Self-Assembly of Pentaphenol Adducts: Formation of 3D Network and

Self-Assembly of Pentaphenol Adducts: Formation of 3D Network and Ladder-type Supramolecular Structures in the Solid State Akhila Jayaraman, Venkataramanan Balasubramaniam, and Suresh Valiyaveettil* Department of Chemistry, National UniVersity of Singapore, Singapore (S 117543)

CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 3 636-642

ReceiVed June 3, 2005; ReVised Manuscript ReceiVed December 5, 2005

ABSTRACT: The interplay of strong and weak hydrogen bonds has been used to produce self-assembled architectures by the complexation of pentaphenol 1 with the diaza compounds such as pyrazine (pyz), 4,4′-bipyridine (bpy), trans-1,2-bis(4-pyridyl)ethylene (bpy-ethe), and 1,2-bis(4-pyridyl)ethane (bpy-etha). In all cases, the primary recognition patterns involve O-H‚‚‚N and O-H‚‚‚O hydrogen bonds. The crystal structure of complex 1‚pyz involves ladder structures stabilized by π‚‚‚π stacking between the benzene rings of 1 and pyz. Interpenetrating ladder architectures were observed in the crystal lattice of complex 1‚bpy. A network of cyclic cavities and ladder structures dominated the solid lattice of complexes 1‚bpy-ethe and 1‚bpy-etha. Both complexes are isomorphous; they crystallize as dihydrates and also have the same space group, P1h. In the complex 1‚bpy-ethe, the existence of C-H‚‚‚π interactions involving the double bond of the ethene moiety provides additional stabilization to the three-dimensional (3D) network structure. The formation of various supramolecular motifs from the complexes can be attributed to the 3D structure of molecule 1 and the flexibility of the linking aza molecules in the crystal lattice. Introduction Construction of novel supramolecular structures through the application of noncovalent interactions are primarily governed by self-assembly and molecular recognition processes.1 Hydrogen bonding with attributes such as robustness, directionality, and high energy represents one of the most important noncovalent interactions, which plays a pivotal role in the rational control and prediction of the self-assembly processes.2,3 Supramolecular interactions such as strong (O-H‚‚‚O, O-H‚‚‚ N) and weak (C-H‚‚‚O, C-H‚‚‚N, etc.) hydrogen bonds have been utilized in crystal engineering strategies.4,5 The ability of these intermolecular forces to facilitate multipoint recognitions and molecular associations has been exploited for the design of supramolecular assemblies such as interpenetrating networks,6 extended sheet structures,7 molecular tapes,8 columnar,9 and helical assemblies.10 Polyhydroxy compounds represent good hydrogen-bond donor acceptor systems. Interesting supramolecular architectures generated by O-H‚‚‚O interactions were observed in the solid lattice of compounds bearing multiple hydroxyl groups.11-15 The formation of various supramolecular motifs in phenol-pyridine/ amine complexes is governed and directed by strong O-H‚‚‚N hydrogen bonds16,17 and has been utilized in the development of new functional materials.18-20 We have recently reported the solid-state self-assembly of pentaphenol 1, which crystallized as a tetrahydrate, and the water molecules in the cavities adopted a chair conformation of cyclohexane.21 The pentaphenol self-assembles into a threedimensional (3D) superstructure and would form self-assembled molecular complexes with hydrogen-bond acceptors such as aromatic amines due to its propensity to establish O-H‚‚‚N hydrogen bonds. We therefore isolated a series of complexes of pentaphenol 1 with pyrazine (pyz), 4,4′-bipyridine (bpy), trans-1,2-bis(4-pyridyl)ethylene (bpy-ethe), and 1,2-bis(4-pyridyl)ethane (bpy-etha) (Figure 1). It is speculated that the two strong competitive O-H‚‚‚O and O-H‚‚‚N interactions along with the 3D rigid architecture of 1 would ultimately control * To whom correspondence should be addressed. Tel: +65 68744327. Fax: +65 67791691. E-mail: [email protected].

Figure 1. Molecular structure of pentaphenol 1 and aza compounds.

the formation of supramolecular structures in these complexes. The electron-rich heterocyclic systems bearing nitrogen atoms predispose the aza compounds to be good π-donors and hydrogen-bond acceptors. The nature of the bipyridyl molecules introduces considerable free volume changes in the crystal lattice leading to variations in the networks thus formed. The many possible modes of association through strong and weak forces make it interesting to explore the self-assembly of such systems involving multiple hydrogen-bonding sites. Experimental Section The synthesis, characterization, and structural features of pentaphenol 1 has been reported recently.21 Single-Crystal X-ray Diffraction Studies. Single crystals were grown using 1:2.5 stoichiometric ratios of the pentaphenol and aza compounds from appropriate solvents. Good quality crystals were carefully chosen and glued onto a thin glass fiber. X-ray diffraction data on single crystals were collected on a Bruker AXS SMART CCD 3-circle diffractometer with a Mo-KR radiation (λ ) 0.71073 Å). The software used was SMART22 for collecting frames of data, indexing reflections, and determining lattice parameters; SAINT22 for integration of the intensity of reflections and scaling; SADABS23 for absorption correction; and SHELXTL24 for space group determination, structure solution, and least-squares refinements on F2. Structures were solved by direct methods and non-hydrogen atoms were refined anisotropically. Hydrogen atoms were introduced at fixed distances from carbon atoms and assigned fixed thermal parameters. All calculations were performed on a Silicon Graphics workstation, using programs provided by Siemens

10.1021/cg050250x CCC: $33.50 © 2006 American Chemical Society Published on Web 01/21/2006

Self-Assembly of Pentaphenol Adducts

Crystal Growth & Design, Vol. 6, No. 3, 2006 637

Table 1. Crystal Data and Structural Refinements Parameters of Pentaphenol Adducts empirical formula crystal system space group a/Å b/Å c/Å R/° β/° γ/° Z V/Å3 Dcalc/g cm3 absorption coefficient (mm-1) F(000) crystal size mm3 index ranges R (int) max/min transmission data/restraints/ parameters R1 wR2 GOF θ range/° reflns collected independent reflns solvent color/crystal shape

1‚pyz

1‚bpy

1‚bpy-ethe

1‚bpy-etha

C19H16O5‚(C4H4N2)0.5 triclinic P1h 8.2811(7) 8.9677(8) 11.3326(10) 84.957(2) 85.908(2) 78.397(2) 2 819.95(12) 1.476 0.106

C19H16O5‚(C10H8N2)2‚2H2O triclinic P1h 10.1552(6) 11.6299(7) 14.7513(8) 85.2550(10) 87.5750(10) 78.6550(10) 2 1701.69(17) 1.313 0.091



382 0.20 × 0.20 × 0.10 -6 e h e 10 -11 e k e 11 -13 e l e 14 0.0224 0.9895/0.9791

708 0.45 × 0.38 × 0.30 -12 e h e 12 -13 e k e 13 -17 e l e 17 0.0488 0.9731/0.9601

764 0.36 × 0.30 × 0.20 -11 e h e 11 -14 e k e 14 -24 e l e 24 0.0288 0.9822/0.9682

772 0.30 × 0.08 × 0.06 -11 e h e 11 -14 e k e 14 -24 e l e 24 0.0671

3750/0/264

5970/0/593

8356/0/524

6695/0/523

0.0583 0.1367 1.020 1.81 to 27.49 5889 3750 acetone red/needle

0.0546 0.1506 1.036 1.79 to 25 17517 5970 methanol/THF red/block

0.0558 0.1310 1.031 1.94 to 27.50 21637 8356 hot methanol red/block

0.0750 0.1629 1.033 1.02 to 25 1635 6695 hot methanol red/needle

Pvt. Ltd. The important structural and refinement parameters for the pentaphenol adducts are given in Table 1.

Results and Discussion Crystallographic data and detailed discussion of the lattice of pentaphenol 1 have been reported by us earlier.21 The phenol crystallizes out as a tetrahydrate (C19H16O5‚4H2O) and shows a triclinic lattice with a P1h symmetry. Solid-State Self-Assembly of 1‚pyz. Cocrystallization of pentaphenol 1 and pyz from acetone solution gave complex 1‚ pyz. The crystal structure belongs to the triclinic system and has P1h space group. The two molecules lie at independent inversion centers. The ORTEP representation of 1‚pyz is given in Figure 2a. The two reactants interact with each other through O-H‚‚‚N and C-H‚‚‚O hydrogen bonds. All -OH groups participate in intermolecular hydrogen bonding with their neighbors. In such a recognition pattern, the molecules of 1 are held together by O-H‚‚‚O hydrogen bonds that form the rods of the ladder (Figure 2b). The rods are further stabilized by C-H‚‚‚O (H10‚‚‚O2: 2.49 Å) hydrogen bonds. The rods are separated by a distance of approximately 8 Å. The pyz molecules are inserted between the rods as rungs and are held together with the pentaphenol at O-H‚‚‚N and C-H‚‚‚O distances of 1.97(3) and 2.57 Å, respectively. Also, aromatic rings from the neighboring rods are sandwiched between pyz moieties and are stabilized via π‚ ‚‚π interactions (shown by blue dotted lines, Figure 2c). Aromatic rings from the neighboring rods are sandwiched between pyz moieties and are stabilized via π‚‚‚π interactions (shown by blue dotted lines, Figure 2c,d). The distances between the centroids of aza/arene and arene/arene are 4.10 and 3.88 Å, respectively. Interestingly, the neighboring rods are stabilized through π‚‚‚π interactions (arene/arene: 4.62 and 4.0 Å),24 which generate hollow tubular channels inside the lattice (Figure 2d). C-H‚‚‚π interactions in 1‚pyz exist between aryl protons H11 and H18 with π-acceptors, Cg1: (C2-C7) at x, 1 + y, z and Cg2: (C8-C13) at 1 - x, 1 - y, -z, where Cg refers to the ring center of gravity and the numbers represent the phenyl rings

involved in the interactions. The corresponding bond distances and bond angles are H‚‚‚Cg1: 2.61 Å, 155° and H‚‚‚Cg2: 3.22 Å, 132°. Solid-State Self-Assembly of 1‚bpy. Good quality single crystals of complex 1‚bpy‚2H2O were obtained from a solution of 1 and bpy in methanol/THF (1:1) via slow evaporation technique. The asymmetric unit consists of one molecule of the pentaphenol, three molecules of bpy, and two molecules of water. The ORTEP representation is given in Figure 3a. As anticipated, the two reactants interact with each other through strong O-H‚‚‚N hydrogen bonds. The packing of the molecules constitutes an interesting network of ladder-type structures (Figure 3b). Molecules of 1 and water form the rods of the ladder through O-H‚‚‚O hydrogen bonds [O1S-H1SA‚‚‚O1: 2.00(3) Å, 165(3)°; O1S-H1SA‚‚‚O2: 2.50(3) Å, 123(3)°; O2H2A‚‚‚O2S: 1.82(2) Å, 145(3)°, O2-H2A‚‚‚O3(intra): 2.41(3) Å, 103(13)°; O2S-H2S2‚‚‚O5: 1.95(4) Å, 160(3)°; O5H5A‚‚‚O1S: 1.68(3) Å, 171(3)°]. The bpy molecules are inserted as rungs between the rods of the ladder and are connected to the rods through O-H‚‚‚N hydrogen bonds [O-H‚‚‚N: 1.75(3) Å, 159(2)°; 2.04(3) Å, 165(2)°; 2.04(3) Å, 165(2)° and water [1.95(3) Å, 171(3°)] as shown in Figure 3b. In the ladder arrangement, the rungs are stabilized by π‚‚‚π interactions (Figure 3b). The distance between the centroids (aza/aza) is 4.07 Å. Alternate rungs along the ladder direction are separated by a distance of 8 and 12 Å. In two dimensions, these ladders are translated into molecular grids of dimensions, ca. 13 × 12 Å2 and 12 × 9 Å2 (Figure 3b). The center -OH group of the trihydroxylated phenyl ring does not interact with bpy or other phenols but interacts with water molecules in the crystal lattice. The water molecules play a crucial role in the formation of the grids or cavities by linking the molecules of 1 through O-H‚‚‚O hydrogen bonds (Figure 3b). The cavities are masked by off-shifted neighboring layers of hydrogen-bonded chains. The neighboring chains are stabilized by interpenetrating bpy units through O-H‚‚‚N [O4H4‚‚‚N4: 1.92(3) Å, 175(2)°] and C-H‚‚‚O hydrogen bonds [C23-H23‚‚‚O2: 2.41(3) Å, 168(2)°; C11-H11‚‚‚O2S: 2.55-

638 Crystal Growth & Design, Vol. 6, No. 3, 2006

Jayaraman et al.

Table 2. Hydrogen-Bonding Parameters (Å, °) for Pentaphenol Adductsa D-H‚‚‚A

1‚pyz

1‚bpy

1‚bpyethe

1‚bpyetha

d(D-H) d(H‚‚‚A) d(D‚‚‚A) ∠(D-H‚‚‚A)

O1-H1‚‚‚N1 O5-H5‚‚‚O1i O4-H4‚‚‚O2ii O3-H3‚‚‚O5iii O2-H2‚‚‚O3 C10-H10‚‚‚O2iV C21-H21‚‚‚O4V O1S-H1SA‚‚‚O1 O1S-H1SA‚‚‚O2 O1-H1A‚‚‚N1 O1S-H1SB‚‚‚N2Vi O2-H2A‚‚‚O2S O2-H2A‚‚‚O3 O2S-H2S2‚‚‚O5Vii O3-H3A‚‚‚N3Viii O4-H4‚‚‚N4Viii O5-H5A‚‚‚O1Six C11-H11‚‚‚O2Sx C23-H23‚‚‚O2xi O1-H1A‚‚‚N2Vi O 1S-H1SA‚‚‚O2S

0.85(3) 0.84(3) 0.84(3) 0.84(3) 0.78(3) 0.94 0.94 0.85(3) 0.85(3) 0.95(3) 0.84(3) 0.90(3) 0.90(3) 0.93(4) 0.81(3) 0.88(3) 0.92(3) 0.95(3) 0.97(3) 0.92(3) 0.96(3)

1.97(3) 2.06(3) 2.04(3) 1.93(3) 2.21(3) 2.49 2.57 2.00(3) 2.50(3) 1.75(3) 1.95(3) 1.82(2) 2.41(3) 1.95(4) 2.04(3) 1.92(3) 1.68(3) 2.55(3) 2.41(3) 1.87(3) 1.8393)

2.809(3) 2.869(2) 2.875(2) 2.766(2) 2.669(2) 3.217(3) 3.356(4) 2.829(2) 3.046(2) 2.657(2) 2.777(3) 2.606(3) 2.754(2) 2.832(3) 2.831(2) 2.797(2) 2.592(2) 3.240(4) 3.362(3) 2.747(3) 2.778(3)

168(3) 162(2) 169(3) 174(3) 118(3) 135 141 165(3) 123(3) 159(2) 171(3) 145(3) 103(2) 160(3) 165(2) 175(2) 171(3) 130(2) 168(2) 158(3) 169(3)

O1-H1A‚‚‚N2xii O2S-H2SA‚‚‚O5iV O2-H2A‚‚‚O1S O1S-H1SB‚‚‚O3iV O3-H3A‚‚‚O4 (intra) O3-H3A‚‚‚N3 O2S-H2SB‚‚‚N4xiii O4-H4A‚‚‚O5(intra) O5-H5A‚‚‚N1 C34-H34‚‚‚O2xiV C37-H37‚‚‚O2Sx O1S-H1SA‚‚‚O1

0.92(3) 0.86(3) 0.88(3) 0.88(3) 0.90(3) 0.90(3) 0.93(4) 0.84(3) 0.92(3) 0.94 0.94 0.89(6)

1.87(3) 1.95(3) 1.81(3) 1.99(3) 2.44(2) 1.80(3) 1.90(4) 2.25(3) 1.7193) 2.49 2.48 1.89(5)

2.747(3) 2.802(2) 2.678(2) 2.826(2) 2.781(2) 2.661(2) 2.803(3) 2.709(2) 2.633(3) 3.406(3) 3.422(3) 2.777(4)

158(3) 168(3) 171(2) 158(3) 103(2) 160(2) 165(3) 115(2) 175(3) 166 177 171(6)

O1-H1A‚‚‚N3 O1S-H1SB‚‚‚N2xV O2S-H2A‚‚‚O1SVii O3-H3A‚‚‚N1 O2S-H2SB‚‚‚O3 O4-H4A‚‚‚N4xVi O5-H5A‚‚‚O2SxVii C26-H26‚‚‚O5xiV C33-H33A‚‚‚O4ix

0.93(6) 0.87(6) 0.93(5) 0.93(5) 0.84(4) 0.88(5) 0.89(5) 0.94 0.98

1.69(6) 1.95(6) 1.86(5) 1.74(5) 1.96(4) 1.86(5) 1.79(5) 2.51 2.49

2.615(5) 2.778(6) 2.757(5) 2.638(4) 2.787(4) 2.715(4) 2.672(5) 3.435(5) 3.361(5)

173(4) 160(5) 161(4) 162(5) 167(4) 163(5) 169(4) 169 149

a Symmetry codes: (i) -x + 2, -y - 1, -z; (ii) x - 1, y + 1, z; (iii) -x + 1, -y, -z + 1; (iv) 1 + x, 1 + y, z; (v) 1 - x, -y, -z; (vi) 2 - x, 1 y, 1 - z; (vii) x, 1 + y, z; (viii) -1 + x, y, -z; (ix) x, -1 + y, z; (x) -x, 1-y, -z; (xi) 1 - x, 1 - y, 1 - z; (xii) 2 - x, 1 - y, 1 - z; (xiii) -1 x, 1 - y, -z; (xiv) -1 + x, y, z; (xv) -1 - x, -y, -z; (xvi) 3 - x, 1 y, 1 - z; (xvii) 1 + x, y, z.

(3) Å, 130(2)°]. As a result of the interpenetration, the bpy units along the ladder direction are stabilized via π‚‚‚π (4.05, 4.07, and 4.10 Å) and C-H‚‚‚π interactions [C15-H15‚‚‚Cg6(i): 3.12(2) Å, 140(2)°; C28-H28‚‚‚Cg1(ii): 2.77(3) Å, 153(2)°; C30-H30‚‚‚Cg3(iii): 2.93(3) Å, 135(2)° where Cg1: C2-C7; Cg3: C14-C19; Cg6: N3, C35-C39. Symmetry operators are (i) 1 - x, 1 - y, -z (ii) 1 + x, y, z (iii) x, y, z] (Figure 3c). Solid-State Self-Assembly of 1‚bpy-ethe. Cocrystallization of 1 and bpy-ethe from a solution of hot methanol at ambient conditions afforded complex 1‚bpy-ethe as a dihydrate. The crystal structure belongs to the triclinic system and exists in space group, P1h. The ORTEP representation of the complex is shown in Figure 4a. Each molecule of pentaphenol provides four potential proton acceptor sites [two from 1 (intra); one from water; and one from bpy-ethe, (Ar-H)] and five proton donor sites for hydrogen bonding with neighboring molecules. The reactants primarily recognize each other through the formation of O-H‚‚‚N (1.71-1.90 Å) hydrogen bonds. The packing of the molecules inside the lattice generates interesting networks yielding ladders and cyclic assemblies (Figure 4b). In such a recognition pattern, the molecules of 1 and water are held

together by O-H‚‚‚O hydrogen bonds which form the rods of the ladder [O1S-H1SB‚‚‚O3: 1.99(3) Å, 158(3)°; O3-H3A‚ ‚‚O4 (intra): 2.44(2) Å, 103(2)°; O4-H4A‚‚‚O5 (intra): 2.25(3) Å, 115(2)°; O2S-H2SA‚‚‚O5: 1.95(3) Å, 168(3)°]. The distance between the rods is ca. 16 Å. The bpy-ethe molecules are inserted between the rods as rungs, forming O-H‚ ‚‚N hydrogen bonds with both 1 [O3-H3A‚‚‚N3: H‚‚‚N 1.80(3) Å, 160(2)°] and water molecules [O2S-H2SB‚‚‚N4: H‚‚‚N 1.90(4) Å, 165(3)°] as shown in the Figure 4b. The alternate rungs of the ladder run in opposite directions (anti) and are separated by a distance of ca. 11 Å. The C-H‚‚‚π interactions (2.5-3.2 Å) exist between aryl protons (H5, H12, H22, H31, H35, and H38) and π-acceptors C20-C24; C2-C7, N3; C34-C38; C14-C19, N4; C39-C43 and also between the adjacent rungs along the ladder direction (3.02 Å, 139° and 2.84, 145° Å) as shown in Figure 4c. Apart from the ladder-type arrangement, the pentaphenol interacts with bpyethe to form cyclic structures with a dimension of ca. 18 × 14 Å2. The backbone of the cyclic assembly is constructed by four O-H‚‚‚N hydrogen bonds [O1-H1A‚‚‚N2: H‚‚‚N 1.87(3) Å, 158(3)°; O5-H5A‚‚‚N1: H‚‚‚N 1.71(3) Å, 175(3)°]. One of the phenyl rings of the pentaphenol (coded purple) directed into the cavity does not participate in the ring formation but instead helps in chain propagation through interactions with water. The central -OH group on the trihydroxylated ring stabilizes the lattice through the formation of intramolecular hydrogen bonds. The adjacent cavities are stabilized by π‚‚‚π interactions in an inverse fashion (aza/aza: 4.47 Å, 4.51 Å and aza/arene: 4.68 Å), Figure 4b.25 The hydroxyl group of the phenyl ring (O2) directed inside the cavity interacts with a water molecule through O-H‚‚‚O hydrogen bonds [O2-H2A‚‚‚O1S: H‚‚‚O 1.81(3) Å, 171(3)°]. The adjacent chains of ladders and cavities are stacked slight offset and are stabilized by C-H‚‚‚O hydrogen bonds between aza-pentaphenol and aza-H2O [C34-H34‚‚‚O2: H‚‚‚O 2.49 Å, 166°; C37-H37‚‚‚O2S: H‚‚‚O 2.48 Å, 177°]. The complexes pack together through a combination of several intermolecular interactions. The aza/arene, aza/aza, and arene/arene rings from the adjacent layers stack on each other through offset π‚‚‚π interactions. The cyclic assembly is stabilized by C-H‚‚‚π interactions that exist between aryl proton H5 and the ethene moiety (C5-H5‚‚‚C20: 2.59 Å, 174°; C5-H5‚‚‚C21: 2.83 Å, 137° at 1 - x, 1 - y, 1 - z). In the 3D arrangement, the cavities align to yield channels that are sustained by interconnected π‚ ‚‚π interactions (center-to-center distances between the (aza/ aza) rings are 3.65, 3.76, and 4.47 Å).25 Solid-State Self-Assembly of 1‚bpy-etha. The crystal structure of complex 1‚bpy-etha belongs to the triclinic system with a space group of P1h and is isomorphous with 1‚bpy-ethe. The ORTEP representation is given in Figure 5a. The two reactants recognize each other through O-H‚‚‚N couplings, which generate interesting networks consisting of ladders and cyclic assemblies (Figure 5b). The pentaphenol and water molecules interact through O-H‚‚‚O hydrogen bonds and pack into the rods of the ladder that are spaced at a distance of ca. 16 Å [d(H2A‚‚‚O1): 2.34(8) Å; d(H3A‚‚‚O2): 2.46(5) Å; d(H2SA‚‚‚O1S): 1.86(5) Å]. The bpy-etha molecules constitute the rungs of the ladder by linking to water and phenol molecules via O-H‚‚‚N bonds [O1S-H1SB‚‚‚N2: 1.95(6) Å, 160(5)°]. The rungs of the ladders are positioned in opposite directions (anti) and are spaced at a distance of ca. 11 Å (Figure 5b). The two-dimensional (2D) cyclic assembly is predominantly formed with O-H‚‚‚N bonds between molecules of pentaphenol and bpy-etha. Along the



Figure 2. (a) ORTEP perspective of the complex 1‚pyz. Thermal ellipsoids are drawn at 50% probability level. (b) Ladder structure formed between 1 and pyz. The reactants recognize each other through O-H‚‚‚N and C-H‚‚‚O hydrogen bonds. Color codes: C, gray; H, green; O, red; N, blue, 3° C, yellow. (c) Representation of interactions between neighboring ladders that are stabilized by weak π‚‚‚π interactions (blue dotted lines). O1-H1‚‚‚N1: 2.809(3) Å, 168(3)°; O5-H5‚‚‚O1(i): 2.869(2) Å, 162(2)°; O4-H4‚‚‚O2(ii): 2.875(2) Å, 169(3)°; O3-H3‚‚‚O5(iii): 2.766(2) Å, 174(3)° O2-H2‚‚‚O3: 2.669(2) Å, 118(3)° C10-H10‚‚‚O2(iv): 3.217(3) Å, 135 °C21-H21‚‚‚O4(v): 3.356(4) Å, 141°. Symmetry operators are (i) -x + 2, -y - 1, -z; (ii) x - 1, y + 1, z; (iii) -x + 1, -y, -z + 1; (iv) -1 + x, 1 + y, z; (v) 1 - x, -y, -z. (d) 3D representation of the packing arrangement. Inset shows the existence of π‚‚‚π interactions between pyz rings and π stabilization in the lattice of 1‚pyz. Strong hydrogen bonds are shown by green dotted lines. Some atoms have been removed for clarity.

hydrogen-bonded chain, weak C-H‚‚‚O bonds exist between the aliphatic -CH and the ortho hydroxyl groups of 1 [C26H26‚‚‚O5: 3.435(5) Å, 169° at (-1 + x, y, z); C33-H33A‚‚‚O4: 3.361(5) Å, 149° at (x, -1 + y, z)]. The hydrogen-

bonded molecular planes are stacked through slight offset to yield channels in 3D, which are stabilized via π‚‚‚π interactions between aza/aza rings (4.59 Å) and aza/arene rings (4.51 Å, 3.81 Å, 3.78 Å).25 C-H‚‚‚π interactions exist between aryl


Figure 3. (a) ORTEP representation of complex 1‚bpy. Thermal ellipsoids are drawn at the 50% probability level. (b) Ladder structure formed between 1 and bpy with the latter involved in the formation of the rungs. Also shown are π‚‚‚π interactions (blue dotted lines) between the bpy molecules. (c) C-H‚‚‚π (blue dotted lines) interactions between neighboring molecules in the ladder. Color codes: C, gray; H, green; O, red; N, blue, 3 °C, yellow. Strong hydrogen bonds are shown by green dotted lines. Some hydrogen atoms have been removed for clarity.

protons, H10, H22, H25, H34, H38, H39 with π-acceptors C4C19, N2-C31, C2-C7, N4-C43, N1-C26, and C4-C19. Comparison of the Packing Motifs. A rational analysis of the supramolecular architectures formed by the self-assembled complexes of pentaphenol 1 with diamines such as pyrazine (1‚pyz), 4,4′-bipyridine (1‚bpy), trans-1,2-bis(4-pyridyl)ethylene (1‚bpy-ethe), and 1,2-bis(4-pyridyl)ethane (1‚bpy-etha) is reported. The supramolecular organization in the resulting 3D network generated was found to be controlled by strong O-H‚‚‚N and O-H‚‚‚O hydrogen bonds (Table 2). A schematic

Jayaraman et al.

Figure 4. (a) ORTEP representation of complex 1‚bpy-ethe. Thermal ellipsoids are drawn at the 50% probability level. Color codes: C, gray; H, green; O, red; N, blue. (b) Arrangement of bpy-ethe molecules, as spacers, between the molecules of 1 as viewed along the a-axis. Ladder and cyclic assembly structures observed in the lattice of 1‚bpy-ethe. bpy-ethe forms the rungs of the ladder. Note the presence of π‚‚‚π interactions between rings of adjacent cavities (aza/arene: 4.68 Å; aza/ aza: 4.47 Å). Some hydrogen atoms have been removed for clarity. Hydrogen bonds are represented by dotted lines (coded green); 3° carbon, yellow. The phenyl rings directing into the cavities are coded purple, while the pyridyl rings involved in π‚‚‚π stacking interactions are represented in orange. (c) Edge-to-edge C-H‚‚‚π interactions (coded blue). The C-H‚‚‚π distances and angles are C39-H39‚‚‚C38 (3.02 Å, 139°); C40-H40‚‚‚C37 (2.84 Å, 145°) at (-x -2, -y, -z).

representation of the packing of molecules in the crystal lattice of the complexes of 1 is given in Figure 6. All complexes crystallize in the triclinic system with space group P1h and pack into ladder-type assemblies that show significant differences in their mode of stacking depending on steric factors associated with the aza compounds. Complexes 1‚pyz, 1‚bpy, 1‚bpy-ethe, and 1‚bpy-etha represent examples of purely organic ladders that are rare when compared to organic-inorganic hybrids.26



of the aza compounds (pyz to bpy-etha) leads to an increase in the free volume in the crystal lattice. Interpenetrating ladder structures were observed in the crystal lattice of 1‚bpy. Cyclic structures were formed in 1‚bpy-ethe and 1‚bpy-etha to accommodate the expansion in the lattice. The isomorphous 1‚ bpy-ethe and 1‚bpy-etha have alternate hydrogen-bonded ladder motifs and cyclic assemblies that are stabilized by an interconnected pattern of strong hydrogen bonds and weak aromaticaromatic interactions. Both the complexes crystallize as dihydrates; the water molecules are involved in the formation of ladder structures through O-H‚‚‚O interactions with the reactants. In all the complexes, both intramolecular and intermolecular hydrogen bonds have been observed among the -OH groups (1‚pyz: O2‚‚‚H2-O3; 1‚bpy: O2‚‚‚H2A-O3; 1‚bpyethe: O3‚‚‚H3A-O4 and O4‚‚‚H4A-O5; 1‚bpy-etha: O2‚‚‚ H2A-O1 and O3‚‚‚H3A-O2). The intramolecular hydrogen bonding in the pentaphenol facilitates the ortho -OH groups to be readily available for intermolecular hydrogen bonding with the added bases. These structures demonstrate the usefulness of phenol-pyridine interactions toward the design of intricate supramolecular architectures and the extent to which weak interactions influence the organization of the molecules inside the lattice. Conclusion Figure 5. (a) ORTEP representation of complex 1‚bpy-etha. Thermal ellipsoids are drawn at the 50% probability level. Color codes: C, gray; H, green; O, red; N, blue. (b) Arrangement of bpy-etha molecules as spacers between the molecules of 1 as viewed along the a-axis. (3° carbon, yellow). Ladder and cyclic assembly structures formed in the lattice of 1‚bpy-etha. bpy-etha forms the rungs of the ladder. Note the presence of π‚‚‚π interactions (coded blue) between rings of adjacent cavities (aza/arene: 4.51 Å; aza/aza: 4.59 Å).25 Some hydrogen atoms have been removed for clarity. Strong hydrogen bonds are represented by dotted lines (coded green).

The ladder arrangement in complex 1‚pyz is sustained by molecular π-stacking interactions in three dimensions. Flexibility

A strategy for constructing novel supramolecular assemblies using a pentaphenol building block is described. The aza compounds serve as spacers linking the pentaphenol molecules through O-H‚‚‚N hydrogen bonds to form ladder-type assemblies. The recurring O-H‚‚‚N and O-H‚‚‚O hydrogen bonds in the crystal structure of the self-assembled complexes control the supramolecular organization. Thus, all four complexes represent good examples of purely organic ladders in which the framework is stabilized by strong and weak hydrogen bonds. In summary, the supramolecular synthesis using phenol and aza compounds offers a promising crystal engineering

Figure 6. Schematic representation of the crystal packing in the phenol-pyridine complexes. (A) Packing motif and formation π-stabilized boxes in the lattice of 1‚pyz. (B) interpenetrating ladder structures of 1‚bpy. The bpy units participate in the formation of interpenetrating structures. (C) Formation of cyclic and ladder structures in the crystal lattice of 1‚bpy-ethe and 1‚bpy-etha complexes. Hydrogen bonds are represented by green dotted lines.


strategy to understand the interplay of competitive O-H‚‚‚N/ O-H‚‚‚O hydrogen bonds during the self-assembly process. Acknowledgment. The authors thank Prof. Koh Lip Lin and Ms. Tan Geok Kheng for their assistance in data collection and structure refinements. We thank the National University of Singapore for financial support. All technical support from various laboratories at the Department of Chemistry, National University of Singapore, is acknowledged. Supporting Information Available: Details of crystal coordinates and torsion angles for 1‚pyz, 1‚bpy, 1‚bpy-ethe, 1‚bpy-etha as a CIF file. This material is available free of charge via the Internet at http:// pubs.acs.org.

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CG050250X

Self-Assembly of Pentaphenol Adducts: Formation of 3D Network and

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