CRYSTAL GROWTH & DESIGN
Tunable Transannular Silver-Silver Interaction in Molecular Rectangles
2004 VOL. 4, NO. 1 23-24
Ok-Sang Jung,* Yun Ju Kim,† Young-A Lee, Shin Won Kang, and Sung Nak Choi Department of Chemistry, Pusan National University, Pusan 609-735, Korea Received June 19, 2003;
Revised Manuscript Received August 25, 2003
ABSTRACT: Slow diffusion of AgX with O(SiMe2(4-Py))2 (L) yields unique molecular rectangles consisting of [Ag(L)]2X2 (X- ) NO3-, ClO4-, PF6-, and CF3SO3-). For the rectangular system, the transannular argentophilic (Ag-Ag) interaction competes with the interaction between Ag(I) and its anions, while the π-π interactions are constantly preserved. The strength of the argentophilic interaction is in the following order: NO3- > ClO4- > PF6- > CF3SO3- and is reversibly stretched via the anion exchange from 3.20(1) to 3.81(1) Å without the destruction of the cyclic skeleton. One of the thematic issues in silver(I) chemistry is the understanding of closed-shell d10 Ag-Ag interactions that give rise to intriguing supramolecular motifs, crystal packing, and specific photophysical properties.1-7 Such metal-metal interactions have often been studied to deduce general structure-stability relationships, and the results can be extended beyond the initial goal to diverse areas such as quantum mechanical calculations, spectroscopic studies, molecular biology, and recognition materials.2,8,9 Thus, the induction and modulation of such metalmetal interactions is a challenging field. Exploitation of silicone-containing pyridine-based units as spacer ligands has not been explored systematically even though only a few cases have shown interesting results.10-12 This communication reports an unprecedented transannular argentophilic interaction that can be modulated via the bite size of counteranions in the molecular rectangles of Ag(I) with 1,3-bis(4-pyridyl)tetramethyldisiloxane (L). L is a new siloxane-containing pyridine that may possess a flexible conformation around the N-Si-Si-N skeleton. Recently, silver(I) ion has been employed as angular directional unit of linear or T-shaped geometry.13 L was prepared by the reaction of 1,3-dichlorotetramethyl-disiloxane with m-bromopyridine.14 Slow diffusion of AgX with L afforded discrete compounds15 in contrast to general bipyridyl analogues (Scheme 1). The reaction was not significantly affected by the change of reactant mole ratios, solvents, and concentrations. The products are colorless crystals that are insoluble in water and common organic solvents. The compounds are not stable in an aqueous suspension state under light. X-ray characterizations16 on single crystals have provided [Ag(L)]2X2 (1, X) NO3-; 2, X- ) ClO4-; 3, X- ) PF6-; and 4, X- ) CF3SO3-) (Figure 1). For 1, L connects two Ag(I) ions (Ag-N ) 2.168(5) to 2.175(5) Å) to form a 24-membered cyclic dimer that may be stabilized via intraligand face-to-face (π-π) stackings (∼3.6 Å). L was used as an unusual horseshoe tectonic. The most salient feature is that the N-Ag-N angle (169.5(2)°) is deviated from an ideal linear geometry. Such a fact indicates that a transannular Ag-Ag interaction (3.20(1) Å) exists in the solid state. The distance is much shorter than the corresponding distance of ligand-unsupported AgAg.3 Interestingly, the NO3- anions weakly bridge to the two Ag(I) ions (Ag‚‚‚O, 2.68 and 2.79 Å). The structures of 2-4 are basically similar to that of 1, but the argentophilic interactions (3.20(1) to 3.81(1) Å) along with their related N-Ag-N angles are very sensitive to the bite size of each anion as shown in Table 1. That is, the Ag-Ag interaction is inversely proportional to the bite size. The NO3- (2.13* Corresponding author. E-mail:
[email protected]. † Present address: Department of Chemistry, Korea University, Seoul 136-701, Korea.
Figure 1. Crystal structures of 1 (top), 3 (middle), and 4 (bottom). The dashed line indicates the transannular argentophilic interactions. The anions of 3 and 4 were omitted for clarity. The structure of 2 was omitted.
Scheme 1
Table 1. Relationship between the Bite Size of Anions and the Argentophilic Interaction compd 1 2 3a 4 a
bite size (Å)
N-Ag-N angle (deg)
Ag-Ag (Å)
Ag‚‚‚X (Å)
2.13(1) 2.36(1)
169.5(2) 171.7(3) 175.5(5) 177.7(2)
3.20(1) 3.41(1) 3.67(1) 3.81(1)
2.68, 2.79 2.75, 2.77
2.39(1)
2.88, 2.88
-
The PF6 anions in 3 hardly interact with the Ag(I) ion and thus are considered to be free anions.
(1) Å), ClO4- (2.36(1) Å), and CF3SO3- (2.39(1) Å) anions exhibit a substantial difference in the bite size. Therefore, the distance of 1 is the shortest, while that of 4 is the longest. In particular, for 4, the molecular rectangle is transformed into a parallelogram to sustain the π-π interactions (3.54 Å for 1; 3.61 Å for 2; 3.51 Å for 3; and 3.61 Å for 4). Thus, a keen competition exists among the Ag-Ag, π-π, and electrostatic interactions.
10.1021/cg0341048 CCC: $27.50 © 2004 American Chemical Society Published on Web 10/23/2003
24
Crystal Growth & Design, Vol. 4, No. 1, 2004
Although the Ag-Ag interaction is inversely proportional to the bite size of the anion, it does not by itself prove that the argentophilic interaction can be tuned via different anions. To investigate such behaviors, anion exchange was accomplished.17 Initial evaluation revealed that the anion exchange anion occurs smoothly, even though the detailed exchange process has been under controversy. The anion exchange of 2 with CF3SO3- was monitored by the appearance of the CF3SO3- band at 1260 cm-1. The ClO4- anions were completely exchanged by the CF3SO3- ions after 20 h (Supporting Information). The elemental analysis of the exchanged species (found: C, 33.20; H, 3.98; and N, 4.85) is satisfactory. The other peaks of the IR spectrum remain virtually unchanged, suggesting that the cyclodimeric skeleton is retained after the anion exchange. The XRD pattern of the exchanged species is also very similar to that of 4 (Supporting Information). The reverse exchange could be easily carried out. All the anions are easily exchanged, but the exchange rate is dependent upon the identity of the anions, the reaction temperature, the mole ratio, and the concentration. A suitable combination of the appropriate length and conformation of L and the linear unit of Ag(I) ion seems to produce the discrete molecular rectangles instead of coordination polymers. Moreover, the intracyclic π-π and argentophlic interactions can contribute to the formation of the discrete molecule irrespective of the anions, the mole ratio, the solvents, and the concentration. In particular, the strength of the transannular aregentophilic interaction corresponds in the order of NO3- > ClO4- > PF6- > CF3SO3- and is reversibly stretched via the anion exchange from 3.20(1) to 3.81(1) Å without the destruction of the cyclic skeleton. What is a critical driving force for the finetuning of the interaction? First of all, this appears to be primarily associated with a nonrigid 24-membered macrocycle. The bite size of each anion plays a crucial role in the tuning of the interaction. The Ag-Ag distance of 3 (3.67(1) Å) is considered to be an anion-free normal interaction since the PF6- is a noncoordinating anion18. In the case of 4, the long biting and coordinating CF3SO3preferably stretches the Ag-Ag interaction. The parallelogram structure of 4 indicates that the Ag-Ag strength is comparable to the π-π interactions. Furthermore, the anion exchange shows that the argentophilic interaction can be controlled without any particular strain. We attribute the formation of each structure to the felicitous combination of size-influence with the electronic effects character. Compounds 1-4 are thermally stable to 192, 230, 230, and 231 °C, respectively (Supporting Information). In conclusion, the unique molecular rectangles demonstrate that the new linker L is a unique horseshoe tectonic that is useful for the construction of molecular rectangles. Our works are the first example to visualize that a transannular argentophilic strength can be tuned by counteranions. The tunable metal-metal interaction, to our knowledge, is an important conceptual advance. The molecular rectangles will be intended to contribute to the development of bond tunable-based materials such as sensors, luminescent materials, or molecular switches. Acknowledgment. This research was supported financially by KRF-2003-015-C00308 in Korea. Supporting Information Available: Details of X-ray data and thermal data of 1-4. IR spectra and XRD powder patterns of samples prepared by anion exchange. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) Jansen, M. Angew. Chem., Int. Ed. Engl. 1987, 26, 10981110.
Communications (2) Pykko¨, P. Chem. Rev. 1997, 977, 597-636. (3) Singh, K. S.; Long, J. R.; Stavropoulos, P. J. Am. Chem. Soc. 1997, 119, 2942-2943. (4) Tong, M.-L.; Chen, X.-M.; Ye, B.-H.; Ji, L. N. Angew. Chem., Int. Ed. 1999, 38, 2237-2240. (5) Jung, O.-S.; Park, S. H.; Park, C. H.; Park, J. K. Chem. Lett. 1999, 923-924. (6) Wang, Q.-M.; Mak, T. C. J. Am. Chem. Soc. 2001, 123, 7594-7600. (7) Jung, O.-S.; Kim, Y. J.; Lee, Y.-A.; Park, J. K.; Chae, H. K. J. Am. Chem. Soc. 2000, 122, 9921-9925. (8) Rawashdeh-Omary, M. A.; Omary, M. A.; Patterson, H. H. J. Am. Chem. Soc. 2000, 122, 10371-10380. (9) Cotton, F. A.; Lin, C.; Murrilo, C. A. Acc. Chem. Res. 2001, 34, 759-771. (10) Schmitz, M.; Leninger, S.; Fan, J.; Arif, A. M.; Stang, P. J. Organometallics 1999, 18, 4817-4824. (11) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A.; Schmitz, M.; Stang, P. J. Inorg. Chem. 2002, 41, 2903-2908. (12) Jung, O.-S.; Kim, Y. J.; Kim, K. M.; Lee, Y.-A. J. Am. Chem. Soc. 2002, 124, 7906-7907. (13) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T. Adv. Inorg. Chem. 1999, 46, 173-303. (14) L: This linker was prepared according to ref 13: Viscous liquid. 70% yield. Anal. Calcd for C14H20N2OSi2: C, 58.29; H, 6.99; N, 9.71. Found: C, 58.10; H, 7.01; N, 9.80. IR (KBr, cm-1): ν(SiO), 1058 (s). 1H NMR (CDCl3, SiMe4): 0.35 (s, 6H), 7.39 (d, 2H), 8.56 (d, 2H). EI-MS (80 eV): 288 [M]+. (15) 1: An ethanol solution (5 mL) of L (58 mg, 0.2 mmol) was slowly diffused into an aqueous solution (5 mL) of AgNO3 (34 mg, 0.2 mmol). Colorless crystals of [Ag(L)](NO3) formed at the interface and were obtained in 3 days in 60% yield. Anal. Calcd for C14H20N3O4Si2Ag: C, 36.69; H, 4.40; N, 9.17. Found: C, 36.50; H, 4.28; N, 9.14. IR (KBr, cm-1): ν(NO3), 1376 (s). 2: 71% yield. Anal. Calcd for C14H20N2ClO5Si2Ag: C, 33.91; H, 4.07; N, 5.65. Found: C, 33.70; H, 4.08; N, 5.63. IR (KBr, cm-1): ν(ClO4), 1088 (s). 3: 75% yield. Anal. Calcd for C14H20N2PF6OSi2Ag: C, 31.06; H, 3.72; N, 5.17. Found: C, 31.20; H, 3.69; N, 5.21. IR (KBr, cm-1): ν(PF6), 830 (s). 4: 73% yield. Anal. Calcd for C15H20N2SF3O4Si2Ag‚CH3OH: C, 33.28; H, 4.19; N, 4.85. Found: C, 33.10; H, 4.01; N, 4.90. IR (KBr, cm-1): ν(CF3SO3), 1260 (s). (16) Crystal data for 1. C14H20N3O4Si2Ag: monoclinic, C2/c, a ) 21.894(2) Å, b ) 14.224(2) Å, c ) 15.819(2) Å, β ) 128.902(2)°, V ) 3834.0(7) Å3, Fc ) 1.588 g cm-3, F(000) ) 1856, λ ) 0.71073 Å, µ ) 1.198 mm-1, crystal size 0.20 × 0.20 × 0.20 mm3, Z ) 4, R (wR2) ) 0.0448 (0.0962) on 4566 reflections with I > 2σ(I), goodness of fit ) 0.0973, 217 parameters refined. Crystal data for 2. C14H20N2O5ClSi2Ag: monoclinic, C2/c, a ) 22.64(1) Å, b ) 14.478(8) Å, c ) 15.369(9) Å, β ) 125.02(1)°, V ) 4125(4) Å3, Fc ) 1.597 g cm-3, F(000) ) 2000, λ ) 0.71073 Å, µ ) 1.248 mm-1, crystal size 0.50 × 0.15 × 0.15 mm3, Z ) 4, R (wR2) ) 0.0746 (0.1816) on 4981 reflections with I > 2σ(I), goodness of fit ) 1.038, 226 parameters refined. Crystal data for 3. C14H20N2F6OPSi2Ag: monoclinic, C2/c, a ) 19.647(5) Å, b ) 8.933(3) Å, c ) 25.427(5) Å, β ) 107.01(3)°, V ) 4267(2) Å3, Fc ) 1.685 g cm-3, F(000) ) 2160, λ ) 0.71073 Å, µ ) 1.189 mm-1, crystal size 0.30 × 0.20 × 0.10 mm3, Z ) 4, R (wR2) ) 0.0771 (0.2132) on 1898 reflections with I > 2σ(I), goodness of fit ) 1.216, 271 parameters refined. Crystal data for 4. C15H20N2F3O4SSi2Ag‚CH3OH: monoclinic, P21/c, a ) 8.6214(7) Å, b ) 27.421(2) Å, c ) 9.9035(9) Å, β ) 92.446(2)°, V ) 2339.2(3) Å3, Fc ) 1.640 g cm-3, F(000) )1168, λ ) 0.71073 Å, µ ) 1.106 mm-1, crystal size 0.30 × 0.30 × 0.20 mm3, Z ) 4, R (wR2) ) 0.0555 (0.1481) on 5639 reflections with I > 2σ(I), goodness of fit ) 0.965, 261 parameters refined. A Bruker SMART automatic diffractometer with a CCD detector at ambient temperature was used. Sheldrick, G. M. SHELXS-97 and SHELXL-97: Programs for Structure Determination and Refinement; University of Go¨ttingen, Germany, 1997. (17) Yaghi, O. M.; Li, H.; Davies, C.; Richardson, D.; Groy, T. L. Acc. Chem. Res. 1998, 31, 474-484. (18) Chew, K. F.; Healy, M. A.; Khalil, M. I.; Logan, N.; Derbyshire, W. J. Chem. Soc., Dalton Trans. 1975, 1315-1358.
CG0341048
