Syntheses, crystal structures, and photocatalytic properties of two zinc(II) coordination polymers based on dicarboxylates and flexible bis(benzimidazole) ligands

Accepted Manuscript Syntheses, crystal structures, and photocatalytic properties of two zinc(II) coordination polymers based on dicarboxylates and flexible bis(benzimidazole) ligands Hui Zhu, Dong Liu, Yue-Hua Li, Guang-Hua Cui PII: DOI: Reference:

S0277-5387(19)30258-X https://doi.org/10.1016/j.poly.2019.04.011 POLY 13871

To appear in:

Polyhedron

Received Date: Revised Date: Accepted Date:

15 March 2019 7 April 2019 9 April 2019

Please cite this article as: H. Zhu, D. Liu, Y-H. Li, G-H. Cui, Syntheses, crystal structures, and photocatalytic properties of two zinc(II) coordination polymers based on dicarboxylates and flexible bis(benzimidazole) ligands, Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.04.011

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Syntheses, crystal structures, and photocatalytic properties of two zinc(II) coordination polymers based on dicarboxylates and flexible bis(benzimidazole) ligands Hui Zhu, Dong Liu, Yue-Hua Li, Guang-Hua Cui* College of Chemical Engineering, Hebei Key Laboratory for Environment Photocatalytic and Electrocatalytic Materials, North China University of Science and Technology, No. 21 Bohai Road, Caofeidian new-city, Tangshan, Hebei, 063210, P. R. China

Corresponding author: Guang-Hua Cui Fax: +86-0315-8805462. Tel: +86-0315-8805460. E-mail: [email protected]

Abstract:

Two

new

ternary

zinc(II)

coordination

polymers

(CPs),

catena-(μ2-phthalato)-(μ2-1,1'-hexane-1,6-diylbis(2-methyl-1H-benzimidazole))-zinc (CP 1) and catena-(μ2-phenylene-1,4-diacetato)-(μ2-1,1'-hexane-1,6-diylbis(1H-benzimidazole))-zinc (CP 2) were synthesized via hydrothermal process. CP 1 and CP 2 are named as [Zn(L1)(PA)]n and [Zn(L2)(PDA)]n

(L1

=

1,1'-hexane-1,6-diylbis(2-methyl-1H-benzimidazole),

L2

=

1,1'-hexane-1,6-diylbis(1H-benzimidazole), H2PA = phthalic acid, H2PDA = 1,4-phenylenediacetic acid)), respectively. Both CPs were characterized by elemental analysis, infrared spectroscopy, single crystal X-ray diffraction analysis. CP 1 possesses a 4-connected 66-dia network, CP 2 displays a 2D hcb layer with point symbol {63}. Luminescence, UV-vis diffuse reflection spectra, and photocatalytic properties of two CPs for the degradation of the methylene blue (MB) dye were investigated. The mechanism of photocatalytic degradation of MB was also suggested. Keywords: Bis(benzimidazole); Coordination polymer; Crystal structure; Photocatalytic property ; Zinc(II)

1.

Introduction Coordination polymers (CPs) have attracted considerable attention in recent years due to their

promising applications in gas storage, separation, catalysis, sensing, magnetism [1-5]. Although many CPs were synthesized and characterized, it is still a huge challenge to obtained CPs with desired properties. The selection of suitable metal ions and organic ligands is the key to the construction CPs [6-11]. Zn(II) ions allow a variety of coordination geometries with coordination numbers(4-6) due to its d10 configuration [12]. Zn(II) CPs show intriguing luminescent behavior and unique reactivity and facilitated the development of new photocatalytic system [13]. When flexible bis(benzimidazole) ligands with –(CH2)n– (n = 1–6) spacers are employed as N-donor ligands, those bis(benzimidazole) linkers can bend and rotate freely when coordinated to the metal center

[14-15].

However,

a

few

CPs

based

on

long

and

flexible

1,1'-hexane-1,6-diylbis(1H-benzimidazole) ligands derivatives were reported, most of them show unique

structures

and

properties

[16-17].

Moreover,

phthalic

acid

(H2PA)

and

1,4-phenylenediacetic acid (H2PDA) as aromatic dicarboxylic acids can partially or completely deprotonated to satisfy the charge balance of CPs and exhibit diverse coordination modes [18]. especially, H2PDA possesses two acetates, which results in two different steric conformations (cisand trans-type) [19]. Methylene blue (MB) is widely used as a common industrial dye for dyeing wood, silk, cotton, [20], however, due to its complicated aromatic structure; this dye is difficult to biodegrade in the natural environment [21]. At present, a number of methods were developed to eliminate MB in wastewater [22]. Photocatalysis is a more environmentally friendly and convenient technology for degrading pollutants in wastewater compared with other process [23]. Our groups have reported a

series of photocatalyst based on flexible bis(benzimidazole) CPs [24-25]. In

this

paper,

two

Zn(II)

CPs,

namely,

catena-(μ2-phthalato)-(μ2-1,1'-hexane-1,6-diylbis(2-methyl-1H-benzimidazole))-zinc (CP 1) and catena-(μ2-phenylene-1,4-diacetato)-(μ2-1,1'-hexane-1,6-diylbis(1H-benzimidazole))-zinc (CP 2) were hydrothermally synthesized and characterized. Two Zn(II) CPs can be written as [Zn(L1)(PA)]n and [Zn(L2)(PDA)]n (L1 = 1,1'-hexane-1,6-diylbis(2-methyl-1H-benzimidazole)), L2 = 1,1'-hexane-1,6-diylbis(1H-benzimidazole), H2PA = phthalic acid), respectively. The photocatalytic and luminescence properties of the two CPs are discussed. 2.

Experimental

2.1.

Materials and methods

Ligands L1 and L2 were synthesized following a literature procedure [26].All other reagents are commercially available and are not further purified. The C, H and N elements were determined using a Perkin-Elmer 240C analyzer. Powder X-ray diffraction (PXRD) data was measured on a Rigaku D/Max-2500PC diffractometer using a Cu target tube (λ = 1.5418 Å) and the operating conditions of the X-ray tube were 40 kV and 40 mA. FT-IR spectra were obtained by KBr compression on an Avatar 360 (Nicolet) spectrophotometer ranging from 4000 to 400 cm-1. The thermogravimetric analysis (TGA) of the two CPs was measured under a N2 protection by a Netzsch STA449 F1 thermal analyzer and heated from ambient temperature to 800 °C at a heating rate of 10 °C/min. The luminescence spectra of the powder solid sample were recorded on an FS5 luminescence spectrophotometer. Solid-state UV/Vis diffuse reflectance spectra were measured using a UV-Vis Puxi T9 UV-visible spectrophotometer with BaSO4 as a reference. 2.2. Synthesis of [Zn(L1)(PA)]n (1)

A mixture of Zn(NO)3·6H2O (0.2 mmol, 58.2 mg), L1 (0.1 mmol, 34.6 mg), H2PA (0.2 mmol, 33.2 mg) and H2O (10 mL) was placed in a 25 mL Teflon-lined high-pressure container. The pH value of the reaction mixture was adjusted to 6.5 by NaOH (0.4 mL, 0.1 mol/L). The mixture was heated at 140 °C for 3 days. Cool to room temperature at 10 °C/h to obtain colorless block crystal (yield: 48.7%, based on L1 ligand. Anal. Calc. for C30H30N4O4Zn (Mr = 575.95): C, 62.35; H, 5.54; N, 9.81%. Found: C, 62.49; H, 5.32; N, 9.67%. IR (KBr pellet, cm−1): 2928w, 1633s, 1509m, 1463w, 1408m, 1292w, 1083w, 744m. 2.3. Synthesis of [Zn(L2)(PDA)]n (2) The synthesis of CP 2 is similar to that of CP 1, except that the mixture is replaced by ZnSO4·7H2O (0.2 mmol, 57.4 mg), L2 (0.1 mmol, 31.8 mg), H2PDA (0.1 mmol, 19.4 mg), H2O (10 mL) and NaOH (0.2 mL, 0.1 mol/L). The pH value of the mixture is 6.6. After cooling at room temperature, colorless crystal CP 2 can be obtained (yield: 39.4%, based on L2 ligand. Anal. Calc. for C30H30N4O4Zn (Mr = 575.95): C, 62.47; H, 5.25; N, 9.76%. Found: C, 62.63; H, 5.13; N, 9.62%. IR (KBr pellet, cm−1): 2927s, 1622s, 1512m, 1377s, 1274w, 1196w, 924m, 752m. 2.4.

X-ray crystallography

The crystal data were measured at room temperature on a Bruker Smart 1000 CCD diffractometer with graphite-monochromatic Mo-Kα radiation using ω scan mode (λ = 0.71073 Å). Empirical absorption correction using the SADABS software packages [27]. The initial structure of CPs 1-2 was calculated by the novel dual-space method of the SHELXT-2018. Refinement using the full matrix least squares method in the SHELXTL package [28]. All non-H atoms were treated anisotropically. H atoms of the organic ligand are geometrically generated using a riding model and isotropically refined. The crystallographic data for CPs 1-2 are given in Table 1, and

the selected bond lengths and angles are shown in Table 2. (Insert Table 1-2) 2.5.

Photocatalytic experiments

The photocatalytic properties of CPs 1-2 were evaluated by degradation of MB under irradiation with a 300 W mercury lamp. 0.01 mmol CP samples were added to 100.0 mL of MB solution (10.0 mg/L). Before the photocatalytic experiment, suspension mixtures were placed and stirred for 1 h in the dark. Dark reaction allows adsorption-desorption equilibrium between the solid catalyst and the solution. After the dark reaction is complete, the Hg lamp is turned on to expose the mixture to ultraviolet light, maintaining magnetic stirring. Then take 3.0 mL of the suspension at 15 minute intervals, and centrifuge to remove residual catalyst. After removing the catalyst, analyze the characteristic absorption of the MB solution. This process was repeated as a blank in the absence of catalysts. The degradation efficiency (D) of MB can be calculated by the following formula: D = [(C0-Ct)/C0] × 100%

(1)

Where C0 is the initial concentration of the MB and Ct is the concentration of the MB during the reaction.

3.

Results and discussion

3.1

Crystal structure of [Zn(L1)(PA)]n (CP 1)

CP 1 crystallized in the monoclinic space group P21/n, and the asymmetric unit of CP 1 contained a Zn(II) ion, two half of L1 ligands and one completely deprotonated PA2– ligand. As shown in Fig.1a, the Zn(II) center is four-coordinated by two N atoms from different L1 ligands (Zn1−N1 = 2.062(2) Å, Zn1−N3 = 2.066(2) Å) and two O atoms from distinct PA2– ligands. (Zn1−O1 = 1.943(2) Å, Zn1−O4A = 1.942(2) Å, symmetry code: A = -x+1/2, y-1/2, -z+1/2), exhibiting a distorted tetrahedron with the geometric parameter τ4 = 0.86. In four-coordinated CPs, τ4 = 0 indicates a perfect plane planar geometry, and τ4 = 1 means a perfect tetrahedral geometry. The τ4 of intermediate structure takes a value from 0 to 1.00 [29]. In addition, the bond angles of the Zn(II) center are in the range of 98.57(9)−123.23(9)°, which are in the normal range compared with the reported Zn(II) CPs [30]. In CP 1, the L1 ligand exhibits trans-conformation and bridges the adjacent Zn(II) centers to form a 1D zigzag [Zn(L1)]n chain. The distance between Zn⋯Zn connected through the L1 ligand is 14.426(2) Å and 14.475(2) Å, and the benzimidazole rings in the L1 ligand are parallel to each other (Fig.S1). The central Zn(II) atoms are coordinated by PA2– ligands with (κ1-κ0)-(κ1-κ0)-μ2 pattern to form 1D zigzag [Zn(PA)]n chain. The distance between Zn⋯Zn linked across the PA2– ligand is 6.735(1) Å (Fig.S2). Two distinct types 1D chains cross-connected by sharing Zn(II) centers to form a complicated 3D framework (Fig.1b). If the Zn(II) atoms are simplified as nodes, and the L1 and PA2–ligands are defined as linkers, the 3D framework of CP 1 can be described as a 4-connected 66-dia network (Fig.1c). (Insert Fig.1)

3.2

Crystal structure of [Zn(L2)(PDA)]n (CP 2)

CP 2 crystallizes in the triclinic space group Pī. The asymmetric unit of CP 2 consists of a Zn(II) atom, an L2 ligand and two half of PDA2– ligands (Fig.2a). Each Zn(II) center is in a tetra-coordinated geometry with two N atoms from different L1 ligands(N1, N4A, symmetry code: A = -x+1, -y+1, -z+1), two O atoms from different PDA2– ligands(O1, O3), forming a distorted tetrahedral structure with the geometric parameter τ4 = 0.86. The bond lengths of Zn1−O1 and Zn1−O3 are 1.925(5) and 1.943(5) Å, respectively, and the bond lengths of Zn1−N1, Zn1−N4A are 2.014(5) and 2.030(5) Å. The bond angles around Zn(II) center (97.38(2)−123.86(2)°) are comparable to those found in other zinc(II) CPs [31]. In CP 2, PDA2– ligands display trans-conformation. The PDA2− ligands link the Zn(II) atoms via a (κ1-κ0)-(κ1-κ0)-μ2 coordination mode to form a 1D [Zn(PDA)]n linear chain (Fig.S3) in which the distance between Zn⋯Zn is 11.356(6) Å and 12.540(8) Å, respectively. The 1D linear chains further extended into a 2D layered structure by sharing Zn(II) centers with L2 coligands (Fig.2b). L2 adopts a cis–conformation, the torsion angle of Ndonor⋯N-Csp3⋯Csp3 is 40.63(1)°, and the dihedral angle between two benzimidazole rings is 84.636(2)°. The distance between the Zn(II) atoms connected through entire L2 ligand is 9.551(6) Å. The 2D layer can be classified as a hexagonal planar hcb network with point symbol {63} network (Fig.2c). The 2D network further stabilized by the π-π stacking interactions between the imidazole (Cg1: N3-C24-N4-C30-C25) and benzene (Cg2: C25B-C26B-C27B-C28B-C29B-C30B, symmetry code B: 1-x, 1-y, 1-z) rings of different L2 ligands. The centroid-to-centroid distance is 3.805(5) Å, and an inter-planar angle α = 0.4(4)° and slipping angles β and γ of 21.35 and 21.73°, and an averaged dπ-π distance of 3.535(3) Å (Fig.S4).

(Insert Fig.2) 3.3

PXRD and IR spectra

The phase purity of the samples of CPs 1-2 was examined by powder X-ray diffraction (PXRD). It can be seen from Fig.S5 and Fig.S6 that the experimental PXRD patterns are in good agreement with the simulated ones. These result suggests that the bulk samples are consistent with the determined single-crystal structures [32]. In the IR spectra, there are no strong absorption peaks around 1700 cm−1, indicating that PA2- in CP 1 and PDA2- in CP 2 are completely deprotonated. The characteristic bands of 1633, 1408 cm−1 for CP 1 and 1622, 1377 cm−1 for CP 2 may be caused by asymmetric and symmetric vibrations of carboxylate groups. The separation between these bands ( = [as(COO)–s(COO)]) indicate that the carboxylate acid groups in CPs 1-2 are in the monodentate coordination mode (225 cm−1 for CP 1, 245 cm−1 for CP 2) [33]. In addition, the appearance of the characteristic bands of CP 1 at 1509 cm−1 and CP 2 at 1512 cm−1 may be caused by the vC=N stretching of the benzimidazole rings of the L1, L2 ligands. 3.4 TGA and luminescence analysis TGA was used to determine the thermal stability of CPs 1-2. As can be seen from Fig.3, CP 1 rises from room temperature to 270 °C with almost no weight loss. Due to the decomposition of the L1 and PA2– ligands, the total weight loss in the temperature range of 271−539 °C is 86.0% (calcd 85.9%). The remaining weight matches the weight of ZnO (obsd 14.0%; calcd 14.1%). There is no obvious weight loss when CP 2 is below 194 °C. CP 2 also has only one weightless phase with L2 and PDA2− ligands decomposition in the range of 195-565 °C (obsd 86.2%; calcd 85.9%). Finally, the remaining residue was 13.8% (calcd 14.1%) consistent with ZnO.

(Insert Fig.3) The luminescence properties of CPs 1-2 and free L1, L2 ligands are investigated in solid state at room temperature (Fig.4). The peak position of the excitation spectra of the N-containing ligands and CPs 1-2 can be seen from Fig.S7. At 280 nm and 307 nm excitations, the maximum emissions of L1 and L2 ligands were 305 nm and 340 nm, respectively. This may be due to the π*→π transition of ligands. At the same time, there is a peak emission at 300 nm for CP 1 (λex = 280 nm) and a peak emission at 301 nm for CP 2 (λex = 240 nm). CP 1 is slightly blue-shifted compared to the peak position in the emission spectrum of the L1 ligand, and compared with L2, CP 2 blue-shift 39 nm. It is difficult to be oxidized or reduced for d10 Zn(II) ions. Therefore, the emission band is not caused by ligand-metal charge transfer (LMCT) or metal-ligand charge transfer (MLCT). The blue shift in CPs 1-2 may be due to ligand-to-ligand charge transfer (LLCT) [34]. (Insert Fig.4) 3.5

UV-vis absorption spectra

The UV-vis absorption spectra of solid-state CPs 1-2, L1, L2 ligands are measured at room temperature and the spectrum ranges from 200 to 800 nm. As shown in Fig.5a, the main absorption of L1 ligand is between 243 and 296 nm (λmax = 284 nm), and the absorption band of free L2 ligand is within the range of 246−287 nm (λmax = 284 nm), which may be assigned by the π*→π transition of aromatic ring [35]. The absorption peak of CP 1 is at 243 nm, ranging from 220 to 282 nm, while for CP 2, the peak is at 280 nm, and the range is 243−290 nm, which can be attributed to ligand-ligand charge transfer (LLCT). To explore semi-conductivity, convert diffuse reflectance data to Kubelka−Munk function (F = (1–R)2/2R, where R is the absolute reflectance of

the samples) to derive their band gap energy (Eg). It can be found from Fig.5b, the energy band gaps of the CPs 1-2 are about 2.98 eV and 3.93 eV, respectively. Therefore, CPs 1-2 may be potential materials for photocatalytic process. (Insert Fig.5) 3.6

Photocatalytic activities of CPs 1-2

Both CPs were employed as photocatalysts to examine the decomposition of MB. As can be seen from Fig.6a, MB solutions are not given any noteworthy change under UV light in the absence of photocatalysts. However, when both CPs were added as catalysts, the absorbance of MB decreased with the increase of reaction time (Fig.6b and Fig.6c). The relationship between the MB solution and the irradiation time can be derived from the Ct/C0 curve in Fig.7 (Ct represents the concentration of the MB solution at time t, and C0 represents the initial concentration of the MB solution). After 150 minutes, the degradation efficiency of MB for CP 1 was 84.2%, and for CP 2 was 88.1%, respectively. The degradation activity of CP 2 is slightly higher than CP 1. (Insert Fig.6, Fig.7) Based on the pseudo-first-order kinetic model, the reaction rate constant can be used to evaluate the photocatalytic MB decomposition. The reaction rate constant is represented by k (min−1), the reaction time is represented by t, and the pseudo-first-order kinetic equation can be written as ln(C0/Ct) = kt [36]. From Fig.8, it can be concluded that using CP 1 and CP 2 as photocatalysts, the rate constant k of degradation of MB is 0.0108 min−1 and 0.0131 min−1, respectively, which is almost five times that of the blank (0.0021 min−1). (Insert Fig.8) In order to understand the possible photocatalytic mechanism of CPs 1-2, tertiary butyl alcohol

(TBA), benzoquinone (BQ) and ammonium oxalate (AO) were added as scavengers for hydroxyl radical (·OH), oxygen radical (·O2-) and hole (h+) in the original photocatalytic experiments [37-38]. Fig.9 shows that in the photocatalytic process, when BQ or AO is present, the photocatalytic degradation efficiency is not significantly reduced, and it is proved that the ·O2- and h+ groups are not the main reactive species. However, when TBA is added, the degradation efficiency of CP 1 for MB is reduced from 84.2% to 31.4%, and the degradation efficiency of CP 2 is reduced from 88.1% to 39.2%. The results indicate that ·OH may play a major role in the degradation of MB by CPs 1-2 as photocatalysts. The possible photocatalytic reaction mechanism for the above degradation reactions is proposed as follows. In the presence of UV light, electrons (e−) could be excited from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), resulting in the same amount of h+ left on HOMO. The HOMO is mainly contributed by oxygen and (or) nitrogen 2p bonding orbitals and the LUMO is mainly contributed by empty Zn orbitals. The excited state e− in LUMO are easily lost, and HOMO strongly requires e− to return to its stable state. Therefore, one electron is captured from water molecules, which are oxygenated into the ·OH active species. Meanwhile, the e− in LUMO could be combined with the oxygen adsorbed on the surfaces of CPs 1-2 to form ·O2-, then they might transform to ·OH. The ·OH can effectively degrade MB into CO2, H2O and other harmless inorganic small molecules. (Insert Fig.9) Further, photocatalysts after use showed that the position of the peak were similar to that of the photocatalysts before the reaction by the PXRD diffraction pattern, indicating that the structure of the photocatalysts did not significantly change after the photocatalytic experiments (Fig.S8) which

indicates that CPs 1-2 can be recycled during photocatalysis. 4.

Conclusions Two zinc(II) CPs were synthesized by hydrothermal process. CP 1 is a 3D dia framework and

CP 2 possesses a 2D network with 3-connection point symbol {63}. CP 2 is superior to CP 1 as a photocatalyst for degrading MB. ·OH radicals play a major role in the photocatalytic degradation of MB.

Appendix A. Supplementary data CCDC 1892133 and 1892151 contain the supplementary crystallographic data for the CP 1 and CP

2,

respectively.

The

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: (+44) 1223-336-033; or e-mail: [email protected]. Acknowledgments The project was supported by the National Natural Science Foundation of China (51474086), Natural Science Foundation-Steel and Iron Foundation of Hebei Province (B2015209299).

References [1] L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P. Van Duyne, J.T. Hupp, Chem. Rev., 112 (2012) 1105-1125. [2] J. Lee, O.K. Farha, J. Roberts, K.A. Scheidt, S.T. Nguyen, J.T. Hupp, Chem. Soc. Rev., 38 (2009) 1450. [3] R.J. Kuppler, D.J. Timmons, Q.R. Fang, J.R. Li, T.A. Makal, M.D. Young, D. Yuan, D. Zhao, W. Zhuang, H.C. Zhou, Coord. Chem. Rev., 253 (2009) 3042-3066. [4] C.C. Wang, J.R. Li, X.L. Lv, Y.Q. Zhang, G. Guo, Energy Environ. Sci., 7 (2014) 2831-2867. [5] T. Zhang, W. Lin, Chem. Soc. Rev., 43 (2014) 5982-5993. [6] P. Falcaro, R. Ricco, C.M. Doherty, K. Liang, A.J. Hill, M.J. Styles, Chem. Soc. Rev., 43 (2014) 5513-5560. [7] Y. Han, J. R. Li, Y. Xie, G. Guo, Chem. Soc. Rev., 43 (2014) 5952-5981. [8] M. Dai, L.W. Zhu, J.H. Yang, H.X. Li, M.M. Chen, Z.G. Ren, J.P. Lang, Inorg. Chem. Commun., 29 (2013) 70-75. [9] C.C. Wang, X.D. Du, J. Li, X.X. Guo, P. Wang, J. Zhang, Appl. Catal., B, 193 (2016) 198-216. [10] Z.J. Lin, J. Lu, M. Hong, R. Cao, Chem. Soc. Rev., 43 (2014) 5867-5895. [11] J.X. Li, Z.B. Qin, Y.H. Li, G.H. Cui, Ultrason. Sonochem., 48 (2018) 127-135. [12] D.Z. Wang, J.Z. Fan, D. Jia, C.C. Du, CrystEngComm., 18 (2016) 6708-6723. [13] S. L. Yao, S. J. Liu, X. M. Tian, T. F. Zheng, C. Cao, C. Y. Niu, Y. Q. Chen, J. L. Chen, Inorg. Chem. 58 (2019) 3578–3581. [14] H.Y. Liu, H. Wu, J.F. Ma, Y.Y. Liu, B. Liu, J. Yang, Cryst. Growth Des., 10 (2010)

4795-4805. [15] X. J. Wei, D. Liu, Y. H. Li, G.H. Cui. J. Solid State Chem. 272(2019) 138-147. [16] W. Jing, Z.G. Ren, M. Dai, Y. Chen, J.P. Lang, CrystEngComm., 13 (2011) 5111-5118. [17] L. Liu, Y. Liu, G. Han, D. Wu, H. Hou, Y. Fan, Inorg. Chim. Acta, 403 (2013) 25-34. [18] S.B. Zhou, X.F. Wang, C.C. Du, D.Z. Wang, D. Jia, CrystEngComm., 19 (2017) 3124-3137. [19] X.Y. Xu, C. Chu, H.F. Fu, X.D. Du, P. Wang, W.W. Zheng, C.C. Wang, Chem. Eng. J., 350 (2018) 436-444. [20] C.C. Wang, X.H. Yi, P. Wang, Appl. Catal., B, 247 (2019) 24-48. [21] W. Wang, Y. Zhao, H. Bai, T. Zhang, V. Ibarra-Galvan, S. Song, Carbohydr. Polym., 198 (2018) 518-528. [22] T. Zeng, L. Wang, L. Feng, H. Xu, Q. Cheng, Z. Pan, Dalton Trans., 48 (2019) 523-534. [23] J.X. Li, Z.C. Hao, L. Ren, G.H. Cui, Z. Anorg. Allg. Chem., 644 (2018) 1196-1202. [24] X.X. Zhao, Z.B. Qin, Y.H. Li, G.H. Cui, Polyhedron, 153 (2018) 197-204. [25] J.X. Li, Y.F. Li, L.W. Liu, G.H. Cui, Ultrason. Sonochem., 41 (2018) 196-205. [26] A.T. Pu, J. Yang, W.Q. Kan, Y. Yang, J.F. Ma, Polyhedron, 50 (2013) 556-570. [27] G.M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 64 (2008) 112-122. [28] G.M. Sheldrick, Acta Crystallogr., Sect. C, 71 (2015) 3-8. [29] L. Yang, D.R. Powell, R.P. Houser, Dalton Trans., (2007) 955-964. [30] A.D. Volodin, A.A. Korlyukov, E.N. Zorina-Tikhonova, A.S. Chistyakov, A.A. Sidorov, I.L. Eremenko, A.V. Vologzhanina, Chem. Commun., 54 (2018) 13861-13864. [31] J.X. Hou, J.P. Gao, J. Liu, X. Jing, L.J. Li, J.L. Du, Dyes Pigm., 160 (2019) 159-164. [32] C.C. Du, X.F. Wang, S.B. Zhou, D.Z. Wang, D. Jia, CrystEngComm., 19 (2017) 6758-6777.

[33] J.W. Cui, S.X. Hou, Y.H. Li, G.H. Cui, Dalton Trans., 46 (2017) 16911-16924. [34] L. Lu, J. He, J. Wang, W.P. Wu, B. Li, A. Singh, A. Kumar, X. Qin, J. Mol. Struct., 1179 (2019) 612-617. [35] E. İnkaya, J. Mol. Struct., 1173 (2018) 148-156. [36] Y.Y. Niu, Z.Y. Li, S.M. Li, F.R. Wang, J. Mol. Struct., 1173 (2018) 763-769. [37] J. Chen, W. Wen, L. Kong, S. Tian, F. Ding, Y. Xiong, Ind. Eng. Chem. Res., 53 (2014) 6297-6306. [38] L.L. Wen, F. Wang, J. Feng, K.L. Lv, C.G. Wang, D.F. Li, Cryst. Growth Des., 9 (2009) 3581-3589.

Table 1 Crystallographic data and refinement parameter for CPs 1 and 2 Table 2 The selected bond lengths (Å) and angles (°) for CPs 1 and 2

Caption to Figures Fig.1 (a) Coordination environment of the Zn(II) center in 1. Hydrogen atoms are omitted for clarity. Symmetry codes for 1: A = -x+1/2, y-1/2, -z+1/2; B = -x+1, -y+2, -z; C = -x+1, -y+2, -z+1; D = -x+1/2, y+1/2, -z+1/2; (b) 3D structure for 1; (c) The 3D 4-connected dia framework for 1. Fig.2 (a) Coordination environment of the Zn(II) center in 2. Hydrogen atoms are omitted for clarity. Symmetry codes for 2: A = -x+1, -y+1, -z+1;B = -x+2, -y+2, -z+2;C = -x+1, -y, -z+2; (b) 2D structure for 2; (c) The hcb network with the point symbol {63} for 2. Fig.3 TGA curve of CPs 1-2 in N2 atmosphere Fig.4 Emission spectra of L1 and L2 ligands and CPs 1-2 Fig.5 (a) Solid state UV-vis absorption spectra of CPs 1-2; (b) Diffuse reflectance spectra of Kubelka-Munk functions versus energy for CP 1 and CP 2 Fig.6 (a) The absorption spectra of the MB solution degraded by ultraviolet irradiation without adding catalysts; (b) The absorption spectra of CP 1 as a photocatalyst for the catalytic degradation of MB solution under ultraviolet irradiation; (c) The absorption spectra of CP 2 as a photocatalyst for the catalytic degradation of MB solution under ultraviolet irradiation Fig.7 MB degradation efficiency under ultraviolet light irradiation Fig.8 Pseudo-first-order curve of MB photodegradation under ultraviolet light irradiation Fig.9 Photocatalytic activity type trapping experiment of CPs 1-2

Table 1 Crystallographic data and refinement parameter for CPs 1 and 2 CPs

1

2

Chemical formula

C30H30N4O4Zn

C30H30N4O4Zn

Formula weight

575.95

575.95

Crystal system

Monoclinic

Triclinic

Space group

P21/n

Pī

a (Å)

14.172(3)

9.564(4)

b (Å)

10.761(2) A

11.451(5)

c (Å)

17.681(4) A

13.919(9)

α (°)

90

102.95(5)

β (°)

92.443(3)

100.73(5)

γ (°)

90

108.90(3)

V (Å3)

2693.9(1)

1349.0(1)

Z

4

2

1.420

1.418

Absorption coefficient, mm–1

0.955

0.954

F(000)

1200

600

Crystal size, mm

0.23 x 0.21 x 0.19

0.22 x 0.22 x 0.20

θ range, deg

1.805–27.582

1.564–27.507

Index range h, k, l

-18/18, -13/14, -15/22

-10/12, -14/14, -17/17

Reflections collected

15895

8047

Independent reflections (Rint)

6147 (0.0410)

5886 (0.0430)

Data/restraint/parameters

6147/0/363

5886/0/352

Goodness-of-fit on F 2

1.028

0.956

Final R1, wR2 (I > 2σ(I))

0.0457, 0.0935

0.0799, 0.2107

Largest diff. peak and hole

0.783, -0.405

1.851, -0.649

Dcalcd

(g/cm3)

Table 2 The selected bond lengths (Å) and angles (°) for CPs 1 and 2 Parameter

Value

Parameter

Value

Zn(1)-O(4)A

1.942(2)

Zn(1)-O(1)

1.943(2)

Zn(1)-N(1)

2.062(2)

Zn(1)-N(3)

2.066(2)

O(4)A-Zn(1)-O(1)

123.23(9)

O(4)A-Zn(1)-N(1)

98.57(9)

O(1)-Zn(1)-N(1)

115.14(9)

O(4)A-Zn(1)-N(3)

109.27(9)

O(1)-Zn(1)-N(3)

101.72(8)

N(1)-Zn(1)-N(3)

108.52(9)

Zn(1)-O(1)

1.925(5)

Zn(1)-O(3)

1.943(5)

Zn(1)-N(1)

2.014(5)

Zn(1)-N(4)A

2.030(5)

O(1)-Zn(1)-O(3)

97.38(2)

O(1)-Zn(1)-N(1)

123.86(2)

O(3)-Zn(1)-N(1)

110.35(2)

O(1)-Zn(1)-N(4)A

104.49(2)

O(3)-Zn(1)-N(4)A

115.81(2)

N(1)-Zn(1)-N(4)A

105.41(2)

CP 1

CP 2

Symmetry codes for 1: A = -x+1/2, y-1/2, -z+1/2; B = -x+1, -y+2,-z; C = -x+1, -y+2, -z+1; D = -x+1/2, y+1/2, -z+1/2; for 2: A = -x+1, -y+1, -z+1; B = -x+2, -y+2, -z+2; C = -x+1, -y, -z+2

(a)

(b)

(c) Fig.1 (a) Coordination environment of the Zn(II) center in 1. Hydrogen atoms are omitted for clarity. Symmetry codes for 1: A = -x+1/2, y-1/2, -z+1/2; B = -x+1, -y+2, -z; C = -x+1, -y+2, -z+1; D = -x+1/2, y+1/2, -z+1/2; (b) 3D structure for 1; (c) The 3D 4-connected dia framework for 1.

(a)

(b)

(c) Fig.2 (a) Coordination environment of the Zn(II) center in 2. Hydrogen atoms are omitted for clarity. Symmetry codes for 2: A = -x+1, -y+1, -z+1; B = -x+2, -y+2, -z+2; C = -x+1, -y, -z+2; (b) 2D structure for 2; (c) The hcb network with the point symbol {63} for 2.

Fig.3 TGA curve of CPs 1-2 in N2 atmosphere.

Fig.4 Emission spectra of L1 and L2 ligands and CPs 1-2.

(a)

(b) Fig.5 (a) Solid state UV-vis absorption spectra of CPs 1-2; (b) Diffuse reflectance spectra of Kubelka-Munk functions versus energy for CP 1 and CP 2.

(a)

(b)

(c) Fig.6 (a) The absorption spectra of the MB solution degraded by ultraviolet irradiation without adding catalysts; (b) The absorption spectra of CP 1 as a photocatalyst for the catalytic degradation of MB solution under ultraviolet irradiation; (c) The absorption spectra of CP 2 as a photocatalyst for the catalytic degradation of MB solution under ultraviolet irradiation.

Fig.7 MB degradation efficiency under ultraviolet light irradiation.

Fig.8 Pseudo-first-order curve of MB photodegradation under ultraviolet light irradiation.

Fig.9 Photocatalytic activity type trapping experiment of CPs 1-2.

Graphical Abstract Pictogram Syntheses, crystal structures, and photocatalytic properties of two zinc(II) coordination

polymers

based

on

dicarboxylates

and

flexible

bis(benzimidazole) ligands Hui Zhu, Dong Liu, Yue-Hua Li, Guang-Hua Cui* Two ternary Zn(II) coordination polymers were synthesized under hydrothermal condition. The crystal structure of CP 1 possesses a 3D dia framework; CP 2 shows a 2D hcb network. CP 2 displays higher photocatalytic activities for degrading methylene blue than CP 1 under UV irradiation.