Communication pubs.acs.org/crystal
A Hexameric Hexagonal Organotin Macrocycle. Supramolecular Entrapment of an Iodide−Iodide Short Contact Chandrajeet Mohapatra,† Sarita Tripathi,† Ganapathi Anantharaman,† and Vadapalli Chandrasekhar*,†,‡ †
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India National Institute of Science Education and Research, Institute of Physics Campus, Sachivalaya Marg, PO: Sainik School, Bhubaneswar 751 005, India
‡
S Supporting Information *
ABSTRACT: A hexanuclear hexagonal organotin macrocycle [(n-Bu3Sn)6(μ-L)6(I−)2(MeOH)6] (1) was synthesized in a 1:1 reaction of (n-Bu3Sn)2O and 4,5-dicarboxy-1,3-dimethyl1H-imidazol-3-ium iodide (LH2I). The molecular structure of 1 reveals that it is a 42-membered hexatin macrocycle possessing a C3 (pseudo-S6) symmetry. The alternate up− down arrangement of imidazolium units allows the molecule to assume a chair topology. The hexagonal packing of these macrocycles, in the solid-state, results in nanoscale onedimensional channels which entrap two I− ions in close proximity (∼3.7 Å) as a result of various supramolecular interactions.
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On the basis of previous studies by Lyssenko and co-workers, the current system seems to possess a rare I−---I− short contact.10 Recently, Wu and co-workers have reported a quite unusual instance of Cl−---Cl− short contact which is trapped as a guest in a foldamer host system.11 Molecular systems which can behave as hosts for anionic guests by utilizing supramolecular interactions may potentially mimic natural anion transporters.12 Although some molecular systems have been reported to stabilize I−---I2 ---I− interactions,13 to the best of our knowledge any system stabilizing a I−---I− short contact is unprecedented. These results are discussed herein. As mentioned above, the reaction between (n-Bu3Sn)2O and (LH 2 I) in a 1:1 ratio afforded [(n-Bu 3 Sn) 6 (μ-L) 6 (I − ) 2 (MeOH) 6 ] (1) (Scheme 1, see also Supporting Information). 1 crystallizes (from methanol) in the R3̅ space group of the trigonal crystal system. The asymmetric unit contains one completely deprotonated ligand (L2−) connected to one tributyl tin center, one I− ion, and one methanol molecule. 1 is a 42-membered macrocycle where six adjacent tributyl tin centers are bridged to each other by the imidazolium dicarboxylate ligand (Figure 1a). The tin center is pentacoordinated in trigonal bipyramidal geometry (tbp) (Supporting Information). Six n-butyl groups, one from each of the tributyl tin units, are orientated toward the center of the macrocycle in a manner similar to the spokes of a wheel (Figure 1a). The alternate up−down orientation of the ligands (L2−) and the
rganooxotin compounds are assembled in reactions involving an organotin oxide, -hydroxide, or -oxidehydroxide with a protic acid.1−3 The types of products isolated depend generally on the nature of the organotin substrate, if the protic acid is kept constant along with the stoichiometry of the reaction.4 Thus, for example, the reaction of carboxylic acids RCOOH with (n-Bu3Sn)2O affords coordination polymers;5a on the other hand the reaction with [n-BuSn(O)OH]n affords molecular hexameric drum-shaped compounds.5b Although a number of cage structures are now quite common among the organostannoxane family,6 macrocycles built from the organotin motif are still not common.7 Further, in contrast to the wellstudied reactions of carboxylic acids with organotin substrates, those involving dicarboxylic acids are relatively few.4a Höpfl and his research group have shown that the reactions of di-nbutyltin and diphenyltin oxide with 2,5-pyridinedicarboxylic acid afforded macrocylic compounds (Supporting Information).8 We have investigated the reactions of different pyridinedicarboxylic acids with (n-Bu3Sn)2O to generate organotin macrocycles within coordination polymers.9 Murugavel and co-workers reported an organotin macrocycle in the reaction of di-n-butyltin oxide and 2-hydroxy-3,5-diisopropylbenzoic acid (Supporting Information).7c With this background, we wished to explore the reactivity of (n-Bu3Sn)2O with 4,5-dicarboxy-1,3-dimethyl-1H-imidazol-3-ium iodide (LH2I), and the reaction afforded a novel hexanuclear macrocyclic compound [(n-Bu3Sn)6(μ-L)6(I−)2(MeOH)6] (1). Interestingly, the iodide counterions present in the ligand are trapped in the hexagonal packing of the macrocycle; the supramolecular interactions of the anion/trapped methanol/ macrocyle seem to force two I− anions to be in close proximity. © 2014 American Chemical Society
Received: May 2, 2014 Revised: May 31, 2014 Published: June 6, 2014 3182
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Scheme 1
Figure 1. (a) Hexagonal Sn6-macrocylic structure of 1 (b) chairlike topology of 1 (c) intermetallic distances between opposite tin centers. (In panels b and 1c, n-butyl groups are deleted for clarity.)
mutual orientation of the two carboxylate groups, with a dihedral angle of ∼40° (Supporting Information) forces 1 to adopt a chairlike conformation, similar to that of cyclohexane, in a C3 (pseudo-S6) symmetry (Figure 1b). All the intermetallic distances between the symmetrically opposite tin centers in the
macrocycle are very similar (16.312 Å) attesting to the overall symmetric nature of 1 (Figure 1c). In the solid state, 1 adopts a hexagonal packing which also involves encapsulation of two iodide anions surrounded by methanol molecules inside supramolecular hexagonal onedimensional (1D) channels (Figure 2a). Detailed analysis of the 3183
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Figure 2. (a) Methanol and I− trapped inside the 1D channels in the hexagonal crystal packing of 1 (b) hydrogen bonding interactions inside the supramolecular pocket. (c) The supramolecular pocket containing the guest molecules is sandwiched by two different macrocycles of 1. (n-Butyl groups are deleted for clarity.)
Figure 3. (a) Supramolecular assembly of two I− ions and six methanol molecules. (b) Supramolecular assembly comparable with staggered form of ethane molecule.
I1, 108.1(1)°; O2−H20A, 3.039(6) Å; C20−H20A-O2,
trapped iodide ions reveals that inside a supramolecular pocket created by equal contribution of six molecules of 1, two I− ions are strongly hydrogen bonded by three methanol molecules each. The latter themselves are hydrogen bonded to one of the carboxylate oxygen atoms of 1 (I1−H5, 2.804(9) Å; O5−H5−
134.5(2)°) (Figure 2b). The supramolecular pocket containing the ensemble of two I− ions and six methanol molecules is sandwiched by two different macrocycles of 1 with a distance of 3184
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D.; Duthie, A.; Mitchell, C. Organometallics 2003, 22, 2161−2164. (c) Ribot, F.; Sanchez, C. Organometallics 2001, 20, 2593−2603. (d) Xie, Y. P.; Ma, J. F.; Yang, J.; Su, M. Z. Dalton Trans. 2010, 39, 1568−1575. (e) Song, S. Y.; Ma, J. F.; Yang, J.; Gao, L. L.; Su, Z. M. Organometallics 2007, 26, 2125−2128. (4) (a) Chandrasekhar, V.; Mohapatra, C.; Metre, R. K. Cryst. Growth Des. 2013, 13, 4607−4614. (b) Chandrasekhar, V.; Kundu, S.; Kumar, J.; Verma, S.; Gopal, K.; Chaturbedi, A.; Subramaniam, K. Cryst. Growth Des. 2013, 13, 1665−1675. (5) (a) Chandrasekhar, V.; Gopal, K.; Nagendran, S.; Singh, P.; Steiner, A.; Zacchini, S.; Bickley, J. F. Chem.Eur. J. 2005, 11, 5437− 5448. (b) Chandrasekhar, V.; Nagendran, S.; Bansal, S.; Kozee, M. A.; Powell, D. R. Angew.Chem., Int. Ed. 2000, 39, 1833−1835. (6) (a) Kumara Swamy, K. C.; Schmid, C. G.; Day, R. O.; Holmes, R. R. J. Am. Chem. Soc. 1988, 110, 7067−7076. (b) Baron, C. E.; Ribot, F.; Steunou, N.; Sanchez, C.; Fayon, F.; Biesemans, M.; Martins, J. C.; Willem, R. Organometallics 2000, 19, 1940−1949. (c) Banse, F.; Ribot, F.; Toledano, P.; Maquet, J.; Sanchez, C. Inorg. Chem. 1995, 34, 6371− 6379. (7) (a) Ma, C.; Li, Q.; Guo, M.; Zhang, R. J. Organomet. Chem. 2009, 694, 4230−4240. (b) Lockhart, T. P. Organometallics 1988, 7, 1438− 1443. (c) Prabusankar, G.; Murugavel, R. Organometallics 2004, 23, 5644−5647. (8) García-Zarracino, R.; Höpfl, H. J. Am. Chem. Soc. 2005, 127, 3120−3130. (9) Chandrasekhar, V.; Mohapatra, C.; Butcher, R. J. Cryst. Growth Des. 2012, 12, 3285−3295. (10) Nelyubina, Y. V.; Antipin, M. Y.; Lyssenko, K. A. J. Phys. Chem. A 2007, 111, 1091−1095. (11) Wu, B.; Jia, C.; Wang, X.; Li, S.; Huang, X.; Yang, X.-J. Org. Lett. 2012, 14, 684−687. (12) (a) Mindell, J. A. Science 2010, 330, 601−602. (b) Smith, B. D.; Lambert, T. N. Chem. Commun. 2003, 2261−2268. (c) Feng, L.; Campbell, E. B.; Hsiung, Y.; MacKinnon, R. Science 2010, 330, 635− 641. (d) Brotherhood, P. R.; Davis, A. P. Chem. Soc. Rev. 2010, 39, 3633−3647. (e) Gale, P. A. Acc. Chem. Res. 2011, 44, 216−226. (f) Davis, J. T.; Okunola, O.; Quesada, R. Chem. Soc. Rev. 2010, 39, 3843−3862. (13) (a) Lin, J.; Martí-Rujas, J.; Metrangolo, P.; Pilati, T.; Radice, S.; Resnati, G.; Terraneo, G. Cryst. Growth Des. 2012, 12, 5757−5762. (b) Nelyubina, Y. V.; Antipin, M. Y.; Dunin, D. S.; Kotovb, V. Y.; Lyssenko, K. A. Chem. Commun. 2010, 46, 5325−5327. (c) Schneider, D.; Schuster, O.; Schmidbaur, H. Organometallics 2005, 24, 3547− 3551. (d) Blake, A. J.; Gould, R. O.; Li, W.-S.; Lippolis, V.; Parsons, S.; Radek, C.; Schro1der, M. Inorg. Chem. 1998, 37, 5070−5077. (14) Yoon, J.; Kim, S. K.; Singh, N. J.; Kim, K. S. Chem. Soc. Rev. 2006, 35, 355−360.
20.282 Å between them (Supporting Information), which effectively closes the pocket from either side (Figure 2c). Imidazolium molecular systems are generally utilized as very good receptors for the recognition of anions by direct interaction between the cationic host and the anionic guest.14 But in the present system of 1, the cationic macrocycles hold the guest I− ions via interactions with neutral methanol molecules. The supramolecular assembly of I− ions and methanol molecules was further inspected to discover a short contact between the two I− ions within a distance of ∼3.7 Å, which is less than the sum of ionic radii of I− ions (4.12 Å). The three methanol molecules are strongly hydrogen bonded to each of the I− ions orienting the anions toward each other (Figure 3a) (Supporting Information). Although the two negatively charged I− ions should strongly repel each other, the overall supramolecular forces inside the pocket compel them to be in close proximity. The orientation of methanol molecules in the supramolecular assembly is comparable to the staggered form of an ethane molecule (Figure 3b). In conclusion, we have successfully synthesized a hexagonal Sn6-organotin 42-membered macrocycle. Moreover, this symmetric macrocycle contains a rare instance of a I−---I− short contact by creating a supramolecular pocket in crystal packing involving noncovalent interactions with solvents of crystallization.
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ASSOCIATED CONTENT
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AUTHOR INFORMATION
S Supporting Information *
Crystallographic information file (CIF) for compound 1, some additional diamond figures and thermogravimetric curve for compound 1. This material is available free of charge via the Internet at http://pubs.acs.org/. Corresponding Author
*E-mail:
[email protected];
[email protected]. Phone: (+91) 512-2597259. Fax: (+91) 521-259-0007/7436. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank the Department of Science and Technology, India, and the Council of Scientific and Industrial Research, India, for financial support. V.C. is thankful to the Department of Science and Technology for a J. C. Bose fellowship. C.M. thanks the UGC, India, for a Senior Research Fellowship and S.T. thanks CSIR, India, for a Senior Research Fellowship.
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REFERENCES
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