Self-assembly and photocatalytic property of a new inorganic-organic hybrid material based on 1,4-bis(4-pyridylthio)butane

Abstract

A new hybrid compound consisting of 1,4-bis(4-pyridylthio)butane ([Bpytb]) ligand, namely {[Bpytb]Ag₂I₃}_n (1), has been prepared and characterized by IR spectroscopy, solid UV-visible diffuse reflectance spectrum, X-ray Powder Diffraction (PXRD) and TG. Compound 1 consists of 1D anion chain structure. Crystal system: Monoclinic, Space group: P₂/c, a = 4.5092(3), b = 11.1895(9), c = 21.3893(14), α= 90°, β= 92.907(2)°, γ= 90°, V = 1077.82(13) Å3, Z = 2, Dcalc = 2.693 g cm–3. The photocatalytic property of compound 1 was also studied and it exhibits a better degradation effect on organic dye MB.

Keywords

Self-assembly inorganic-organic thermostability

1 Introduction

Supramolecular compounds because of its crystal structure, magnetic, and electrical conductivity have the potential application of biology, catalysis and so on. It has gradually become one of the most active areas of research in chemical engineering and molecular science [1 –8]. With the rapid development of supramolecular polymers, more and more supramolecular compounds with novel structures and functional properties have been synthesized and reported and have developed into a large family of diverse types, such as rotaxane [9], chordine hydrocarbon [10], cyclodextrin [11], crown ether [12], etc.

Constructing functional organic-inorganic hybrid supramolecular polymers are a long-term research direction of many research group. In recent years, a series of organic-inorganic hybrid cluster rotaxanes have been synthesized by self-assembly with heterocyclic cation as template. During the study, it was found that it is easier to self-assemble with CuSCN to synthesize 2–3D penetrating cluster rotaxane structure, when the heterocyclic cation template has a side group [13]. The modification of organic cation templates, the introduction of functional groups, such as the addition of double bonds, the addition of side groups containing coordination sites, and the construction of functional supramolecular polymers with clustered rotaxane structures are still the focus of researchers [14, 15].

During the development of industrialization, industrial wastewaters with organic pollutants have become one of the serious environmental problems. Dyes that are electrically neutral, positive, or negative are usually difficult to degrade. Therefore, dyes must be removed before discharge. Recently, metal-organic frameworks (MOFs) have been widely used in the domain of selective adsorption and separation of dyes [16]. Therefore, developing some stable, low cost and available compounds are still a hard nut to crack in the photocatalysis field [17].

In this subject, 4-mercaptopyridine was used as a raw material to synthesize 1,4-bis(4-pyridylthio)butane. The compound was synthesized with silver iodide at 130°C with MeOH and DMF solvents. It was found that factors such as reaction conditions, solvents, and crystallization time will affect the structure of the compound. We have studied the crystal structure, photocatalytic properties of the compound. The ligand is shown in the Scheme 1.

Scheme 1

1,4-bis(4-pyridylthio)butane.

2 Experimental

2.1 Reagents

AgI (Aladdin, 99%), KI (Aladdin, 99%), 4-mercaptopyridine (J&K Scientific Ltd, 98%), CH₃OH (Sinopharm, 99%), DMF (Sinopharm, 99%), 1, 4-dibromoethane (J&K Scientific Ltd, 99%). All chemicals used in the synthesis were of A.R. grade (≥99%) and used without further purification. Distilled water was used for all procedures.

2.2 Materials and methods

The organic cation template 1,4-bis(4-pyridylthio)butane [Bpytm] was synthesized according to the reported procedure [18]. The IR spectra were 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. Uv-vis diffuse reflectance spectra (DRS) was recorded with the aid of a Cary 5000 UV-vis infrared spectrophotometer. Powder XRD patterns were collected on a Philips X-pert X-ray diffractometer at a scanning rate of 4°min^–1 in the 2θ range from 6 to 53° with graphite monochromatized Cu-Kα radiation (λ= 0.15418 nm) with an X’ Celerator detector.

2.3 Synthesis of {[Bpytb]Ag₂I₃}_n (1)

Compound 1 was prepared by solvothermal synthesis method. For compound 1, First put [Bpytb] (0.1 mmol), AgI (0.1 mmol), KI (0.4 mmol) in a 25 mL reaction kettle, then add 10 mL of deionized water, stir for 30 min to make it mix well, After 96 hours of reaction at a constant temperature of 120°C, After being completely cooled, colorless massive crystals were obtained with a yield of 64%. IR (KBr, cm–1): ν= 3440(m), 1589(w), 1477(w), 1384(s), 1278(w), 1110(s), 803(s), 724(w), 619(m), 482(m). Anal. Calcd for C₁₄H₁₇Ag₂I₃N₂S₂: C, 19.22; H, 1.95; N, 2.75%. Found: C, 19.18; H, 1.92; N, 2.78%.

2.4 X-ray crystallography study

The X-ray single crystal diffraction data of compound 1 was recorded on the Bruckner SMART CCD diffractometer with graphite-monochromatic Cu-Kα radiation (λ= 0.71073 Å) at 293K. Data reduction and absorption correction was done using the SADABS software package. After absorption correction, employ SHELXTL-97, OLEX-2 and other packages for analysis [19].

3 Results and discussion

3.1 Description of crystal structure

Crystal structure of compound {[Bpytb]Ag₂I₃}_n (1) X-ray SINGLE crystal diffraction shows that compound 1 was crystallized in monoclinic system with space group P₂/c. The unit cell parameters were a = 4.5092 (3), b = 11.1895 (9), c = 21.3893 (14) Å, and α= 90°, β= 92.907(2), γ= 90°. Compound 1 is composed of an inorganic moiety [Ag₂I₃]_n and a discrete organic ligand, meanwhile, [Bpytb] is protonated and loses the coordination ability. As shown in Fig. 1a, there are two central coordination metals Ag, which are different in coordination mode. Ag(1) forms four coordination with four iodine atoms; Ag(2) forms three coordination with three iodine atoms. Ag(1) and Ag(2) are bridged by Ag···Ag bonds to form a small three-membered ring structure with I(2). Two Ag(1), two Ag(2) and one I(2) are bridged by Ag···Ag bonds to form a five-membered ring, and extended infinitely into a 1D chain structure, as shown in Fig. 2b. Compound 1 forms a stable crystal stacking structure in the a-axis direction as shown in Fig. 2c. A compound most similar to 1 is compound 2. Compound 1 is a supramolecule, compound 2 is a complex. Compound 2 was crystallized in triclinic system with space group P-1 [20]. Cu(II) of compound 2 has a pentagonal coordination, in which Cu coordinates not only with nitrogen atoms on the two pyridine rings on the ligand and nitrogen atoms on the CSN^–, but also with oxygen atoms in the DMF in the solvent, as shown in Fig. 2(d–e). Comparison of some important parameters of compounds 1 and 2 are listed in Table 3.

Fig.1

(a) Minimum structural unit of compound 1; (b) One-dimensional chain structure of the inorganic part in the b-axis direction; (c) Stacked diagram of compound 1. (d) The structure unit diagram of 2. (e) Stacked diagram of compound 2.

Fig.2

Power X-ray Diffraction of compound 1.

Table 1

Crystal data and structure refinement details for compound 1

Compound	1
Empirical formula	C₁₄H₁₇Ag₂I₃N₂S₂
Formula weight	873.86
Crystal system	Monoclinic
Space group	P₂/c
a/Å	4.5092(3)
b/Å	11.1895(9)
c/Å	21.3893(14)
α (°)	90.00
β (°)	92.907(2)
γ (°)	90.00
V/Å³	1077.82(13)
Z	2
D_c/g cm^–3	2.693
μ/mm^–1	6.306
F(000)	800
Crystal size/mm	0.19x0.12x0.07
T/K	296(2)
Reflections collected	8534
Independent reflections(R_int)	1970(0.0620)
Data/restrains/parameters	1970/0/114
GOF on F²	1.030
Final R indices [I > 2σ(I)]	R1 = 0.0445,
	wR2 = 0.0987
R indices (all data)	R1 = 0.0834,
	wR2 = 0.1132
Largest diff. peak	0.833
hole(e Å^–3)	–0.758

Table 2

Selected bond lengths (Å) and bond angles (°) for compound 1

1
Ag1–Ag2	2.651(7)	Ag1–I1	2.724(5)	Ag1–I2²	3.065(7)
Ag1–I2	2.855(6)	Ag1–Ag2²	3.208(5)	Ag2–I2	2.617(3)
Ag1–I1²	2.834(7)	Ag2–I2²	2.855(3)	Ag2–Ag1	2.651(7)
Ag2–Ag1²	3.208(5)	Ag2–I2³	3.008(2)
Angle	°	Angle	°	Angle	°
1
Ag2¹–Ag1–I1	81.0(2)	Ag2¹–Ag1–I1²	170.49(15)	I1–Ag1–I1²	108.43(9)
Ag2¹–Ag1–I2	66.11(14)	I1–Ag1–I2	129.5(4)	I1²–Ag1–I2	105.9(2)
Ag2¹–Ag1–I2¹	59.42(13)	I1–Ag1–I2¹	103.2(2)	I1²–Ag1–I2¹	117.6(3)
I2–Ag1–I2¹	92.23(8)	Ag2¹–Ag1–Ag2	100.20(9)	I1²–Ag1–Ag2¹	70.32(15)
I2–Ag1–Ag2¹	50.74(8)	I2¹–Ag1–Ag2¹	78.20(14)	I2⁴–Ag2–Ag1¹	131.2(2)
I2⁴–Ag2–I2	157.84(9)	Ag1¹–Ag2–I2	67.5(2)	I2⁴–Ag2–I2¹	106.34(8)
Ag1¹–Ag2–I2¹	60.21(14)	I2–Ag2–I2¹	93.41(7)	I2–Ag2–Ag1⁴	112.57(19)
I2⁴–Ag2–Ag1¹	57.64(17)	Ag1¹–Ag2–Ag1	100.20(9)	I2¹–Ag2–Ag1	139.18(16)
Ag1–I1–Ag1¹	108.43(9)	Ag1–I1–Ag1²	108.43(9)	Ag2¹–I2–Ag1	71.63(18)
Ag2¹–I2–Ag2²	106.34(8)	Ag1–I2–Ag2¹	53.68(14)	Ag2–I2–Ag1¹	53.06(17)

Table 3

Comparison of some important parameters of compounds 1 and 2

Compounds	Crystal cell parameters	Crystal system	Space group	Refs
1	a = 4.5092(3) Å, b = 11.1895(9) Å, c = 21.3893(14) Å, α= 90°, β= 92.907(2)°, γ= 90°	Monoclinic	P₂/c	this article
2	a = 9.4271(3) Å, b = 11.3593(4) Å, c = 12.0958(5) Å, α= 71.095(4)°, β= 80.394(3)°, γ= 81.640(3)°	Triclinic	P-1	20

3.2 Powder X-ray Diffraction (PXRD)

Powder X-ray diffraction has been used to confirm the purity of the samples in the solid state. For compound 1 the PXRD patterns closely match the simulated patterns generated from the results of the single crystal diffraction data, the purity of compound 1 is confirmed by powder XRD analyses, in which the main peaks of the experimental spectra of compound 1 are almost consistent with its simulated spectra Fig. 2.

3.3 UV-vis diffuse reflectance property and study of optical band gap

Ultraviolet and visible absorption spectrum is a state where molecules or ions absorb a certain amount of radiant energy under the irradiation of ultraviolet or visible light (200–800 nm), and the electrons transition to a higher energy level. There are many forms of electrons in organic compound molecules: n electrons, σ electrons and π electrons. These electrons absorb energy to transition to higher energy levels. This electronic transition phenomenon is closely related to the internal structure of the compound. As shown in Fig. 3 a, compound 1 has a similar absorption peak in the 200–360 nm range, which can be attributed to the π–π* transition absorption peak of the organic ligand pyridine ring [21, 22]. In addition, the absorption peak of compound 1 also appeared at 344 nm. According to the Ag–Ag interaction in the crystal structure of compound 1, this absorption peak is classified as Ag⟶Ag* charge transition. For the sake of study the conductivity of compound 1, the band gap (Eg) is acquired by the measurements of diffuse reflectance. The band gap energy was evaluated to be 1.94 eV for 1 (Fig. 3 b). It display that compound 1 has feaible semiconductor peculiarity as underlying photocatalytic activity [23].

Fig.3

(a) Solid UV-visible diffuse reflectance spectrum of compound 1 (b) Band gap diagram of compound 1.

3.4 Photocatalytic properties

Recently, much attention has been paid to the decomposition of organic dyes by a semiconductor catalyst to purify waste water [24]. In order to investigate the removal of organic dyes (MO, RHB, MB) from water, compound 1 was immersed into an aqueous solution of MO (4.0×10^–5 M, 100 mL) RHB (2×10–5 mol/L) and MB (1.0×10^–5 M, 100 mL) for a designed time with 500 W mercury vapor lamp irradiation. The photodegradation processes of MO, RHB and MB without any catalyst have also been studied for the control experiment. The absorption peak of MO decreased from 0.9864 to 0.3892 for compound 1 over 100 min. And then, the absorption peak of RHB decreased obviously from 1.019 to 0.623 for compound 1 (120 mg) over 100 min. the absorption peak of MB decreased obviously from 0.7810 to 0.2064 for compound 1 over 10 min in a short time and with high efficiency. UV-irradiation of compound 1 leads to considerable holes and electrons, which can oxidize the organic dyes in the solution [25].

3.5 Thermogravimetric analyses

To investigate the thermal stability of compound 1. The thermogravimetric analyses (TGA) experiment was performed up to 800°C in a flowing N₂ atmosphere, With the increase of temperature, the mass of the compound changed accordingly. In compound 1, before rising to 200°C, the weightlessness process tends to be stable in the temperature range. Compound 1 has good thermal stability and less weight loss in crystals. The rapid loss of weight can be attributed to the decomposition of the organic ligand part of the crystal and the decomposition of most inorganic components within the temperature range of 283–462°C. During 462–797°C, there is a stage of thermal stability occurs, with the mass percentage remaining basically unchanged, possibly resulting in the formation of a new substance that is stable at high temperature. The weightlessness at this stage is mainly due to the thermal decomposition of a small part of the inorganic components (Fig. 5).

Fig.4

The insets are photos of the corresponding solutions at various times. (b–f) photocatalysis of MO solution (b), RHB solution (d), and MB solution (f) with the use of compound 1. (a–c) the control experiment without any catalyst.

Fig.5

TG plot of compound 1.

4 Conclusion

In this article, we successfully synthesized one new compound using 4-mercaptopyridine templated self-assembly. The infrared, solid UV-visible diffuse reflectance spectrum, X-ray powder diffraction and TG of compound 1 were fully characterized. The stability of compound 1 may be due to the presence of π–π stacking between the cationic ligand. The photocatalytic properties of compound 1 were studied and it exhibit a better degradation effect on organic dye MB.

5 Associated content

Important crystallographic data (Tables 1–3). CCDC reference numbers: 1582773 for 1. This data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: t441223336033 or Email: deposit@ccdc.cam.ac.uk.

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Self-assembly and photocatalytic property of a new inorganic-organic hybrid material based on 1,4-bis(4-pyridylthio)butane

Abstract

Keywords

1 Introduction

2.1 Reagents

2.2 Materials and methods

2.3 Synthesis of {[Bpytb]Ag2I3}n (1)

2.4 X-ray crystallography study

3 Results and discussion

3.1 Description of crystal structure

3.3 UV-vis diffuse reflectance property and study of optical band gap

3.5 Thermogravimetric analyses

5 Associated content

References

2.3 Synthesis of {[Bpytb]Ag₂I₃}_n (1)