CRYSTAL GROWTH & DESIGN 2001 VOL. 1, NO. 2 103-106
Communications Diamondoid and Square Grid Networks in the Same Structure. Crystal Engineering with the Iodo‚‚‚Nitro Supramolecular Synthon Ram Thaimattam,† C. V. Krishnamohan Sharma,‡ Abraham Clearfield,*,‡ and Gautam R. Desiraju*,† School of Chemistry, University of Hyderabad, Hyderabad 500 046, India, and Department of Chemistry, Texas A&M University, College Station, Texas, 77843-3255 Received January 25, 2001
ABSTRACT: In principle, an organic diamondoid structure could follow from any of four possibilities: a single molecule of the type AX4 assembles via X‚‚‚X interactions; two molecules, e.g. AX4 and BY4, assemble via X‚‚‚Y interactions; either of the first two possibilities is modified with appropriate linear spacer molecules; a single molecule AX2Y2 assembles via X‚‚‚Y interactions. This communication deals with the last possibility, wherein the X‚‚‚Y link is based on the polarizationassisted I‚‚‚O2N synthon. A notable feature of the crystal structure of 4,4′-diiodo-4′′,4′′′-dinitrotetraphenylmethane (1) is the existence of a divergent mode of iodo-nitro association. The Td nodes of 1 are interconnected with the I atom bifurcated by O atoms from two NO2 groups such that each molecule of 1 is connected to eight others through I‚‚‚O contacts. The result is a combination of 5-fold diamondoid and 3-fold square grid networks. All I‚‚‚O interactions observed are short and strong, and there is a pronounced tendency to achieve close packing with the two coexisting networks. A key concept in crystal engineering is modularity, which is the tendency of particular combinations of molecular functionality to form predictable supramolecular arrangements.1,2 Diamondoid networks provide convenient targets for the testing of this concept, as may be seen from the variety of organic, organometallic, and inorganic diamondoid structures that may be obtained by connecting tetrahedral (Td) nodes.3,4 The engineering of organometallic or inorganic diamondoid structures is aided by the preferences of certain metal ions for tetrahedral coordination.4 Many metal ions fulfill this condition, and so, such structures are prolific. Purely organic diamondoid structures are not so common, because their formation necessarily follows from the availability of appropriately functionalized tetrahedral molecules.3 In principle, an organic diamondoid structure could follow from any of four possibilities (Chart 1): (i) a single molecule of the type AX4 assembles via X‚‚‚X interactions, as in structure I; (ii) two molecules, e.g. AX4 and BY4, assemble via X‚‚‚Y interactions (structure II); (iii) either of the former possibilities is modified with appropriate linear spacer molecules, as in X‚‚‚W-W‚‚‚X or X‚‚‚W-Z‚‚ ‚Y (structure III); (iv) a single molecule AX2Y2 assembles via X‚‚‚Y interactions (structure IV). This communication deals with this final possibility, with the X‚‚‚Y link based on the polarization-assisted I‚‚‚O2N synthon.5 We describe here the crystal structure of 4,4′-diiodo-4′′,4′′′-dinitrotetraphenylmethane (1) and report the first occurrence of an all-organic diamondoid network based on an AX2Y2 tecton. † ‡
University of Hyderabad. Texas A&M University.
Chart 1
Compound 1 was synthesized in six steps from 4-ni10.1021/cg010286z CCC: $20.00 © 2001 American Chemical Society Published on Web 02/17/2001
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Figure 1. Adamantanoid cage (left) and the square grid network (right) in the crystal structure of 1. The iodo‚‚‚nitro interactions are shown as dotted lines.
trobenzaldehyde.6 Efforts to crystallize 1 from various commonly available organic solvents and their mixtures (e.g., alcohols, ethers, esters, ketones, chlorinated solvents, and hydrocarbons) were not fruitful. However, and with some difficulty, we were able to grow very small single crystals (or rather crystal clusters) from nitromethane.7 The crystal structure of 1 was solved and refined satisfactorily, though the (best) crystal used was still very small. A notable feature of the structure is the existence of a divergent mode of iodo-nitro association, via synthon A, rather than with the convergent synthon B. It can be appreciated that if synthon B were to be employed exclusively in the packing, the crystal structure would be of the “normal” diamondoid variety because of donor-acceptor complementarity. However, the Td nodes of 1 can also be interconnected with the I atom bifurcated by O atoms from two NO2 groups (synthon A).8 This is the situation that occurs here, and each molecule of 1 is connected to eight other molecules through synthon A (I‚ ‚‚O contacts: 3.303(11), 3.379(13) Å). This 8-fold coordination follows from the fact that each I atom is linked to two NO2 groups and each NO2 group to two I atoms (Scheme 1). The lengths of these contacts are significantly below the van der Waals sum (3.50 Å), and given the polarizable nature of the I atom, they may be taken to be strongly stabilizing interactions.9
When each of the two I‚‚‚O connections is taken separately, an unprecedented combination of 5-fold diamondoid and 3-fold square grid networks may be discerned (Figures 1 and 2). The two I‚‚‚O contacts in 1 can be differentiated by considering the way in which the I atom interacts with the O atoms of the NO2 group (i.e. in plane or out of plane with respect to the plane of the nitro group). The fourconnected network formed with the out-of-plane I‚‚‚O contacts (3.379(13) Å) is of the diamondoid type (Figure 1), and five such independent networks interpenetrate in the normal manner (Figure 2). This diamondoid framework is additionally stabilized by C-H‚‚‚O hydrogen bonds (H‚ ‚‚O, C-H‚‚‚O: 2.60 Å, 144°; 2.71 Å, 145°).10 The shorter I‚‚‚O contacts (3.303(11) Å) occurring in the plane of the NO2 group generate a two-dimensional square grid network (Figure 1), which undergoes 3-fold parallel interpenetration, as shown in Figure 2. As to why the crystal structure of 1 is not of the “normal” 5-fold interpenetrated type mediated only by synthon B, suffice it to say here that experimental crystal structures do not necessarily follow the dictates of aesthetics. Both I‚‚‚O interactions observed in the structure are short and strong,9 and so there is a pronounced tendency to achieve close packing with two coexisting networks. In all (organic) diamondoid structures that are interpenetrated, there must be significant internetwork interactions. Most often these are of van der Waals variety and so do not usually elicit specific comment. In the present case, the main internetwork and intranetwork interactions are of the same type, namely I‚‚‚O2N. It is therefore possible to dissect the structure in terms of two networks with shared nodes. That 1 is stabilized exclusively via the dissymmetric synthon A in the solid state and that both the diamondoid and square grid networks undergo odd fold (i.e., 5 and 3)
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Figure 2. Stereoview of the networks observed in the crystal structure of 1. Molecules are represented as nodes, and the connections between molecules are shown as lines. Solid lines define the 5-fold diamondoid networks (color-coded), and broken lines show the 3-fold interwoven square grid networks.
Scheme 1
interpenetration could reflect upon the noncentrosymmetric nature of the bulk material (space group Fdd2). Indeed, most current strategies aimed at building polar organic structures are based on near-planar molecules, and as a consequence, structural control in such strategies is limited to only one or at most two dimensions. Interconnection of Td tectons of the AX2Y2 type with X‚‚‚Y synthons may therefore constitute a new and promising strategy for
three-dimensional control in the design of noncentrosymmetric crystals.11 In conclusion, compound 1 provides an interesting case of a Td molecule which upon crystallization leads via fourcoordination to distinct diamondoid and square grid networks. The crystal structure of 1 is also a good example of retrosynthetic-assisted crystal engineering in that a dia-
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mondoid architecture based on I‚‚‚O2N interactions was obtained and no I‚‚‚I contacts are observed. Acknowledgment. We thank Dr. A. Nangia for helpful discussions and suggestions regarding the synthesis of compound 1. R.T. thanks the University Grants Commission for fellowship support. C.V.K.S. and A.C. wish to acknowledge with thanks the National Science Foundation for their support of this work under Grant No. DMR9707151. Supporting Information Available: Text and tables giving synthesis and X-ray structural information on 1. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Nangia, A.; Desiraju, G. R. Acta Crystallogr. 1998, A54, 934-944. (b) Aakero¨y, C. B. Acta Crystallogr. 1997, B53, 569-583. (c) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311-2327. (2) (a) Zaworotko, M. J. In Coordination Polymers In Crystal Engineering: The Design and Applications of Functional Solids; Seddon, K. R., Zaworotko, M. J., Eds.; NATO ASI Series; Kluwer: Dordecht, The Netherlands, 1998; pp 383408. (b) Yaghi, O. M.; Li, G.; Li, H. Nature 1995, 378, 703706. (3) (a) Galloppini, E.; Gilardi, R. Chem. Commun. 1999, 173174. (b) Reddy, D. S.; Craig, D. C.; Desiraju, G. R. J. Am. Chem. Soc. 1996, 118, 4090-4093. (c) Wuest, J. D. In Mesomolecules: From Molecules to Materials; Mendenhall, G. D., Greenberg, A., Liebman, J. F., Eds.; Chapman & Hall: New York, 1995; pp 107-131, and references therein. (d) Ermer, O. J. Am. Chem. Soc. 1988, 110, 3747-3754. (4) (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. Engl. 1998, 37, 1460-1494 and references therein. (b) Blake, A. J.; Champness, N. R.; Chung, S. S. M.; Li, W.-S.; Schro¨der, M. Chem. Commun. 1997, 1005-1006. (c) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Sironi, A. J. Chem. Soc., Chem. Commun. 1994, 2755-2756.
Communications (5) Sarma, J. A. R. P.; Allen, F. H.; Hoy, V. J.; Howard, J. A. K.; Thaimattam, R., Biradha, K.; Desiraju, G. R. Chem. Commun. 1997, 101-102 and references therein. (6) The syntheses of three intermediate compounds have been reported previously, and the synthetic procedures for the final three steps are provided in the Supporting Information. 4,4′-Diiodo-4′′,4′′′-dinitrotetraphenylmethane (1): mp 266 °C; 1H NMR (200 MHz, CDCl3, 25 °C, TMS) δ 8.14 (d, 3J(H,H) ) 9 Hz, 4H), 7.66 (d, 3J(H,H) ) 9 Hz, 4H), 7.37 (d, 3J(H,H) ) 9 Hz, 4H), 6.89 (d, 3J(H,H) ) 9 Hz, 4H). (7) (a) Crystal Data for 1: C25H16N2O4I2, Mr ) 662.2, orthorhombic, Fdd2, a ) 18.704(2) Å, b ) 33.145(4) Å, c ) 7.429(8) Å, R ) β ) γ ) 90°, V ) 4605(5) Å3, Z ) 8, Dc ) 1.910 Mg m-3, GOF ) 0.91. A total of 2322 absorption-corrected reflections out of 7151 reflections measured on convergence gave final values of R ) 0.064 and Rw ) 0.144. X-ray data on a single crystal of 1 (0.02 × 0.03 × 0.08 mm) were collected at -110 °C on a Bruker CCD diffractometer (4 < θ < 56°). (8) We have carried out a Cambridge Structural Database (CSD, version 5.19, 215 403 entries) analysis of halogen‚‚‚ O (NO2) interactions. The distribution ratios for synthon A versus synthon B for Cl, Br, and I are 5/7, 19/3 and 52/12, respectively, which suggest that iodo compounds have an equal preference for synthons A and B, while for chloro and bromo compounds, synthon A is definitely preferred. (9) Desiraju, G. R.; Pedireddi, V. R.; Sarma, J. A. R. P.; Zacharias, D. E. Acta Chim. Hung. 1993, 130, 451-465. (10) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond in Structural Chemistry and Biology; Oxford University Press: Oxford, U.K., 1999. (11) (a) Zyss, J.; Brasselet, S.; Thalladi, V. R.; Desiraju, G. R. J. Chem. Phys. 1998, 109, 658-669. (b) Thalladi, V. R.; Brasselet, S.; Weiss, H.-C.; Bla¨ser, D.; Katz, A. K.; Carrell, H. L.; Boese, R.; Zyss, J.; Nangia, A.; Desiraju, G. R. J. Am. Chem. Soc. 1998, 120, 2563-2577.
CG010286Z
