Supramolecular Structural Inorganic-organic Hybrid [(4-Bromoanilimiun)([18]crown-6)]3[PMo12O40]·CH3CN①

ZHANG Yu-Heng CAO Sheng Lü Shao-Fang XIONG Jun

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Supramolecular Structural Inorganic-organic Hybrid [(4-Bromoanilimiun)([18]crown-6)]3[PMo12O40]·CH3CN①

ZHANG Yu-Heng CAO Sheng Lü Shao-Fang XIONG Jun②

(430200)

A novel supramolecular structural inorganic-organic hybrid [(4-bromoanili- miun)([18]crown-6)]3[PMo12O40]·CH3CN has been synthesized through standard solvent eva- porated method. The structure of the title compound was determined through single-crystal X-ray diffraction analysis. It crystallizes in monoclinic system with21/space group. The crystal data are= 18.9529(4),= 26.4444(5),= 19.0985(4) ?,= 90.132(6)o,= 9572.1(3) ?3,= 4,D= 2.203 g·cm–1,= 14.956 mm–1,(000) = 6192,= 1.098, the final= 0.0859 and(> 2()) = 0.2100. Supramolecular cations are constructed through strong N–H…O hydrogen bonding interaction between the six oxygen atoms of [18]crown-6 molecule and nitrogen atom of (4-bromoanilimiun) cation. Three kinds of different arranged supramolecular cations exist in the title compound, which are filled into the large space formed by [PMo12O40] polyoxoanions. Thermogravimentic differential thermal analysis revealed that hydrogen bonding interaction and intermolecular interaction play an important role in maintaining the stability of the title compound.

supramolecular structure, inorganic-organic hybrids, polyoxometallates, crown ether;

1 INTRODUCTION

Crystal engineering is defined as the design and preparation of versatile crystalline architecture based on molecular building blocksself-assem- bly interaction and the pursuit of expected functional materials[1-4]. Over the past several decades, crystal engineering has been developed by the connection between crystallography and chemistry. Supramolecular structural inorganic- organic hybrids as a significant branch of crystal engineering has attracted attention due to their versatile structures and far range applications such as molecular rotor and nonlinear optical ma- terials[5-7].

Polyoxometallates (POMs) are discrete early transition metal-oxide cluster anions and comprise a class of inorganic complexes, which are composed of several assembled [MO] (M belongs to the-block element in high oxidation state) units with high symmetry. POMs as the inorganic building blocks have many advantages for constructing supramolecular structures due to their structural characteristics. (a) POMs have numerous oxygen atoms, which can be treated as the potential hydrogen bonding sites[8-10]. Take Lindqvist [W6O19]polyoxoanions for example. It contains three types of oxygen atoms, which are terminal oxygen O, bridging oxygen Oand central oxygen O, respectively. Six terminal oxygen Oand twelve bridging oxygen Oare potential hydrogen bonding sites; (b) POMs with giant structure can form large polyoxoanionic packing void, which can embed large size of organic cations[11]. An interesting struc- ture [(-aminoanilinium)([15]crown-5)]4[PMo12O40] was reported by Nakamura group. In this compound, [PMo12O40] polyoxoanionic forms a large cave for embedding supramolecular cation [(-aminoanili- nium)([15]crown-5)] and providing enough space for (-aminoanilinium) rotating[12]; (c) The charge of POMs can be modified by electrochemical method for changing the electrostatic interaction with organic cation, resulting in interesting mole- cular assembled structure[13]. Based on the structural advantages, many supramolecular POMs based inorganic-organic hybrids have been designed with tetrathiafulvalene and ferrocenyl derivatives[14-18].

Crown ethers are macrocyclic compounds con- taining hetero donor atoms such as O, N, S or Se with many of structural characteristics as organic building blocks. First, crown ethers with large ring structures have the ability that can incorporate cations to from supramolecular cation with anili- nium derivatives through hydrogen bonding interaction[19-23]. In addition, crown ethers are composed of carbon, oxygen and other atoms, which are the potential hydrogen bonding sites to form supramolecular structure with inorganic building blocks[24, 25].

Some of supramolecular POMs based inor- ganic-organic hybrids have been reported with crown ethers by Nakamura group who have syste- mically researched the relationship between the size of supramolecular cation and crystalline packing pattern through eight supramolecular crystalline structures[26]. They also studied the effect of Keggin POMs on the (3-flouoranilinium)rotor[27]. In this paper, we designed a novel supramolecular structure of inorganic-organic hybrids [(4-bromoanili- miun)([18]crown-6)]3[PMo12O40]·CH3CN based on Keggin POMs and crown ethers (Scheme 1). The detailed structural characteristics and thermogravi- metric analysis (TGA) of the title compound will be discussed.

Scheme 1. Structures of 4-bromoanilinium, [18]crown-6 and [PMo12O40]

2 EXPERIMENTAL

2. 1 Instruments and reagents

[18]Crown-6 was purchased from Shanghai Aladdin Bio-Chem Technology Co., LTD and used without further purification. (4-Bromoanilimiun) and [TBA]3[PMo12O40] were prepared in similar procedures reported previously[28, 29]. IR (400～7800 cm–1) spectra were measured by using a Thermo Scientific Nicolet 6700 FT-IR spectrometer. Elemental analysis was carried out on a CARLO ERBA 1106 analyzer, which can detect the percentages of nitrogen, carbon and hydrogen of the title compound. Thermogravimentic differential thermal analysis (TG-DTA) was carried out using a Rigaku Thermoplus TG8120 thermal analysis station employing an Al2O3reference in the temperature range from 303 to 773 K at a heating rate of 10 K· min–1under flowing nitrogen gas.

2. 2 Synthesis of [(4-bromoanilimiun)([18]crown-6)]3[PMo12O40]·CH3CN

The title compound was synthesized through the standard solvent diffusion method. 10 mL of ace- tonitrile solution with (4-bromoanilimiun) (3 mg) and [18]crown-6 (3 mg) was slowly added to 10 mL [TBA]3[PMo12O40] (30 mg) acetonitrile solution with stirring. After 10 minutes stirring, the solution turned to green, and then was put in a dark quiet place at room temperature. Green block crystals were obtained about one week later. Anal. Calcd. for C56H96Br3Mo12N4O58P (%): C, 21.16; H, 3.02; N, 1.76. Found (%): C, 21.08; H, 2.99; N, 1.82. IR (KBr pellet, cm–1): 1160(m), 1060(s), 980(s), 870(s), 790(s).

2. 3 Crystal data and structure determination

A green block crystal with approximate dimen- sions of 0.15mm × 0.12mm × 0.09mm was mounted on a glass fiber. All measurements were made on a Rigaku R-AXIS RAPID diffractometer with multi-layer mirror monochromated Cu-(= 1.54187 ?) radiation using anscan mode in the range 3.28<<68.25°at 296(2) K. The crystal- to-detector distance was 127.40 mm. A total of 450 oscillation images were collected. The data were corrected for Lorentz and polarization effects. An empirical absorption correction was applied which resulted in transmission factors ranging from 0.195 to 0.261. The unit cell dimensions were obtained with the least-squares refinements. All the structures were solved by direct methods with SHELXS program[30]and refined by full-matrix least-squares method on2with anisotropic thermal parameters for some non-hydrogen atoms, while the rest was refined isotropically using SHELXL[30]. Hydrogen atoms were refined using the riding model. A total of 110339 reflections were collected, where 17420 were unique (int= 0.0859), among which 1161 (–22≤≤22, –31≤≤31, –22≤≤22) were observed. The final cycle of refinement converged to= 0.0859 and(> 2()) = 0.2100 (= 1/[2(F2) + (0.0709)2+218.6909], where= (F2+ 2F2)/3),= 1.098, (/)max= 3.53 and (/)max= –3.75 e/?3.

3 RESULTS AND DISCUSSION

3. 1 Crystalline structure of the title compound

Single-crystal X-ray diffraction analysis revealed that the title compound crystallizes in the mono- clinic system with21/space group. In the asymmetric unit, the title compound consists of one [PMo12O40]polyoxoanion, three (4-bromoanilimiun) cations, three [18]crown-6 molecules and one CH3CN molecule. In the title compound, three kinds of different arranged supramolecular cations [(4-bromoanilimiun)([18]crown-6)] (Fig. 1) are constructed through N–H…O hydrogen bonding interaction between nitrogen atom of (4-bromoani- limiun) cation and six oxygen atoms of [18]crown-6 molecule. The average hydrogen bonding lengths are 2.856, 2.941 and 2.848 ? (Table 1) for supramolecular cations 1, 2 and 3, respectively, which are similar to the standard N–H…O hydrogen bonding length[31], indicating strong hydrogen bonding interaction between (4-bromoanilimiun) cations and [18]crown-6 molecule. For the supra- molecular cations 1 and 3, two nitrogen atoms (N1 and N3) are located at the center of [18]crown-6 molecule. The distances between N1 (or N3) and the plane constructed by six oxygen atoms of [18]crown-6 molecule are 0.666 ? (or 0.652 ?). The (4-bromoanilimiun) cationic plane and [18]crown-6 molecular plane in the supramolecular cations 1 and 3 are nearly perpendicular to each other with the dihedral angle to be 87.157° and 87.76°, respectively. However, for the supramole- cular cation 2, the [18]crown-6 molecules are extremely distorted, resulting in the dihedral angle between (4-bromoanilimiun) cationic plane and [18]crown-6 molecular plane being 74.592°, and the distance from N2 atom to the [18]crown-6 molecu- lar plane of 1.113 ?.

Fig. 1. Structures of the supramolecular cations in the title compound. Hydrogen atoms are omitted for clarity, and dotted cyan represents hydrogen bonds

Table 1. Distances (?) between the Nitrogen and Oxygen Atoms in Supramolecular Cation of the Title Compound

Fig. 2. (a) Detailed interaction between adjacent [PMo12O40] polyoxoanions; (b) Packing diagram of [PMo12O40] polyoxoanins in theplane. Fig. a is the enlargement figure of dotted square Fig. b; Dotted green line presents the O…O interaction

In the title compound, through X-ray crystalline structural analysis, short O…O distance (3.160 ? for O(5)…O(27) and 3.302 ? O(17)…O(20)) between adjacent [PMo12O40] polyoxoanions was observed, as depicted in Fig. 2a, which indicate intermolecular O…O interaction that can construct a three-dimen- sional polyoxoanion structure. The most closest polyoxoanion packing diagram is theplace, as shown in Fig. 2b.

For the title compound, the [PMo12O40] poly- oxoanins and supramolecular cations 2 and 3 are alternatively arranged along theaxis. At the same time, [PMo12O40] polyoxoanins layer (theplane) and supramolecular cation 1 layer are arrayed along theaxis, as shown in Fig. 3. [PMo12O40] poly- oxoanins and supramolecular cation 1 have two different arrangements, which are judged according to their arranged direction. Multiply hydrogen bonding site [PMo12O40] polyoxoanions and [18]crown-6 show weak hydrogen bonding interac- tion, as shown in Fig. 4. Each [PMo12O40] poly- oxoanion is connected with supramolecular cations 1, 2 and 3 through weak hydrogen bonding interac- tion. The detailed hydrogen bonding interaction between POMs and crown ethers are shown in Table 2. These intermolecular interactions play an important role in constructing and maintaining the stability of the title compound.

Fig. 3. Packing diagram of the title crystal viewed along theaxis

Fig. 4. Weak hydrogen bonding interaction among [PMo12O40] polyoxoanions, [18]crown-6 molecule and (4-bromoanilimiun) cation. Cyan dotted represents the hydrogen bonding interaction

Table 2. Hydrogen Bonds for the Title Compound (?, °)

Symmetry codes: #1: –1/2+, 3/2–, –1/2+; #2: –1/2+, 3/2–, 1/2+; #3: –1+,,;#4: 5/2–, –1/2+, 3/2–; #5: 3/2–, –1/2+, 3/2–; #6: 2–, 1–, 1–

3.2 Thermogravimetric analysis of the title crystal

The thermal stability of the title crystal has been studied through the TG-DTA measurements from 300 to 730 K, as shown in Fig. 5. The title com- pound starts to lose the CH3CN molecule from room temperature. One CH3CN molecule will be lost (1.32%, calcd. 1.30%) up to 460 K because no hydrogen bonding interaction exists in CH3CN through single-crystal X-ray diffraction analysis. The title compound will lose one CH3CN molecule, two [18]crown-6 molecules and one (4-bromoanili- miun) cation (23.02%, calcd. 22.95%) when reaching 530 K. Supramolecular cations can exist in the title compound at high temperature due to the hydrogen bonding interaction with [PMo12O40] polyoxoanions. The TG-DTA results are similar to the crystalline structure analysis, and prove that the hydrogen bonding interaction plays an important role in maintaining the stability of the title com- pound.

Fig. 5. TG-DTA curve of the title compound

4 CONCLUSION

Supramolecular structural inorganic-organic hybrid [(4-bromoanilimiun)([18]crown-6)]3[PMo12O40]·-CH3CN has been designed based on the structural advantages of POMs and crown ethers. Adjacent [PMo12O40] polyoxoanions have interac- tion, and hydrogen bonding interaction between POMs and crown ether maintains the stability of the title compound through X-ray diffraction analysis and TG-DTA studied. In the title compound, large space formed by POMs can embed crown ether based supramolecular cation, which provides the possi- bility for designing supramolecular rotor in future.

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18 December 2017;

11 April 2018 (CCDC 1811377)

①The authors thank the foundation of Wuhan Textile University (No. 165002) and Hubei Key Laboratory of Biomass Fibers and Eco-dyeing＆Finishing for supporting this work

. Tel: 027-59367336, E-mail: jxiong@wtu.edu.cn

10.14102/j.cnki.0254-5861.2011-1925