Coordination Polymers Assembled From 3, 3′, 5, 5

Article pubs.acs.org/crystal

Coordination Polymers Assembled From 3,3′,5,5′Azobenzenetetracarboxylic Acid and Different Bis(imidazole) Ligands with Varying Flexibility Mürsel Arıcı,† Okan Zafer Yeşilel,*,† and Murat Taş‡ †

Department of Chemistry, Faculty of Arts and Sciences, Eskişehir Osmangazi University, 26480 Eskişehir, Turkey Department of Science Education, Education Faculty, Ondokuz Mayıs University, 55139, Samsun, Turkey

‡

S Supporting Information *

ABSTRACT: Five new mixed-ligand coordination polymers, formulated as {[Cd2(μ6ao2btc)(μ-1,4-bmeib)(H2O)2]·2H2O}n (1), [Mn2(μ6-ao2btc)(μ-obix)2]n (2), [Cd2(μ6ao2btc)(μ-obix)2]n (3), [Zn2(μ4-aobtc)(μ-dib)2]n (4), and {[Zn2(μ4-ao2btc)(μ-dmib)2]· 2H2O}n (5) (aobtc and ao2btc = mono- and dioxygenated forms of 3,3′,5,5′azobenzenetetracarboxylate, 1,4-bmeib = 1,4-bis(2-methylimidazol-1yl)butane, obix = 1,2-bis(imidazol-1ylmethyl)benzene, dib = 1,4-bis(imidazol-1yl)benzene, and dmib = 1,4-bis(imidazol-1yl)-2,5-dimethylbenzene) have been synthesized using different bis(imidazole) ligands and characterized by elemental analyses, IR spectra, singlecrystal X-ray diffraction, powder X-ray diffraction, and thermal analyses (TG/DTA). Complexes 1−5 displayed diverse structures depending on flexible, semiflexible, and rigid bis(imidazole) linkers. Complex 1 has a three-dimensional (3D) structure with the rare sqc27 topology. Complexes 2 and 3 are isostructural with 3,6L19 topology. Complexes 4 and 5 display 2-fold interpenetrated 3D structures with new topology (the point symbol of 62·84) and bbf topology (the point symbol of {64.82}{66}2), respectively. Ao2btc and aobtc ligands show new coordination modes in 1 and 4, respectively. Moreover, thermal and photoluminescence properties of the complexes were discussed in detail. ions.16,17 In the literature, there are rare studies with respect to its mono- and dioxygenated forms. Furthermore, in the mixedligand assembly, bis(imidazole) derivatives as N-donor ligands have been extensively utilized to connect to metal ions easily. Imidazole rings of flexible and semiflexible bis(imidazole) ligands can freely rotate around -CH2- groups to generate a variety of conformations.18 The reported studies show that entanglement structures (interpenetration or polycatenation, etc.) can usually occur when flexible or semiflexible linkers are used in the synthesis of coordination polymers.12,14,18−20 However, as known, reaction conditions (pH and temperature, etc.) also have an important effect in the rational and controllable synthesis of the structures. Inspired by the above considerations, in this work, flexible, semiflexible, and rigid bis(imidazole) ligands were prepared. Their Zn(II), Mn(II), and Cd(II) coordination polymers, {[Cd2(μ6-ao2btc)(μ-1,4bmeib)(H2O)2]·2H2O}n (1), [Mn2(μ6-ao2btc)(μ-obix)2]n (2), [Cd2(μ6-ao2btc)(μ-obix)2]n (3), [Zn2(μ4-aobtc)(μ-dib)2]n (4), and {[Zn2(μ4-ao2btc)(μ-dmib)2]·2H2O}n (5) with 3,3′,5,5′azobenzenetetracarboxylic acid were synthesized to investigate their effects on the structures of the synthesized complexes. They were structurally characterized by elemental analysis, IR

1. INTRODUCTION During the last few decades, there has been a continued interest in the rational design and synthesis of coordination polymers due to not only their application fields such as gas storage/ separation, catalysis, luminescence, and sensors, but also their fascinating topological structures.1−8 Despite the syntheses of many coordination polymers, the controllable synthesis of coordination polymers has been still difficult. In the assembly of coordination polymers, several factors, such as organic ligands, metal ions, pH, solvents, and temperature, are the key factors.8−10 Hence, it is important to choose the organic ligands and metal ions and regulate the reaction conditions for desired structures. In the construction of coordination polymers with desired topology, mixed-ligand assembly has been an effective way.11 In the mixed-ligand assembly, polycarboxylates and N-donor ligands have been widely utilized for tunability of structural frameworks.11−13 Among the polycarboxylates, multidendate aromatic polycarboxylates as building blocks have been widely chosen in the construction of coordination polymers due to their diverse coordination modes. In this study, 3,3′,5,5′-azobenzenetetracarboxylic acid, used an anionic ligand, is easily oxidized to generate mono- or dioxygenated azoxy structures in its complexes in air.14,15 It has four carboxylate groups which can bind to metal ions in diverse coordination modes and is a rigid ligand which enhances the thermal stability when coordinated to metal © XXXX American Chemical Society

Received: March 28, 2015 Revised: April 30, 2015

A

DOI: 10.1021/acs.cgd.5b00432 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Table 1. Crystal Data and Structure Refinement Parameters for Complexes 1−5 empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) V (Å3) Z Dc (g cm−3) μ (mm−1) θ range (deg) measured refls independent refls Rint S R1/wR2 Δρmax/Δρmin (e·Å−3)

1

2

3

4

5

C14H16CdN3O7 450.70 triclinic P1̅ 8.5340 (1) 9.6573 (1) 10.2602 (1) 78.93 75.695 (1) 76.400 (1) 788.31 (2) 2 1.899 1.43 2.1−26.4 15299 3195 0.014 1.09 0.027/0.078 0.94/−1.06

C22H17MnN5O5 486.35 triclinic P1̅ 8.6073 (1) 10.2090 (2) 12.6781 (2) 108.254 (1) 97.836 (1) 97.302 (1) 1030.89 (3) 2 1.567 0.69 2.4−33.2 20605 4200 0.020 1.04 0.092/0.252 4.38/−3.78

C22H17CdN5O5 543.81 triclinic P1̅ 8.6453 (4) 10.3129 (5) 12.7250 (6) 109.491 (2) 95.535 (2) 97.425 (2) 1048.66 (9) 2 1.722 1.09 2.4−33.2 21800 4273 0.024 1.10 0.054/0.145 2.90/−5.60

C20H13N5O5Zn 468.72 orthorhombic Pbcn 11.8471 (2) 18.1104 (3) 17.8499 (3) 90.00 90.00 90.00 3829.80 (11) 8 1.626 2.19 4.9−73.8 7977 3736 0.029 1.05 0.082/0.251 1.98/−2.80

C22H19N5O6Zn 514.79 monoclinic P21/n 11.0990 (2) 12.1358 (2) 16.4905 (2) 90.00 103.305 (1) 90.00 2161.57 (6) 4 1.582 1.19 2.0−27.5 53188 4976 0.043 1.08 0.037/0.116 0.81/−0.91

0.558 mmol) and obix (0.067 g, 0.279 mmol) were used instead of CdCl2·2.5H2O and 1,4-bmeib. After 2 days, yellow crystals were obtained. Yield: 0.084 g, 31% (based on H4abtc). Anal. Calcd for C22H17MnN5O5: C, 54.33; H, 3.52; N, 14.40%. Found: C, 54.79; H, 3.01; N, 14.18%. IR (KBr, cm−1): 3097 (w), 2950 (w), 1624 (vs), 1591 (s), 1554 (s), 1515 (m), 1440 (s), 1377 (vs), 1234 (m), 1093 (m), 742 (m) cm−1. [Cd2(μ6-ao2btc)(μ-obix)2]n (3). The synthetic procedure of 3 was similar to that of 2, except that Cd(NO3)2·4H2O (0.172 g, 0.558 mmol) was used instead of Mn(NO3)2·6H2O. Yield: 0.221 g, 73% (based on H4abtc). Anal. Calcd for C22H17CdN5O5: C, 48.59; H, 3.15; N, 12.88%. Found: C, 49.03; H, 3.12; N, 12.43%. IR (KBr, cm−1): 3099 (w), 2953 (w), 1614 (vs), 1554 (s), 1518 (m), 1437 (s), 1367 (vs), 1236 (m), 1095 (m), 727 (m) cm−1. [Zn2(μ4-aobtc)(μ-dib)2]n (4). A mixture of H4abtc (0.1 g, 0.279 mmol), ZnCl2 (0.076 g, 0.558 mmol), and dib (0.059 g, 0.279 mmol) ligand was stirred at 60 °C in the mixture of DMF:H2O (10:2, v:v) for 30 min. After 30 min, HNO3 was added dropwise into the mixture until a clear solution was obtained. Then a clear solution was placed in a Pyrex tube (20 mL) and heated at 120 °C for 72 h. After 72 h, yellow crystals of 4 were obtained. Yield: 0.068 g, 26% (based on H4abtc). Anal. Calcd for C20H13N5O5Zn: C, 51.24; H, 2.80; N, 14.94%. Found: C, 51.43; H, 3.11; N, 14.84%. IR (KBr, cm−1): 3134 (m), 1625 (vs), 1570 (s), 1529 (vs), 1435 (s), 1350 (s), 1063 (s), 835 (m), 734 (m) cm−1. {[Zn2(μ4-ao2btc)(μ-dmib)2]·2H2O}n (5). The synthetic procedure of 5 was similar to that of 4, except that dmib (0.066 g, 0.279 mmol) was used instead of dib. Yield: 0.198 g, 69% (based on H4abtc). Anal. Calcd for C22H19N5O6Zn: C, 51.33; H, 3.72; N, 13.60%. Found: C, 51.58; H, 3.51; N, 13.09%. IR (KBr, cm−1): 3423 (m), 3132 (m), 3093 (m), 2962 (w), 1630 (vs), 1521 (s), 1441 (m), 1350 (vs), 1251 (m), 1074 (m), 785 (m), 725 (m) cm−1.

spectra, single crystal X-ray diffraction, powder X-ray diffraction (PXRD), and thermal analysis techniques. Furthermore, photoluminescence properties of complexes 1, 3−5 were studied due to fluorescence properties of d10 metal complexes.

2. MATERIALS AND PHYSICAL MEASUREMENTS All chemicals were purchased and were used without further purification. H4abtc,21 1,4-bmeib,22 obix,23 dib, and dmib8 ligands were synthesized according to previously reported methods. IR spectra were recorded on a Bruker Tensor 27 FT−IR spectrometer using KBr pellets in the range 400−4000 cm−1. A PerkinElmer 2400C elemental analyzer was used for elemental analyses (C, H, and N). PXRD data were recorded on a Rikagu Smartlab X-ray diffractometer with Cu−Kα radiation (λ = 1.5406 nm) in the range 5−50° 2θ at a rate of 5°/min. Thermal analyses were performed on a PerkinElmer Diamond TG/ DTA thermal analyzer with a heating rate of 10 °C/min in the static air atmosphere. The photoluminescence spectra for the solid complex sample were determined with a PerkinElmer LS-55 spectrophotometer. Diffraction measurements of 1−3 and 5 were performed on Bruker AXS SMART CCD diffractometer by using Mo Kα (0.71073 Å) radiation. Diffraction measurement of 4 was carried out on an Agilent SuperNova AtlasS2 diffractometer equipped with Cu X-ray source (Cu Kα 1.54184 Å). The structures were solved by SHELXS and refined by full-matrix least-squares on all F2 data using SHELXL in conjunction with the OLEX2 graphical user interface.24,25 For all compounds, the anisotropic thermal parameters were refined for nonhydrogen atoms, and hydrogen atoms were calculated and refined with a riding model. Mercury program was used to draw molecules.26 Topological analyses were performed using ToposPro software.27 2.1. Syntheses of the Complexes. {[Cd2(μ6-ao2btc)(μ-1,4bmeib)(H2O)2]·2H2O}n (1). A mixture of H4abtc (0.1 g, 0.279 mmol), CdCl2·2.5H2O (0.127 g, 0.558 mmol), and 1,4-bmeib ligand (0.061 g, 0.279 mmol) was stirred at 60 °C in a mixture of DMF/H2O (10:2, v:v) for 30 min. After 30 min, HNO3 was added dropwise into the mixture until a clear solution was obtained. Then a clear solution was placed in a Pyrex tube (20 mL) and heated at 100 °C for 48 h, and yellow crystals were obtained after 2 days. Yield: 0.092 g, 38% (based on H4abtc). Anal. Calcd for C14H16CdN3O7: C, 37,31; H, 3.58; N, 9.32%. Found: C, 39.09; H, 3.22; N, 9.47%. IR (KBr, cm−1): 3321 (m), 2937 (w), 1608 (s), 1552 (s), 1442 (s), 1373 (vs), 737 (m) cm−1. [Mn2(μ6-ao2btc)(μ-obix)2]n (2). The procedure for the synthesis of 2 was similar to that used for 1, except that Mn(NO3)2·4H2O (0.140 g,

3. RESULTS AND DISCUSSION 3.1. Synhesis and Characterization. Five new coordination polymers were synthesized in a mixture of DMF:H2O at 100 °C for 1−3 and at 120 °C for 4 and 5. Moreover, we attempted to synthesize complexes 1−3 and complexes 4 and 5 at 120 and 100 °C, respectively, to compare the results of products, but no crystals were obtained at those temperatures. The synthesized complexes were characterized by elemental B



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Figure 1. Molecular structure of 1 showing the atom numbering scheme.

Figure 2. (a) 2D structure in 1, (b) 3D framework of 1, (c) a schematic representation of 3,6-connected sqc27 net.

Description of Structures. The crystal data and the refinement details of complexes are given in Table 1. Selected bond distances and angles and hydrogen bond geometries are listed in Tables S1−S5, Supporting Information, respectively. {[Cd2(μ6-ao2btc)(μ-1,4-bmeib)(H2O)2]·2H2O}n (1). The crystal structure of 1 with atom numbering scheme is shown in Figure 1. X-ray single-crystal diffraction analysis indicates that complex 1 crystallizes in the triclinic space group P1̅. The asymmetric unit of 1 consists of one Cd(II) ion, one-half 1,4bmeib, one-half ao2btc, one aqua ligand, and one crystal water. Ao2btc ligand displays a new coordination mode in 1, and each ao2btc ligand acts a decadentate ligand in which 3,3′-carboxyl groups display a bidentate chelating mode and 5,5′-carboxyl groups exhibit bidentate chelating and monodentate bridging modes, connecting to six metal centers. Each Cd(II) ion is coordinated by five carboxylate oxygen atoms from three different ao2btc ligands and one nitrogen atom from one 1,4bmeib ligand and one oxygen atom from one aqua ligand to

analysis, IR spectra, single crystal X-ray diffraction, PXRD, and thermal analysis techniques. Elemental analysis results are consistent with the assigned formulations. In the IR spectra of 1 and 5, the broad bands observed at 3321 and 3423 cm−1 are due to ν(O−H) stretching vibrations of coordinated and uncoordinated water molecules, respectively. For complexes 1− 5, the weak bands observed in the range 3132−3093 cm−1 and in the range 2958−2937 cm−1 are attributed to aromatic and aliphatic ν(C−H) stretching vibrations, respectively. The bands observed at 1710 and 1278 cm−1 are due to asymmetric and symmetric stretching vibrations of carboxylate groups of H4abtc, respectively. The asymmetric vibration at 1710 cm−1 of H4abtc disappeared after conversion to complexes 1−5, indicating the full deprotonation of carboxylate groups of H4abtc. The asymmetric and symmetric stretching vibrations for 1−5 appeared in the range 1630−1608 cm−1 and 1377− 1350 cm−1, respectively. C



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Figure 3. Molecular structures of (a) 2 and (b) 3 showing the atom numbering scheme.

Figure 4. (a) 2D structure in 2 and 3 (hydrogen atoms and obix ligands are omitted for clarity), (b) 3D supramolecular networks in 2 and 3.

give a distorted pentagonal-bipyramidal geometry. Cd(II) ions are bridging by 3,3′,5,5′-carboxylate oxygen atoms of the ao2btc ligand to form 1D double chains with the 26-membered rings. Adjacent 1D double chains are linked by 5,5′-carboxy groups of ao2btc with a Cd···Cd distance of 3.876 Å to generate 2D planar structures (Figure 2a). 2D structures are extended to a 3D porous structure by the coordination of 1,4-bmeib ligand (2b). The free void volume of 1 is 1.8% as calculated by PLATON.28 Topologically, complex 1 is 3D binodal (3,6)connected rare sqc27 net with the point symbol of {4.62}2{42.610.83}29 (Figure 2c). [Mn2(μ6-ao2btc)(μ-obix)2]n (2) and [Cd2(μ6-ao2btc)(μobix)2]n (3). Flexible bmeib ligand was changed with semiflexible obix ligand. X-ray analysis studies reveal that complexes 2 and 3 are isostructural. The molecular structures of 2 and 3 with the atom numbering schemes are shown in Figure 3a,b. The complexes crystallize in the triclinic systems with the space group P1̅. The asymmetric units of 2 and 3 contain one M(II) ion (M(II) = Mn(II) in 2 and Cd(II) in 3), one obix and one-

half ao2btc ligands. Each M(II) ion is coordinated by three carboxylate oxygen atoms from three different ao2btc ligands and two nitrogen atoms from two different obix ligands to give a distorted octahedral geometry. The ao2btc ligand acts a hexadentate ligand to connect to six metal(II) centers in 2 and 3, and 3,3′-carboxylate groups and 5,5′-carboxylate groups of ao2btc display bidendate chelating and bis(monodentate) bridging modes, respectively. Two M(II) ions are bridged by 5,5′-carboxylate groups with M···M distances of 4.618 Å (for 2) and 4.550 Å (for 3) to generate an eight-member ring (Figure 4a). All carboxylate oxygen atoms in ao2btc coordinate to six M(II) ions to form 2D layers, and these layers are stabilized by the coordination of obix ligand in trans-position. Adjacent 2D layers are further extended into a 3D supramolecular structure via C−H···π interactions for 2 between C21−H21 and phenyl ring (Cg1) and weak π···π interactions between imidazole rings (Cg2 and Cg3) for 3 [C21···Cg1 = 3.5997, H21···Cg1 = 2.72 Å, and C21−H21···Cg1 = 158°, Cg2···Cg2 = 4.0385, and Cg2··· Cg3 = 4.0385 Å] (Figure 4b). Topologic analyses showed that D



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Figure 5. (a) A topologic representation of 2D 3,6-connected binodal net. (b) The view of -AAA- type stacking of 2D layers in 2 and 3.

Figure 6. Molecular structures of 4 showing the atom numbering scheme.

Figure 7. (a) View of 3D single framework of 4. (b) A topologic representation of 2-fold interpenetrated 3D framework.

Pbcn. The asymmetric unit consists of one Zn(II) ion, one-half aobtc, and one dib ligands. The Zn(II) center adopts a distorted tetrahedral geometry being surrounded by two carboxylate oxygen atoms from two different aobtc ligands and two nitrogen atoms from two dib ligands (Figure 6). The aobtc ligand displays a new coordination mode in 4. The aobtc ligand acts as a tetradentate ligand to connect to four Zn(II) ions. Zn(II) ions are bridged by 5,5′-carboxyl groups of the aobtc ligand and the nitrogen atoms of dib ligand to form 1D chains which are further coordinated to 3,3′-carboxlate oxygen

complexes had 3,6L19 topology with the point symbol of {3.62}2{34.42.62.74.83} (Figure 5a). Moreover, 2D layers adopt -AAA- stacking to form a 3D supramolecular network (Figure 5b). [Zn2(μ4-aobtc)(μ-dib)2]n (4). When a rigid ligand was used instead of flexible or semiflexible ligands, the effect of a rigid ligand on the structure was investigated. In complex 4, the mono-oxygenated form of the abtc ligand occurred. Complex 4 is 3D−3D interpenetrated coordination polymer. Complex crystallizes in the orthorhombic system with the space group E



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Figure 8. Molecular structures of 5 showing the atom numbering scheme.

Figure 9. (a) A view of 3D single framework in 5. (b) A view of of 2-fold interpenetrated 3D framework.

9a. As seen in Figure 9a, the framework has large pores with a dimension of 19.372 × 11.559 Å along the a*-axis. The large pores are filled due to mutual interpenetration of the other equivalent framework giving rise to a 2-fold interpenetrating bbf topology with the point symbol of {64.82}{66}2 (Figure 9b). 3.2. Structural Comparison. Complexes 1−3 were synthesized at 100 °C, while complexes 4 and 5 were synthesized at 120 °C in the same solvent mixture. In all complexes, azo-groups of abtc are oxidized to generate mono(in 4) or dioxygenated forms (in 1−3 and 5), and its oxygenated forms exhibit diverse coordination modes to connect to metal(II) ions (Scheme 1). The phenyl rings of dioxygenated ao2btc are planar, while the phenyl rings of monooxygenated aobtc are deviated from planar. N-Donor bis(imidazole) ligands bind to metal(II) ions as μ-bridging ligands in all complexes. In the synthesis of 1, the flexible aliphatic 1,4bmeib ligand was used and 3D framework was obtained with the sqc27 topology. In the literature, the [Co3(H2abtc)3(btb)(H2O)6] complex with bis(triazole)butane was synthesized at 120 °C in H2O containing NaOH (0.01 mmol), and a 3-fold interpenetrating 3D pillar-layered framework was obtained.12 Moreover, Zn(abtc) complexes which were synthesized at 165 °C in H2O:DMF (10:2) containing NaOH with 1,3-bis(imidazol-1yl)propane and 1,4-bis(imidazol-1yl)butane resulted in 2-fold interpenetrating and self-penetrating 3D frameworks.19 As seen from above, the complexes synthesized by using flexible bis(imidazole) and abtc ligands in neutral or

atoms of aobtc to generate a 3D framework (Figure 7a). In the 3D framework, 59-membered rings occur with three aobtc, five Zn(II) ions, and two dib ligands. In the structure, aobtc ligands connect to Zn(II) ions like a wave. Complex 4 has a 2-fold interpenetrated 4,4-connected 3D structure with the point symbol of 62·84 which is the new topology (Figure 7b). {[Zn2(μ4-ao2btc)(μ-dmib)2]·2H2O}n (5). When the dib ligand was changed with dmib containing -CH3 groups in 5, a 2-fold interpenetrated 3D structure was obtained again, and in the structure of complex 5, a dioxygenated form of abtc was seen. Single crystal X-ray diffraction reveals that complex 5 crystallizes in the monoclinic system with the space group P21/n. There are one Zn(II) ion, one-half ao2btc, and one dimb ligands and one crystal water molecule in the asymmetric unit of 5 (Figure 8). Each Zn(II) ion adopts a distorted [ZnO2N2] tetrahedral geometry by coordinating to two carboxylate oxygen atoms from two different ao2btc ligands and two nitrogen atoms from two different dmib ligands. The ao2btc ligand acts as tetradentate ligand to connect to four Zn(II) ions like complex 4. Zn(II) ions are bridged by 3,3′- and 5,5′carboxyl groups of the ao2btc ligand and nitrogen atoms of dmib ligand to form a 1D structure which is further extended to a 3D structure by coordination of ao2btc and dmib ligands (Figure 9a). Forty-one-membred rings with two ao2btc, four Zn(II) ions, and two dmib ligands and 72-membered rings with two ao2btc, six Zn(II) ions, and four dmib ligands occur in 3D structure. A single framework of complex 5 is given in Figure F



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dmib. When compared to dib, there are -CH3 groups on the benzene ring of dmib, and these substitute -CH3 groups can affect the final structure of the complex because of the change of electron density of the benzene ring. 3.3. Thermal, X-ray Powder Diffraction, and Photoluminescent Properties. The thermal stabilities of the complexes were examined by thermal analysis in the temperature range 30−700 °C in a static air atmosphere (Figures S1− S5, Supporting Information). For 1 and 5, the weight losses of 7.87% from 72 to 198 °C and 2.82% from 41 to 143 °C correspond to release of one coordinated water and one uncoordinated water molecule and one uncoordinated water molecule, respectively (calcd.: 7.98% for 1, calcd.: 3.49% for 5). After dehydration steps, complexes 1−5 are stable up to 329, 332, 308, 355, and 348 °C, respectively. Interpenetrated complexes 4 and 5 are more stable than the other complexes. Then, the weight losses which are seen until 557 °C for 1, 480 °C for 2 and 560 °C for 3, 555 °C for 4, and 600 °C for 5 are attributed to decomposition of networks with exothermic picks, respectively. The remaining products identified by IR spectroscopy are possibly CdO (found: 29.29%; calcd.: 28.49%) for 1, MnO (found: 15.03%; calcd.: 14.53%) for 2, CdO (found: 23.46%; calcd.: 23.61%) for 3, and ZnO (found: 15.58%; calcd.: 17.28% and found: 14.43%; calcd.: 15.73%) for 4 and 5, respectively. The PXRD measurements of the synthesized complexes were carried out to check the phase purities. PXRD patterns of the complexes which are well-matched the simulated patterns from their single-crystal structures demonstrate their crystalline phase purity (Figure S6, Supporting Information). The solid state photoluminescence spectra of complexes 1, 3−5 with d10 metal center and free ligand H4abtc (conjugated π system) were employed at room temperature under the same conditions (Figure 10). The free ligand H4abtc displays emissions at 410, 420, 463, 487, and 532 nm upon excitation at 344 nm. These emissions are due to π* → n or π* → π transitions of H4abtc.16 The photoluminescence spectra of complexes 1 and 3−5 are similar to H4abtc and emission maxima are 408, 422, 463, 487 and 530 nm for 1, 425, 463, 486, and 529 nm for 2, 406, 422, 462, 487, and 531 nm for 4, and 405, 422, 463, 487, and 431 nm for 5 upon excitation at 344 nm. The emissions of the complexes are neither ligand to metal charge transfer nor metal to ligand charge transfer. Because Zn(II) and Cd(II) ions are difficult to reduce or oxidize due to

Scheme 1. (a−d) Coordination Modes of Oxidized Forms of Azobenzenetetracarboxylate Observed in This Paper

basic mediums resulted in interpenetration or polycatenation at high temperature.12,19 As mentioned in the introduction, reaction conditions are one of most important parameters for rational design and synthesis of coordination polymers. Interpenetration or polycatenation were not observed in the structure of 1 because synthesis was carried out at low temperature and acidic medium. When a flexible 1,4-bmeib ligand was replaced with a semiflexible obix ligand, two 2D isostructural complexes were obtained. In 2 and 3, obix ligand binds to metal ions in trans-positions. When rigid ligands were used instead of flexible or semiflexible ligands, 2-fold interpenetrated 3D structures were obtained in 4 and 5 due to a high reaction temperature. These results were similar to those in the literature of a 2D + 2D → 3D parallel polycatenation network formed when rigid 4,4′-bis(imidazol-1-yl)biphenyl was used.14 The complexes have the same structures with the different topologies. The structural difference between the structures of 4 and 5 stems from positions of aobtc or ao2btc in which the phenyl rings of aobtc are not planar, while the phenyl rings of ao2btc are planar. Complex 4 displays a 4,4-connected binodal net with the point symbol of 62·84, while complex 5 shows a 4,4-connected binodal net with the bbf topology. Moreover, the difference between 4 and 5 can be due to dib or

Figure 10. Photoluminescence spectra of complexes 1, 3−5, and free ligand H4abtc. G



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d10 configuration of them.30,31 The emissions of complexes 1, 3−5 may be tentatively intraligand transitions of H4abtc.17 There are no effects of the oxygenated forms of the abtc ligand on the emission spectra of complexes. The emission intensities of complexes 1, 3−5 are higher than that of H4abtc. This situation may be due to coordination of ligand to metal centers.

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4. CONCLUSIONS In summary, five new coordination polymers with oxidized forms of abtc and flexible, semiflexible, and rigid bis(imidazole) ligands were constructed and characterized. The ao2btc and aobtc ligands exhibited new coordination modes in 1 and 4, and complex 4 had a new topological structure. Structural diversities according to bis(imidazole) ligands were observed in the complexes. These results enrich our knowledge that flexible or semiflexible linkers do not always exhibit interpenetration or polycatenation in the self-assembly of coordination polymers depending on reaction conditions. This study can provide a promising way to synthesize coordination polymers without interpenetration or polycatenation using flexible long linkers. Thermal analysis results showed that interpenetrated structures were more stable than other single frameworks. Moreover, photoluminescence spectra of complexes 1 and 3−5 which were due to intraligand transitions were similar.

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ASSOCIATED CONTENT

S Supporting Information *

TG and PXRD curves and tables for bond distances and angles of complexes 1−5. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.cgd.5b00432. Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 1051655 for 1, 1047864 for 2, 1047865 for 3, 1051657 for 4, and 1051656 for 5. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).

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AUTHOR INFORMATION

Corresponding Author

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

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work has been supported by The Scientific and Technological Research Council of Turkey (Project No: 113Z313).

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REFERENCES

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Coordination Polymers Assembled From 3, 3′, 5, 5

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