Protonated Dipyrromethenes and Tetrahalozinc Anions as Synthons in the Solid State Ji-Young Shin, David Dolphin,* and Brian O. Patrick Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 4 659-661
Received January 2, 2004
ABSTRACT: (HL)2ZnBr4 and (HL)2ZnCl4 were prepared by the addition of HBr or HCl into a CH3CN solution of Zn(II)L2, and their structures were determined by X-ray diffraction analysis. The X-ray crystallographic data show super structures that have hydrogen bonds between the tetrahalozinc anions ([ZnX4]2-) and the protonated dipyrromethene cations. The chemistry of inter- and intramolecular interactions that result in the self-assembly of supramolecules is attracting considerable interest in many diverse areas of chemistry, physics, engineering, and crystal design.1-8 While the covalent bond strength is typically 400 kJ/mol, the bond strengths associated with hydrogen bonding and π-π stacking interactions, which have been recognized as playing key roles in the formation of supramolecular structures, are less than 40 kJ/mol. The identification of such weak noncovalent interactions between chemical species in crystals and the comprehension of the roles of these interactions are two of the major issues in crystal engineering and design today. Porphyrins and related polypyrrolic systems have been suggested as interesting building blocks for such assemblies since they can exhibit all of these interactions,9,10 and several of our studies in related areas have been previously reported.11-13
Figure 1. X-ray structure of a portion of the unit cell of 4; the hydrogen bonds are denoted by dotted lines. The thermal ellipsoids are scaled to the 50% probability level. The hydrogen atoms, except those on NH, are omitted for clarity.
Dipyrromethenes such as 1 become more stable when substituted by electron withdrawing groups and more conformationally mobile when unsubstituted in the β-positions. To this end, we have examined pentafluorophenyl dipyrromethenes and examined their incorporation into super structures. The dipyrromethene (1) was prepared by oxidation of the corresponding dipyrromethane with 2,3-dichloro5,6-dicyano-1,4-benzoquinone followed by metalation with Zn(II), Cu(II), and Fe(III) using the chloride salts. The Zn(II)L2 (2) and Cu(II)L2 complexes have tetrahedral coordination while Fe(III)L3 (3) has an octahedral coordination. The title compounds, (HL)2ZnBr4 (4) and (HL)2ZnCl4 (5), may be prepared by the addition of H2ZnX4 to the metal-free dipyrromethenes but are best prepared (in 50-60% yield) by the addition of HBr or HCl into a CH3CN solution of 2. HLBr (6) was obtained by treating 3 with excess HBr. The structures were determined by X-ray diffraction analysis.14-16 The insertion of protons between the nitrogen and the Zn(II) center gives rise to the formation of large supramolecules via newly formed hydrogen bonding between the * To whom correspondence should be addressed. E-mail: ddolphin@ qltinc.com.
resulting tetrahalozinc anions, [ZnBr4]-2 or [ZnCl4]-2, and the protonated dipyrromethene cations.14 Figures 1 and 2 show the structural results of the X-ray crystallographic analysis of 4.14 The [ZnBr4]-2 anion is tetrahedral, and the symmetry of the dipyrromethene synthons, along with the C-N-C interior bond angles [(109.7, 109.3, 110.9, and 110.0° for C(8)-N(1)-C(11), C(12)-N(2)-C(15), C(23)-N(3)-C(26), and C(27)-N(4)C(30)], confirm that they are protonated and that the charge is delocalized over the π-system. Each [ZnBr4]-2 forms four different hydrogen bonds with four different dipyrromethene units while the NH groups on each dipyrromethene hydrogen bond to two different [ZnBr4]-2 anions (Figure 2), such that the total charge on the supramolecule is zero. The [ZnBr4]-2 anions are strongly hydrogen bonded within each layer as denoted by the red and blue lines, which exemplify the continuous interaction between the synthons. The hydrogen bond lengths were determined to be between 2.45 and 2.74 Å, which are a little longer than those found with compound 6, due to the Zn(II) center in 4. The molecules of acetone, which was used as a solvent for crystallization, were found in the structure. The longest hydrogen bond of 2.73 Å is formed by an NH
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Figure 3. Crystal structure of 5; the dotted lines are hydrogen bonds. The thermal ellipsoids are scaled to the 50% probability level.
Figure 4. Ribbonlike structure and the packing diagram in a crystal of 6; the dotted lines are hydrogen bonds {bond lengths (Å): 2.15 [N(1)H‚‚‚Br(1)]; 2.26 [N(2)H‚‚‚Br(2)]; 2.39 [N(3)H‚‚‚Br(2)]; 2.41 [N(4)H‚‚‚Br(1)]}.
Figure 2. Supramolecular structures of 4. (a) A single layer; the hydrogen bonds are denoted by dotted lines {bond legths (Å): 2.46 [N(1)H‚‚‚Br(3)]; 2.52 [N(2)H‚‚‚Br(4)]; 2.63 [N(3)H‚‚‚Br(2)]; 2.73 [N(4)H‚‚‚Br(1)]; 2.60 [N(4)H‚‚‚O(1)]}. (b) Packing diagram of the layers. (c) A side view showing π-π stacking interactions.
group and the oxygen of the acetone. In addition, π-π interactions are found between the layers as determined by an interplanar distance of 3.59 Å (Figure 2c, letter a). The nearest Zn atoms were found to be at 11.60 and 10.06 Å within a layer and at 10.46 and 9.75 Å between the layers (i.e., the distances between Zn1 and Zn2, Zn1 and Zn3, Zn1 and Zn1′, and Zn1 and Zn2′, respectively). The structure of 5 was also verified by X-ray diffraction analysis,15 and the resulting structure is shown in Figure 3. Similarly to compound 6, the pyrrole interior C-N-C
angles reveal amino type nitrogen atoms [109.3° for C(1)N(1)-C(8) and 109.6° for C(12)-N(2)-C(15)] in the pyrrole rings, and the bond lengths of the dipyrromethene skeleton reveal delocalization of the charge through the conjugated π-system. However, in the case, each extended layer is related by a C2 axis to the one above and below it (a,a′,a,a′,a) whereas in compound 4 the layers are a,a,a,a,a (see the Supporting Information). The hydrogen bond lengths for N-H‚‚‚Cl were between 2.28 and 2.54 Å, a little shorter than in 4 due to the smaller van der Waals radius of chlorine. Contrary to the layered structures exhibited in the former two solids, the structure of 6 (Figure 5),16 lacking the tetrahalozinc anions, shows a ribbonlike system with H-bond lengths between 2.14 and 2.42 Å. Interestingly, the ribbonlike structure exhibits a composite structure of Rand β-helixes (Figure 4). The anion binding properties of dipyrromethenes described here follow previous studies on anion binding using other polypyrrolic systems including calixpyrroles17 as well as porpyrins18 and expanded porphyrins.19 The dipyrromethenes exhibit rotation of the pyrrolyl groups around the central methine linkage, and configurations such as a, b, and c can exist. Metal complexes, of course, adopt configuration b while all of the complexes reported here exhibit configuration a. We have also shown,
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References
Figure 5. Crystal structure of 6; the dotted lines are hydrogen bonds. The thermal ellipsoids are scaled to the 50% probability level.
and will report shortly,20 on a dipyrromethene-quinone complex that contains configuration c.
The synthetic methods reported here allow for the assembly of dipyrromethens and anions into three-dimensional arrays. Studies on these systems with other dipyrromethenes, metals and anions, are continuing. Acknowledgment. This work was supported by the Natural Science and Engineering Council (NSERC) of Canada. We thank the NMR spectroscopy lab of the Department Chemistry and the Mass spectroscopy lab of the Department of Chemistry. Supporting Information Available: Experimental procedure, spectral data for compounds 2-6, and structural proof (CIF). This material is available via the Internet at http://pubs.acs.org.
(1) Desiragu, G. R. Crystal Engineering: The Design of Organic Solids; Elsevier: Amsterdam, 1989. (2) Lehn, J.-M. Supramolecular Chemistry: Concepts and Perspectives; VCH: Weinheim, 1995. (3) Comprehensive Supramolecular Chemistry; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Vogtle, F., Eds.; Pergamon: Oxford, 1996. (4) Desiraju, G. R. Nature 2001, 412, 397-400. (5) Hollingsworth, M. D. Science 2002, 295, 2410-2413. (6) MacDonald, J. C.; Dorrestein, P. C.; Pilley, M. M.; Foote, M. M.; Lundburg, J. L.; Denning, R. W.; Schultz, A. J.; Manson, J. L. J. Am. Chem. Soc. 2000, 122, 11692. (7) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629. (8) Sommerdijk, N. A. J. M. Angew. Chem., Int. Ed. 2003, 42, 3572. (9) Sharma, C. V. K.; Broker, G. A.; Huddleston, J. G.; Baldwin, J. W.; Metzger, R. M.; Rogers, R. D. J. Am. Chem. Soc. 1999, 121, 1137-1144. (10) Yanagi, H.; Mukai, H.; Ikuta, K.; Shibutani, T.; Kamikado, T.; Yokoyama, S.; Mashiko, S. Nano Lett. 2002, 2, 601-604. (11) Chen, Q.; Dolphin, D. Can. J. Chem. 2002, 80, 1668. (12) Thompson, A.; Rettig, S. J.; Dolphin, D. Chem. Commun. 1999, 631. (13) Zhang, Y.; Thompson, A.; Rettig, S. J.; Dolphin, D. J. Am. Chem. Soc. 1998, 120, 13537. (14) Crystal data of 4: C30H16N4F10ZnBr4‚C3H6O, T ) 173 K, Mw ) 1065.54, monoclinic, P21/n (14), a ) 10.4590(7) Å, b ) 18.2100(9) Å, c ) 20.058(1) Å, β ) 105.072(2)°, V ) 3688.8(3) Å3, Dc ) 1.919 g cm-3, Z ) 4, R1 ) 0.031 [I > 3σ(I)], wR2 ) 0.096 (all data), GOF ) 0.84. (15) Crystal data of 5: C30H16Cl4N4F10Zn, T ) 173 K, Mw ) 829.66, orthorhombic, Pbcn (60), a ) 14.6458(6) Å, b ) 11.9140(6) Å, c ) 18.0743(9) Å, V ) 3153.8(4) Å3, Dc ) 1.747 g cm-3, Z ) 4, R1 ) 0.027 [I > 3σ(I)], wR2 ) 0.070 (all data), GOF ) 0.93. (16) Crystal data of 6: C15H8N2F5Br, T ) 173 K, Mw ) 391.14, triclinic, P1 h (2), a ) 8.2509(2) Å, b ) 10.9918(1) Å, c ) 17.5200(6) Å, R ) 79.767(9)°, β ) 79.310(9)°, γ ) 73.066(7)°, V ) 1480.7(1) Å3, Dc ) 1.754 g cm-3, Z ) 4, R1 ) 0.043 [I > 3σ(I)], wR2 ) 0.149 (all data), GOF ) 1.13. (17) Bucher, C.; Zimmerman, R. S.; Lynch, V.; Kra, V.; Sessler, J. L. J. Am. Chem. Soc. 2001, 123, 2099-2100. (18) Kral, V.; Furuta, H.; Shreder, K.; Lynch, V.; Sessler, J. L. J. Am. Chem. Soc. 1996, 118, 1595-1607. (19) Shionoya, H.; Furuta, H.; Lynch, V.; Harriman, A.; Sessler, J. L. J. Am. Chem. Soc. 1992, 114, 5714-5722 and references therein. (20) Shin, J.-Y.; Dolphin, D.; Patrick, B. O. Unpublished results.
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