergo structural changes upon exchange of anions: (a) Khlobystov, A. N.; Champness, N. R.; Roberts, C. J.; Tendler, S. J. B.; Thompson, C.; Schro˜der, M. CrystEngComm 2002, 4, 426. (b) Du, M.; Guo, Y.-G.; Chen, S.-T.; Bu, X.-H.; Batten, S. R.; Ribas, J.; Kitagawa, S. Inorg. Chem. 2004, 43, 1287. Crystal data for 4: tetragonal, I4h, a ) 12.493(2) Å, b ) 12.493(2) Å, c ) 31.885(6) Å, V ) 4976.5(14) Å3, Z ) 4, Dc ) 1.316 g cm-3, 3515 reflections out of 4380 unique reflections with I > 2σ(I), 1.28 < θ < 24.98°, final R factors R1 ) 0.0492, wR2 ) 0.1085. Only half of the PF6- ions were located and refined. The Flack parameter is -0.07(2). Anal. Calcd: C, 39.35; H, 4.50; N, 11.47. Found: C, 39.92; H, 4.59; N, 11.52. Stretching frequencies of ClO4- at 1100 cm-1 for 2 and at 1095 cm-1 for 3 are observed. The absence of those bands and the presence of bands at 832 and 555 cm-1 for 4 confirms the the presence of the PF6- anion. (a) Gable, R. W.; Hoskins, B. F.; Robson, R. Chem. Commun. 1990, 1667. (b) Noro, S.; Kitaura, R.; Kondo, M.; Kitagawa, S.; Ishii, T.; Matsuzaka, H.; Yamashita, M. J. Am. Chem. Soc. 2002, 124, 2568.
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