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Paper Статья
DOI: 10. 6060/mhc235090m
Construction of Supramolecular Self-Assembled Frameworks Comprised of p-Nitrophenol and Four Modified Cucurbit[n]urils
Jun Zheng,a,b Jiakang He,a Linwei Yuan,a and Peihua Mab@
aChina Zhenhua Electronics Group Yuguang Electric Works Co., Ltd. Guiyang 550025, China
bKey Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang 550025, China
@E-mail: [email protected]
Herein, we report the supramolecular self-assembly of fully substituted cyclopentyl-derived cucurbit[5]uril (CyP5Q[5]), cucurbit[6]uril (CyP6Q[6]), symmetrical dicyclopentyl-substituted cucurbit[6]uril (CyP2Q[6]) and fully substituted cyclobutyl-derived cucurbit[5]uril (CyB5Q[5]) with p-nitrophenol (G). Single-crystal X-ray diffraction was employed to characterize these supramolecular complexes [C81H81CaCl2N26O29 (1), C60H85Ca2Cd2Cl8N25O25 (2), C27H37CaCl4N13O14Zn (3) and C58H63CaCl4N23O23Zn (4)]. In these four systems, calcium ions were introduced to coordinate with the cucurbit[n]uril and G was enriched on the outer surface of the cucurbit[n]uril to construct four supramolecular frameworks.
Keywords: ¿»-Nitrophenol, calcium ion, modified cucurbit[n]uril, supramolecular self-assembled frameworks.
Конструирование супрамолекулярных самособирающихся каркасов, состоящих из п-нитрофенола и четырех модифицированных кукурбит[л]урилов
Джун Чжэн,а,ь Джиакан Хе,а Линвэй Юань,а Пэйхуа Маь@
aКомпания 'China Zhenhua Electronics Group Yuguang Electric Works Co., Ltd.' 550025 Гуйян, Китай bКлючевая лаборатория макроциклической и супрамолекулярной химии провинции Гуйчжоу, Университет Гуйчжоу, 550025 Гуйян, Китай @E-mail: [email protected]
Сообщается о супрамолекулярной самосборке полностью замещенного циклопентильного производного кукурбит[5]урила (CyPQ[5]), кукурбит[6]урила (CyP6Q[6]), симметричного дициклопентилзамещенного кукурбит[6]урила (CyP2Q[6]) и полностью замещенного циклобутильного кукурбит[5]урила (CyBQ[5]) с п-нитрофенолом (G). Образующиеся супрамолекулярные комплексы [C81H81CaCl2N26O29 (1), C60H85Ca2Cd2Cl8N25O25 (2), C27H37CaCl4N13O14Zn (3) и C58H63CaCl4N23O23Zn (4)] были охарактеризованы методом рентгеноструктурного анализа. Для построения четырех супрамолекулярных каркасов были введены ионы кальция для координации с кукурбит^урилами, дополненными по периферии фрагментами G.
Ключевые слова: п-Нитрофенол, ион кальция, модифицированный кукурбит^урил, супрамолекулярные самособирающиеся каркасы.
Introduction
Cucurbit[n]uril (CB[n] or Q[n]) is a new generation of supramolecular macrocyclic compounds following crown ethers, cyclodextrins and calixarenes. Cucurbit[6]uril (Q[6]) was the first compound reported in the Q[n] family.[1] Ordinary Q[n] range from the smallest Q[4][23] to the largest twisted Q[15],[4] and a series of modified Q[n] have been subsequently reported, including methyl-,[5] cyclohexyl-,[6] cyclopentyl-,[7'8] hydroxyl-,[9] phenyl-[10] and cyclobutyl-modified cucurbit[n]urils.[11] The discovery of these modified Q[n]s has greatly changed the solubility of cucurbit[n]urils, providing favorable conditions for Q[n] compounds in the fields of coordination chemistry, host-guest chemistry and nanomaterials. Consequently, several supramolecular compounds have been constructed by studying the interaction of the carbonyl portal of Q[n]s with metal ions[12-17] and the host-guest interaction between the hydrophobic cavity of Q[n]s and organic guest molecules.[18-24] In addition, supramolecular frameworks have also been constructed by studying the interactions formed between the outer surface of Q[n]s and negatively charged molecules or anions.[25-27]
Recent studies have shown that there were weak interactions formed between Q[n]s, such as hydrogen bonding, rc-rc stacking, C-H-rc interactions, and ion-dipole interactions.[28-31] There is an ion-dipole interaction formed between the [CdCl4]2- or [ZnCl4]2- anion and the positive potential outer surface of the Q[n], which is conducive to the construction of supramolecular self-assembled complexes based on the Q[n] and small organic molecules, which is considered to be effective structure inducer/17' 26] In this paper, p-nitrophenol (G) was selected as the guest molecule and fully-substituted cyclopentyl-derived cucurbit[5]uril (CyP5Q[5]) and cucuTbit[6]uril (CyP6Q[6]), symmetrical dicyclopentyl-substituted cucurbit[6]uril (CyP2Q[6]) and fully-substituted cyclobutyl-derived cucurbit[5]uril (CyB5Q[5]) used as hosts, and the supramolecular framework constructed. The structures of p-nitrophenol and the four modified Q[n]s are shown in Figure 1.
Experimental
General materials
All materials were reagent grade and used without any further purification. CyP5Q[5], CyP2Q[6], CyP6Q[6] and CyB5Q[5] (purity >97%) were prepared in the Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, China.
Synthesis of the complexes 1-4
A mixture of CyP5Q[5] (10 mg, 9.73 ^mol), p-nitrophenol (10 mg, 71.89 ^mol) and CaCl2 in 3 mL of 3 mol/L aqueous hydrochloric acid was heated until dissolution. Then, the solution was heated and stirred for 7-10 min in a water bath at 50 °C. Finally, the solution was allowed to stand at room temperature for 10-15 days to obtain single crystals of C81H81CaCl2N26O29 (1) (33.8% yield). A mixture of CyP6Q[6] (10 mg, 8.08 pmol), p-nitrophenol (10 mg, 71.89 ^mol), CdCl2 (5 mg, 27.28 ^mol) and CaCl2 (5 mg, 45.05 ^mol) in 3 mL of 3 mol/L aqueous
hydrochloric acid was heated until dissolution. Then, the solution was heated and stirred for 7-10 min in a water bath at 50 °C. Finally, the solution was allowed to stand at room temperature for 10-15 days to obtain single crystals of C60H85Ca2Cd2Cl8N25O25 (2) (35.4% yield). A mixture of CyP2Q[6] (10 mg, 9.29 pmol), p-nitrophenol (10 mg, 71.89 pmol), ZnCl2 (10 mg, 73.38 pmol) and CaCl2 (5 mg, 45.05^mol) in 3 mL of 3 mol/L aqueous hydrochloric acid was heated until dissolution. Then, the solution was heated and stirred for 7-10 min in a water bath at 50 °C. Finally, the solution was allowed to stand at room temperature for 10-15 days to obtain single crystals of C27H37CaCl4N13O14Zn (3) (37.3% yield) and a mixture of CyB5Q[5] (10 mg, 10.41 pmol), p-nitrophenol (10 mg, 71.89 ^mol), ZnCl2 (10 mg, 73.38^mol) and CaCl2 (5 mg, 45.05 ^mol) in 3 mL of 3 mol/L aqueous hydrochloric acid was heated until dissolution. Then, the solution was heated and stirred for 7-10 min in a water bath at 50 °C. Finally, the solution was allowed to stand at room temperature for 10-15 days to obtain single crystals of C58H63CaCl4N23O23Zn (4) (41.5% yield).
Crystal structure determination
A crystal with the appropriate size and transparency was selected and fixed on a glass probe with using petroleum jelly for X-ray single crystal diffraction analysis on a Bruker D8 Venture X-ray single crystal diffractometer in (»-scan mode using graphite to monochromatize the Mo-Ka rays (X = 0.71073 A, ^ = 0.828 mm-1). The crystal data were collected and Lorentz polarization and absorption correction carried out. SHELXT-14 and SHELXL-14 program packages were used for structural analysis and full matrix least squares refinement. All non-hydrogen atoms were anisotropically refined using the analytical expression of the neutral atom scattering factor and combined with anomalous dispersion correction. The SQUEEZE program in the PLATON package was used to delete some of the disordered solvent molecules. The X-ray crystallographic data for structures reported in this study have been deposited in the Cambridge Crystallographic Data Center under accession numbers CCDC: 2031927 (1), 2023194 (2), 2156026 (3) and 2156027 (4). These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/data request/cif. The crystal parameters, data acquisition conditions, and parameters of the complexes 1-4 are listed in Table 1.
Figure 1. The structures of ^p-nitrophenol and four modified Q[n]s: (a) CyP5Q[5], (b) CyP2Q[6], (c) CyP6Q[6], (d) CyB5Q[5] and (e) ^p-nitrophenol (G).
Table 1. Crystallographic data for complexes 1-4._
Complex 1 2 3 4
Empirical formula C81H81CaCl2N26O29 C6cH85Ca2Cd2Cl8N25O25 C27H37CaCl4N13O14Zn C^HgCaC^O^Zn
Mr 1993.69 2145.08 1014.94 1697.56
Crystal system Monoclinic Triclinic Triclinic Triclinic
Space group P21/c P-1 P-1 P-1
a (A) 25.3747(16) 10.396(3) 10.458(2) 10.6771(18)
b (A) 20.3378(15) 15.684(4) 14.957(3) 15.343(2)
c (A) 17.3896(11) 16.552(4) 15.260(3) 23.040(4)
a (deg) 90 115.720(8) 117.530(5) 102.675(5)
P (deg) 90.087(2) 99.619(10) 98.114(6) 94.198(5)
Y (deg) 90 96.034(10) 96.867(6) 99.900(5)
V [A3] 8974.2(10) 2348.7(11) 2048.6(7) 3603.5(10)
Z 4 1 2 2
Dc (g cm -3) 1.476 1.517 1.645 1.565
F(000) 4140 1092 1040 1748
H (mm -1) 0.226 0.869 1.065 0.653
Date/Params 15757/1264 11588/620 6925/546 12553/935
0(deg) 2.23-26.70 2.49-28.25 2.55-27.87 2.31-28.05
Rint 0.0785 0.0552 0.0890 0.1470
R[I > 2a(I)][a] 0.1861 0.0533 0.0847 0.1330
wR[I > 2a(I)][b] 0.4383 0.1567 0.2437 0.3622
R(all data) 0.1995 0.0650 0.1196 0.1559
wR(all data) 0.4430 0.1680 0.2565 0.3776
GOF (F2) 1.102 1.034 1.046 1.448
^Conventional R on Fhkl: X||Fo| - |Fc||/X|Fo|. [b]Weighted R on |Fhkl|2: £[w(Fa2 - Fc2)2]/X[w(Fo2)2]1/2.
Figure 2. Crystal structure of complex 1: (a) Asymmetric unit; (b, c, d) intermolecular interaction.
Results and Discussion
Description of the crystal structure of complex
The asymmetric unit of supramolecular self-assembly complex 1 contained one CyP5Q[5] molecule, six p-nitrophenol (G) molecules, two chloride ions, and one Ca2+
ion (Figure 2(a)). One chlorine ion was directly coordinated to the calcium ion and the other is free. Figure 2(b and c) show the surrounding G molecules of CyP5Q[5] interact through C-H-rc bonds C48-H33B, C49-H33B, C57-H32B and C77-H7A with the distances between them being 2.791, 2.754, 2.843 and 2.886 A, respectively. In addition, there were C-H—O and C-H—N interactions formed
between CyP5Q[5] and G (O11-H29B, N24-H33A, O26-H11B, O23-H15A and O4-H68) with the distances between them being 2.555, 2.700, 2.646, 2.614 and 2.589 A, respectively. The chloride ion interacted with the outer surface of the CyP5Q[5] (C21) via an ionic dipole interaction. Due to the coordination of the Ca2+ ions with the carbonyl oxygen atoms at the portal of CyP5Q[5], the outer surface of CyP5Q[5] had more positive charges, so G was enriched around CyP5Q[5], as shown in Figure 2d, which clearly showed CyP5Q[5] had fourteen G molecules bound to its outer surface via weak interactions.
Figure 3(a) shows the calcium ions act as a bridge connecting two CyP5Q[5] molecules, thereby forming a one-dimensional supramolecular chain. Figure 3(b and c) are the packing diagrams of the crystal structures of supramolecular self-assembled complex 1 viewed along two different directions. It can be seen that G was enriched around CyP5Q[5] and presents a regular arrangement (Figure 3(b)). Figure 3(c) shows G was embedded in the large pores formed between the CyP5Q[5] molecules. It was
further demonstrated that there was enough space around the CyP5Q[5] host for guest molecules to enter.
The asymmetric unit of supramolecular self-assembly complex 2 contained one CyP6Q[6] molecule, one p-nitrophenol (G) molecule, one [CdCl4]2- counter ion, one Ca2+ ion and five coordinated water molecules (Figure 4(a)). Figure 4(b and d) show that an ion-dipole interaction was formed between the [CdCl4]2- counter ion and CyP6Q[6]. Each CyP6Q[6] was surrounded by six [CdCl4]2-counter ion that interacted with it (Figure 4(b)), the G molecule not only formed a C-H-rc interaction with the outer surface of CyP6Q[6], but also had an C-H-Cl interaction with the [CdCl4]2- counter ion (Figure 4(d)). The calcium ions not only coordinated with the carbonyl oxygen atom of CyP6Q[6], but also coordinated with free water molecules; the coordinated water molecule formed a hydrogen bond with the carbonyl oxygen atom of CyP6Q[6] (O12-O8, O12-O4, O12-O7, O4-O1, O7-O14, O7-O8), the distances between them were 2.959, 2.801, 2.851, 2.836 A, 2.716 and 2.924 A, respectively.
Figure 3. Crystal structure of complex 1: (a) One-dimensional supramolecular chain; (b) and (c) Stacking diagram viewed along the c and b-axis.
Figure 4. Crystal structure of complex 2: (a) Asymmetric unit; (b, d) Ion-dipole interaction; (c) Hydrogen bond interaction.
Figure 5. Crystal structure of complex 2: (a), (b) and (c) Stacking diagram viewed along the b-axis; (d) Stacking diagram viewed along the a-axis; (e) One-dimensional supramolecular chain.
Figure 6. Crystal structure of complex 3: (a) Asymmetric unit; (b, c) Ion-dipole interaction; (d) Hydrogen bond interaction.
Figure 5(a, b and c) show the stacking diagram of the crystal structure viewed along the b-axis. Many holes were formed between the G molecules and the complexes of CyP6Q[6] and calcium ions were embedded in them. Figure 5(d) shows the stacking diagram of the crystal structure of the complex viewed along the a-axis and Figure 5(e) shows the one-dimensional supramolecular chain of the complex 2 with two CyP6Q[6] coordinated with two calcium ions.
The asymmetric unit of supramolecular self-assembly complex 3 contained one molecule of CyP2Q[6], one molecule of ^-nitrophenol (G), and one [ZnCl4]2- counter ion (Figure 6(a)). Figure 6(b) shows the [ZnCl4]2- counter interacts with CyP2Q[6] via a C-H---Q interaction and p-nitrophenol interacts with CyP2Q[6] via a C-H--O interaction. Figure 6(c) shows that there were six [ZnCl4]2-ions around each CyP2Q[6] bonded via ion-dipole interactions (shown by the purple curve in Figure 6(c)). Interestingly, in addition to the Ca2+ ion forming a coordination bond with the carbonyl oxygen atom at the portal of the CyP2Q[6], there was a hydrogen bond (O8-O5, 010-02) formed between the coordination water molecule interacting with Ca2+ and the carbonyl oxygen atom, as shown by the blue curve in Figure 6(d), and the distances between them are 2.802 and 2.902 A, respectively.
Figure 7(a) shows the one-dimensional supramolecular chain of complex 3, in which two CyP2Q[6] were connected via Ca2+ coordination to form a one-dimensional chain supramolecular. The specific form was the coordination of the portal carbonyl oxygen atoms of the two CyP2Q[6] molecules surrounded by [ZnCl4]2- counter ions and inlaid with G molecules. Figure 7(b) shows the crystal structure stacking diagram of the complex viewed
along the a-axis. It can be clearly seen that the G molecule was embedded in the pores of the CyP2Q[6] molecule, forming a supramolecular complex framework.
The asymmetric unit of supramolecular self-assembly complex 4 contained one molecule of CyB5Q[5], three molecules of ^-nitrophenol (G), one Ca2+ ion and one [ZnCl4]2- counter ion (Figure 8(a)). Figure 8(b) shows the calcium ions not only coordinated with the carbonyl oxygen atom of CyB5Q[5], but also coordinated with the free water molecules; the coordinated water molecule formed a hydrogen bond with the carbonyl oxygen atom of CyB5Q[5] (019-06, 020-08) and the distances between them were 2.816 and 2.773 A, respectively. The coordination water molecule formed a hydrogen bond with G (015-019, 01502) and the distances between them were 2.843 and 3.385 A, respectively. Figure 8(c) shows the one-dimensional supramolecular chain of the complex 4 had two CyB5Q[5] coordinated with one calcium ion.
Figure 9(a) shows there are five G molecules and four [ZnCl4]2- counter ions around each CyB5Q[5] molecule and the [ZnCl4]2- counter ions form C-H---Q interactions with the outer surface of CyB5Q[5]. G formed weak C-H- • n and C-H--0 interactions with the outer surface and portal of CyB5Q[5]. There were three CyB5Q[5] molecules around each metal ion forming a C-H-Cl interaction connecting the CyB5Q[5] molecules. At the same time, there was a dipole-dipole interaction formed between the CyB5Q[5] (Figure 9(a)). Figure 9(c) is the crystal structure stacking diagram of complex 4 viewed along the a-axis. It can be clearly seen that holes were formed between the CyB5Q[5] molecules and the G molecules were embedded in these holes, thereby forming a supramolecular self-assembly.
Figure 7. Crystal structure of complex 3: (a) One-dimensional supramolecular chain; (b) Stacking diagram viewed along the a-axis.
Figure 8. Crystal structure of complex 4: (a) Asymmetric unit; (b) Hydrogen bond interaction; (c) One-dimensional supramolecular chain.
Conclusions
In this paper, the supramolecular self-assembly of p-nitrophenol and four modified cucurbit[n]urils was designed and carried out. A quaternary supramolecular complex using cucurbit[n]uril as the host, calcium ion as the bridge connecting the supramolecular chain of the cucurbit[n]uril, [ZnCl4]2- or [CdCl4]2- as the structure inducer and G as the guest was formed. In these four systems, the Ca2+ ions were introduced to coordinate with the cucurbit[n]uril and ^-nitrophenol was enriched on the outer surface of the cucurbit[n]urils to construct four supramolecular frameworks. Through the study of the crystal structures of the four complexes, the research scope of cucurbit[n]urils has been further expanded and research on phenolic compounds has been further developed in the field of cucurbit[n]urils.
Supplementary information. The experimental sections and crystal data are listed in the supporting materials.
Acknowledgements. This work was supported by the National Natural Science Foundation of China (Grant No. 22161010).
Conflict of interests. The authors declare no conflict of interests.
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Received 11.04.2023 Accepted 06.05.2023
