Abstract
A novel supramolecular compound
Introduction
Polyoxometalates (POMs) is an anion cluster of metal oxygen atom, which is formed by the combination of metal ions (such as V, Mo, W, Ta and Nb in the pre-transition state) with oxygen [1, 2]. In recent years, POMs have attracted the attention of many researchers, mainly because of its excellent physicochemical properties, diverse electronic structure, size, thermal stability and redox. Based on the above characteristics, it has become a suitable building unit, so it has great potential in biology, solar cells, environment, and catalysis [3–8]. Mo (VI) and W (VI) are the most common transition metals in polyacid anion clusters. The basic units of POMs anion clusters are MO6 octahedron and MO4 tetrahedron, and then they are connected to form different anion structures through coplanar, coedge and copex [9]. In the past decade, researchers have made the synthesis of POMs into a new stage of molecular tailoring and assembly, that is, transition from the synthesis of relatively stable compounds in the oxidation state to the synthesis of metastable compounds and the synthesis and research of supramolecular compounds. As a result, a variety of new POMs functional systems have been expanded, and a number of functionally oriented new materials have been established. Polyoxometalates can be widely used as organic-inorganic structural units because they have the advantages of many terminal oxygen atoms (Ot and Ob), shape and size controllability, high negative charge density, and structural diversity. We can obtain more acid radical transition metal - organic compounds by introducing lone pair electrons and transition metal organic units in polyoxometalates. Therefore, organic amine compounds and related compounds are widely used as organic cationic template agents. On the one hand, organic cations can balance the charge, on the other hand, they can fill the cavity of the crystal to stabilize the framework structure. Organic cations can also guide the structure of crystals to obtain a variety of crystal structures. In this way, we can prepare hybrid materials with richer structure and further obtain hybrid materials with better functionality. Since Dickinson [10] discovered in 1923 that hexamethylenetetramine (HMT) could be obtained by evaporation of ammonia and formaldehyde aqueous solution in vacuum. Hexamethylenetetramine (HMT) has four different coordination forms due to the four reactive nitrogen atoms, including end group mode (monodentate) and μn-bridge (n = 2–4) modes. So, this compound could be used as a multidentate ligand [11] to form different compounds or supramolecule. HMT [12–18] (hexamethylenetetramine), a potential tetradentate ligand or hydrogen bond acceptor, has been used by us and other research groups to react with metal ions to prepare supramolecular polymer.
In recent decades, our research group has been devoted to synthesizing attractive
supramolecular structures and exploring their photodegradability to methylene blue (MB) and
rhodamine B (RhB) and the properties of semiconductor materials [20]. Based on the above studies, we synthesized the ligand L1 for the
first time. Then, under the action of a similar catalyst (MnCl2), the ligand L1
(Scheme 1) and ammonium molybdate
(NH4) Mo7O24·4H2O were reacted at high
temperature and pressure to obtain a new supramolecular compound
The cationic template L1. Ligand L1 is hydrolyzed in-situ to obtain L1’.
Synthesis of the organic cation template L1
All chemicals and solvents are of A. R. grade (≥99%) and used without further purification. Distilled water was used for all procedures. Firstly, 0.3568 g 1,3,5-tris (bromomethyl)benzene was placed in a beaker, and then 30 mL ethanol was added to the beaker to completely dissolve it. Then weigh 0.49 g HMT in a three-mouth bottle with 50 mL ethanol. Next, The reflux device was then installed, and when the reflux temperature reached 50°C, the alcohol solution of 1,3,5-tris(bromomethyl)benzene was added to the three-mouth bottle drop by drop with a constant pressure drop funnel. After 24 h reaction, the turbid fluid can be obtained, and then it was filtered, dried and finally ligand L1 was obtained.
Synthesis of [(C6H3) (CH2 NH3) 2+ (CH2NH2)]2·(β-Mo8O26) ·3H2O
A (NH4)6Mo7O24·4H2O (0.06175 g 0.05 mmol), L1 (0.0194 g 0.025 mmol), MnCl2 (0.0198 g 0.02 mmol) and H2O (10 mL) was stirred for 1 hour on a magnetic stirrer. Then mixture transferred and sealed in 18 mL teflon lining, which was heated at 100°C for 5 h. The reaction solution was then cooled to room temperature at a rate of 10°C·h–1 to obtain colorless rod-like crystals. Elemental analyses calcd for C18H40Mo8N6O31, C,13.48; H,2.51; N,5.34. Found: C,13.53; H,2.55; N,5.39. IR (KBr, cm–1): 3438 (s), 1619 (s), 1115 (w), 936 (s), 896 (w), 833 (w), 798 (w), 604 (m).
Materials and methods
The organic cation template L1 was synthesized for the first time. The IR spectra was measured on a Shimazu IR 435 spectrometer adopting KBr pellets in the scale of 400–4000 cm–1. Element analyses of C, H and N were performed using a Perkin-Elmer 240 elemental analyzer. Powder XRD patterns were collected on a Philips X-pert X-ray diffractometerat a scanning rate of 4 min–1 in the 2θ range from 6°C to 53°C with graphite monochromatized Mo-Kα radiation (λ= 0.71073Å) with an X’ Celerator detector. We also took crystal images using a digital microscope (magnification of 100 X).
X-ray diffraction
The single crystal X-ray diffraction data of compound
Crystal data details for 1
Crystal data details for
Selected bond lengths (Å) and angles (∘) for
Comparison of some important parameters of compounds
Description of crystal structures
Crystal structure of compound 1 (C6H3) (CH2NH3)2+ (CH2NH2)]2· (β-Mo8O26)·3H2O
At present, the methods for the synthesis of arylmethylamines are: (1) Reductive
amination of aldehydes; (2) Gabriel Method; (3) Hexamethylenetetramine method [21, 22];
(4) other methods, such as reduction of alcohol, reduction of nitro compounds, improved
Mitsunobu reaction and Bucherer reaction, etc. Based on the above studies, compound
(a) The simplified repeated unit plots of compound
To prove the purity of the samples in the solid, X-ray powder diffraction analysis was
implemented for compound
Power X-ray Diffraction of compound
Figure 3 displays the UV spectrum
of the compound
UV spectrum of the compound
To investigate thermostability of compound
TG plot of compound
Optical band gap of compound 1
The forbidden band width is called the optical band gap (indicated by Eg),
which is a significant parameter for estimating semiconductor materials. In this
experiment, the corresponding band gap values were calculated by measuring UV–vis of
compound
Optical band gap of compound
The study of using semiconductor materials to purify pollutants in wastewater under
visible light has attracted more and more attention [19]. We investigated the photodegradation ability of compound
Curve of photodegradation MB solution and blank control.
Curve of photodegradation RhB solution and blank control.
To investigate the ability that compound
Adsorption diagram for RhB of compound
Adsorption diagram for MB of compound
In this paper, compound
Footnotes
Acknowledgments
Research efforts in the Niu group are supported by the National Science Foundation of China (No. 21671177).