Supramolecular Architectures of Metal-Containing Macrocycles and a

Jul 11, 2007 - Telecommunication Technology Labs, China Academy of ... ABSTRACT: Three new supramolecular structures, [(CuCl)2L2](Cl)2‚3H2O (1), ...
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Supramolecular Architectures of Metal-Containing Macrocycles and a One-Dimensional Supramolecular Structure Based on a Flexible Ligand with an Azobenzene Group Qingdao Zeng,*,† Min Li,† Dongxia Wu,† Caiming Liu,† Shengbin Lei,‡ Shiyan An,§ and Chen Wang*,‡

CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 8 1497-1500

Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100080, P. R. China, National Center for Nanoscience and Technology, Beijing 100080, P. R. China, and EnVironmental Protection Test Department, China Telecommunication Technology Labs, China Academy of Telecommunication Research of MII, Beijing 100045, P. R. China ReceiVed March 16, 2007; ReVised Manuscript ReceiVed May 24, 2007

ABSTRACT: Three new supramolecular structures, [(CuCl)2L2](Cl)2‚3H2O (1), [(CuBr)2L2](Br)2‚3.5H2O (2), and L‚2HClO4 (3), have been prepared by ligand L (L ) 2-py-CH2NHOCPhNdNPhCONHCH2-py-2, py ) pyridine) with CuCl2, CuBr2, and HClO4, respectively. The crystal structures of 1-3 have been determined by single-crystal X-ray diffraction. Both 1 and 2 form interesting [2+2] rectangular macrocycles whose sizes are ca. 15.968 Å × 5.345 Å and 16.007 Å × 5.256 Å, respectively. 3 forms a onedimensional supramolecular structure. Introduction The design and study of various self-assembled hybrid organic-inorganic macrocyclic or polymeric compounds, which form a class of molecular materials with potential applications in catalysis, gas sorption and desorption, fluorescence sensing, optoelectronic devices, molecular magnetism, and receptors,1 is currently one of the most productive and interesting areas of chemical research in modern supramolecular chemistry.2 Ligands containing one or more amide functionality have proved to be useful in self-assembly because they give predictable patterns of hydrogen bonding that can add extra dimensionality and helicity to the supramolecular structures.3 Azobenzene derivatives, typical photochromic compounds, experience photochemical isomerization, which is often accompanied by dramatic changes in molecular geometry, and can offer a wide range of potential functional materials including optical switching, holographic storage, light harvesting, long-term energy storage, and nonlinear optical materials.4 Because of their attractive photosensitive properties, the azobenzene derivatives have been utilized as photoswitching units to control the structure and function of supramolecular systems.5 For such an efficient and controlled assembly to be achieved, a particular metal-ligand combination should give only one optimal metallo-supramolecular structure. In our case, such a design requires a ligand with the correct orientation of coordination sites to form defined closed structures with CuX2. For these purposes, the conformationally flexible dipyridyl ligand consisting of azobenzene group and amide functionality was chosen as a promising dinucleating ligand. The preorientation of L should favor the formation of a rectangle-shaped [2+2] complex on coordination to CuX2. Over the past few years, Fujita et al.,6 Puddephatt et al.,7 Barbour et al.,8 and Stang et al.9 have reported a variety of rectangle-shaped [2+2] complexes. Of great challenge yet importance is to design and discover a new * To whom correspondence should be addressed. Tel: 86-10-82614350. Fax: 86-10-82614350. E-mail: [email protected] (Q.Z.); wangch@ nanoctr.cn (C.H.). † The Chinese Academy of Sciences. ‡ National Center for Nanoscience and Technology. § China Academy of Telecommunication Research of MII.

combination of transition metal, ligand, and other components that can assemble themselves to form stable rectangle-shaped [2+2] complexes with a well-defined geometry and cavity. Recently, we have reported two rare one-dimensional nanometer-sized polycatenane complexes obtained by metal-connected U-shaped ligand.10 As an extension of our study of the construction of new MOFs derived from long flexible ligands via self-assembly, we selected CuX2 units for our assembled systems. Herein, we report three new supramolecular structures, [(CuCl)2L2](Cl)2‚3H2O (1), [(CuBr)2L2](Br)2‚3.5H2O (2), and L‚2HClO4 (3). Both 1 and 2 form interesting [2+2] rectangular macrocyclic structures obtained by a flexible ligand L (L ) 2-py-CH2NHOCPhNdNPhCONHCH2-py-2, py ) pyridine, Chart 1) with Cu(II), whereas 3 forms a one-dimensional supramolecular structure in which the protonated L adopts a Z-like configuration. Experimental Section Synthesis of Ligand L. The ligand was prepared by the reaction of azobenzene-4, 4′-dicarbonyl dichloride (3.07 g, 10 mmol) with 2-(aminomethyl)pyridine (2.16 g, 20 mmol) in dry tetrahydrofuran (100 mL) in the presence of triethylamine (5.7 mL, 40 mmol) under N2. The product was recrystallized from acetone/hexane in 65% yield (2.93 g). 1 H NMR (DMSO): δ 4.62 (s, 4H), 7.29 (s, 2H), 7.37 (m, 2H), 7.78 (m, 2H), 8.03 (m, 4H), 8.16 (m, 4H) 8.54 (s, 2H), 9.36 (s, 2H). Anal. Calcd (%) for C26H22N6O2 (450.5): C, 69.32; H, 4.92; N, 18.66. Found: C, 69.18; H, 4.89; N, 18.73. Synthesis of 1. In an H-tube, L (7 mg, 0.015 mmol) dissolved in 4 mL of EtOH was allowed to diffuse into the water (6 mL) solution of CuCl2·2H2O (3 mg, 0.015 mmol). Single crystals of 1 suitable for singlecrystal X-ray analysis were obtained growing on the wall of the glass recipient in a yield of 51% based on Cu2+. Anal. Calcd (%) for C52H50Cl4Cu2N12O7: C, 51.03; H, 4.12; N, 13.73. Found: C, 51.19; H, 4.19; N, 13.63. Synthesis of 2. A procedure similar to that described above was applied with CuBr2 in place of CuCl2 to obtain small blue crystals in 15 days. Yield: 48% based on Cu2+. Anal. Calcd (%) for C52H51Br4Cu2N12O7.5: C, 44.27; H, 3.64; N, 11.91. Found: C, 44.35; H, 3.72; N, 11.79. Synthesis of 3. In an H-tube, 5 mg (0.015 mmol) of L dissolved in 4 mL of EtOH was allowed to diffuse into the water (6 mL) solution of HClO4 (0.030 mmol). Single crystals of 3 suitable for single-crystal X-ray analysis were obtained growing on the wall of the glass recipient.

10.1021/cg070260t CCC: $37.00 © 2007 American Chemical Society Published on Web 07/11/2007

1498 Crystal Growth & Design, Vol. 7, No. 8, 2007

Zeng et al. Chart 1

Anal. Calcd (%) for C26H24Cl2N6O10: C, 47.94; H, 3.71; N, 12.90. Found: C, 47.85; H, 3.74; N, 12.98. X-ray Crystallographic Analyses. The diffraction data for 1-3 were collected on a Rigaku RAXISRAPID automated diffractometer at room temperature using graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). The structure was solved by direct methods and successive difference maps (SHELXS 97)11 and refined by full-matrix least-squares on F2 using all unique data (SHELXL 97).12 The nonhydrogen atoms were refined anisotropically. Hydrogen atoms were placed in the ideal positions except for those in solvent water molecules in 1 and 2. Crystal data and experimental details for the crystals of 1-3 are given in Table 1.

Results and Discussion Compounds 1 and 2 were synthesized by slow diffusion of an ethanolic solution of L into the water solution of CuCl2 or CuBr2 to give small blue crystals, which were formulated as [(CuCl)2L2](Cl)2‚3H2O (1) or [(CuBr)2L2](Br)2‚3.5H2O (2), on the basis of elemental analysis. Compound 3 was synthesized by slow diffusion of an ethanolic solution of L into the water solution of HClO4 to give yellow crystals, which were formulated as L‚2HClO4 (3). 1-3 are very stable in air at ambient temperature and are almost insoluble in common solvents such as water, alcohol, acetonitrile, chloroform, acetone, and toluene. The X-ray crystal structure analyses at 293 K reveal that compounds 1-3 are crystallized in the monoclinic space group C2/c (Table 1). Crystal Structure of [(CuCl)2L2](Cl)2‚3H2O (1). As shown in Figure 1a, in each L ligand, two phenyl units linked with the azo group take on a trans-conformation, thus forming a Z-shaped ligand, whereas two pyridyl units at the end of each L ligand take on a cis-conformation and are almost parallel with each other, thus forming a flexible ligand. The Cu2+ center in 1 is penta-coordinated by two oxygen atoms of two carbonyl groups from two L ligands, a chloro anion. and two nitrogens of two

pyridine units of two L ligands. The bond lengths of Cu(1)N(1), Cu(1)-N(6), Cu(1)-O(1), Cu(1)-O(2), and Cu(1)-Cl(1) are 1.994(3), 2.003(3), 2.080(2), 2.165(2), and 2.2389(12) Å, respectively. The bond angles of N(1)-Cu(1)-N(6), N(1)Cu(1)-O(1), N(6)-Cu(1)-O(1), N(1)-Cu(1)-O(2), N(6)-Cu(1)-O(2), O(1)-Cu(1)-O(2), N(1)-Cu(1)-Cl(1), N(6)-Cu(1)-Cl(1), O(1)-Cu(1)-Cl(1), O(2)-Cu(1)-Cl(1) are 174.49(12), 90.44(11), 87.72(10), 90.05(11), 95.18(11), 91.28(10), 89.67(9), 89.24(8), 149.01(9), and 119.71(9)°, respectively. All bond distances and angles of the molecule are normal.13 Thus, the coordination polyhedron for Cu(II) is a distorted trigonal bipyramid with two oxygen atoms and one chloro anion at the equatorial positions and two pyridine molecules at the apical positions. 1 forms interesting [2+2] rectangular macrocycles, whose sizes are ca. 15.968 Å × 5.345 Å, and all macrocycles are parallel with one aother (Figure 1b). It is noteworthy that the spaces among the macrocycles are filled with the chlorine atoms that do not participate in coordination (Figure 1c). Crystal Structure of [(CuBr)2L2](Br)2‚3.5H2O (2). The crystal structure of 2 is similar to that of 1. In Figure 2a, the crystal structure of 2 reveals that the Cu2+ center in 2 is also penta-coordinated by two oxygen atoms of two carbonyl groups from two L ligands, a bromo anion, and two nitrogens of two pyridine units from two L ligands. The bond lengths of jCu(1)-N(1), Cu(1)-N(6), Cu(1)-O(1), Cu(1)-O(2), and Cu(1)Br(1) are 2.001(5), 1.998(4), 2.081(4), 2.165(4), and 2.3501(11) Å, respectively. The bond length of Cu(II)-Br is longer than that of Cu(II)-Cl but shorter than that of Cu(I)-Br.14 The bond angles of N(1)-Cu(1)-N(6), N(1)-Cu(1)-O(1), N(6)-Cu(1)O(1), N(1)-Cu(1)-O(2), N(6)-Cu(1)-O(2), O(1)-Cu(1)O(2), N(1)-Cu(1)-Br(1), N(6)-Cu(1)-Br(1), O(1)-Cu(1)Br(1), O(2)-Cu(1)-Br(1) are 173.79(19), 90.00(17), 87.80(17), 90.17(17), 95.66(17), 90.78(16), 89.63(13), 89.29(12), 149.25(13), and 119.97(11)°, respectively. Thus, the coordination

Table 1. Crystallographic Data for 1-3

formula Mr cryst size (mm3) cryst syst space group T (K) a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) Z V (Å3) Dcalcd (g cm-3) µ (mm-1) 2θ scan range (deg) range h range k range l no. of reflns collected no. of unique reflns no. of obsd reflns GOF R1, wR2 [I > 2σ(I)]

1

2

3

C52H50Cl4Cu2N12O7 1223.921 0.81 × 0.28 × 0.19 monoclinic C2/c 293(2) 27.768(6) 12.097(2)) 19.558(4) 90 118.99(3) 90 4 5747(2) 1.408 0.986 4.30-54.96 0-36 0-15 -25 to 22 27 860 6578 4167 0.960 0.0624, 0.1638

C52H51Br4Cu2N12O7.5 1410.776 0.33 × 0.25 × 0.21 monoclinic C2/c 293(2) 27.775(6) 12.304(2) 19.722(4) 90 119.61(3) 90 4 5860(2) 1.591 3.513 3.88-54.96 0-36 0-15 -25 to 22 26 009 6681 3784 1.004 0.0695, 0.1949

C26H24Cl2N6O10 651.42 0.78 × 0.27 × 0.14 monoclinic C2/c 293(2) 37.067(7) 5.1017(10) 15.358(3) 90 108.86(3) 90 4 2748.4(9) 1.574 0.307 3.52-54.96 0-47 0-6 -19 to 18 12 030 3115 2731 1.059 0.0427, 0.1224

Supramolecular Architectures of Metal-Containing Macrocycles

Crystal Growth & Design, Vol. 7, No. 8, 2007 1499

Figure 2. Crystal structure of 2. Hydrogens were omitted for clarity. (b) 2 leads to [2+2] rectangular macrocycles, whose sizes are ca. 16.007 Å × 5.256 Å. The spaces among the macrocycles are filled with the bromine atoms that do not participate in coordination.

Figure 1. (a) Crystal structure of 1. Hydrogens were omitted for clarity. (b) Crystal packing of 1. Notice that 1 leads to [2+2] rectangular macrocycles, whose sizes are ca. 15.968 Å × 5.345 Å. (c) The spaces among the macrocycles are filled with the chlorine atoms that do not participate in coordination.

polyhedron for Cu(II) can be also described as distorted trigonal-bipyramidal with two pyridine molecules occupying the “axial” positions. 2 also forms [2+2] rectangular macrocycles whose sizes are 16.007 Å × 5.256 Å. Figure 2b shows that the spaces between the macrocycles are filled with the bromine atoms that do not participate in coordination. Crystal Structure of L‚2HClO4 (3). As shown in Figure 3a, in each L ligand, two phenyl units linked with the azo group take on a trans-conformation, whereas unlike the L ligand in 1 and 2, two pyridyl units at the end of the protonated L ligand in 3 take on a trans-conformation and are almost parallel to each other, thus forming a Z-shaped cation. Two sorts of hydrogen bonds were observed in the crystal packing of 3: (1) An intermolecular N-H‚‚‚O-Cl hydrogen bond formed through the protonated H attached to the pyridine nitrogen atom from L ligand and an oxygen atom in a perchloride anion (N(1)H‚‚‚O(5): 0.86, 1.96, and 2.806(2) Å, 169.7°, symmetry code 1 ) -x, -y - 1, -z); (2) Another amide-to-amide hydrogen bond (N(2)-H‚‚‚O(1): 0.86, 2.19, and 2.923(2) Å, 143.5°,

Figure 3. (a) Crystal structure of 3. Two pyridyl units at the end of L ligand in 3 take on a trans-conformation. (b) Two types of N-H‚‚‚O hydrogen bonds forming a one-dimensional supramolecular structure.

symmetry code 2 ) x, y - 1, z). Thus, 3 forms a onedimensional supramolecular structure (Figure 3b).

1500 Crystal Growth & Design, Vol. 7, No. 8, 2007

In our recent supramolecular work, we have described two polycatenane structures obtained by Cd(ClO4)2 and Co(ClO4)2 with a flexible U type ligand.10 In this work, two macrocyclic structures were obtained by CuCl2 and CuBr2 with a flexible ligand L. The differences between them may depend on coordination numbers for metal ions and the flexibility of L. The coordination number for Cd2+ or Co2+ is six, thus forming polycatenane structures, whereas the coordination number for Cu2+ is five, favorable to the formation of macrocyclic structures. Unexpectedly, no intermolecular ligand-ligand N-H‚‚‚O hydrogen bonds aligned between layer-layer were observed in 1 and 2 because the Cu2+ center is coordinated by two oxygen atoms of two carbonyl groups from all L ligands in complexes 1 and 2.3

Zeng et al.

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Conclusions In this study, we successfully synthesized and characterized three new supramolecular structures based on ligand L (L ) 2-py-CH2NHOCPhNdNPhCONHCH2-py-2, py ) pyridine). Both 1 and 2 form interesting [2+2] rectangular macrocycles whose sizes are ca. 15.968 Å × 5.345 Å and 16.007 Å × 5.256 Å, respectively. 3 forms a one-dimensional supramolecular structure. The L ligand may take on a cis-conformation to act as a flexible ligand, whereas its protonated L ligand takes on a trans-conformation to form a Z-shaped cation. The L ligands in both 1 and 2 act as flexible ligands to form macrocyclic structures, whereas the L ligand in 3 acts as a Z type cation to form a one-dimensional supramolecular structure. Acknowledgment. The authors thank the National Natural Science Foundation (20103008 20573116 50573089 and 20473097) and the Foundation of the Chinese Academy of Sciences for financial support.

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