Design and Synthesis of Self-assembly Supramolecular Entities

DOI: 10.1021/cg901309b

Design and Synthesis of Self-assembly Supramolecular Entities Based on Noncovalent Interaction of Cucurbit[5]uril, Metal Ions, and Hydroxybenzene or Its Derivatives

2010, Vol. 10 2901–2907

Xing Feng,† Hao Du,† Kai Chen,† Xin Xiao,† Shi-Xia Luo,‡ Sai-Feng Xue,*,† Yun-Qian Zhang,† Qian-Jiang Zhu,† Zhu Tao,† Xiao-Yi Zhang,‡ and Gang Wei*,§ †

Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang 550025, P. R. China, ‡School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550001, P. R. China, and §CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield NSW 2070, Australia Received October 21, 2009; Revised Manuscript Received May 14, 2010

ABSTRACT: Nine supramolecular self-assembly entities consisting of cucurbit[5]uril, potassium salts, and hydroxybenzene or its derivatives were constructed by conventional methods. In this supramolecular architectural system, Q[5]s and the metal ions (Kþ) form infinite chains through coordination and ion-dipole interaction, and the stacking of these supramolecular chains then forms wavelike “walls”. The layers of hydroxybenzene or its derivatives are sandwiched by these wavelike walls, and the counteranions are captured in the molecular channels formed by the supramolecular chains. The gap between the adjacent walls is dependent on the size of the hydroxybenzene or its derivatives.

Introduction Supramolecular self-assembly entities have several attractive features. Various organic building blocks and metal ions have been used to self-assemble a variety of porous one-dimensional, two-dimensional, and three-dimensional networks through or mediated by noncovalent bonds, such as hydrogen bonds, van der Waals interactions, π-π bonding, or metal coordination.1-4 Supramolecular self-assembly entities have attracted widespread scientific attention, owing to their intriguing structure and unusual properties, as well as their potential applications in storage,5-7 separation,8,9 and heterogeneous catalysis.10-12 Therefore, the design and synthesis of materials with nanosized layers, tubes, and pores is of fundamental and practical interest.13-15 Identifying and the rational design of the molecular architecture of various organic building blocks linked by metal ions through self-assembly of multiple molecular components are important subjects in supramolecular chemistry. It is often difficult to predict the exact nature of the final supramolecular self-assembly entity because their structures are highly dependent on the shape, size, and function of the ligands that are used to hold the building blocks together.16 Cucurbit[n]urils (Q[n = 5-10]) are composed of n glycoluril units covalently linked by 2n methylene bridges to form a rigid macrocavitand with two highly polar carbonyl openings.17-22 Similar to the cyclodextrins, each member of the cucurbit[n]uril family has a hydrophobic cavity and two hydrophilic portals. Q[5], as shown in Figure 1, is the smallest member of the cucurbit[n]uril family and has attracted little attention due to the small portals and the small capacity of the cavities. Q[5] and one of its derivatives, decamethylcucurbit[5]uril (Me10Q[5]),23 have been shown to bind small molecules, such as CH4, C2H4, N2, O2, CO2, methanol, and acetonitrile.24-31

Figure 1. Structures of cucurbit[5]uril (a), R-naphthol (1), β-naphthol (2), hydroquinone (3), resorcin (4), and phenol (5).

*To whom correspondence should be addressed. E-mail: (S.-F.X.) gzutao@ 263.net; (G.W.) [email protected]. Fax: (S.-F.X.) (þ86) 851-362-0906; (G.W.) (þ61) 294137044.

Anion encapsulation32,33 has been demonstrated,34 and Cl- is encapsulated in preference to NO3- with La3þ at the portals.35 Recent research has revealed that the Q[5]s have the potential to interact with alkali, alkaline earth, lanthanides, and even uranium metal ions to form interlinked structures or metalorganic frameworks.36-38 Earlier, we found that Q[5] can be used as an inducer to enhance the room temperature phosphorescence (RTP) of R-naphthol (1) and β-naphthol (2) in the presence or in the absence of deoxidant, and in the presence of a heavy atom perturber. The corresponding crystal structures of these RTP systems show similar supramolecular architectures, in which the coordinated Q[5]s and metal ions formed infinite 3 3 3 Mþ-Q[5]-Mþ(H2O)-Mþ-Q[5]-Mþ(H2O)-Mþ-Q[5]-Mþ 3 3 3 chains and the luminophors Rnaphthol (1) and β-naphthol (2) are surrounded by these supramolecular chains. Such novel structures of Q[5]-luminophors-heavy-atom perturber systems could be used to explain the Q[5]-induced RTP of R-naphthol (1) and β-naphthol (2).39 The discovery of these complexes prompted us to design and synthesize novel materials with this supramolecular architecture. In particular, the sandwiched hydroxybenzene or its derivatives could present unusual properties, and the molecular channel constructed from the supramolecular chains and hydroxybenzenes could capture different anions.

r 2010 American Chemical Society

Published on Web 06/18/2010

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On the other hand, the imide moieties on the surface of a Q[n] could be receptors for resorcinol or hydroquinone, which could further strengthen the interaction of the organic molecules with the Q[n] through the hydrogen bonding. Similar works, such as the behavior of hydroquinone in a variety of hydrogen bond donating environments, were explored by Warner and co-workers;40 cocrystallization of phenazine and acridine with phloroglucinol41 and of resorcinol with pyridine42,43 also showed such hydrogen bonding networks. Here, we present a series of crystal structures of Q[5]potassium salts-hydroxybenzene or its derivatives. The potassium salts include KCl, KBr, KI, and KNO3; the hydroxybenzene and its derivatives include R-naphthol (1), β-naphthol (2), hydroquinone (3), resorcin (4), and phenol (5) (Figure 1). A crystal structure of Q[5]-KI is described for comparison, and they all have similar self-assembly architecture. Experimental Section General Materials and Instruments. All the reagents and solvents were commercially available and were used without further purification. Elemental analysis for C, H, and N was done with a PerkinElmer 240C instrument. Infrared spectra were recorded on a Bruker Vertex70 FT-IR spectrophotometer in the region 4000-400 cm-1 using KBr pellets. Thermal analysis was performed on a Netzsch STA 409 PC thermal analyzer at a heating rate of 10 °C/min in nitrogen. X-ray diffraction (XRD) measurements of all sample films on glass were carried out in the transmission mode on a PANalytical-x’pert Pro instrument operating at 40 kV voltage and a current of 30 mA with Cu KR radiation. Preparation of [K2(H2O)3 3 (C30H30N20O10)] 3 2(C10H7OH) 3 2Br 3 2(H2O) (A). A mixture of Q[5] (0.048 g, 0.05 mmol) and KBr (0.036 g, 0.3 mmol) in 10 mL of water was refluxed for 5 min and then filtered. A saturated solution of R-naphthol (0.029 g, 0.02 mmol) in 2 mL of benzene was added to the mixture, and the hierarchical solution was allowed to evaporate slowly in air. Brown X-ray quality crystals formed after 24 h in 46% yield. The crystals had a stoichiometry of [K2(H2O)3(C30H30N20O 10)] 3 2(C10H7OH) 3 2Br 3 2(H2O) (A). Anal. Calcd for A (C50H56N20O17K2Br2): C, 41.50; H, 3.90; N, 19.39. Found: C, 41.82; H, 3.75; N, 19.66. IR spectra (cm-1): 3448 s, 3110 s, 1750 s, 1630 m, 1475 s, 1398 s, 1327 m, 1243 m, 1189 m, 1139 m, 961 m, 797 s, 674 m, 627 s. Preparation of [K2(H2O)3 3 (C30H30N20O10)] 3 2(C10H7OH) 3 2(NO3) 3 2(H2O) (B). A solution of R-naphthol in benzene (3.0 10-3 mol L-1, 2 mL) was added gently to 6 mL of an aqueous solution of Q[5] (1.0 10-4 mol L-1) and KNO3 (4.5 10-4 mol L-1) in a 10 mL test tube. Colorless X-ray quality crystals formed overnight in the layer between the benzene and the aqueous solution in 53% yield. The crystals of the 1-Q[5]-KNO3 system had a stoichiometry of [K2(H2O)3(C30H30N20O10)] 3 2(C10H7OH) 3 2(NO3) 3 2(H2O) (B). Anal. Calcd for B (C50H56N22O23K2): C, 42.55; H, 4.00; N, 21.83. Found: C, 42.76; H, 3.95; N, 22.08. IR spectra (cm-1): 3450 s, 3121 s, 1751 s, 1629 m, 1474 s, 1389 s, 1327 m, 1243 m, 1190 m, 1140 m, 961 m, 798 s, 675 m, 627 s. Preparation of [K2(H2O)3 3 (C30H30N20O10)] 3 (C10H7OH) 3 (C6H6) 3 2(NO3) 3 4(H2O) (C). KNO3 (0.016 g, 0.16 mmol) was added to 10 mL of Q[5] (0.053 g, 0.05 mmol) in water. The solution was heated for 5 min at 60 °C and then added gently to the surface of 3.5 mL of β-naphthol (0.018 g, 0.13 mmol) in trifluoromethane in a 10 mL test tube. Colorless X-ray quality crystals formed in the layer between the trifluoromethane and the aqueous solution in 48% yield. The crystals of the 2-Q[5]-KNO3 system had a stoichiometry of [K2(H2O)3(C30H30N20O10)] 3 (C10H7OH) 3 (C6H6) 3 2(NO3) 3 4(H2O) (C). Anal. Calcd C46 H58N22O24K2: C, 40.00; H, 4.23; N, 22.31. Found: C, 40.25; H, 4.28; N, 22.14. IR spectra (cm-1): 3469 s, 3172 s, 1740 m, 1630 m, 1480 m, 1385 s, 1329 m, 1188 m, 1136 m, 963 m, 799 s, 760 m, 472 s. Preparation of [K2(H2O)3 3 (C30H30N20O10)] 3 2(C6H6O2) 3 2I 3 2(H2O) (D). A mixture of Q[5] (0.095 g, 0.1 mmol) and KI (0.054 g, 0.32 mmol) in 10 mL of water was refluxed for 5 min and then filtered. Hydroquinone (0.002 g, 0.02 mmol) in 3 mL of benzene was

Feng et al. added gently to the surface of the mixture in a 10 mL test tube. The solution was sealed and kept at room temperature for 1 week. Colorless X-ray quality crystals of D formed in 42% yield. The crystals of the 3-Q[5]-KI system had a stoichiometry of [K2(H2O)3(C30H30N20O10)] 3 2(C6H6O2) 3 2I 3 2(H2O) (D). Anal. Calcd (C42H52N20O19K2I2): C, 34.25; H, 3.56; N, 19.02. Found: C, 34.48; H, 3.42; N, 19.67. IR spectra (cm-1): 3377 s, 3158 s, 1736 m, 1633 m, 1513 m, 1472 m, 1400 s, 1333 m, 1194 m, 1098 m, 960 m, 796 s, 758 m, 525 s. Preparation of [K2(H2O)5 3 (C30H30N20O10)] 3 2(C6H6O2) 3 2Br 3 5(H2O) (E). A solution of resorcin (1.2 10-3 mol L-1) in 2.5 mL of water was added gently to a mixture of Q[5] (1.5 10-4 mol L-1) and KBr (3.5 10-4 mol L-1) in 6 mL of water in a 10 mL test tube. Brown X-ray quality crystals formed in 33% yield. The crystals of the 4-Q[5]-KBr system had a stoichiometry of [K2(H2O)5(C30H30N20O 10)] 3 2(C6H6O2) 3 2Br 3 5(H2O) (E). Anal. Calcd (C42H62N20O24K2Br2): C, 34.34; H, 4.25; N, 19.07. Found: C, 34.55; H, 4.10; N, 19.34. IR spectra (cm-1): 3437 s, 3182 s, 1749 m, 1616 m, 1479 m, 1402 s, 1330 m, 1182 m, 1143 m, 963 m, 795 s, 762 m, 629 s. Preparation of [K2(H2O)5 3 (C30H30N20O10)] 3 2(C6H6O2) 3 2(NO3) 3 2(H2O) (F). A solution of resorcin (1.3 10-3 mol L-1) in 2.5 mL of aqueous solution was added gently to Q[5] (1.5 10-4 mol L-1) and KNO3 (3.5 10-4 mol L-1) in 6 mL of water in a 10 mL test tube. Colorless X-ray quality crystals formed overnight in the layer between the benzene and the aqueous solution in 56% yield. The crystals of the 4-Q[5]-KNO3 system had a stoichiometry of [K2(H2O)5(C30H30N20O10)] 3 2(C6H6O2) 3 2(NO3) 3 2(H2O) (F). Anal. Calcd (C42H56N22O27K2): C, 36.58; H, 4.09; N, 22.34. Found: C, 36.87; H, 4.04; N, 22.51. IR spectra (cm-1): 3441 s, 3180 s, 1742 s, 1616 m, 1479s, 1384 s, 1329 m, 1240 m, 1192 m, 1143 m, 962 m, 794 s, 673 m, 627 s. Preparation of [K2(H2O)5 3 (C30H30N20O10)] 3 2(C6H6O2) 3 2I 3 2(H2O) (G). KI (0.058 g, 0.35 mmol) was added to 10 mL of Q[5] (0.085 g, 0.09 mmol) in water. The solution was refluxed for 10 min, and 3 mL of a saturated solution of resorcin (0.016 g, 0.15 mmol) was added. The mixture was cooled and kept at room temperature for five days. Yellow crystals were formed in 38% yield. The crystals obtained had a stoichiometry of [K2(H2O)5(C30H30N20O10)] 3 2(C6H6O2) 3 2I 3 2(H2O) (G). Anal. Calcd (C42H56N20O21K2I2): C, 33.43; H, 3.74; N, 18.56. Found: C, 33.66; H, 3.69; N, 18.63. IR spectra (cm-1): 3448 s, 3169 s, 1746 s, 1612 m, 1480 s, 1400 s, 1330 m, 1240 m, 1191 m, 1142 m, 963 m, 795 s, 673 m, 629 s. Preparation of [K2(H2O)5 3 (C30H30N20O10)] 3 2(C6H5OH) 3 2(NO3) 3 5(H2O) (H). A mixture of Q[5] (0.07 g, 0.07 mmol) and KNO3(0.030 g, 0.34 mmol) in 10 mL of water was refluxed for 15 min and filtered, and 3 mL of 5 (0.026 g, 0.28 mmol) in water was added gently to the mixture in a 10 mL test tube. The solution was sealed and kept at room temperature for 1 week. Colorless X-ray quality crystals of H formed in 15% yield. The crystals of the 5-Q[5]-KNO3 system had a stoichiometry of [K2(H2O)5(C30H30N20O10)] 3 2(C6H5OH) 3 2(NO3) 3 5(H2O) (H). Anal. Calcd (C42H58N22O26K2): C, 36.95; H, 4.28; N, 22.57. Found: C, 37.17; H, 4.24; N, 22.73. IR spectra (cm-1): 3433 s, 3132 s, 1740 m, 1626 m, 1475 m, 1400 s, 1329 m, 1239 m, 1190 m, 793 s, 764 m, 566 s. Preparation of [K2(H2O)4 3 (C30H30N20O10)] 3 2I 3 5(H2O) (I). A mixture of Q[5] (0.098 g, 0.1 mmol) and KI (0.053 g, 0.32 mmol) in 10 mL of water was refluxed for 15 min and filtered, and 3 mL of benzene was added gently to the surface of the mixture. The solution was sealed and kept at room temperature for 1 week. Yellow X-ray quality crystals of I formed in 42% yield. The crystals of the Q[5]KI system had a stoichiometry of [K2(H2O)4(C30H30N20O10)] 3 2I 3 5(H2O) (I). Anal. Calcd C30H48N20O19 K2I2: C, 27.20; H, 3.65; N, 21.14. Found: C, 27.41; H, 3.51; N, 21.68. IR spectra (cm-1): 3442 s, 3137 s, 1734 m, 1623 m, 1479 m, 1400 s, 1331 m, 1189 m, 1138 m, 962 m, 794 s, 766 m, 629 s. X-ray Crystallography. Crystallographic data of inclusion complexes A-I (see Table 1) were collected on a SMART ApexII CCD diffractometer with graphite monochromated Mo KR radiation (λ = 0.71073 A˚) in the ω scan mode. Data (excluding structure factors) on the structures reported here have been deposited with the Cambridge Crystallographic Data Centre with the following deposition numbers: CCDC748638 for A, CCDC748639 for B, CCDC748640 for C, CCDC748641 for D, CCDC748642 for E, CCDC748643 for F, CCDC748644 for G, CCDC748645 for H, CCDC748646 for I.

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Table 1. Crystallographic Data for Complexes 1-9 complex

A

B

C

D

E

F

G

H

I

empirical formula

C50H56N20O17K2Br2 1447.17 orthorhombic P 21 21 2 11.991(3) 15.163(4) 15.718(4)

C50H56N22O23K2 1411.37 orthorhombic P 21 21 2 15.898(3) 11.920(3) 15.222(3)


C42H52N20O19K2I2 1473.04 orthorhombic P 21 2 21 12.0852(6) 13.9747(7) 15.8477(8)

C42H62N20O24K2Br2 1469.14 orthorhombic P 21 21 21 11.8668(9) 15.8040(11) 30.323(2)




2857.7(12) 2 1.682 223(2) 5340 3617 413 0.0666 0.0600 0.1527 0.1003 0.1838 1.022

2884.7 2 1.625 223(2) 5339 4105 436 0.0451 0.0600 0.1648 0.0808 0.1828 1.051

5635.7(17) 4 1.628 223(2) 10456 8007 847 0.0406 0.0560 0.1348 0.0773 0.1475 1.052

2676.5(2) 2 1.828 223(2) 5219 4598 793 0.0440 0.0329 0.0725 0.0409 0.0764 1.047

5686.9(7) 4 1.716 223(2) 11113 8977 822 0.0556 0.0514 0.1316 0.0696 0.1445 1.024

C42H56N22O27K2 1379.29 monoclinic P 21 11.997(3) 16.249(4) 14.099(3) 91.711(3) 2747.5(11) 2 1.667 223(2) 9128 7930 838 0.0230 0.0468 0.1232 0.0555 0.1291 1.046

2775.2(7) 2 1.806 223(2) 5176 4774 414 0.0242 0.0265 0.0650 0.0302 0.0665 1.067

5613.4(18) 4 1.616 223(2) 10455 7932 829 0.1992 0.0594 0.1359 0.0780 0.1456 0.987

4814.6(7) 4 1.828 223(2) 9461 7283 673 0.0443 0.0444 0.1154 0.0634 0.1272 1.022

Conventional R on Fhkl:

P

Fo| - |Fc /σ|Fo|. b Weighted R on |Fhkl|2: )

a

)

formula weight crystal system space group a (A˚) c (A˚) b (A˚) β (deg) volume (A˚3) Z Dcalcd (g 3 cm-3) temp (K) unique reflns obsd reflns parameters R(int) R[I > 2σ(I)]a wR[I > 2σ(I)]b R (all data) wR (all data) GOF on F2

P P [w(Fo2 - Fc2)2]/ [w(Fo2)2]1/2.

Copies can be obtained free of charge upon application to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, þ44 1223/336 033; e-mail, [email protected]).

Results and Discussion Description of Crystal Structures. The identification and rational design of supramolecular architectures built with various organic building blocks and metal ions through selfassembly of multiple molecular components constitute a challenge and an opportunity for supramolecular chemists. Fortunately, we found a series of supramolecular architectures constructed of cucurbit[5]uril, potassium salts, and hydroxybenzene or its derivatives by using conventional methods. In this supramolecular architectural system, Q[5]s and Kþ ions form infinite chains through coordination and ion-dipole interaction, and the stacking of these supramolecular chains forms a series of wavelike “walls”. The layers of hydroxybenzene or its derivatives are present between these walls, and the counteranions are present in the molecular channel constructed of the supramolecular chains and the rows of hydroxybenzene or its derivatives. It is to be noted that the K1 cation and I1 anion are disordered in compound G, and the occupancy rate is 0.919 for K1 and I1 and 0.081 for K10 and I10 , respectively, while the Br2 ion is also disordered in compound E, and the occupancy rate is 0.919 for Br2 and 0.081 for Br20 . In compound A, one can see supramolecular chains that appear to be constructed of alternating Q[5]s and Kþ ions. Close inspection reveals that the supramolecular chain contains a series of molecular capsules, each of which comprises two potassium ions (K1) that are coordinated to two opening portal carbonyl oxygens of the Q[5] molecule with a water molecule (O4W) in the cavity (Figure 2b). Each K1 also coordinates with two latticed water molecules (O1W and O3W) with bond lengths between 2.969 A˚ (K1-O1W) and 2.781 A˚ (K1-O3W). The adjacent molecular capsules connect by sharing water molecule O1W, and through hydrogen bonding with the carbonyl oxygens, such as O3W-O2 with a bond length of 2.752 A˚. The neighboring chains are offset by about one-half of the repeating unit along the a axis. The “bumps” of a chain fit into hollows of neighboring chains

Figure 2. (a) Supramolecular chain composed of Mþ-Q[5]-Mþ(H2O)-Mþ-Q[5]-Mþ(H2O)-Mþ-Q[5]-Mþ molecular capsules and a sandwiched row of R-naphthol molecules arranged along the supramolecular chain. (b) Wavelike wall constructed of neighboring chains. (c) Alternating layers of the supramolecular chain and R-naphthol. (d) Side view of the molecular channel containing bromine anions.

and form a wavelike wall, as shown in Figure 2a. An interesting feature of the crystal structure is that every two

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Figure 3. (a) Supramolecular chain constructed of K-Q[5] molecular capsules. (b) Overall self-assembly supramolecular construction of compound C. (c) Side view of the molecular channel containing nitrate anions.

neighboring wavelike walls sandwich a layer of R-naphthol molecules that are arranged along the supramolecular chain, as shown in Figure 2b. In addition, every three supramolecular chains and two sandwiched R-naphthol molecular rows are arranged in such a way as to produce a trigonal-like molecular channel extending along the direction of the supramolecular chain (Figure 2c and d). The distance between two supramolecular chains that sandwich an R-naphthol molecular row or the gap between two neighboring wavelike walls is 4.513 A˚, and the cross section of the trigonal of molecular channel is about 6.623 A˚ 7.292/2 A˚. The channels are filled with the counter Br1 anions, which interact with hydroxyl groups through hydrogen bonding with a bond length of 3.187 A˚ (Br1-O6). Most of the compounds involved in this work have very similar structural features: (1) supramolecular chains {KþQ[5]-Kþ}(H2O)n-{Kþ-Q[5]-Kþ}(H2O)n-{Kþ-Q[5]-Kþ} composed of molecular capsules {Kþ-Q[5]-Kþ} linked by water molecules; (2) wavelike walls constructed of the supramolecular chains; (3) the molecular layer of hydroxybenzene or its derivatives is sandwiched by the supramolecular chain walls, and the organic molecules can be β-naphthol (2),

hydroquinone (3), resorcin (4), and phenol (5); (4) the counteranions in potassium salts are captured in the channels constructed of the supramolecular chains and the rows of organic molecules, and the anions can be Br-, I-, or NO3-. The corresponding structural details are given in the Supporting Information. For the system involving β-naphthol (2), there were some differences in the formation of the supramolecular chain and the molecular channel.37 Figure 3b shows the self-assembled supramolecular construction of compound C. One can see a supramolecular chain consisting of a series of molecular capsules, each of which comprises two potassium ions (K1 and K2) coordinated to two opening portal carbonyl oxygens with a water molecule (O19) in the cavity of the Q[5] molecule. K1 coordinates also with the three latticed water molecules O1W, O3W, and O5W. K2 coordinates additionally with two latticed water molecules, O2W and the shared O3W. The K-O bond lengths are between 2.665 A˚ (K2-O2) and 3.178 A˚ (K1-O5W). The neighboring molecular capsules connect through the shared water molecule O3W and through hydrogen bonding with the carbonyl oxygens, such as O1W-O2, O2W-O7, and O3W-O1 or O8, with bond

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Figure 4. (a) Supramolecular chain constructed of Kþ-Q[5]-Kþ molecular capsules. (b) Overall self-assembly supramolecular construction of compound I. (c) Side view of the molecular channel containing two rows of iodine anions.

Figure 5. DSC and TG curves of resorcin, Q[5], and compound E in N2.

lengths between 2.823 A˚ (O3W-O1) and 2.791 A˚ (O2W-O7). In addition, the interaction of the hydroxyl group (O11) of β-naphthol (2) with the portal carbonyl oxygen (O5) of Q[5] through hydrogen bonding (Figure 3a) could lead to the formation of a larger molecular channel constructed of six supramolecular chains and two rows of β-naphthol molecules. The captured NO3- anions in the channels connect with the portal carbonyl oxygens of Q[5]s in the supramolecular chains by shared interactions with water molecules O4W and O6W through hydrogen bonding (Figure 3b and c). The distance between the two supramolecular chains that sandwich the R-naphthol molecular row is 4.440 A˚, and the

cross section of the polygonal channel is about 13.857 A˚ 4.599 A˚. Here, we describe two typical systems in which the organic molecules have a role as “springs” that adjust the gaps between the wavelike walls. When the springs are withdrawn in compound I, composed of Q[5] and KI only, the gaps almost disappear; each molecular channel is constructed of only six supramolecular chains and captures two rows of iodine anions. Figure 4 shows details of the structure of compound I. The basic structure—one-dimensional supramolecular chains {Kþ-Q[5]-Kþ}(H2O)n-{Kþ-Q[5]-Kþ}(H2O)n{Kþ-Q[5]-Kþ}—is shown in Figure 4a. The molecular

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capsule {Kþ-Q[5]-Kþ} comprises two potassium ions (K1 and K2) coordinated to two opening portal carbonyl oxygens with a water molecule (O6W) in the cavity of the Q[5] molecule. K1 is coordinated with three latticed water molecules, O1W, O3W, and O5W, and K2 is coordinated additionally with two latticed water molecules, O4W and O7W. The K-O bond lengths are between 3.300 A˚ (K1-O3W) and 2.661 A˚ (K1-O7). The neighboring molecular capsules connect through hydrogen bonding of the coordinated water molecules with the portal carbonyl oxygens, such as O4WO6, O5W-O3, and O1W-O4, with bond lengths between 2.748 A˚ (O1W-O4) and 2.904 A˚ (O4W-O6). Similarly, the Table 2. Structural Data of the Related Compounds

compound

gap between walls for organic compounds (A˚)

cross-sectional area of the channel for the counteranions (A˚)

A B C D E F G H I

4.513 (1) 4.501 (1) 4.440 (2) 4.122 (3) 4.380 (4) 4.422 (4) 4.311 (4) 4.106 (5) 0.916 (5)

7.292 6.623/2 (Br-) 7.964 6.760/2 (NO3-) 13.857 4.599 (NO3-) 7.002 5.507/2 (I-) 7.211 6.756/2 (Br-) 7.678 5.559/2 (NO3-) 7.015 6.357/2 (I-) 7.510 6.203/2 (NO3-) 12.875 4.009 (I-)

Figure 6. FT-IR spectra of resorcin, the free Q[5], the compound E before and after heating, and the sublimation.

Feng et al.

wavelike walls constructed of the neighboring supramolecular chains can be observed, and the grooves in the walls are ready to contain the counteranions. The cross section of the channel within a molecular channel constructed of six supramolecular chains is a polygon large enough to contain two iodine anions (Figure 4b and c). Although various organic molecules are inserted, some of them contain polyaromatic rings, and some contain only a single aromatic ring. The size or symmetry of the organic compounds could influence the size of the gaps between the wavelike walls. Generally, the cross section of the channel is larger than that of the counteranion selected in this work; it seems that the size of the anion is not related to the size of the channel of the molecular channel. The structural data are given in Table 2. Characterization of the Related Compounds. Thermal analysis reveals that the DSC and TG curves of compounds A-I are basically consistent with their crystal structures (referring to SI-Figure 10 in the Supporting Information). For example, parts a and b of Figure 5 show DSC and TG curves of resorcin, Q[5], and compound E in N2, respectively. Comparison of the DSC with TG curves indicates that compound E has a very broad endothermic band in Figure 5a corresponding to weight loss of resorcin in Figure 5b. According to the formula of compound E, it is reasonable that the endothermic band around 146.8 °C with a weight loss of 6.12% corresponds to a fast dehydration of ca. 5 H2O molecules (the expected weight loss of 5 H2O in compound E is 6.13%). The broad endothermic band with a weight loss of 12.39% corresponds to sublimation of resorcin molecules (the expected weight loss of resorcin in compound E is 14.98%). Compared to the free Q[5], the decomposition temperature of Q[5] in compound E is changed from 519.7 to 506.6 °C. Comparison of the FT-IR spectra of the compounds before and after heating in N2 with the free Q[5] reveals the apparent shift of the vibration of the portal carbonyl of Q[5] in the presence of the hydroxy aromatics. Generally, before heating a compound, one can see that the absorption band of portal carbonyl shifts up with 3-15 cm-1 compared to that of the free Q[5], and after heating in N2 at 280 °C, one can see the obvious sublimation of the hydroxy aromatics, and the absorption band of portal carbonyl shifts down with 2-7 cm-1. This indicates the hydroxy aromatics in the compounds interact with the portal carbonyls of Q[5] (referencing

Figure 7. Powder patterns for comparison of the compounds in the presence of the same anion (a, left) and the same organic species (b, right).

Article


SI-Figure 11 in the Supporting Information). For example, compared to the case of the free Q[5], the absorption band of the portal carbonyl of Q[5] in compound E shifts up with 9.7 cm-1 from 1736.5 to 1741.1 cm-1, while it shifts down 2.8 cm-1 from 1741.1 to 1739.3 cm-1 after heating, compared to that before heating (referring to Figure 6). Moreover, the spectrum of the pure resorcin is the same as that of the sublimation which is collected on the wall of the test tube when the sample of compound E is heated. The powder patterns of the compounds show that the obvious crystalline phases of the compounds before heating change into the amorphous phase of the compounds after heating in N2, indicating that the sublimation of the hydroxy aromatics in the compounds results in the crystal deterioration (referring to SI-Figure 12 in the Supporting Information). Parts a and b of Figure 7 present three powder patterns of the compounds with NO3- anion and with resorcin, respectively. The results show that the kinds of anions or hydroxy aromatics do not obviously influence the crystalline phase of the compounds. Conclusion We have described an approach adopted for the synthesis of supramolecular architectures based on the self-assembly of Q[5], the metal ion Kþ, and hydroxybenzene or its derivatives through coordination, ion-dipole interaction, and hydrogen bonding. This strategy for synthesis could be suitable for other supramolecular architectures containing hydroxybenzene or its derivatives, and aromatic or polyaromatic compounds other than those used in this work, and the metal ions could be other alkalies, alkaline metal ions, or even lanthanide ions. This approach has the potential to (1) replace the anions in the channels of the molecular channel with other anions and (2) change the properties of the sandwiched aromatic compounds, such as their RTP, and changes of this type are our next aim. Acknowledgment. This work was supported by the National Natural Science Foundation of China (NSFC; Nos 20961002 and 20767001), the “Chun-Hui” Funds of the Chinese Ministry of Education, the Foundation of the Governor of Guizhou Province, the Science and Technology Foundation of Guizhou Province, and the International Collaborative Project Fund of Guizhou Province. All are gratefully acknowledged. Supporting Information Available: Figures showing the structural arrangement, plots of thermochemical activity, and FTIR spectra of compounds A-I, and powder patterns of some of the compounds. X-ray crystallographic file in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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Design and Synthesis of Self-assembly Supramolecular Entities

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