“Cyclic Tetramer” vs “Dimer of Cyclic Dimer”: Subtle Anion Effects on

CRYSTAL GROWTH & DESIGN

“Cyclic Tetramer” vs “Dimer of Cyclic Dimer”: Subtle Anion Effects on the Cyclization of AgBF4 vs AgClO4 with Bis(3-pyridyl)dimethylsilane

2002 VOL. 2, NO. 6 497-499

Ok-Sang Jung,*,† Young-A Lee,† Yun Ju Kim,† and Jongki Hong‡ Materials Chemistry Laboratory, Korea Institute of Science and Technology, Seoul 136-791, Korea, and Korea Basic Science Institute, Seoul 136-701, Korea Received July 19, 2002;

Revised Manuscript Received August 21, 2002

Downloaded by UNIV OF MANITOBA on September 8, 2015 | http://pubs.acs.org Publication Date (Web): September 10, 2002 | doi: 10.1021/cg025555f

ABSTRACT: Subtle anion effects have been observed for the cyclization of AgX (X- ) BF4- vs ClO4-) with bis(3-pyridyl)dimethylsilane. For the two similar anions, BF4- affords a “cyclic tetramer” with two independent spaces, while ClO4affords a “dimer of cyclic dimer” via an unusual intercyclic argentophilic interaction. For BF4-, the specific X-‚‚‚H-C interactions seem to play an important role in the formation of the cyclic tetramer. Recent developments on anion chemistry include exciting advances in anion template assembly, ion-pair recognition, ionic liquids, lithium battery, catalysis, and biological processes.1-8 Formation of specific macrocyclic receptors capable of recognizing anions is dependent upon effectively addressing the anionic features.9-12 However, the constructions of new motifs via anion templates are often serendipitous owing to the coexistence of subtle factors such as π-π stackings, specific noncovalent interactions, and hydrogen bonds.13-18 Among polyatomic anions, BF4- and ClO4- are very similar in geometry, charge, size, coordinating ability, and hydrophilicity, and thus delicate differences between both anions have been controversial.10,19,20 Furthermore, the two anions have been used in diverse fields such as oxidants, explosive materials, solid rocket propellants, and electrolytes in dry cells.5,21,22 This communication reports subtle anion effects and structures on the discrete macrocyclization of AgX (X- ) BF4- vs ClO4-) with bis(3pyridyl)dimethylsilane (Me2Si(3-Py)2 ) L). L is a new ligand that may possess a unique tetrahedral angle around the silicon atom, flexible angles (N-Si-N), an appropriate bipyridyl length, conformational nonrigidity, and manageable properties. Silver(I) ion has been employed as angular directional units of linear or T-shaped geometry.24-26 L was simply prepared by the reaction of dichlorodimethylsilane with m-bromopyridine.27 The slow diffusion of AgX (X- ) BF4- and ClO4-) with L afforded unique macrocycles (Scheme 1). The products were not significantly affected by the change of reactant mole ratios, solvents, and the concentrations. The colorless crystalline compounds are air-stable, and are insoluble in water and common organic solvents. They are easily dissociated in Me2SO or acetonitrile. The products are remarkable in that there is no evidence for usual polymerization even under the high concentration despite the lack of protective groups. X-ray characterizations28 on single crystals have provided discrete skeletons composed of the building block, [Ag(L)]X (1: X- ) BF4-; 2: X- ) ClO4-) (Figure 1). For 1, L connects two Ag(I) ions (Ag-N ) 2.127(4)-2.135(4) Å) to form a 32membered cyclic [Ag(L)]4. The angles around the twocoordinate Ag(I) ion (N-Ag-N ) 169.4(2)° and 176.3(2)°) are slightly deviated from an ideal linear geometry. The most salient feature is that the dimethyl groups of L divide the 32-membered ring in half, resulting in the formation of two independent cyclic cages, which can be described as * To whom correspondence should be addressed. Fax: +82-2-958-5089. E-mail: [email protected]. † Korea Institute of Science and Technology. ‡ Korea Basic Science Institute.

Scheme 1

“molecular goggles”. Each BF4- anion is nestled in an independent cyclic cage. For 2, L connects two Ag(I) ions (Ag-N ) 2.128(6)-2.159(5) Å) to form a 16-membered cyclic [Ag(L)]2. Each ClO4- anion is inserted in the 16membered ring. The cyclic dimer further associates into another dimer via an intermolecular Ag‚‚‚Ag interaction (3.145(1) Å);23 this leads to a tetranuclear superstructure, [[Ag(L)]2]2, “dimer of cyclic dimer”. As concrete evidence of the argentophilic interaction, the angle around the Ag(I) ion without the Ag‚‚‚Ag interaction approximates linear (N-Ag-N ) 178.0(2)°), whereas the corresponding angle (168.9(2)°) with the Ag‚‚‚Ag interaction is fairly bent from 180°. Furthermore, a ClO4- is around the argentophilicfree Ag(I) ion (2.83 Å). The shortest intersuperstructural Ag‚‚‚Ag distance is 3.65 Å. The overall molecular structure looks like “eyeglasses”. To investigate the receptor features of the macrocyclic compounds, anion exchange was accomplished according to the literature procedures.29,30 Initial evaluation revealed that the anion exchange of 1 with ClO4- anion occurs smoothly. The anion exchange was monitored by the appearance of the ClO4- bending band at 622 cm-1 since the ClO4- stretching bands (1096 cm-1) overlap with the corresponding band of the BF4- (1060 cm-1). The BF4anions were completely exchanged by the ClO4- ions after

10.1021/cg025555f CCC: $22.00 © 2002 American Chemical Society Published on Web 09/10/2002

Downloaded by UNIV OF MANITOBA on September 8, 2015 | http://pubs.acs.org Publication Date (Web): September 10, 2002 | doi: 10.1021/cg025555f

498

Crystal Growth & Design, Vol. 2, No. 6, 2002

Communications

Figure 1. Crystal structures of 1 (top) and 2 (bottom).

20 h (Supporting Information). The elemental analysis of the exchanged species (Found: C, 34.50; H, 3.27; N, 6.65) is satisfactory. The other peaks of the IR spectrum remain virtually unchanged, suggesting that the tetrameric skeleton is retained after the anion exchange. Furthermore, the XRD pattern of the exchanged species is very similar to that of 1 but is quite different from that of 2 (Supporting Information). Thus, the anion exchange may be applied as a tailored strategy that cannot be synthesized by the direct reaction. For the reverse exchange of the exchanged species, [Ag(L)]4(ClO4)4 with BF4-, after 1 day about 50% has occurred. The reverse exchange suggests that only the anions outside the cavity are exchanged. The anion exchange of 2 with BF4- does not occur even for the outside anions, presumably due to the ClO4-‚‚‚Ag(I) interactions (2.83 Å). Of course, the ClO4- anions within the cavity are hardly exchanged by BF4- anions. Thus, the present anion exchange seems to be significantly affected by both the shape of cyclic ring and the nature of anions. L cannot exist as skewed conformations owing to the dimethyl moieties in contrast to the helical tectonics, 3,3′Py2X (X ) O, S).25,26 Thus, L affords unique macrocycles to sustain the tetrahedral geometry of Si(IV) atom. What is the critical driving force for the delicate differences between 1 and 2? Both compounds do not reveal significant angle strains. The differences in size25 and shape between BF4- (51.0 cm3/mol; tetrahedral) and ClO4- (52.1 cm3/mol; tetrahedral) are negligible. Each anion interacts with the acidic 2-H of the pyridyl moiety (X-‚‚‚H-C (BF4- ) 2.47 Å; ClO4- ) 2.56 Å). For 1, specific interaction between BF4and CH3 (BF4-‚‚‚HCH2 ) 2.62 Å) exists, which may be attributed to the goggle cyclic tetramer. The strong electron withdrawing nature of the fluorine atom may induce the interaction. Thus, the orientation of each anion within the cycle is quite different: a BF4- ion occupies the larger space suitable for the BF4-‚‚‚CH3, while a ClO4- ion is inserted into the smaller space through the one oxygen atom. We attribute the formation of each structure to the felicitous “specific noncovalent bonding” rather than the “size-

influence” character. The decomposition temperature of 1 (maximized at 229 °C) is much lower than that of 2 (maximized at 310 °C) (Supporting Information). The thermal stability can be explained in terms of the structural properties including the ring size and anion stability. In conclusion, the self-assemblies of AgX (X- ) BF4- vs ClO4-) with the new linker L afforded an interesting pair of discrete macrocyclic receptors. A direct comparison on very similar anions represents an important conceptual advance: a delicate difference of spacer results in a delicate difference of product. The anion exchange affords a new compound that cannot be synthesized via a direct selfassembly. More systematic studies including related ligands are in progress for more effective rational control. Experimental Section: L: To a solution of 3-bromopyridine (7 mmol) in dry ethyl ether (20 mL) under nitrogen was added dropwise n-butyllithium (7.2 mmol, 2.5 M solution in hexane) at -78 °C. The resulting mixture was stirred at the temperature for 40 min. Dichlorodimethylsilane (3.2 mmol) was slowly added to the yellow suspension at the temperature. Distilled water (20 mL) was added into the reaction solution, and the organic solution layer was separated. The organic solution was washed with water (2 × 10 mL), and then was dried over MgSO4. The crude product was purified by column chromatography on silica gel with ethyl acetate. Yield, 52%. Anal. Calcd for C12H14N2Si: C, 67.24; H, 6.58; N, 13.07. Found: C, 67.10; H, 6.48; N, 13.14. 1H NMR (300 MHz, CDCl3, Me4Si): δ ) 0.63 (s, 3H), 7.14 (m, 1H), 7.65 (dd, 1H), 8.49 (dd, 1H), 8.59 (s, 1H). 13C NMR (125.76 MHz, CDCl3, Me4Si): δ ) -2.7, 123.5, 132.1, 141.9, 150.7, 154.6. EI-MS (80 eV): 214.1 [M+]. 1: A methanol solution (6 mL) of L (43 mg, 0.2 mmol) was slowly diffused into an aqueous solution (6 mL) of AgBF4 (39 mg, 0.2 mmol). Colorless crystals formed at the interface, and were obtained in 3 days in 72% yield. Anal. Calcd for C12H14N2AgBF4Si‚H2O: C, 33.75; H, 3.78; N, 6.56. Found: C, 33.50; H, 3.68; N, 6.54. IR (KBr, cm-1): ν(BF4),

Communications

Crystal Growth & Design, Vol. 2, No. 6, 2002 499

1060 (s). Using acetone or ethanol instead of methanol, the same crystals were obtained. 2: A methanol solution (6 mL) of L (43 mg, 0.2 mmol) was slowly diffused into an aqueous solution (6 mL) of AgClO4 (41 mg, 0.2 mmol). Yield, 82%. Anal. Calcd for C12H14N2AgClO4Si: C, 34.18; H, 3.35; N, 6.64. Found: C, 34.10; H, 3.38; N, 6.64. IR (KBr, cm-1): ν(ClO4), 1086 (s). Acknowledgment. This work is supported in part by the Ministry of Science and Technology in Korea. Supporting Information Available: Details of X-ray data of 1 and 2. X-ray powder patterns, TGA and DSC overlays, and IR spectra of 1, Ag(L)]ClO4, and 2. This material is available free of charge via the Internet at http://pubs.acs.org.

Downloaded by UNIV OF MANITOBA on September 8, 2015 | http://pubs.acs.org Publication Date (Web): September 10, 2002 | doi: 10.1021/cg025555f

References (1) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 487. (2) Fleming, J. S.; Mann, K. L. V.; Carraz, C. A.; Psillakis, E.; Jeffery, J. C.; McCleverty, J. A.; Ward,M. D. Angew. Chem., Int. Ed. 1998, 37, 1279. (3) Schmidtchen, F. D.; Berger, M. Chem. Rev. 1997, 97, 1609. (4) Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772. (5) Jureviciute, I.; Bruckenstein, S.; Hillman, A. I. J. Electroanal. Chem. 2000, 488, 73. (6) Fenton, D. E. Pure Appl. Chem. 1986, 58, 1437. (7) LaPointe, R. E.; Roof, G. R.; Abboud, K. A.; Klosin, J. J. Am. Chem. Soc. 2000, 122, 9560. (8) Scheffzek, K.; Klebe, C.; Tritz-Wolf, F.; Kabsch, W.; Wittinghofer, A. Nature 1995, 374, 378. (9) Keller, S. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 247. (10) Schnebeck, R.-D.; Freisinger, E.; Lippert, B. Angew. Chem., Int. Ed. 1999, 38, 168. (11) Campos-Fernandez, C. S.; Clerac, R.; Dunbar, K. R. Angew. Chem., Int. Ed. 1999, 38, 3477. (12) O′Keefe, B. J.; Steel, P. J. Inorg. Chem. Commun. 2000, 3, 473. (13) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311. (14) Mason, S.; Clifford, T.; Seib, L.; Kuczera, K.; BowmanJames, K. J. Am. Chem. Soc. 1998, 120, 8899. (15) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460.

(16) Cotton, F. A.; Lin, C.; MuRillo, C. A. Acc. Chem. Res. 2001, 34, 759. (17) Biradha, K.; Zaworotko, M. J. J. Am. Chem. Soc. 1998, 120, 6431. (18) Lee, Y.-A.; Jung, O.-S. Angew. Chem., Int. Ed. 2001, 40, 3868. (19) Gale, P. A. Coord. Chem. Rev. 2001, 213, 79. (20) Migdal-Mikuli, A.; Mikuli, E.; Hetmanczyk, L.; Sciesinska, E.; Sciesinki, J.; Wrobel, S.; Gorska, N. J. Mol. Struct. 2001, 596, 123. (21) Paskal, J.-L.; Favier, F. Coord. Chem. Rev. 1998, 178-180, 865. (22) Susarla, S.; Collette, T. W.; Garrison, A. W.; Wolfe, N. L.; Mccutcheon, S. C. Environ. Sci. Technol. 1999, 33, 3469. (23) Jung, O.-S.; Park, S. H.; Park, C. H.; Park, J. K. Chem. Lett. 1999, 923. (24) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T. Adv. Inorg. Chem. 1999, 46, 173. (25) Jung, O.-S.; Kim, Y. J.; Lee, Y.-A.; Park, J. K.; Chae, H. K. J. Am. Chem. Soc. 2000, 122, 9921. (26) Jung, O.-S.; Kim, Y. J.; Lee, Y.-A.; Chae, H. K.; Jang, H. G.; Hong, J. Inorg. Chem. 2001, 40, 2105. (27) Schmitz, M.; Leninger, S.; Fan, J.; Arif, A. M.; Stang, P. J. Organometallics 1999, 18, 4817. (28) Crystal data for 1, C24H28N4Ag2B2F8Si2‚2H2O: triclinic, P•, a ) 8.5296(3) Å, b ) 13.4064(4) Å, c ) 14.8556(4) Å, R ) 80.821(2)°, β ) 83.580(2)°, γ ) 76.835(2)°, V ) 1627.89(9) Å3, Fc ) 1.742 Mg m-3, F(000) ) 848, λ ) 0.71073 Å, µ ) 1.352 mm-1, crystal size 0.30 × 0.20 × 0.30 mm, Z ) 2, R (wR2) ) 0.0588 (0.1575) on 7370 unique reflections with I > 2σ(I), GOF ) 1.070, 397 parameters refined. Crystal data for 2, C48H56N8Ag4Cl4O16Si4: momoclinic, P21/c, a ) 12.5075(2) Å, b ) 32.3068(7) Å, c ) 15.6988(3) Å, β ) 101.081(1)°, V ) 6225.3(2) Å3, Fc ) 1.800 Mg m-3, F(000) ) 3360, λ ) 0.71073 Å, µ ) 1.559 mm-1, crystal size 0.20 × 0.20 × 0.50 mm, Z ) 4, R (wR2) ) 0.0637 (0.1716) on 13 398 unique reflections with I > 2σ(I), GOF ) 1.1037, 757 parameters refined. Program used: SHELXS-97 and SHELXL-97: G. M. Sheldrick, University of Go¨ttingen, Germany, 1997. (29) Yaghi, O. M.; Li, H.; Davies, C.; Richardson, D.; Groy, T. L. Acc. Chem. Res. 1998, 31, 474. (30) Jung, O.-S.; Kim, Y. J.; Kim, K. M.; Lee, Y.-A. J. Am. Chem. Soc. 2002, 124, 7906.

CG025555F