CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 9 1669-1671
Communications Supramolecular Assemblies Generated from Both Lone-Pair‚‚‚π and C-H‚‚‚π Binding Interactions Zhengliang Lu,† Patrick Gamez,*,† Ilpo Mutikainen,‡ Urho Turpeinen,‡ and Jan Reedijk*,† Leiden Institute of Chemistry, Leiden UniVersity, P.O. Box 9502, 2300 RA Leiden, The Netherlands, and Department of Chemistry, Laboratory of Inorganic Chemistry, P.O. Box 55 (A. I. Virtasenaukio 1), FIN-00014 UniVersity of Helsinki, Helsinki, Finland ReceiVed May 9, 2007; ReVised Manuscript ReceiVed August 1, 2007
ABSTRACT: Two triazine-based synthons have been designed to generate unique supramolecular self-assembly networks generated by CH/π and lone pair/π interactions. C-H···π and cation‚‚‚π contacts are well-established supramolecular interactions,1,2 and numerous crystallographic examples are regularly reported. In the past 5 years, a new type of noncovalent supramolecular interaction involving aromatic molecules is being considered, namely, the binding association between an anion and an electron-deficient π-ring,3 or even between a lone-pair and an electron-deficient aromatic ring.4 A number of theoretical investigations have shown that the electron-poor 1,3,5-triazine ring may experience favorable binding interactions with an anion.5-7 In 2004, the first two crystallographic proofs of such anion‚‚‚π contacts were concurrently described,8,9 and new examples are now increasingly reported in the literature.3 In the last few years, we have been involved in the design and preparation of triazine-based anion receptors,10 and remarkable solid-state evidence of lone-pair (l.p.)/π pairing was obtained in 2006.11 In the present study, two very simple triazine-based molecules have been synthesized (Scheme 1), which both possess all functional groups required to favor their supramolecular self-assembly via the simultaneous occurrence of C-H‚‚‚π and l.p.‚‚‚π interactions. Compounds 1 and 2 thus hold C-H bonds, C-X bonds (where X is an atom containing electron lone-pairs), electron-rich π rings (phenyl groups), and an electron-poor π ring (1,3,5-triazine moiety) (Scheme 1). 2,4-Chloro-6-diphenylamino-{1,3,5}triazine (1) is easily obtained by the reaction of 1 equiv of diphenylamine with 1 equiv of 2,4,6-trichloro-1,3,5-triazine.12 The crystal structure of 1 is depicted in Figure 1.13 The crystal packing of 1 reveals the expected supramolecular features (Figure 2). Indeed, molecules of 1 are assembled via Csp2-H‚‚‚π and Cl(l.p.)‚‚‚π binding contacts to generate a two-dimensional network. Each molecule of 1 interacts with four neighboring molecules by means of two Cl‚‚‚π associations (the distance Cl17‚‚‚centroid A is 3.396(1) Å; Figure 2) and two weak C-H‚‚‚phenyl supramolecular bonds (the distance H36A‚‚‚centroid B is 2.935(2) Å; Figure 2 and Table 1). The C-H‚‚‚π contact distance is typical for this type of interaction,1,14 and the Cl(l.p.)‚‚‚π separation is in the range of the calculated values15,16 and also in the range of the few experimental examples so far reported.4,11,17 However, the angle θ (which corresponds to the angle between the Cl, the ring centroid, and the aromatic plane; * To whom correspondence should be addressed. Tel: +31 71 5274260. Fax: +31 71 5274671. E-mail:
[email protected]. † Leiden University. ‡ University of Helsinki.
Figure 1. ORTEP drawing and atom numbering of compound 1. Thermal ellipsoids are drawn at the 30% probability level. Table 1. Hydrogen-bonding Parameters for 1 and 2 (see Figures 2 and 4) compound
D-H‚‚‚A
D‚‚‚A (Å)
H‚‚‚A (Å)
DHA (°)
1 2
C36-H36A‚‚‚B C1-H1A‚‚‚B
3.640 3.735
2.935 3.047
132.06 127.42
see Table 2) is 71.86°, which is 28° below the ideal value of 90°,3,5 and thus indicative of weak Cl‚‚‚π interactions. A second supramolecular synthon, namely, 2-diphenylamino4,6-diethoxy-{1,3,5}triazine (2) (Scheme 1), has been prepared from compound 1, through its straightforward reaction with 2 equiv of sodium ethanolate.12 In addition to all functional groups present in 1 (i.e., lone pairs, electron-poor, and electron-rich π-rings), compound 2 also contains Csp3-H bonds, which might also participate in supramolecular bonding interactions. The crystal structure of 2 is depicted in Figure 3.13 As anticipated, the crystal packing of 2 shows that even ethoxy Csp3-H bonds are engaged in C-H/π interactions, albeit these contacts can be considered as weak (Figure 4 and Table 1).18 Thus, each ethoxy group of 2 is connected to an adjacent molecule via a C-H‚‚‚π contact between the proton H1A and a phenyl ring (the distance H1A‚‚‚centroid B amounts to
10.1021/cg0704302 CCC: $37.00 © 2007 American Chemical Society Published on Web 08/15/2007
1670 Crystal Growth & Design, Vol. 7, No. 9, 2007
Communications
Scheme 1. Representation of Compounds 1 and 2, Showing the Functional Groups That Can Be Involved in Supramolecular Interactions
3.047(2) Å; Figure 4 and Table 1). Similarly to 1, the triazine rings are involved in l.p./π associations, and contacts are observed between the oxygen atoms O3 and the triazine ring centroids A (the distance O3‚‚‚centroid A is 3.330(2) Å and the θ angle is equal to 81.55°, reflecting a significant interaction between the two entities; Figure 4 and Table 2). Remarkably, the triazine ring also interacts with the oxygen atoms of two ethoxy groups (belonging to two different molecules of 2; Figure 4), giving rise to an unprecedented l.p.‚‚‚π‚‚‚l.p. motif (see Figure 4). As a result, each molecule of 2 experiences as much as eight supramolecular contacts
Figure 2. Crystal packing of 1 showing the supramolecular network generated from C-H/π and l.p./π interactions. Cl17‚‚‚A ) 3.396(1) Å; C-H36A‚‚‚B ) 2.935(2) Å. Only the hydrogen atoms involved in supramolecular interactions are shown for clarity.
Table 2. l.p.···π Bonding Parameters for 1 and 2a compound
l.p.‚‚‚π
r (Å)
θ (°)
1
Cl17‚‚‚A
3.396
71.86
2
O3‚‚‚A
3.330
81.55
a
See Figures 2 and 4.
Figure 4. Crystal packing of 2 showing the supramolecular one-dimensional chain generated from C-H/π and l.p./π interactions. O3‚‚‚A ) 3.330(2) Å; C-H1A‚‚‚B ) 3.047(2) Å. Only the hydrogen atoms involved in supramolecular interactions are shown for clarity. The red spot are the centers of the aromatic rings; the blue spots are at the centers of the triazine rings.
(four CH/π and four l.p./π noncovalent bonds) producing a onedimensional chain whose building blocks are four-connected to two neighbors (Figure 4). In summary, simple, new multifunctional synthons have been designed with the objective to create supramolecular architectures based on C-H‚‚‚π (which can be symbolized as δ+‚‚‚δ-) and l.p.‚‚‚π (δ-‚‚‚δ+) noncovalent bonding interactions. The successful approach herein reported clearly demonstrates that l.p./π contacts should be considered by the supramolecular chemist as an important type of potential noncovalent bond, like the well-accepted CH/π interaction, to produce novel types of networks. Acknowledgment. This work has been supported financially by the Graduate Research School Combination “Catalysis”, a joint activity of the graduate research schools NIOK, HRSMC and PTN. Financial support from COST Action D35/0011, Dutch WFMO (Werkgroep Fundamenteel Materialen-Onderzoek) CW (Foundation for the Chemical Sciences), and NWO is gratefully acknowledged. Supporting Information Available: Crystal data for compounds 1 and 2 as CIF files. This material is available free of charge via the Internet at http://pubs.acs.org.
References Figure 3. ORTEP drawing and atom numbering of compound 2. Thermal ellipsoids are drawn at the 30% probability level.
(1) Nishio, M.; Hirota, M.; Umezawa, Y. The C-H/π Interactions (EVidence, Nature and Consequences); Wiley-VCH: New York, 1998.
Communications (2) Ma, J. C.; Dougherty, D. A. Chem. ReV. 1997, 97, 1303-1324. (3) Gamez, P.; Mooibroek, T. J.; Teat, S. J.; Reedijk, J. Acc. Chem. Res. 2007, 40, 435-444. (4) Egli, M.; Sarkhel, S. Acc. Chem. Res. 2007, 40, 197-205. (5) Mascal, M.; Armstrong, A.; Bartberger, M. D. J. Am. Chem. Soc. 2002, 124, 6274-6276. (6) Kim, D.; Tarakeshwar, P.; Kim, K. S. J. Phys. Chem. A. 2004, 108, 1250-1258. (7) Quinonero, D.; Garau, C.; Frontera, A.; Ballester, P.; Costa, A.; Deya, P. M. J. Phys. Chem. A. 2005, 109, 4632-4637. (8) de Hoog, P.; Gamez, P.; Mutikainen, H.; Turpeinen, U.; Reedijk, J. Angew. Chem., Int. Ed. 2004, 43, 5815-5817. (9) Demeshko, S.; Leibeling, G.; Dechert, S.; Meyer, F. J. Am. Chem. Soc. 2004, 3782-3787. (10) Mooibroek, T. J.; Gamez, P. Inorg. Chim. Acta 2007, 360, 381404. (11) Mooibroek, T. J.; Teat, S. J.; Massera, C.; Gamez, P.; Reedijk, J. Cryst. Growth Des. 2006, 6, 1569-1574. (12) The solvents used in the reactions were dried according to standard procedures. All reactions were performed under an inert atmosphere, under strictly anhydrous conditions. All chemicals were used as received. Preparation of 1: 5.2 mL (29.9 mmol) of N,N-diisopropylethylamine (DiPEA) were added to a solution of 5.0 g (27.2 mmol) of 2,4,6-trichloro-1,3,5-triazine in tetrahydrofuran (THF) (55 mL). The reaction mixture was cooled to 0 °C, and a solution of 4.6 g (27.2 mmol) of diphenylamine in THF (50 mL) was added dropwise over 1 h at this temperature. After completion of the addition, the reaction mixture was warmed to room temperature, and stirred for an additional two hours. The resulting white precipitate was filtered off through a P4 glass filter, and the orange filtrate was evaporated under reduced pressure. The pure product 1 was obtained after column chromatography as a white crystalline solid. Yield: 4.8 g (55%). Anal. calcd for C15H10Cl2N4 (%): C, 56.80; H, 3.18; N, 17.66. Found: C, 57.80; H, 3.58; N, 17.29. 1H NMR (300 MHz, CDCl3) δ 7.44-7.14 (m, 10H) ppm; 13C NMR (75 MHz, CDCl3) δ 170.6, 165.9, 141.6, 129.5, 127.8, 127.2 ppm. MS-EI+ (m/z) [M]+• 315.98 (calcd 316.03). Preparation of 2: 380 mg of NaH (60% dispersion in mineral oil) was suspended in 30 mL of absolute ethanol. The resulting mixture was stirred for 30 minutes. Next, a solution of 0.75 g (2.37 mmol) of 2,4-chloro-6-diphenylamino-{1,3,5}triazine (1) in THF (20 mL) was added dropwise. After completion of the addition,
Crystal Growth & Design, Vol. 7, No. 9, 2007 1671
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(14) (15) (16) (17) (18)
the reaction mixture was stirred for 2 h at room temperature. The solvent was subsequently removed under reduced pressure. The residue was dissolved in 10 mL of water and extracted with ethyl acetate. The pooled organic layers were dried over MgSO4. The solvent was evaporated under reduced pressure. The crude compound was purified by column chromatography, and the pure compound was obtained as a white crystalline solid. Yield: 0.796 g (97%). Anal. Calcd for C19H20N4O2 (%): C, 67.84; H, 5.99; N, 16.66. Found: C, 67.83; H, 5.79; N, 16.59. 1H NMR (300 MHz, CDCl3) δ 7.37-7.19 (m, 10 H), 4.25 (q, 4H, J ) 7.1 Hz), 1.29 (t, 6H, J ) 7.1 Hz) ppm; 13C NMR (75 Mhz, CDCl ) δ 171.8, 168.1, 143.1, 128.9, 127.8, 3 127.5, 126.2, 63.5, 14.2 ppm. MS-EI+ (m/z) [M]+• 336.85 (Calcd 336.39). Single-crystal X-ray data were collected on a Nonius Kappa CCD diffractometer using Mo-Ka radiation. All the structures were solved by direct methods and refined on F2 using the programs COLLECT and SHELXL-97. The nonhydrogen atoms were refined anisotropically. The H atoms were introduced in calculated positions and refined with fixed geometry with respect to their carrier atoms. Crystal data for C15H10Cl2N4 1: orthorhombic, space group P212121, M ) 317.17, a ) 8.358(2) Å, b ) 9.105(2) Å, c ) 18.954(4) Å, R ) β ) γ ) 90°, V ) 1442.4(6) Å3, Z ) 4, T ) 173(2) K, Dc ) 1.461 g cm-3, F(000) ) 648, Mo-KR radiation (λ ) 0.71073), µ ) 0.447 mm-1, R1 ) 0.0372 and wR2 ) 0.0755, S ) 1.06. Crystal data for C19H20N4O2 2: monoclinic, space group C2/c, M ) 336.39, a ) 16.588(3) Å, b ) 13.599(3) Å, c ) 7.735(2) Å, R ) 90, β ) 107.72(3), γ ) 90°, V ) 1662.1(7) Å3, Z ) 4, T ) 173(2) K, Dc ) 1.344 g cm-3, F(000) ) 712, Mo-KR radiation (λ ) 0.71073), µ) 0.090 mm-1, R1 ) 0.0400 and wR2 ) 0.0907, S ) 1.06. Goswami, S.; Gupta, V. K.; Brahmbhatt, D. I.; Pandya, U. R. J. Chem. Crystallogr. 2007, 37, 213-217. Gallivan, J. P.; Dougherty, D. A. Org. Lett. 1999, 1, 103-105. Reyes, A.; Fomina, L.; Rumsh, L.; Fomine, S. Int. J. Quantum Chem. 2005, 104, 335-341. Ganis, P.; Valle, G.; Pandolfo, L.; Bertani, R.; Visentin, F. Biopolymers 1999, 49, 541-549. Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; John Wiley & Sons, Ltd: Chichester, 2000; p 23.
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