3D â 3D Interpenetrated Coordination Polymers ... - ACS Publications

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A Series of Zinc(II) 3D → 3D Interpenetrated Coordination Polymers Based On Thiophene-2,5-dicarboxylate and Bis(Imidazole) Derivative Linkers Hakan Erer,* Okan Zafer Yeşilel, and Mürsel Arıcı Department of Chemistry, Faculty of Arts and Sciences, Eskişehir Osmangazi University, 26480 Eskişehir, Turkey S Supporting Information *

ABSTRACT: Six coordination polymers of Zn(II) ions and three organic linkers namely, [Zn(μ4-tdc)(μ-bmeib)0.5]n (1), [Zn(μ4-tdc)(μ-betib)0.5]n (2), [Zn(μ4-tdc)(μ-bisopib)0.5]n (3), [Zn(μ4-tdc)(μ-pbmeix)0.5]n (4), [Zn(μ4-tdc)(μ-pbetix)0.5]n (5), [Zn(μ4-tdc)(μ-pbisopix)0.5]n (6), bisopib, pbetix, and pbisopix, where H2tdc = thiophene-2,5-dicarboxylic acid, bmeib = 1,4bis(2-methyl-1H-imidazol-1-yl)butane, betib = 1,4-bis(2-ethyl-1H-imidazol-1-yl)butane, bisopib = 1,4-bis(2-isopropyl-1Himidazol-1-yl)butane, pbmeix = 1,4-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene, pbetix = 1,4-bis((2-ethyl-1H-imidazol-1yl)methyl)benzene, pbisopix = 1,4-bis((2-isopropyl-1H-imidazol-1-yl)methyl)benzene, have been synthesized and structurally characterized by elemental analysis, IR spectra, NMR spectra and single-crystal and powder X-ray diffractions. Compounds 1−6 are isostructural and display a 3D cubic structure with 2-fold interpenetrated nets. Two crystallographically independent Zn(II) ions are bridged by four different thiopehene-2,5-dicarboxlylate linkers adopting a bis(monodentate) coordination mode to form a paddle-wheel unit forming two-dimensional layers. These 2D layers containing paddle-wheel unit are further pillared by bridging bis(imidazole) derivative linkers forming a 3D framework. Moreover, topological analyses show that two 3D frameworks are interlocked with each other to give a 2-fold interpenetrating pcu net with 412.63 topology. Interestingly, compound 3 is a 2fold heterointerpenetrating 2(1 + 1) three-dimensional (3D) framework. In addition, photoluminescence properties, thermal stabilities and Cu(II) ion exchange properties of the compounds were also investigated.

1. INTRODUCTION There has been great interest in the design and synthesis of coordination polymers because of their potential application in the fields including gas storage/separation, magnetic properties, sensor, catalysis, drug delivery, etc., and their fascinating topological structures.1−6 Organic linkers and metal clusters containing secondary building units (SBUs) are very important to obtain three-dimensional (3D) coordination polymers with the desired structures.7,8 However, it has been still difficult to estimate the final structure of coordination polymer because various factors, such as organic linkers, coordination geometry of metal centers, pH, temperature, and solvents, have great influence in the self-assembly process of coordination polymer.4,9−11 Among these factors, especially, organic linkers have effective role in the design and construction of coordination polymer.12 Among the organic linkers, multitopic polycarboxylates, especially aromatic dicarboxylates and N-donor bridging © XXXX American Chemical Society

ligands have been frequently chosen as building blocks in the construction of coordination polymers owing to their diverse coordination modes.13−15 In the syntheses of coordination polymers, interpenetration can occur due to the existence of large voids within the single framework and results in homo- or heterointerpenetrated nets.16,17 Interpenetration which has been mostly seen in the structures was investigated by Batten and Robson18 in detail and a lot of interpenetrated coordination polymers have been synthesized in the literature.9,19,20 It is wellknown that the usage of flexible or semiflexible linkers in the synthesis of coordination polymers usually ends up with the formation of interpenetration. Flexible and semiflexible bis(imidazole) linkers, as N-donor ligands, are good candidates to Received: February 25, 2015 Revised: May 27, 2015

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DOI: 10.1021/acs.cgd.5b00276 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Table 1. Crystallographic Data and Structural Refinement Summary for 1−6 complexes formula MW (g mol−1) diffractometer

1 C12H11N2O4SZn 344.66 Stoe IPDS-II

rad. /λ (Å) temperature (K) color crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z d (g cm−3) μ (mm−1) θ range (deg) measured reflns independent reflns Rint S R1/wR2 Δρmax/Δρmin (eÅ−3)

MoKα/0.71073 293 light yellow monoclinic P21/c 8.4979 (3) 13.2677 (3) 14.2857 (5) 90 120.695 (3) 90 1383.39 (8) 4 1.655 1.94 2.4−28.0 28050 2865 0.025 1.08 0.028/0.073 0.67/-0.64

2 C13H13N2O4SZn 358.68 Bruker APEXII Quazar


4 C14H11N2O4SZn 368.68 Agilent Supernova Eos



296 colorless monoclinic P21/n 8.588 13.660 12.433 90 92.08 90 1457.6 4 1.635 1.84 2.2−27.4 10771 3315 0.028 1.03 0.031/0.081 0.81/-0.51

150 colorless orthorhombic Pbcn 13.5930 (1) 15.4070 (2) 30.6000 (1) 90 90 90 6408.48 (10) 16 1.545 1.68 2.4−27.4 59372 7313 0.062 1.04 0.035/0.089 0.69/-0.48

293 colorless monoclinic C2/c 14.2067 (13) 16.6292 (14) 14.7442 (14) 90 90.963 (8) 90 3482.8 (5) 8 1.406 1.55 3.3−28.8 6919 3812 0.111 1.01 0.096/0.300 1.39/-1.90

145 colorless monoclinic C2/c 14.1870 (3) 16.5430 (4) 14.7590 (3) 90 90.686 (1) 90 3463.62 (13) 8 1.468 1.56 2.4−27.4 14082 3967 0.037 1.02 0.029/0.073 0.37/-0.31

145 light yellow monoclinic P21/n 10.151 13.086 13.062 90 94.93 90 1728.7 4 1.524 1.56 2.2−27.5 28934 3946 0.033 1.05 0.025/0.070 1.23/-0.35

heating rate of 10 °C min−1 in the temperature range 30−700 °C. The decomposition enthalpies (ΔH, kJ/mol) of each stage were examined by differential scanning calorimetry (DSC) at a heating rate of 10 °C min−1 in a Seiko DSC 6200 (Exstar 6000, Seiko Instruments Inc.). Powder Xray diffraction patterns (PXRD) were acquired on a Rikagu Smartlab Xray diffractometer operating at 40 kV and 30 mA with Cu Kα radiation (λ = 1.5406 nm). The photoluminescence spectra for the solid complex sample was determined with a PerkinElmer LS 55 Fluorescence spectrometer. AAS and EDX analysis was carried out with PerkinElmer AAnalyst 400 Atomic Absorption Spectrometer and Jeol JEM-1220 Electron Microscope. Diffraction data for 1 was collected on STOE IPDS-II diffractometer at 293 K; diffraction data for 4 was collected on Oxford Diffraction Agilent SuperNova diffractometer at 293 K; diffraction data for 2, 3, 5, and 6 were collected on Bruker APEXII QUAZAR three-circle diffractometer using Mo Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods using the program SHELXS9725 with anisotropic thermal parameters for all nonhydrogen atoms. All non-hydrogen atoms were refined anisotropically by full-matrix least-squares methods SHELXL-97.25 Molecular drawings were obtained using MERCURY.26 Topological analyses were performed using ToposPro software.27 Details of the refinement are presented in Table 1. Selected bond lengths and angles are listed in Supporting Information Table S1−S6. Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 918344 for 1, 948570 for 2, 948567 for 3, 918352 for 4, 948571 for 5, 948568 for 6, and 1045090 for pbisopix. 2.1. Preparation of the Ligands. 1,4-Bis(2-isopropyl-1Himidazol-1-yl)butane (bisopib). The product was synthesized according to modified procedure from literature.22 A mixture of 2isopropylimidazole (6.61 g, 60 mmol) and NaOH (2.40 g, 60 mmol) was stirred in 60 mL of DMSO at 60 °C for 2 h. Then, 1,4dibromobutane (6.05 g, 28 mmol) was added into mixture and stirred at 60 °C for 1 day. After 1 day and cooling to room temperature, DMSO was removed through evaporator. The crude product was stirred in 100 mL ethyl acetate and filtered. The filtrate was evaporated in water bath to obtain yellow oily product. bisopib was further purified with column chromatography using a mixture of MeOH/CH2Cl2 (1:10 v/v) as eluent

obtain interpenetrating structures because of alkyl −CH2− spacers.19 In this study, two -methyl, -ethyl, and -isopropyl groups were inserted into the bis(imidazole) to systematically investigate the effect of substituted groups on the final structures of coordination polymers. Moreover, the combining of N-donor ligands and multicarboxylates have been widely studied for construction of novel coordination polymers with the intriguing versatile architectures to satisfy the coordination needs of metal ions.21 Inspired from the above-mentioned, six bis(imidazole) derivatives containing three new linkers, namely, bisopib, pbetix and pbisopix, were synthesized and their three-dimensional (3D) interpenetrated zinc coordination polymers with H2tdc ligand, namely, [Zn(μ4-tdc)(bmeib)0,5]n (1), [Zn(μ4-tdc)(μ-betib)0,5]n (2), [Zn(μ 4 -tdc)(μ-bisopib) 0,5 ] n (3), [Zn(μ 4 -tdc)(μpbmeix)0,5]n (4), [Zn(μ4-tdc)(μ-pbetix)0,5]n (5), and [Zn(μ4tdc)(μ-pbisopix)0,5]n (6) were obtained. They were characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. Topological, photoluminescence, thermal, and Cu(II) ion exchange properties of synthesized compounds were studied.

2. MATERIALS AND PHYSICAL MEASUREMENTS All chemicals used were analytical reagents and commercially available. Ligands, 1,4-bis(2-methyl-1H-imidazol-1-yl)butane (bmeib),22 1,4-bis(2-ethyl-1H-imidazol-1-yl)butane (betib),23 and 1,4-bis((2-methyl-1Himidazol-1-yl)methyl)benzene (pbmeix)24 ligands were synthesized according to the literatures. The IR spectra were recorded on a Bruker Tensor 27 FT-IR spectrometer with KBr pellets in the range of 400− 4000 cm−1. 1H NMR spectra were recorded on Varian 500 MHz spectrometer using CDCl3 solvent. Elemental analyses for C, H, and N were carried out with PerkinElmer 2400C Elemental Analyzer. A PerkinElmer Diamond TG/DTA Thermal Analyzer was used to record simultaneous TG, DTG and DTA curves in the static atmosphere at a B



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Figure 1. (a) Molecular structure of 1, (b) 2D layer, and (c) single 3D framework in 1. (d) Schematic representation of 2-fold interpenetrating topological structure in 1. to obtain yellow solid product. Yield: 73%. m.p.: 65−67 °C. Anal. Calcd for C16H26N4: C, 70.03; H, 9.55; N, 20.42%. Found: C, 69.93; H, 10.05; N, 20.46%. FT-IR (KBr, cm−1): 3108, 2968, 2932, 2872, 1738, 1668, 1558, 1442, 1382, 1276, 1070, 932, 727. 1H NMR (500 MHz, CDCl3): δ (ppm) = 1.20 (d, J = 10 Hz, 12H), 1.65−1.68 (m, 4H), 2.88−2.81 (m, 2H), 3.78 (t, J = 7.5 Hz, 4H), 6.65 (d, J = 5 Hz, 2H), 6.83 (d, J = 5 Hz, 2H). The 1H NMR spectrum of bisopib was given in Supporting Information Figure S1. 1,4-Bis(2-ethyl-1H-imidazol-1-yl)methyl)benzene (pbetix). The synthetic procedure of pbetix was similar to that of bisopib, except 2ethylimidazole (6.61 g, 60 mmol) and 1,4-bis(bromomethyl)benzene (7.39 g, 28 mmol) were used instead of 2-isopropylimidazole and 1,4dibromobutane. The crude orange oily product was precipitated by adding it dropwise into the mixture of CH2Cl2/ether (1:10, v/v) to obtain light yellow solid product. Yield: 52%. m.p.: 167−169 °C. Anal. Calcd for C18H22N4: C, 73.44; H, 7.53; N, 19.03%. Found: C, 73.25; H, 7.68; N, 19.14%. FT-IR (KBr, cm−1): 3111, 3087, 2978, 2941, 2879, 1639, 1521, 1492, 1469, 1429, 1375, 1249, 1053, 756. 1H NMR (500 MHz, CDCl3): δ (ppm) = 1.10 (t, J = 10 Hz, 6H), 2.47−2.42 (m, 4H), 4.89 (s, 4H), 6.66 (d, J = 5 Hz, 2H), 6.80 (d, J = 1.5 Hz, 2H), 6.87 (s, 4H). The 1H NMR spectrum of pbetix was given in Supporting Information Figure S2.

1,4-Bis((2-isopropyl-1H-imidazol-1-yl)methyl)benzene (pbisopix). The synthetic procedure of pbisopix was similar to that of bisopib, except 2-isopropylimidazole (6.61 g, 60 mmol) and 1,4-bis(bromomethyl)benzene (7.39 g, 28 mmol) were used instead of 2isopropylimidazole and 1,4-dibromobutane. The remaining product was precipitated in 400 mL of ice water, collected by filtration and washed with water. The crude product was recrystallized with the mixture of MeOH/H2O (1:4, v/v) to obtain colorless block crystals. Yield: 67%. m.p.: 146−148 °C. Anal. Calcd for C20H26N4·H2O: C, 70.56; H, 8.29; N, 16.46%. Found: C, 70.43; H, 8.15; N, 16.48%. FT-IR (KBr, cm−1): 3421, 3132, 3105, 2966, 2929, 2868, 1517, 1490, 1454, 1361, 1278, 1070, 925, 729. 1H NMR (500 MHz, CDCl3): δ (ppm) = 1.20 (d, J = 5 Hz, 12H), 2.92−2.83 (m, 2H), 5.03 (s, 4H), 6.73 (d, J = 5 Hz, 2H), 6.94 (d, J = 1.5 Hz, 2H), 6.98 (s, 4H). The 1H NMR spectrum of pbisopix was given in Supporting Information Figure S3. Crystal data for C20H26N4·H2O: FW = 340.46, orthorhombic, space group Pbna, a = 11.686 Å, b = 11.971 Å, c = 14.314 Å, α = 90°, β = 90°, γ = 90°, V = 2002.4 Å3, Z = 4, Dcalcd = 1.129 mg/m3, λ = 0.71073 Å, T = 150 K, Rint = 0.086, and wR = 0.192, Bruker APEX II QUAZAR three-circle diffractometer, Mo Kα radiation. The molecular structure of pbisopix is given in Supporting Information Figure S4. 2.2. Preparation of the Complexes. [Zn(μ4-tdc)(μ-bmeib)0.5]n (1). A mixture of Zn(NO3)2·6H2O (0.47 g; 1.6 mmol), H2tdc (0.27 g, 1.6 mmol), bmeib (0.35 g; 1.6 mmol), and water (30 mL) was stirred at 90 C



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Figure 2. (a) Molecular structure of 2, (b) 2D layer, and (c) single 3D framework in 2. (d) Schematic representation of 2-fold interpenetrating topological structure in 2. °C for half an hour. Then the mixture was sealed in a 45 mL Parr brand Teflon-lined acid digestion bomb and heated at 170 °C for 4 days, and then cooled to room temperature at a rate of 5 °C/h. Pale yellow crystals of 1 were obtained (yield: 0.347 g, 63% based on Zn(NO3)2·6H2O). Anal. Calcd for C12H11N2O4SZn: C, 41.81; H, 3.22; N, 8.13; S, 9.30%. Found: C, 41.91; H, 3.31; N, 8.22; S, 9.38%. IR data (KBr, cm−1): 3165w, 3143w, 2935w, 2856vw, 1643s, 1558m, 1527s, 1375vs, 1278m, 1153m, 1012w, 802m, 771s, 736m, 673m, and 499m. The IR spectrum of 1 was given in Supporting Information Figure S5a. [Zn(μ4-tdc)(μ-betib)0.5]n (2). Complex 2 was obtained in a similar method to that of 1, but bmeib was replaced by betib (0.39 g, 1.6 mmol). Colorless crystals of 2 were obtained (yield = 0.378 g, 66% based on Zn(NO3)2·6H2O). Anal. Calcd for C13H13N2O4SZn: C, 43.53; H, 3.65; N, 7.81; S, 8.94%. Found: C, 43.49; H, 3.79; N, 7.88; S, 8.97%. IR data (KBr, cm−1): 3163w, 3140w, 2972w, 2939m, 2862w, 1643s, 1527s, 1496m, 1377vs, 1278m, 1155m, 1126m, 1083w, 1045m, 846w, 802m, 771s, 723m, 680m, 622w, 499m and 412w. The IR spectrum of 2 was given in Supporting Information Figure S5b. [Zn(μ4-tdc)(μ-bisopib)0.5]n (3). Complex 3 was obtained in a similar method to that of 1, but bmeib was replaced by bisopib (0.43 g, 1.6 mmol). Colorless crystals of 3 were obtained (yield = 0.691 g, 58% based on Zn(NO3)2·6H2O). Anal. Calcd for C14H15N2O4SZn: C, 45.11; H, 4.06; N, 7.52; S, 8.60%. Found: C, 44.85; H, 4.16; N, 7.52; S, 8.33%. IR data (KBr, cm−1): 3128m, 2962m, 2933m, 2873w, 1645vs, 1533s, 1485m, 1440m, 1382vs, 1276m, 1207m, 1163m, 1130m, 1078m,

1016m, 954w, 842vw, 800m, 769s, 727m, 678w, 553vw, 503m and 451w. The IR spectrum of 3 was given in Supporting Information Figure S5c. [Zn(μ4-tdc)(μ-pbmeix)0.5]n (4). Complex 4 was obtained in a similar method to that of 1, but bmeib was replaced by pbmeix (0.42 g; 1.6 mmol). Colorless crystals of 4 were obtained (yield = 0.365 g, 62% based on Zn(NO3)2·6H2O). Anal. Calcd for C14H11N2O4SZn: C, 45.60; H, 3.01; N, 7.60; S, 8.70%. Found: C, 45.17; H, 3.01; N, 7.24; S, 8.76%. IR data (KBr, cm−1): 3130w, 3032w, 2962w, 2924w, 1643s, 1535m, 1483m, 1380vs, 1288m, 1207w, 1161w, 1145w, 1078w, 1014w, 840vw, 804m, 769m, 742m, 680w, 669w, 505w, and 437w. The IR spectrum of 4 was given in Supporting Information Figure S5d. [Zn(μ4-tdc)(μ-pbetix)0.5]n (5). Complex 5 was obtained in a similar method to that of 1, but bmeib was replaced by pbetix (0.47 g, 1.6 mmol). Colorless crystals of 5 were obtained (yield = 0.434 g, 71% based on Zn(NO3)2·6H2O). Anal. Calcd for C15H13N2O4SZn: C, 47.07; H, 3.42; N, 7.32; S, 8.38%. Found: C, 47.04; H, 3.41; N, 7.39; S, 8.50%. IR data (KBr, cm−1): 3128m, 2979m, 2939w, 2879w, 1641vs, 1535s, 1500s, 1479s, 1380vs, 1163m, 1145m, 1085m, 1051m, 1016m, 952w, 842w, 804s, 769s, 729m, 680w, 648w, 599vw and 507m. The IR spectrum of 5 was given in Supporting Information Figure S5e. [Zn(μ4-tdc)(μ-pbisopix)0.5]n (6). Complex 6 was obtained in a similar method to that of 1, but bmeib was replaced by pbisopix (0.51 g, 1.6 mmol). Pale yellow crystals of 6 were obtained (yield = 0.437 g, 69% based on Zn(NO3)2·6H2O). Anal. Calcd for C16H15N2O4SZn: C, 48.43; D



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Figure 3. (a) Asymmetric unit of 3. View of the parallel two-dimensional layers of 3 along the c axis (b) and b axis (c). Hydrogen atoms and bisopib linkers were omitted for clarity. H, 3.81; N, 7.06; S, 8.08%. Found: C, 48.08; H, 4.02; N, 7.10; S, 8.16%. IR data (KBr, cm−1): 3168w, 3126w, 2964m, 2931w, 2873w, 1643s, 1523m, 1487m, 1375vs, 1288m, 1228m, 1128m, 1078m, 1020w, 956w, 877vw, 842w, 802m, 769s, 678w, 630w, 545w, 497m and 428w. The IR spectrum of 6 was given in Supporting Information Figure S5f.

total potential solvent volume of the 1D channel was found to be 72.9 Å3, which account for 5.3% of the total cell volume as calculated by PLATON.29 Complex 1 displays a pcu topology with the point symbol of 412.63. Additionally, there are π···π interactions between thiophene (Cg1) and imidazole (Cg2) rings which further stabilized the 3D framework [Cg1 = S1, C1, C2, C3, C4; Cg2 = N1, C7, C8, N2, C9; Cg1···Cg2i = 3.4902 Å, (i) −x, −y, −z]. Furthermore, there are the C−H···π interactions between the C12−H12A and Cg2 ring [H12A···Cg2 ii = 2.93 Å and C12−H12A···Cg2ii = 121°, (ii) 1 − x, −y, 1 − z]. [Zn(μ4-tdc)(μ-betib)0.5]n (2). The asymmetric unit of complex 2 contains one Zn(II) ion, one tdc ligand, and half betib ligand. The Zn(II) ion exhibit similar coordination to those in complex 1 (Figure 2a). The Zn(II) ion displays an square pyramidal geometry (ZnO4N), with equatorial positions occupied by four oxygen atoms of carboxylate groups from four different tdc ligands (τ = 0.0051). The axial position is occupied by a nitrogen atom from a betib ligand. Four different carboxylate groups coordinate two Zn(II) ions to form a paddle-wheel [Zn2(COO)4] secondary building unit (SBU) with the Zn···Zn distances of 3.1122(3) Å. The axial sites of the paddle-wheel are occupied by betib linkers to form a 2-fold interpenetrated 3D → 3D framework with 1D rectangle-like channel (Figure 2c). The structural topology analysis shows that compound 2 is classified as a pcu net with 41263 topology (Figure 2d). Two neighboring 3D frameworks are further connected by through π···π stacking between thiophene and imidazole rings with an interplanar distance of 3.6246 Å. [Zn(μ4-tdc)(μ-bisopib)0.5]n (3). Single crystal X-ray analysis reveals that complex 3 crystallizes in the orthorhombic space group Pbcn. The asymmetric unit consists of two Zn(II) ions, two tdc, and two half bisopib ligands. As shown in Figure 3a, two independent Zn(II) ions have similar coordination environments, and each Zn(II) ion is coordinated by one nitrogen atom from bisopib ligands and four oxygen atoms from four different

3. RESULTS AND DISCUSSION 3.1. Crystal Structures. The crystals of 1−3 were obtained by hydrothermal reaction of Zn(NO3)2·6H2O, thiophene-2,5dicarbocylicacid (H2tdc), and flexible linkers in water at 170 °C. When flexible linkers were replaced by semiflexible linkers under similar synthetic process, complexes 4−6 were obtained. Singlecrystal X-ray diffraction studies reveal that complexes 1−6 are isostructural and possess a 3D + 3D → 3D 2-fold interpenetrating framework. [Zn(μ4-tdc)(bmeib)0.5]n (1). Single-crystal X-ray analysis reveals that the complex 1 crystallizes in a monoclinic system with space group P21/c. The asymmetric unit of 1 contains one Zn(II) ion, one tdc and a half of bmeib ligands. As shown in Figure 1a, the Zn1 ion is five-coordinated locating in a nearly ideal square pyramidal coordination environment (τ = 0.00033)28 [ZnNO4], which is completed by four oxygen atoms from four different tdc ligands occupying equatorial plane with Zn1−O1 bond distance is 2.060(2) Å and one bmeib nitrogen atom occupying the axial site [Zn1−N1 = 1.998(2) Å] (Supporting Information Table S1). Two Zn(II) ions are bridged by carboxylate oxygen atoms of four tdc ligands to form paddlewheel [Zn2(CO2)4] units forming a 2D network (Figure 1b). This paddlewheel unit can be regarded as a secondary building unit (SBU), where the neighboring Zn(II) ions are separated by 3.0850(4) Å. The adjacent 2D layers are connected to each other by the exobidentate bmeib linker to further extend a 3D framework (Figure 1c). The most striking structural feature of 1 is that it possesses a 2-fold interpenetrating 3D architecture with 1D rectangle-like channel running along the c axis direction (6.455 × 8.567 Å) (Figure 1d). Despite the interpenetration, the E



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Figure 4. Single 3D framework in 3 with Zn1 ions (a) with Zn2 ions (b). (c) Schematic representation of racemic 2-fold (1 + 1) interpenetrating topological structure in 3 (red, framework with Zn1 ion; blue, framework with Zn2 ion).

hydrothermally synthesized. Complex 4 was obtained with Zn(NO3)2·6H2O and thiophene-2,5-dicarbocylic acid under the similar synthetic conditions when semiflexible 1,4-bis((2-methyl1H-imidazol-1-yl)methyl)benzene (pbmeix) was used instead of flexible linker. Compound 4 crystallizes in monoclinic, C2/c space group. The asymmetric unit of 4 contains one Zn(II) ion, one tdc anion and half pbmeix ligand. The Zn(II) ion has a distorted square pyramidal geometry (τ = 0.0083), coordinated by four carboxylate oxygen atoms in the equatorial plane and one imidazole nitrogen atom from pbmeix ligand in the axial positions (Figure 5a). Two crystallographically independent Zn(II) ions are bridged by four different thiophene-2,5dicarboxlylate ligands adopting a bis(monodentate) coordination mode to form a paddlewheel unit with the Zn···Zn distances of 3.063(1)Å. Paddlewheel type Zn2 clusters are connected together by tdc linkers to form a two-dimensional layer structure (Figure 5b). These 2D layers containing paddlewheel unit are further pillared by pbmeix linkers forming a 3D framework (Figure 5c). Further topological analysis suggests that two 3D frameworks are interlocked with each other to give a 2-fold interpenetrating pcu topology (Figure 5d). This 3D interpenetrated framework is further stabilized by strong π···π interaction between the imidazole rings (Cg1···Cg1 = 3.6728 Å). Furthermore, there are the C−H···π interactions between the C13−H13 and Cg1 ring [H13···Cg1 = 2.80 Å and C13−H13···

tdc ligands in a square pyramidal geometries [τ = 0.0086 and 0.0983, respectively]. All the Zn−N [Zn1−N1 = 2.015(18) and Zn2−N3 = 2.030(18) Å] and Zn−O bond distances are within the normal range.9 The two Zn(II) ions are bridged by four carboxylate groups from four different tdc ligand, forming a paddle-wheel SBU. In the SBU, the Zn1···Zn1 and Zn2···Zn2 distances are 3.124(4) and 3.177(4) Å, within the normal range found in other reported structures. Adjacent 2D [Zn2(tdc)2]n layers are pillared by μ-bisopib bridging linkers to form the 3D framework (Figure 4a and 4b). Bisopib linkers display an angular exobidentate bridging coordination mode with the interimidazole dihedral angle of 180° (through N1−N2−N2ii−N1ii) and −166.02° (through N3−N4−N4i−N3i). The distances between the Zn(II) ions bridged by the bisopib pillar are 12.422 and 12.308 Å. Interestingly, the final structure of complex 3 occurs interpenetration of two chiral single frameworks, leading to 2-fold heterointerpenetrating three-dimensional (3D/3D) frameworks (Figure 4c). Despite the interpenetration, the total potential solvent area volume of the compound 3 was found to be 480.2 Å3, which comprised 7.5% of the unit cell volume, according to a calculation performed with PLATON. [Zn(μ4-tdc)(μ-pbmeix)0.5]n (4). Complex 4 has been synthesized previously in the literature.30 To investigate the relationship between the flexibilities of the ligands and the structure of coordination polymers, [Zn(μ4-tdc)(μ-pbmeix)0,5]n (4) was also F



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Figure 5. (a) Molecular structure of 4, (b) 2D layer, and (c) single 3D framework in 4. (d) Schematic representation of 2-fold interpenetrating topological structure in 4.

penetration, the solvent-accessible volume of the unitcell of 5 is reduced to be 353.5 Å3, which is 10.2% of per unit cell volume. The neighboring 3D frameworks are linked to each other by the π···π interactions between adjacent imidazole rings (Cg1···Cg1 = 3.6537 Å, Cg1 = N1−C7−C8−N2−C9) which further stabilized the 3D framework. Additionally, there are C−H···π interactions between C12−H12 and imidazole ring (Cg1) [C12···Cg1 = 3.4325 Å, H12···Cg1 = 2.84 Å and C12−H12···Cg1 = 123°]. [Zn(μ4-tdc)(μ-pbisopix)0.5]n (6). To further examine the influence of the semiflexible ligands on the structure, we used pbisopix instead of pbetix ligand. When pbisopix ligand was used as the auxiliary ligand, a 2-fold interpenetrating 3D framework was obtained. The asymmetric unit of compound 6 contains one Zn(II) ion, one tdc and half pbisopix ligands. As shown in Figure 7a, the environment around Zn(II) ion can be described as a distorted square-pyramidal geometry, in which it is coordinated by four oxygen atoms from four tdc ligands in an equatorial plane and one nitrogen atom from pbisopix ligand occupy the axial position. The tdc ligand exhibits an exotetradentate coordination mode, which constructs Zn2C4O8 paddlewheel dimers with Zn···

Cg1 = 126°]. The total potential solvent area after interpenetration is 729.8 Å3 which represent 21.0% per unit cell volume. [Zn(μ4-tdc)(μ-pbetix)0.5]n (5). When pbetix linker was introduced into the reaction system, complex 5 was obtained. Single-crystal X-ray diffraction analysis reveals that the complex 5 crystallizes in the monoclinic system with the C2/c space group. Similarly to 4, the asymmetry unit consists of one Zn(II), one tdc and half pbetix ligands. The Zn(II) also shows a distorted squarepyramidal coordination geometry (τ = 0.003), being coordinated by four carboxylate oxygen atoms from four different tdc ligands and one nitrogen atoms from pbetix ligands (Figure 6a). The tdc ligand displays a similar μ4-η1:η1:η1:η1 coordination mode with 1−4 and similar Zn2C4O8 paddle-wheel unit with a Zn···Zn distance of 3.0562(3) Å is observed in compound 5. The dinuclear SBUs are then connected by the tdc ligands to form a 2D layers and adjacent [Zn(tdc)]n layers are further linked by pbetix linkers to form a 3D framework (Figure 6b and 6c). The compound 5 also shows 2-fold interpenetrated network of α-Po primitive cubic units (Figure 6d). Because of the interG



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upon excitation at 380 nm. The emission bands of the free ligand may be attributed to the π* → n or π* → π transitions.9 Emission spectra of complexes 1−6 are similar but complexes 2 and 5 exhibit very strong emission while complexes 1 and 6 show weak emission. Emission maxima at 442 nm for 1, 447 nm for 2, 444 nm for 3, 451 nm for 4, 453 nm for 5, and 460 nm for 6 are observed upon excitation at 380 nm (Supporting Information Table S7). Blue-shifts (about 30 nm) of the emission bands of complexes 1−6 are observed when compared to the emission of tdc. These emissions may be assigned to ligand-to-metal chargetransfer (LMCT). Moreover, these situations may be due to coordination of the tdc ligand to the Zn(II) centers, which significantly increase the rigidity and asymmetry of the ligand.9,31 The experimental PXRD patterns of the complexes 1−3 are agree with simulated patterns from their single-crystal structures to confirm the phase purity of the complexes at room temperature (Supporting Information Figures S6−11). Thermal analyses (TG/DTA) were performed to verify the thermal stability of the complexes (Supporting Information Figures S12−

Zn distances of 3.1370(3) Å as seen in complexes 1−5 (Figure 7b). Considering the paddlewheel dimers as six-connected node and tdc and pbetix ligand as two connected linkers, a topological analysis of the compound 6 was determined to be a interpenetrated pcu topology with the point symbol of 412.63. Despite the interpenetration, the PLATON analysis show the solvent-accessible volume accounts for 10.9% of per unit cell volume. The C−H···π interactions between the C16−H16 and imidazole ring (Cg1) [H16···Cg1 = 2.85 Å, C6···Cg1 = 3.4701 Å, and C6−H6···Cg1 = 125°] and C13−H13B and thiophene ring (Cg2) [H13B···Cg2 = 2.79 Å, C13···Cg2 = 3.3887 Å, and C21−H21A···Cg2 = 121°] play important roles in stabilizing the 3D framework (Figure 7c). 3.2. Photoluminescent, Powder X-ray Diffraction (PXRD), and Thermal Stabilities. As shown in Figure 8 and 9, solid-state photoluminescence spectra of complexes 1−6 and free H2tdc ligand were studied at room temperature. The free ligand H2tdc displays intense emission bands at 487 and 537 nm H



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Figure 8. Photoluminescence emission spectra of 1−3 and H2tdc.

S17). The TG curves show that thermograms of 1−6 are similar. The complexes 1−6 are stable up to 309, 312, 325, 306, 337, and 341 °C, respectively. In 1−6, thermal stabilities of bisimidazole complexes containing -methyl, -ethyl and -isopropyl substitute groups increase, respectively, when the number of substitute carbon increases on imidazole rings. This situation can be explained with increasing of basic force of ligands as a result of the increasing of electron densities on imidazole rings including

-methyl, -ethyl, and -isopropyl substitute groups, respectively. Thermal decomposition of complexes proceeds in two stages. The first stage results in a successive decomposition of the bis(imidazole) ligands. Last stage involves the highly exothermic decomposition of tdc ligands. The final products of the thermal decomposition were ZnO for 1−6. The thermo analytical results are summarized in Supporting Information Table S8. I



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Figure 9. Photoluminescence emission spectra of 4−6 and H2tdc.

3.3. Cu Exchanges of the Complexes. The synthesized complexes (30 mg) were immersed into 3 mL of Cu(NO3)2· 6H2O (0.014 mM) solutions at room temperature. After 3 days, Cu(II) exhanged complexes with color change were obtained. Cu(II) exchange complexes were washed with water and dried in air. The ratios of metal ions (Cu(II) and Zn(II)) in the complexes were determined by using AAS which was confirmed by EDX spectra. For AAS, the exchanged complexes were dissolved in conc. HNO3. The AAS and EDX (Supporting Information Figure S18) results show that Zn(II) ions in the complexes can be replaced by Cu(II) ions and the Cu(II)/Zn(II) ratios are given in Table 2, respectively. The Zn(II) ions in the

for optical devices. Moreover, Zn(II) ions were replaced by Cu(II) ions in the complexes and Cu(II) exhange properties of complexes were independent of ligands.

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NMR and IR spectra, TG and PXRD curves, and tables for bond distances and angles of complexes 1−6. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b00276.

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1

2

3

4

5

6

AAS EDX

3.38 2.95

8.83 9.51

5.86 4.57

2.73 1.97

8.69 9.80

8.81 10.20

AUTHOR INFORMATION

Corresponding Author

Table 2. AAS and EDX Results of Cu(II)/Zn(II) Ratios in Cu(II)-Exchanged Complexes 1−6 Cu(II)-exchanged complexes

ASSOCIATED CONTENT

S Supporting Information *

*E-mail: [email protected]. Tel: +902222393750. Fax: +902222393578. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Research Fund of Eskişehir Osmangazi University by Project Number 201219C101.

complexes 1−6 becomes Zn0.25Cu0.75, Zn0.1Cu0.9, Zn0.19Cu0.81, Zn0.34Cu0.66, Zn0.09Cu0.91, and Zn0.09Cu0.91, respectively. There are no effects of substitue groups on the Cu(II) ion exchanges of the synthesized complexes.

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4. CONCLUSIONS Six bis(imidazole) derivative ligands (three of them are the new) and their six 2-fold interpenetrated 3D coordination polymers were synthesized with Zn(II). Topological analyses showed that all complexes had pcu topology with the point symbol of 412·63. Two -methyl, -ethyl, and -isopropyl groups were introduced into the bis(imidazole) ligands to investigate the effect of substituted groups on structures of coordination polymers. The results showed that substituted groups inserted on bis(imidazole) ligands did not affect the topological structures of synthesized complexes. However, thermal stabilities increased with the changing of -methyl, -ethyl and -isopropyl substitute groups on imidazole rings. Moreover, photoluminescence spectra of the complexes showed that complexes 2 and 5 exhibited high emission in the other complexes and the emissions of complexes shifted blue compared to free tdc ligand. Complexes can be used J



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