Two 2D Zinc(II) Coordination Polymers and their Orange IV Composites

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Cite This: Cryst. Growth Des. 2019, 19, 211−218

Two 2D Zinc(II) Coordination Polymers and Their Orange IV Composites: Preparation, Structures, and Photocurrent Responses Published as part of a Crystal Growth and Design virtual special issue on Crystalline Functional Materials in Honor of Professor Xin-Tao Wu Xuan Zhou,‡,§,# Dan Liu,‡,# Fei-Fan Lang,⊥ Zhi-Gang Ren,*,‡ and Jian-Ping Lang*,‡,§

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College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, People’s Republic of China § State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China ⊥ Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, U.K. S Supporting Information *

ABSTRACT: Reactions of Zn(OAc)2·2H2O with N1,N4-bis(5fluoropyridin-3-yl)succinamide (bfps) and 1,2,3-benzenetricarboxylic acid (1,2,3-H3BTC) or 1,3,5-benzenetricarboxylic acid (1,3,5-H3BTC) under hydrothermal conditions produce two Zn(II)-based coordination polymers (CPs), {[Zn3(bfps)(1,2,3BTC) 2 (H 2 O) 6 ]·4H 2 O} n (1·4H 2 O) and {[Zn(bfps)(1,3,5HBTC)]·H2O}n (2·H2O). Both compounds show two-dimensional layer structures derived from interconnecting dinuclear [Zn2(1,2,3-BTC)2(H2O)2] units through the bfps bridges and the [Zn(H 2 O) 4 ] species (1·4H 2 O) or interlinking dinuclear [Zn2(1,3,5-HBTC)2] units via pairs of bfps bridges and pairs of 1,3,5-HBTC dianions (2·H2O). They display high absorptive capacities toward Orange IV (OIV) in water, i.e., 718 mg·g−1 (1· 4H2O) and 794 mg·g−1 (2·H2O), respectively. The resulting CP-OIV composites with the chemical formulas of 1·2.0OIV (3) and 2·1.1OIV·2.5H2O (4) exhibit enhanced photocurrent responses in relation to those of the two precursors.

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INTRODUCTION For decades, coordination polymers (CPs) have continued to be one of the most attractive topics in modern inorganic chemistry due to their numerous potential applications in energy storage/conversion,1−7 organic catalysis,8−11 sensors,12−15 optics,16 pollutant treatments,17−23 and electronics.24,25 In recent years, in order to improve performances of CPs in physical and/or chemical properties, people are trying to prepare the CPs-based composites by loading or mixing various active species such as metal nanoparticles/ nanorods (NPs/NRs),26−33 metal oxides,34−38 quantum dots (QDs),39 polyoxometalates (POMs),40 graphene, carbon nanotubes (CNTs),41,42 and so on. Among them, organic dyes are one of such species which could be composited with CP-based substrates as they are good at capturing light,43−45 and have been applied successfully in detecting volatile compounds and being luminescent thermometers.46 Orange IV is one of the typical model compounds in polluted water treatment and has been used to improve the photovoltaic performance of some semiconductive materials such as ZnO.47 To date, although many CPs may exhibit interesting semiconductive performances, the electronic properties by CP−dye composites are less investigated.48−50 © 2018 American Chemical Society

Recently we have found that some one-dimensional (1D) CPs showed excellent adsorption capacities toward organic dyes, and the resultant CP-dye composites displayed better electronic performances. For example, the 1D CP {[Ag(bfps)]NO 3 } n (bfps = N 1 ,N 4 -bis(5-fluoropyridin-3-yl)succinamide) (Scheme 1) could absorb Orange II (OII) with a capacity of 662 mg·g−1).48 The as-prepared CP-OII composite demonstrated enhanced photocurrent responses and improved dielectric properties relative to those of the parent CP. The preliminary results encouraged us to expand the 1D CPs into higher dimensional structures which might have diversiform topologies and better thermal and water stabilities. In this work, we attempted to replace Ag(I) ions by Zn(II) and employed two tricarboxylic ligands, 1,2,3benzenetricarboxylic acid (1,2,3-H3BTC) and 1,3,5-benzenetricarboxylic acid (1,3,5-H3BTC), as the ancillary linkers. The two-dimensional (2D) CPs {[Zn 3 (bfps)(1,2,3-BTC) 2 (H2O)6]·4H2O}n (1·4H2O) and {[Zn(bfps)(1,3,5-HBTC)]· H2O}n (2·H2O) were isolated from the hydrothermal reactions Received: August 28, 2018 Revised: November 2, 2018 Published: December 14, 2018 211

DOI: 10.1021/acs.cgd.8b01295 Cryst. Growth Des. 2019, 19, 211−218

Crystal Growth & Design

Article

Scheme 1. Structures of bfps and OIV Used in This Work

of Zn(OAc)2·2H2O with bfps and 1,2,3-H3BTC or 1,3,5H3BTC. Compounds 1·4H2O and 2·H2O were revealed to hold high adsorptive capacities toward Orange IV (OIV) in water. Compared to those of the two parent CPs, the two resulting CP-OIV composites presented augmented photocurrent responses. Described herein are their preparations, structural characterization, OIV adsorption performances, and photocurrent responses.

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Å, T = 223 K). The reflection data were collected and reduced by using the program CrysAlisPro (Agilent Technologies, 2013), while adsorption correction (multiscan, SADABS53−55), and corrections for Lorentz and polarization effects were also applied. The structures 1· 4H2O and 2·H2O were solved by the direct method and refined on F2 by full-matrix least-squares using the SHELXTL-2016 Program package.56 All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were added theoretically. Selected crystallographic data and refinement parameters are listed in Table 1.

Table 1. Selected Crystallographic Data and Refinement Parameters for 1·4H2O and 2·H2O

EXPERIMENTAL SECTION

General Procedures. The preparation of bfps and analytic instruments utilized in this work are the same as those used in our previous works.51,52 All other reagents were obtained from commercial sources and used without further treatment. Preparation of {[Zn3(bfps)(1,2,3-BTC)2(H2O)6]·4H2O}n (1· 4H2O). A mixture containing Zn(OAc)2·2H2O (66 mg, 0.3 mmol), 1,2,3-H3BTC (42 mg, 0.2 mmol), bfps (30 mg, 0.1 mmol), and NaOH aqueous solution (15 mL, 0.01M) was sealed in a Pyrex glass tube (L = 15 cm, Φ = 7 mm). The tube was heated at 120 °C for 48 h and then slowly cooled (5 °C·h−1) to room temperature. Compound 1·4H2O was formed as pale yellow crystals from this solution, and then separated by filtration, washed with ethanol, and dried in air. Yield: 60.5 mg (34% based on Zn). Anal. Calcd for C32H38F2N4O24Zn3: C 35.04, H 3.49, N 5.11%; found: C 34.71, H 3.41, N 4.82%. IR (KBr disk): 3418 (m), 1690 (m), 1613 (s), 1598 (m), 1570 (m), 1467 (s), 1453 (m), 1430 (m), 1384 (s), 1368 (m), 1257 (w), 1192 (m), 908 (m), 779 (w) cm−1. Preparation of {[Zn(bfps)(1,3,5-HBTC)]·H2O}n (2·H2O). Compound 2·H2O was isolated as pale yellow crystals in a method similar to that used in the synthesis of 1·4H2O by using Zn(OAc)2·2H2O (22 mg, 0.1 mmol), 1,3,5-H3BTC (21 mg, 0.1 mmol), bfps (30 mg, 0.1 mmol), and H2O (10 mL). Yield: 32.2 mg (43% based on Zn). Anal. Calcd for C23H18F2N4O9Zn: C 46.21, H 3.04, N 9.37%; found: C 46.06, H 3.29, N 9.59%. IR (KBr disk): 3480 (m), 1700 (m), 1690 (s), 1623 (s), 1592 (m), 1565 (m), 1550 (s), 1476 (m), 1421 (m), 1384 (s), 1332 (m), 1283 (m), 1246 (s), 1186 (s), 1156 (s), 1030 (m), 905(w), 742 (m) cm−1. Preparations of 1·2.0OIV (3) and 2·1.1OIV·2.5H2O (4). Compound 1·4H2O (10.96 mg, 0.01 mmol) or 2·H2O (59.7 mg, 0.01 mmol) was carefully ground, and then added into 40 mL of the aqueous solution of OIV (0.02 mmol for 1·4H2O and 0.11 mmol for 2·H2O). The resulting suspension was stirred for 30 min and then separated by centrifugation. The solid of 3 or 4 was washed by water and dried in vacuo. Yield for 3: 17.7 mg (96% based on Zn). Anal. Calcd for C68H58Zn3Na2F2N10O26S2: C 45.84, H 3.76, N 7.32, S 3.21%; found: C 46.00, H 3.29, N 7.89, S 3.61%. IR (KBr disk): 3416 (m), 1655 (m), 1595 (s), 1516 (s), 1467 (w), 1455 (w), 1430 (m), 1385 (m), 1368 (m), 1322 (m), 1192 (s), 1123 (s), 1038 (s), 1008 (w), 847 (w), 828 (w), 758(m), 696 (w), 651 (w), 615 (w) cm−1. Yield for 4: 98.0 mg (97% based on Zn). Anal. Calcd for C42.8H31.4ZnNa1.1F2N7.3O11.3S1.1: C 49.63, H 4.02, N 10.33, S 3.61%; found: C 49.54, H 3.54, N 9.85, S 3.40%. IR (KBr disk): 3417 (m), 1655 (s), 1595 (s), 1515 (s), 1468 (m), 1455 (m), 1430 (m), 1385 (m), 1368 (m), 1322 (w), 1191 (s), 1124 (m), 1036 (m), 1008 (m), 848 (w), 829 (w), 758 (w), 723 (w), 695 (w), 651 (w) cm−1. Single-Crystal X-ray Crystallography of 1·4H2O and 2·H2O. The single-crystal X-ray diffraction measurements were performed on an Agilent Xcalibur CCD X-ray diffractometer (Mo Kα, λ = 0.71073

empirical formula formula weight crystal system space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 ρcalc/g·cm−3 Z μ/mm−1 F(000) R1a wR2b GOFc

1·4H2O

2·H2O

C32H38F2N4O24Zn3 1096.77 triclinic P1̅ 7.2588(6) 10.7300(11) 13.3673(13) 78.525(9) 75.258(8) 75.913(8) 966.11(16) 1.885 1 1.960 558 0.0387 0.0798 1.066

C23H18F2N4O9Zn 597.78 triclinic P1̅ 10.1238(5) 10.1546(5) 13.1084(6) 79.290(4) 70.630(4) 73.037(5) 1210.06(10) 1.641 2 1.092 608 0.0551 0.1031 1.061

R1 = Σ||F0| − |Fc||/Σ|F0|. bwR2 = {Σw(F02-Fc2)2/Σw(F02)2}1/2. cGOF = {Σw((F02-Fc2)2)/(n-p)}1/2, where n = number of reflections and p = total number of parameters refined. parameters refined. a

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RESULTS AND DISCUSSION Synthesis and Structural Characterization. Compounds 1·4H2O and 2·H2O were prepared via the one-pot hydrothermal reactions of Zn(OAc)2·2H2O, bfps, and 1,2,3H3BTC (or 1,3,5-H3BTC) in a molar ratio of 3:1:2 or 1:1:1. Changing the molar ratios of reactants and the pH values of the solutions could not increase their yields. The two compounds were air and moisture stable, and insoluble and stable in water and common organic solvents such as CHCl3, CH2Cl2, CH3CN, CH3OH, and CH3CH2OH, which was confirmed by powder X-ray diffraction (PXRD) patterns (Figure S1). Their elemental analyses were in agreement with their chemical formulas. The IR spectra of 1·4H2O and 2· H2O showed strong bands for CO of bfps at 1690 and 1700 cm−1, respectively. The characteristic bands at 1570, 1467, 1430, and 779 cm−1 for 1·4H2O, and 1565, 1476, 1421, and 724 cm−1 for 2·H2O were assigned as the C−N stretching vibrations of the pyridyl ring of bfps. Strong peaks at 1384 cm−1 for 1·4H2O and 2·H2O may be attributed to the 212



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Figure 1. (a) View of the coordination environments of Zn1 and Zn2 in 1. Symmetry codes: A: 1 − x, 2 − y, − z; B: 2 − x, 1 − y, 1 − z; C: 2 − x, 1 − y, 2 − z. (b) View of the 2D network of 1. (c) Packing diagram of the 2D layers in 1. Different layers were plotted as red, yellow and blue, respectively. All H atoms and lattice H2O molecules are omitted. Selected bond lengths (Å): Zn1−N1 2.016(2), Zn1−O4B 1.9222(18), Zn1−O6 1.9251(17), Zn1−O8 1.9743(19), Zn2−O2 2.0643(18), Zn2−O2C 2.0642(18), Zn2−O9 2.0592(19), Zn2−O9C 2.0592(19), Zn2−O10 2.1958(18), Zn2−O10C 2.1957(18).

carboxylate groups. The broad peaks at ∼3400 cm−1 indicated the presence of the coordinated and crystal lattice water molecules. Thermogravimetric analyses of 1·4H2O and 2·H2O (Figure S3a) revealed that after the elimination of water molecules before 190 °C (1·4H2O, weight loss 15.3%, calcd 16.4%) and 210 °C (2·H2O, weight loss 3.7%, calcd 3.0%), these compounds came to lose the bfps and 1,2,3-BTC (or 1,3,5-HBTC) ligands at higher temperatures, and finally they left the ZnO residue at 570 °C (1·4H2O: 25.3%, calcd. 22.3%) and 640 °C (2·H2O: 15.0%, calcd 13.6%), respectively. Compound 1·4H2O crystallizes in the triclinic space group P1̅, and the asymmetric unit contains half of a [Zn3(bfps)(1,2,3-BTC)2(H2O)6] molecule and two lattice H2O molecules. Zn1 is tetrahedrally coordinated by two O atoms from two adjacent carboxylate groups of one 1,2,3-BTC trianion, one N atom from bfps, and one O atom from the coordinated H2O molecule, while Zn2 is octahedrally coordinated by four H2O molecules and two O atoms from the third carboxylic group of two 1,2,3-BTC trianions (Figure 1a). Two Zn1 centers in 1 are joined together by two 1,2,3-BTC trianions to

form a dinuclear [Zn2(1,2,3-BTC)2(H2O)2] unit with a crystallographic center of symmetry located at the midpoint of the Zn1···Zn1B separation. This unit is further interconnected to its equivalent ones by the bridging bfps ligands and the [Zn(H2O)4] species along two directions, thereby generating a 2D layer structure extending approximately along the bc plane (Figure 1b). The lattice H2O molecules are located in-between the 2D layers via the H-bonding interactions with the coordinated H2O molecules around Zn2. The distance between the neighboring layers was calculated to be 6.34 Å (Figure 1c). For the four-coordinated Zn1 atom, the average Zn−N, Zn−O(water), and Zn− O(carboxylate) bond lengths (2.016(2) Å vs 1.9743(19) Å vs 1.9237(18) Å) are comparable to those of the corresponding ones observed in other tetrahedrally coordinated Zn(II) compounds {[Zn(4-Br-ip)(bpa)(H 2 O)]} n (2.016(2) vs 2.001(2) vs 1.951(2) Å, 4-Br-ip = 4bromoisophthalic acid, bpa = 1,2-bi(4-pyridyl)ethane)57 and [Zn(aben) 2 (py)(H 2 O)] (2.021(2) vs 2.0565(18) vs 1.9619(17) Å, Haben = 4-aminobenzoic acid).58 While for 213



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the octahedrally coordinated Zn2, the mean Zn−O(water) and Zn−O(carboxylate) distances (2.1365(19) Å vs 2.0643(18) Å) are close to those found in [Zn1.5(1,3,5-BTC)(L1)(H2O)2]· 1.5H2O (2.167(4) vs 2.026(3) Å, L1 = 1,2-bis(imidazol-1ylmethyl)benzene)59 and {[Zn(2-stp)(bpy)(H2O)(H2O)0.25]2[Zn(bpy)(H2O)4]·4H2O}n) (2.169(4) vs 2.101(3) Å, 2-stp = 2-sulfoterephthalate, bpy = 4,4′-bipyridine), respectively.60 Compound 2·H2O crystallizes in the triclinic space group P1̅, and its asymmetric unit consists of [Zn(bfps)(1,3,5HBTC)] and one lattice H2O molecule. Zn1 is octahedrally coordinated by four O atoms from three carboxylate groups of three 1,3,5-HBTC dianions and two N atoms from two bfps ligands (Figure 2a). Notably, one carboxyl group of each 1,3,5HBTC dianion remains protonated and uncoordinated. Two Zn centers are joined together by a pair of 1,3,5-HBTC dianions to form a centrosymmetric dinuclear [Zn2(1,3,5HBTC)2] unit. This unit is interlinked via pairs of bfps bridges and pairs of 1,3,5-HBTC dianions at vertical directions, producing a double-layer 2D network extending along the [0, −1, 1] plane (Figure 2b). The distance between the neighboring layers was calculated to be 7.26 Å (Figure 2c). The mean Zn−N and Zn−O bond lengths (2.153(3) Å vs 2.150(2) Å) are slightly longer than those of the corresponding ones found in {[Zn(2-stp)(bpy)(H2O)(H2O)0.25]2[Zn(bpy)(H2O)4]·4H2O}n (2.086(5) vs 2.101(3) Å).60 The lattice H2O molecules are situated in-between the 2D layers via the Hbonding interactions with the CO group of the bfps linker, COOH and COO groups of the 1,3,5-HBTC dianions of the neighboring layers. Adsorption Properties. The adsorption properties of 1· 4H2O and 2·H2O toward OIV were examined by adding the well-ground crystalline solid of 1·4H2O (32 mg, 0.03 mmol) or 2·H2O (17 mg, 0.03 mmol) into a 40 mL aqueous solution of OIV, followed by continuous stirring for 30 min. The amount of OIV used in the former case was 23 mg (0.063 mmol), while that in the latter was 13.5 mg (0.036 mmol). The amount of the residual OIV in the solutions was measured at each 5 min interval by monitoring the absorbance at 445 nm from the UV−vis spectra. As shown in Figure 3, the decreasing intensities of the UV−vis adsorption curves indicated that most of OIV were purged within 30 min. Attempts using more OIV did not lead to more absorption even in a longer time. The maxima absorptive capacities for 1·4H2O and 2·H2O were calculated to be 718 mg·g−1 and 794 mg·g−1, respectively. The resulting CP-OIV composites were separated by centrifugation and rinsed repeatedly with water, and named as 3 and 4, respectively. Their colors were obviously changed from pale yellow into dark-yellow (Figure 4). The UV−vis spectra of 3 and 4 showed broad absorptions between 360 and 520 nm (Figure S2a). Elemental analyses for C, H, N, and S coupled with the zinc contents obtained by using inductive coupled plasma emission spectroscopy (ICP) (3: 10.92%, calcd 11.05% and 4: 6.25%, calcd 6.30%) tentatively confirmed their chemical formulas to be 1·2.0OIV (3) and 2·1.1OIV· 2.5H2O (4), which also matched well with the results calculated from the above-mentioned UV−vis measurements. According to the survey X-ray photoemission spectroscopy (XPS) spectra (Figure S4) of 1·4H2O, 2·H2O, 3, and 4, peaks attributed to Zn 2p3/2 were all found at ∼1022 eV, suggesting the Zn centers in these complexes all maintained the oxidation state of +2. In addition, the S 2p peak at ∼168 eV in 3 and 4 could be attributed to the existence of the OIV− anion. The IR spectra of 3 and 4 (Figure S5) showed the bands related to the

Figure 2. (a) View of the coordination environment of Zn1 in 2. Symmetry codes: A: 2 − x, 1 − y, −z; B: 1 − x, 1 − y, −z; C: 1 − x, −y, −z; D: 1 − x, −1 − y, −1 − z. (b) View of the 2D network of 2. (c) Packing diagram of the 2D layers in 2. Different layers were plotted as red, yellow, and blue, respectively. All H atoms and lattice H2O molecules are omitted. Selected bond lengths (Å): Zn1−N1 2.168(3), Zn1−N4D 2.138(2), Zn1−O3 2.383(2), Zn1−O4 2.1390(19), Zn1−O5B 2.0456(19), Zn1−O6C 2.0330(18).

C = O (1690 cm−1), the py group (1595, ∼1570, ∼1467, and 1430 cm−1) and the −COO− group (1385 cm−1) of the bfps ligand, and the bands of −SO3− (∼1123, ∼1037, and 1008 cm−1) of the OIV− anion. The thermogravimetric analysis of 3 and 4 (Figure S3b) showed the weight loss of water molecules at 105 °C (3: 7.1%, calcd 6.1% and 4: 4.6%, calcd 4.3%). Upon heating up to 630 °C, it showed the combined loss of bfps, 1,2,3-BTC (or 1,3,5-HBTC), and OIV species, and finally left ZnO as a residual component (3: 14.9%, calcd 13.8% and 4: 7.7%, calcd 7.8%). 214



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Figure 3. Absorption spectra of the OIV solutions and the dynamic curves after mixed with (a) 1·4H2O or (b) 2·H2O at each 5 min interval.

Figure 5. PXRD patterns of 1·4H2O, 2·H2O, 3, and 4 coupled with those simulated from the single-crystal X-ray diffraction data of 1· 4H2O, 2·H2O, and those of pure OIV solid. The peaks marked with squares in 3 and circles in 4 were the newly appeared ones compared to those of 1·4H2O and 2·H2O.

belong to those of OIV were also observed. Pawley fittings of the PXRD patterns (Pawley refinement using TOPASAcademic program)61 of 3 or 4 were employed, which demonstrated that two phases might coexist in each case. Therefore, 3 may consist of 1·4H2O and a new phase, namely, 1-adsorb, which was indexed to have the rough unit cell parameters: triclinic, a = 9.763(4) Å, b = 12.302(5) Å, c = 15.822(6) Å, α = 81.48 (3)°, β = 116.93 (4)°, γ = 73.14 (3)°, V = 1532.1(14) Å3 (Figure S6). Similarly, 4 may contain 2· H2O and another new phase, namely, 2-adsorb, which held the following unit cell parameters: triclinic, a = 9.587(2) Å, b = 12.029(7) Å, c = 13.404(4) Å, α = 100.23 (2)°, β = 109.54 (3)°, γ = 104.52 (3)°, V = 1350.6(11) Å3 (Figure S7). In 1·4H2O and 2·H2O, the introduction of the negatively charged 1,2,3-BTC and 1,3,5-HBTC anions could balance the positive charges of the Zn2+ ions, giving two neutral 2D networks. Thus, the adsorption of OIV using 1·4H2O or 2· H2O seem unlikely being an ion-exchange process. We monitored the concentration of Na+ (c(Na+)) during the adsorption experiments (Figure S8). The c(Na+ ) was continuously decreased as time went on, and kept in line with the amount of the residual OIV measured by the UV−vis spectra. This phenomena suggested that both OIV− and Na+

Figure 4. Pictures of 1·4H2O, 2·H2O, 3, and 4 showing the color changes after the adsorption of OIV.

According to Figure 5, the PXRD patterns of the bulk samples of 1·4H2O and 2·H2O correlated well with those simulated from the their corresponding single crystal data. Nevertheless, the PXRD patterns of 3 and 4 indicated that the main structures of 1·4H2O and 2·H2O were partially maintained, while some new peaks (marked with squares and circles in the patterns, respectively for 3 and 4) which did not 215



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μA (2·H2O), 7.48 μA (3), and 7.62 μA (4), respectively. The photocurrents of the OIV composites 3 and 4 were 23.4 times and 3.1 times higher than those of 1·4H2O and 2·H2O. Such an enhancement in photocurrent responses was assumed to be the introduction of the light-adsorptive OIV species, which caused a remarkable reduction in the band gap from 1·4H2O (3.46 eV) to 3 (1.98 eV) or from 2·H2O (3.43 eV) to 4 (2.00 eV, Figure S2b, measured form the solid-state diffusionreflectance spectra) and was helpful to the electron transportation. Notably, when the OIV contents of 4 were larger than that of 3 (based on the above-mentioned absorptive capacities 718 mg·g−1 and 794 mg·g−1 for 1·4H2O and 2· H2O), the photocurrent of 4 was slightly larger than that of 3.

were absorbed simultaneously from the solution. Since the unit cell volume of the new phases 1-adsorb or 2-adsorb was larger than that of 1·4H2O or 2·H2O, some OIV− and Na+ ions might squeeze into the free space in-between the 2D layers of 1· 4H2O or 2·H2O, which caused the expansion between the layers. The driving force of such an insertion was supposed to be the H-bonding and electrostatic interactions62,63 between the 2D layer and OIV−/Na+, which might cause the elimination or addition of the lattice H2O molecules from/ into the layer structures. These interactions did lead to the decrease or increase of lattice H2O molecules in 3 and 4. SEM and TEM images (Figure S9) revealed that there was no obvious stratification of the complexes after adsorption, which demonstrated that some interactions were still maintained between the 2D layers. Photocurrent Responses. The cyclic voltammograms (CV) and photocurrent responses of the parent complexes 1· 4H2O and 2·H2O and their OIV composites 3 and 4 were examined by the method described in our previous work.64 CV measurements (Figure S10) in aqueous Na2SO4 solutions (0.1 mol/L) with or without the irradiation of an Xe light (150 W, 40 mW·cm−2, 400−1100 nm) indicated that these compounds remain stable at higher potentials on ITO glass, and might be reduced at a lower potential (0.7 V for 3 or 0.75 V for 4 vs SCE). Thus, only the anodic currents (bias 0.75 V for 1·4H2O, 3 and 0.8 V for 2·H2O, 4 vs SCE) that caused the H2O → O2 reaction were recorded by using a manual shutter to block the Xe light at each 20 s interval. As presented in Figure 6, the four compounds brought about the recurring anodic photocurrents of 0.32 μA (1·4H2O), 2.46

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CONCLUSION In this work, we demonstrated the preparation of two 2D CPs (1·4H2O and 2·H2O) by the reactions of Zn(OAc)2 with bfps and two tricarboxylic acids under hydrothermal conditions. Compounds 1·4H2O and 2·H2O hold dinuclear [Zn2(1,2,3BTC)2(H2O)2] or [Zn2(1,3,5-HBTC)2] units which are connected by bfps linkers and the [Zn(H2O)4] species (1· 4H2O) or couples of bfps and 1,3,5-HBTC dianions (2·H2O), forming two different 2D layer structures. The two CPs showed good adsorption performances toward OIV in water with maxima capacities of 718 mg·g−1 and 794 mg·g−1, respectively. The resulting CP-OIV composites correlated with the formulas 1·2.0OIV (3) and 2·1.1OIV·2.5H2O (4). The insertion of OIV led to the expansion between the 2D layers and the formation of new phase (1-adsorb or 2-adsorb). With the increasing amount of OIV contents, the composite could capture more light irradiation and exhibited better electron transportation. Thus, the photocurrent responses of 3 and 4 were 23.4 times and 3.1 times larger than those of the two parent CPs. It is anticipated that the aforementioned approach could be a promising pathway to prepare more CPs−dye composites with better optoelectronic performances.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.8b01295. Additional information regarding the TGA curves, XPS and IR spectra, and PXRD patterns of 1−4, Pawley refinement results, c(Na+) during the adsorption, and the cyclic voltammograms of 1−4 (PDF) Accession Codes

CCDC 1862650−1862651 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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*E-mail: [email protected]. Fax: 86-512-65880328; Tel: 86512-65882865 (J.-P.L). *E-mail: [email protected] .Tel: 86-512-65880328 (Z.G.R).

Figure 6. Photocurrent responses of (a) 1·4H2O, 3 and (b) 2·H2O, 4 coated on ITO electrodes. Conditions: bias 0.75 V (1·4H2O, 3) and 0.8 V (2·H2O, 4) vs SCE, [Na2SO4] = 0.1 mol/L.

ORCID

Jian-Ping Lang: 0000-0003-2942-7385 216



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Author Contributions

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X.Z. and D.L. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 21531006, 21671144, and 21773163), the State Key Laboratory of Organometallic Chemistry of Shanghai Institute of Organic Chemistry (Grant No. 2018kf-05), the Priority Academic Program Development of Jiangsu Higher Education Institutions, the “SooChow Scholar” Program of Soochow University and the Project of Scientific and Technologic Infrastructure of Suzhou (Grant No. SZS201708). We are grateful to the editor and the reviewers for their useful comments and suggestions.

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DEDICATION Dedicated to Professor Xin-Tao Wu on the occasion of his 80th birthday. REFERENCES

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Two 2D Zinc(II) Coordination Polymers and their Orange IV Composites

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