Multifunctional Cobalt(II) Coordination Polymers ... - ACS Publications

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Multifunctional Cobalt(II) Coordination Polymers Tuned by Flexible Bis(pyridylamide) Ligands with Different Spacers and Polycarboxylates Xiu-li Wang,* Fang-fang Sui, Hong-yan Lin, Ju-wen Zhang, and Guo-cheng Liu Department of Chemistry, Bohai University, Jinzhou 121000, P. R. China S Supporting Information *

ABSTRACT: Ten multifunctional cobalt(II) coordination polymers with the formulas of [Co(L1)0.5(5-AIP)]·H2O (1), [Co(L2)(5-AIP)(H2O)2] (2), [Co(L3)0.5(5-AIP)] (3), [Co(L4)0.5(5-AIP)(H2O)]·2H2O (4), [Co(L5)(5AIP)] (5), [Co(HBTC)(L3)]·H2O (6), [Co(HBTC)(L6)(H2O)]·3H2O (7), [Co(L2)(1,3-BDC)(H2O)2] (8), [Co2(L3)2(1,3-BDC)2]·4H2O (9), and [Co2(L4)1.5(1,2-BDC)(μ2-OH)(μ3-OH)(H2O)]·H2O (10) have been prepared by a hydrothermal technique employing six flexible bis(pyridylamide) ligands with different spacers (L1 = N,N′-bis(3-pyridyl)oxamide, L2 = N,N′bis(3-pyridyl)malonamide, L3 = N,N′-di(3-pyridyl)succinamide, L4 = N,N′bis(3-pyridyl)adipamide, L5 = N,N′-bis(3-pyridyl)heptandiamide, L6 = N,N′bis(3-pyridyl)sebacicdiamide) and four aromatic polycarboxylic acids mixed ligands (5-H2AIP = 5-aminoisophthalic acid, H3BTC = 1,3,5-benzenetricarboxylic acid, 1,3-H2BDC = 1,3-benzenedicarboxylic acid, and 1,2-H2BDC = 1,2-benzenedicarboxylic acid). Compound 1 exhibits a two-dimensional (2D) double-layer network. Compounds 2 and 8 are isostructural and possess onedimensional (1D) circle-connecting-circle chain structures derived from 1D [Co(L2)]n “Ω”-like chain and 1D [Co(5-AIP)]n/ [Co(1,3-BDC)]n wavelike chain. Compound 3 possesses a 3,8-connected three-dimensional (3D) coordination framework with {42.6}2{44.610.79.85} topology. Compound 4 is a 2D network containing a ladder-like chain. Compound 5 reveals a novel 3-fold interpenetrating CdSO4-like framework. Compound 6 is a double-layer coordination network with a (3,5)-connected {42·67· 8}{42·6} topology. Complex 7 shows a 2D (4,4) grid layer. Compound 9 features a 2-fold interpenetrating 3D α-Po-related topological framework. Compound 10 is a 6-connected 3D coordination polymer with a {412.63} topology. The spacer length of the bis(pyridylamide) ligands, as well as the substituent group and carboxyl group number of polycarboxylates, shows a significant effect on the ultimate architectures of various cobalt(II) compounds 1−10. The electrochemical behaviors of carbon paste electrodes (CPEs) bulk-modified by compounds 1−10 and the electrocatalytic activities of 1-, 6-, 9-, 10-CPEs have been investigated. The photocatalytic properties of compounds 1−10 toward the degradation of methylene blue (MB) in visible light irradiation have been investigated. The variable temperature magnetic susceptibilities for compounds 3, 5, 9, and 10 indicate the existence of antiferromagnetic exchange interactions.

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INTRODUCTION The designing assembly of coordination polymers (CPs) becomes an important research branch in coordination chemistry and crystal engineering, not only for their potential applications as functional materials in catalysis, fluorescence, gas adsorption/separation and magnetism but also for their diverse structures and novel topologies.1,2 Nevertheless, how to reasonably construct the expected architectures with unique properties is still a huge challenge. In the last two decades, much effort was devoted to design and synthesize new CPs containing polynuclear metal clusters as the secondary building units (SBUs) for their exceptional magnetic properties, such as binuclear, trinucluear, tetranuclear, or higher-nuclearity clusters.3,4 Those CPs containing Co(II) clusters are particularly interesting because of the potential source of anisotropy that the Co(II) ions may provide, in which ferromagnetic or antiferromagnetic coupling between cobalt ions may be observed.5 Polycarboxylates are prominent bridging ligands for the construction of polynuclear Co(II) clusters because the © XXXX American Chemical Society

carboxyl groups may induce core aggregation or link these discrete clusters into extended networks,6 which may be ascribed to their various coordination modes that will supply magnetically coupled superexchange pathways among paramagnetic Co(II) ions. Taking these into account, we chose four aromatic polycarboxylic acids 5-aminoisophthalic acid (5H2AIP), 1,3,5-benzenetricarboxylic acid (H3BTC), 1,3-benzenedicarboxylic acid (1,3-H2BDC), and 1,2-benzenedicarboxylic acid (1,2-H2BDC) as the main bridging ligands and attempt to construct high-dimensional Co(II) complexes including polynuclear Co(II) clusters. Additionally, the neutral N-containing ligands have already been widely introduced into the metal-carboxylates systems to construct new CPs, which may modify the final architectures and physical properties of target coordination polymers.7 The Received: March 17, 2014 Revised: June 4, 2014

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dx.doi.org/10.1021/cg500371n | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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flexible bis(pyridylamide) ligands with different −(CH2)n− spacers, as the analogues of the dipyridyl-type ligands, have been proven to be suitable N-containing ligands for generating novel CPs.8 This kind of ligand can meet the coordination requirements of metal ions by its -(CH2)n- backbones bending larger twist-degree and interact via hydrogen bonding interactions among their amide groups, which are crucial for the formation of metal−organic coordination frameworks and supramolecular networks.9 For example, Chen’s and Cao’s groups have synthesized a variety of transition metal (Zn, Cd, Hg) CPs derived from the flexible bis(pyridylamide) ligands with different spacers of -(CH2)n- (n = 0, 4, 10).10 Our group has prepared three Co(II) CPs and several Cu(II) CPs based on the flexible bis(pyridylamide) ligands with various -(CH2)n(n = 1, 2, 4, 5, 6, 8) spacers and different polycarboxylates, which exhibit significant photocatalytic activities.11 However, to our knowledge, the reports about Co(II) CPs based on the mixed ligands of aromatic polycarboxylates and flexible bis(pyridylamide) are relatively limited.8b,c,10a,12 Considering that the CPs constructed from flexible bis(pyridylamide) ligands may possess a photocatalytic ability to degrade certain organic dyes, in this work, six flexible bis(pyridylamide) ligands N,N′-bis(3-pyridyl)oxamide (L 1 ), N,N′-bis(3-pyridyl)malonamide (L2), N,N′-di(3-pyridyl)succinamide (L3), N,N′bis(3-pyridyl)adipamide (L 4 ), N,N′-bis(3-pyridyl)heptandiamide (L5), and N,N′-bis(3-pyridyl)sebacicdiamide (L6) have been purposefully selected as main ligands incorporating polycarboxylates coligands to synthesize Co(II) complexes, with the aim of obtaining novel CPs with magnetic and photocatalytic properties, as well as investigating the influence of the different polycarboxylates and spacer lengths of the flexible bis(pyridylamide) ligands on the various structures of Co(II) CPs (Scheme 1). Here, we report the syntheses and structures of ten Co(II) CPs with six flexible bis(pyridylamide) ligands and four aromatic polycarboxylates mixed ligands, with formulas [Co(L1)0.5(5-AIP)]·H2O (1), [Co(L2)(5-AIP)(H2O)2] (2), [Co(L3)0.5(5-H2AIP)] (3), [Co(L4)0.5(5-AIP)(H2O)]·2H2O (4),

[Co(L5)(5-AIP)] (5), [Co(HBTC)(L3)]·H2O (6), [Co(HBTC)(L6)(H2O)]·3H2O (7), [Co(L2)(1,3-BDC)(H2O)2] (8), [Co2(L3)2(1,3-BDC)2]·4H2O (9), and [Co2(L4)1.5(1,2BDC)(μ2-OH)(μ3-OH)(H2O)]·H2O (10). The magnetic behaviors of compounds 3, 5, 9, and 10 and the electrochemical behaviors and photocatalytic activities of ten title compounds have been studied.

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EXPERIMENTAL SECTION

Materials and Measurements. The six flexible bis(pyridylamide) ligands L1, L2, L3, L4, L5, and L6 were synthesized according to a previous report.13 All other chemicals were obtained from commercial sources and used without further purification. The C, H, and N elemental analyses were recorded on a PerkinElmer 240C elemental analyzer. The FT-IR spectra (KBr pellets) were carried out on a Varian FT-IR 640 spectrometer in the range of 500−4000 cm−1. Powder XRD investigation was taken on a Ultima IV with D/teX Ultra diffractometer at 40 kV, 40 mA with Cu Kα (λ = 1.5406 Å) radiation. Thermogravimetric (TG) analyses of the title compounds were performed on a Pyris Diamond TG/DTA thermal analyzer. Electrochemical measurements were carried out using a CHI 440 electrochemical station. A conventional three-electrode system was used. The carbon paste electrodes (CPEs) bulk-modified with title compounds were used as working electrodes. A saturated calomel electrode (SCE) and a platinum wire were used as reference and auxiliary electrodes, respectively. Magnetic data were collected using crushed crystals of the sample on a Quantum Design MPMS-XL SQUID magnetometer. The data were corrected using Pascal’s constants to calculate the diamagnetic susceptibility. UV−vis absorption spectra were obtained using a SP-1900 UV−vis spectrophotometer. Synthesis of [Co(L1)0.5(5-AIP)]·H2O (1). The mixture of CoCl2· 6H2O (0.048 g, 0.20 mmol), L1 (0.025g, 0.10 mmol), 5-H2AIP (0.027 g, 0.15 mmol), NaOH (0.016 g, 0.40 mmol), and H2O (12 mL) was stirred for 30 min in air, then moved to a 23 mL Teflon reactor, sealed, and heated to 120 °C. It was kept at 120 °C for 4 days, and then the reactor was cooled slowly to room temperature. Purple block crystals of compound 1 were collected. Yield 56% based on Co. Anal. Calc. for C14H12CoN3O6 (377.20): C, 44.54; H, 3.18; N, 11.13%. Found: C, 44.56; H, 3.21; N, 11.19%. IR (KBr, cm−1): 3442w, 3248w, 2924m, 2361m, 1691w, 1605w, 1571s, 1428m, 1359s, 1320s, 1272s, 1108s, 799s, 718s, 734m, 618s, 780m, 542m. Synthesis of [Co(L2)(5-AIP)(H2O)2] (2). The synthesis process for 2 was similar to that of 1 except that L2 (0.026 g, 0.10 mmol) was used instead of L1, and NaOH (0.015 g, 0.38 mmol) was added to adjust pH of the mixture. Light pink crystals of 2 were isolated. Yield 53% based on Co. Anal. Calc. for C21H21CoN5O8 (530.36): C, 47.51; H, 3.96; N, 13.19%. Found: C, 47.57; H, 4.03; N, 13.24%. IR (KBr, cm−1): 3404s, 3250m, 2269s, 1689s, 1531s, 1482w, 1430s, 1378s, 1329w, 1279w, 1129m, 784w, 720s, 677w, 618m. Synthesis of [Co(L3)0.5(5-AIP)] (3). The similar procedure reported for compound 2 was utilized to synthesize 3, except that L3 (0.027 g, 0.10 mmol) was employed replacing L2 and a different amount of NaOH (0.017 g, 0.42 mmol) was added to generate pink bulk crystals of 3. Yield 69% based on Co. Anal. Calc. for C15H14CoN3O6 (391.22): C, 46.01; H, 3.58; N, 10.74%. Found: C, 46.06; H, 3.52; N, 10.79%. IR (KBr, cm−1): 3440s, 3263m, 2920w, 1684s, 1631s, 1584s, 1557w, 1477s, 1389w, 1334m, 1270w, 1121s, 1012w, 959s, 718w, 618s. Synthesis of [Co(L4)0.5(5-AIP)(H2O)]·2H2O (4). Compound 4 was obtained with a process similar to that of 3 except for employing L4 (0.031 g, 0.10 mmol) instead of L3, and a different amount of NaOH (0.017 g, 0.42 mmol) and H2O (9 mL) was added. Purple block crystals of 4 were obtained in yield 52% based on Co. Anal. Calc. for C16H20CoN3O8 (441.28): C, 43.51; H, 4.53; N, 9.52%. Found: C, 43.56; H, 4.57; N, 9.56%. IR (KBr, cm−1): 3543w, 3399s, 1635s, 1553s, 1485w, 1426s, 1325s, 1289s,1164w, 801s, 778w, 698m, 615w. Synthesis of [Co(L5)(5-AIP)] (5). The synthetic method for 5 is similar to that of 4, in which L5 (0.031 g, 0.10 mmol) was used to replace L4. In addition, a different dosage of NaOH (0.015 g, 0.38

Scheme 1. Six Flexible Bis(pyridylamide) Ligands and Four Aromatic Polycarboxylic Acids Used in This Paper

B



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Table 1. Crystal Data and Structure Refinements for Compounds 1−10 compound

1

2

3

4

5

formula formula wt cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalc (g/cm3) μ/mm−1 F(000) θmax (°) Rint R1a [I > 2σ(I)] wR2b (all data) GOF Δρmax (e Å−3) Δρmin (e Å−3) compound

C14H12CoN3O6 377.20 triclinic P1̅ 7.8130(7) 7.9406(7) 11.6727(10) 100.0900(10) 95.8430(10) 99.3740(10) 697.09(11) 2 1.797 1.272 384 25.00 0.0164 0.0322 0.0983 1.006 0.536 −0.504 6

C21H21CoN5O8 530.36 monoclinic C2/c 18.793(3) 19.363(3) 14.5880(19) 90 119.792(2) 90 4606.7(11) 8 1.529 0.803 2184 25.10 0.0373 0.0435 0.1322 1.024 0.666 −0.411 7


C16H20CoN3O8 441.28 triclinic P1̅ 8.5578(13) 10.1318(15) 11.8526(17) 69.808(2) 78.753(3) 74.670(2) 924.1(2) 2 1.586 0.979 456 25.17 0.0229 0.0471 0.1247 1.034 0.792 −0.608 9


C44H44Co2N8O16 1058.73 triclinic P1̅ 10.1112(19) 15.943(3) 16.764(3) 111.325(3) 103.680(4) 102.598(3) 2303.7(8) 2 1.526 0.801 1092 25.00 0.0324 0.0602 0.1615 1.054 1.379 −0.444

C32H39Co2N6O12 817.55 triclinic P1̅ 11.1531(13) 12.9963(15) 13.4198(15) 75.916(2) 75.109(2) 70.039(2) 1740.8(3) 2 1.560 1.025 846 25.00 0.0327 0.0489 0.1110 1.009 0.735 −0.776

formula formula wt cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalc (g/cm3) μ/mm−1 F(000) θmax (°) Rint R1a [I > 2σ(I)] wR2b (all data) GOF Δρmax (e·Å−3) Δρmin (e·Å−3) a

C23H20CoN4O9 555.35 triclinic P1̅ 10.1586(4) 10.2200(5) 12.7787(6) 79.1250(10) 71.9810(10) 72.3830(10) 1195.83(9) 2 1.540 0.779 568 25.00 0.0106 0.0357 0.1100 1.043 1.807 −0.305

C29H38CoN4O12 693.56 triclinic P1̅ 9.5278(7) 10.1157(7) 17.7684(13) 97.959(6) 90.300(6) 110.198(7) 1589.1(2) 2 1.447 0.609 724 25.00 0.0314 0.0558 0.1685 1.007 0.832 −0.651

C21H20CoN4O8 515.33 monoclinic C2/c 19.286(5) 19.445(5) 14.322(5) 90 121.182(3) 90 4595.1(17) 8 1.490 0.801 2112 26.03 0.0292 0.0367 0.1085 1.056 0.448 −0.416

R1 = Σ(||Fo| − |Fc||)/Σ|Fo|. bwR2 = [Σw(|Fo|2 − |Fc|2)2/(Σw|Fo|2)2]1/2. 3453s, 3266w, 3203w, 2933m, 1692s, 1630s, 1546s, 1487s, 1388s, 1340s, 1283s, 1196s, 1176s, 1108s, 1028s, 912m, 866s, 756s, 722s, 647m, 543m, 524m. Synthesis of [Co(HBTC)(L6)(H2O)]·3H2O (7). The synthesis method of 7 is similar to that of 6 except for L6 (0.038 g, 0.10 mmol) as the substitute of L3, and a different amount of NaOH (0.016 g, 0.40 mmol) was added to adjust the pH of the reaction mixture. Pink crystals of 7 were collected. Yield 43% based on Co. Anal. Calcd for C29H38CoN4O12 (693.56): C, 50.18; H, 5.48; N, 8.07%. Found: C, 50.22; H, 5.52; N, 8.11%. IR (KBr, cm−1): 3616w, 3403w, 3266m, 3126m, 2916s, 2850s, 2359s, 1667s, 1609s, 1586s, 1552s, 1428s, 1382s, 1273s, 1189s, 1054m, 809s, 753s, 700m, 642m, 575w. Synthesis of [Co(L2)(1,3-BDC)(H2O)2] (8). The synthetic procedure for 8 is the same as that for 2 except that 1,3-H2BDC

mmol) was added. The massive pink crystals for 5 were isolated with a yield of 72% (based on Co). Anal. Calc. for C25H25CoN5O6 (550.43): C, 54.50; H, 4.54; N, 12.72%. Found: C, 54.56; H, 4.58; N, 12.77%. IR (KBr, cm−1): 3422w, 3371s, 3086w, 2930s, 2863w, 1682s, 1476s, 1428w, 1376s, 1324s, 1285s, 1194w, 1131s, 1051w, 1001m, 801w,779s, 718w, 617w. Synthesis of [Co(HBTC)(L3)]·H2O (6). A mixture of CoCl2·6H2O (0.048 g, 0.20 mmol), L3 (0.027 g, 0.10 mmol), H3BTC (0.032 g, 0.15 mmol), NaOH (0.018 g, 0.44 mmol), and H2O (12 mL) was stirred for 30 min in air, then transferred and sealed in a Teflon-lined reactor, and heated at 120 °C for 4 days. After the mixture was cooled to room temperature, the red crystals of 6 were obtained. Yield 56% based on Co. Anal. Calcd for C23H20CoN4O9 (555.35): C, 49.70; H, 3.60; N, 10.08%. Found: C, 49.75; H, 3.64; N, 10.12%. IR (KBr, cm−1): 3650w, C



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(0.024 g, 0.2 mmol) was used instead of 5-H2AIP, and a different amount of NaOH (0.018 g, 0.44 mmol) was added to adjust the pH of the reaction mixture. Purple block crystals of 8 were obtained. Yield 68% based on Co. Anal. Calc. for C21H20CoN4O8 (515.34): C, 48.90; H, 3.89; N, 10.87%. Found: C, 48.86; H, 3.82; N, 10.93%. IR (KBr, cm−1): 3448w, 3409m, 3197w, 2360s, 2335s, 1691s, 1668w, 1531s, 1481w, 1433s, 1384s, 1328w, 1276w, 1197m, 987w, 877m, 806s, 707s, 675w, 651m. Synthesis of [Co2(L3)2(1,3-BDC)2]·4H2O (9). The synthesis process of 9 was similar to that of 8 except for L3 (0.027 g, 0.10 mmol) as the replacement of L2, and NaOH (0.0160 g, 0.40 mmol) was added to adjust the pH of the reaction mixture. Light pink crystals of 9 were collected. Yield 58% based on Co. Anal. Calc. for C44H44Co2N8O16 (1058.73): C, 49.87; H, 4.16; N, 10.58%. Found: C, 49.89; H, 4.20; N, 10.57%. IR (KBr, cm−1): 3425s, 3062m, 1676s, 1615s, 1555s, 1485s, 1400s, 1344s, 1285w, 1238m, 1110w, 957w, 805s, 767s, 618m. Synthesis of [Co2(L4)1.5(1,2-BDC)(OH)2(H2O)]·H2O (10). A mixed solution of CoCl2·6H2O (0.048 g, 0.20 mmol), L4 (0.031 g, 0.10 mmol), 1,2-H2BDC (0.024 g, 0.20 mmol), NaOH (0.016 g, 0.40 mmol), and H2O (10 mL) was stirred for 30 min in air, which was transferred into a 23 mL Teflon reactor and heated to 120 °C keeping for 4 days. After the mixture was slowly cooled to room temperature, violet crystals of 10 were obtained (Yield: 42%, based on Co). Anal. Calc. for C32H39Co2N6O12 (817.55): C, 46.97; H, 4.78; N, 10.27%. Found: C, 46.95; H, 4.79; N, 10.26%. IR (KBr, cm−1): 3473s, 3224m, 2921w, 1699s, 1623s, 1575s, 1569w, 1471s, 1427w, 1336m, 1305w, 1263s, 1149s,1068s, 973w, 890w, 769s, 615s. X-ray Crystallographic Study. Single-crystal X-ray diffraction data for complexes 1−10 were collected on a Bruker Smart APEX II diffractometer with Mo Kα (graphite monochromator, λ = 0.71073 Å). All of the structures were solved by direct methods and refined by the full-matrix least-squares methods on F2 using the SHELXTL package.14 For these complexes, all non-hydrogen atoms were found from the Fourier difference maps refined anisotropically, and the hydrogen atoms of the ligands L1−L6 were generated theoretically onto the specific atoms and refined isotropically with fixed thermal factors. The detailed crystallographic data and structure refinement parameters for compounds 1−10 are summarized in Table 1. Selected bond distances and angles of the title complexes are listed in Tables S1−S10 in the Supporting Information. The hydrogen-bonding parameters of compounds 2, 4, 6, 7, and 8 are summarized in Tables S11−S15. The CCDC nos. 948721−948723 for compounds 1−3, 949441 for 4, 948724 for 5, 967863 for 6, 967862 for 7, and 948725−948727 for compounds 8−10 are the supplementary crystallographic data in this paper. These data can be obtained free of charge via www.ccdc.cam.ac. uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44) 1223−336−033; or [email protected]].

Figure 1. (a) The coordination environment of the Co(II) ion in complex 1 with 50% thermal ellipsoids. (b) The 2D [Co(5-AIP)]n hexagonal grid layer. (c) A schematic drawing of the 2D double-layer framework of 1.

by L1 ligands with a bidentate bridging coordination mode to give a honeycomb-like double-layer network. The L1 ligand connects two Co(II) ions from two different layers with the nonbonding Co···Co distance of 12.767 Å, and the dihedral angle between its two pyridyl rings is 0°. If the Co(II) ion is simplified as a 4-connected node, 5-AIP anion and L1 ligand are considered as a 3-connected node and a linear linker, respectively, and the 2D network in 1 can be described as a (3,4)-connected binodal topological network with Schläfli symbol of {63}{66} (Figure 1c). The neighboring 2D bilayers are finally extended to a 3D supramolecular framework by the π−π weak interactions among the benzene rings of 5-AIP anions with a face-to-face distance of 3.715 Å (Figure S1).15 Structural Description of [Co(L2)(5-AIP)(H2O)2] (2) and [Co(L2)(1,3-BDC)(H2O)2] (8). The X-ray crystallographic studies reveal that compounds 2 and 8 crystallize in monoclinic crystal system and C2/c space group, which show a similar 1D chain structure except that their bond lengths and angles are slightly different. Their general formulas are composed of one Co(II) ion, one L2 ligand, one dicarboxylate ligand (5-AIP for 2, 1,3-BDC for 8), and two coordinated water molecules (Figure 2a and Figure S3a). Here, we will describe the structure

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RESULTS AND DISCUSSION Structural Description of [Co(L1)0.5(5-AIP)]·H2O (1). Single crystal X-ray diffraction analysis indicates that 1 crystallizes in triclinic crystal system and P1̅ space group. The asymmetric unit contains one cobalt(II) ion, one 5-AIP anion, half a L1 ligand, as well as one lattice water molecule. The crystallographically independent Co(II) ion is four-coordinated by one pyridine N(1) atom from the L1 (Co(1)−N(1) = 2.042(2) Å), one amino nitrogen atom from one 5-AIP anion (Co(1)−N(3)#2 = 2.101(2) Å), and two carboxyl oxygen atoms [O(2) and O(5)#1] from two 5-AIP anions (Co(1)− O(2) = 1.9896(17) Å, exhibiting a distorted tetrahedral geometry {CoN2O2} (Figure 1a). In 1, each 5-AIP ligand adopts a tri(monodentate) coordination mode (Table 2) connecting three Co(II) ions with one amino group and two carboxyl groups. The central Co(II) ions are bridged by the 5AIP anions to produce a 2D (6,3) hexagonal [Co(5-AIP)]n network (Figure 1b). Then two adjacent layers are interlinked D



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Table 2. Coordination Modes of Cobalt Ions, Polycarboxylates (5-AIP, HBTC, 1,3-BDC, 1,2-BDC) and Bis(pyridylamide) Ligands (L1, L2, L3, L4, L5, and L6) in Compounds 1−10

2, the 5-AIP ligand showing a bis(monodentate) coordination mode (Table 2) links Co(1) and Co(2) ions through its two carboxyl groups to construct a 1D [Co(5-AIP)]n wavelike chain (Figure S2a, 1D [Co(1,3-BDC)]n chain for 8 in Figure S3b). The bidentate L2 molecules bridge the Co(II) ions forming a 1D [Co(L2)]n “Ω”-like chain (Figure S2b, Figure S3c for 8). For L2, the dihedral angle between two pyridyl rings is 8.212° (8.590° in 8). The [Co(1,3-BDC)]n chains and [Co(L2)]n chains are combined by Co(II) ions to give the 1D circleconnecting-circle chain (Figure 2b, Figure S 3d for 8). As shown in Figure S2c (Figure S3e for 8), the adjacent 1D double chains are extended to a 2D supramolecular network by a weak hydrogen bond [N(2)−H(2B)···O(1W) = 3.000(2) Å] between the amide groups and the coordinated water molecules. Then, the intermolecular O−H···O hydrogen bonds [O(1W)−H(1WA)···O(5) = 2.690(6) Å] between the coordination water molecules and 5-AIP ligands further expanded the 2D network to a 3D supramolecular framework.16 Structural Description of [Co(L3)0.5(5-AIP)] (3). Compound 3 crystallizes in the monoclinic crystal system and C2/c space group, which exhibits a 3D framework. There is only one crystallographic independent Co(II) ion in 3 (Figure 3a). Co(1) ion shows a typical five-coordinated square-pyramidal arrangement {CoN2O3}, completed by three carboxyl oxygen atoms (Co(1)−O(3) = 2.022(2) Å, Co(1)−O(4)#1 = 2.040(2) Å, Co(1)−O(6)#2 = 2.061(2) Å) from three separated 5-AIP ligands, a pyridyl N atom [Co(1)−N(1) = 2.128(3) Å] from a L3 molecule and a N atom [Co(1)−N(5) #3 = 2.235(3) Å] from a 5-AIP anion. Two Co(II) ions are held together by two carboxyl groups from two 5-AIP anions to yield a binuclear {Co2} SBU with a Co(1)···Co(1)#1 distance of 4.253 Å. In 3, the 5-AIP ligand exhibits a monodentate-

Figure 2. (a) The coordination environments of Co(II) ions in 2 with 50% thermal ellipsoids. (b) The 1D circle-connecting-circle chain of 2.

of 2 in detail. Compound 2 contains two crystallographic independent Co(II) ions [Co(1), Co(2)]. Both Co(1) and Co(2) ions show a similar distorted octahedral geometry, which are completed by two pyridyl N atoms from two L2 ligands, two carboxyl O atoms from two 5-AIP anions, and two coordination water molecules. The bond lengths of Co(1)−N(1) (or Co(1)−N(1)#1) and Co(2)−N(4) (or Co(2)−N(4)#2) are 2.183(3) Å and 2.178(3) Å, respectively. The bond distances of Co(1)−O and Co(2)−O are in the range of 2.073(2)− 2.159(2) Å, 2.049(2)−2.119(2) Å, respectively. In compound E



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monodentate-bis(monodentate) coordination mode (Table 2): one carboxyl group coordinates to one Co(II) ion with a monodentate mode, the other one coordinates to two Co(II) ions showing a bis(monodentate) bridging mode, and the amino group also coordinates with one Co(II) ion. Without considering the connection of L3, the 5-AIP anions serve as the μ4-bridging ligands and connect with four Co(II) ions from three {Co2} SBUs (Figure 3b) to build the 3D [Co(5-AIP)]n metal−organic framework (Figure 3c). Obviously, there is a very interesting feature in the 3D [Co(5-AIP)]n framework of compound 3: Co(II) ions are linked by 5-AIP anions producing four subrings A, B, C, and D (Figure S4), which are 12-, 14-, 8-, and 14-membered rings with Co···Co separations of 7.626, 8.1431, 4.253, and 7.807 Å, respectively. That is to say, the 3D [Co(5-AIP)]n framework is constructed from the [A + B + C + D] interlocking motifs by sharing Co(II) ions. In compound 3, the L3 serving as a bridging ligand adopts the bidentate coordination fashion and consolidates the whole 3D coordination network. The L3 ligands connect two Co(II) ions from two different {Co2} SBUs with a Co···Co distance of 15.356 Å, and the dihedral angle between the two pyridyl rings of L3 is 0°. From topological viewpoint, each binuclear {Co2} SBU is linked to eight {Co2} SBUs by six 5-AIP anions and two L3 molecules, which should be considered as an 8-connected node, each 5-AIP anion linking three {Co2} SBUs can be regarded as a 3-connected node, and each L3 molecule can be viewed as a linear linker. Thus the overall 3D network of 3 is described as a binodal (3,8)-connected topological structure with the Schläfli symbol of {42.6}2{44.610.79.85} (Figure 3d). Structural Description of [Co(L4)0.5(5-AIP)(H2O)]·2H2O (4). Different from compound 3, the selection of the longer flexible bis(pyridylamide) ligand L4 results in a 2D layer structure of compound 4. Compound 4 crystallizes in triclinic P1̅ space group. The asymmetric unit consists of one Co(II) ion, a half of L4 molecule, one 5-AIP anion, one coordination water molecule, and two noncoordinated water molecules. The Co(II) ion is six-coordinated by three oxygen atoms from 5AIP ligand [Co(1)−O(2) = 2.008(2) Å, Co(1)−O(5)#1 = 2.197(2) Å, Co(1)−O(4)#1 = 2.202(2) Å], a pyridyl N atom from a L4 molecule [Co(1)−N(1) = 2.134(3) Å], one N atom belonging to the amino of 5-AIP [Co(1)−N(3)#2 = 2.263(3) Å], and one O atom from a coordination water molecule [Co(1)−O(1W) = 2.055(3) Å], completing the distorted octahedral geometry (Figure 4a). Similar to that in 1, each 5AIP ligand links three Co(II) ions by its carboxyl groups and amino group. However, the coordination modes of two carboxyl groups are different (Table 2): One coordinates to a Co(II) center with a monodentate mode, while the other one coordinates with another Co(II) center in a chelating coordination fashion. So the three-connected 5-AIP anions linked adjacent Co(II) ions forming a railroad-like polymeric chain (Figure S5a). The chains are further connected by the L4 ligands with a bidentate mode to construct the 2D network (Figure 4b). The L4 ligand connects two Co(II) ions with nonbonding Co···Co distance of 16.348 Å, and the dihedral angle between its pyridyl rings of 0°. From a topological view, each 5-AIP is viewed as a 3-connected node, Co1 ion is regarded as a 4-connected node, and the L4 molecule can be considered as a linear linker; thus the 2D network of 4 can be described as a 3,4-connected {62.10}{6} topology, as shown in Figure 4c. Further, these 2D sheets are extended into a 3D supramolecular architecture via hydrogen bonds between the coordination water molecules O(1W) and the oxygen atoms

Figure 3. (a) View of the coordination environments of Co(II) ions in 3 with 50% thermal ellipsoids. (b) View of the linkage of the binuclear core with eight adjacent cores by six 5-AIP ligands. (c) A view of 3 showing how the organization of the four different subrings (marked with A, B, C, and D) contributes to the construction of the infinite honeycomb sheet. (d) The schematic of the 3,8-connected 3D network with {42.6}2{44.610.79.85} topology. F



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Figure 4. (a) The coordination environment of Co(II) ion in 4 with 50% thermal ellipsoids. (b) The 2D polymeric layer of 4. (c) The schematic of 2D layer in 4.

O(5) of amide groups from L4 ligands [O(1W)−H(1WB)··· O(5) = 2.730(1) Å] (Figure S5b). Structural Description of [Co(L5)(5-AIP)] (5). Compound 5 shows a 3D framework with monoclinic C2/c space group. The asymmetric unit of 5 consists of one Co(II) ion, one L5 molecule, and one 5-AIP anion. The Co(II) ion displays a fivecoordinated mode, completed by three carboxyl oxygen atoms from three individual 5-AIP ligands [Co(1)−O(3) = 2.0096(12) Å, Co(1)−O(4)#2 = 2.0700(12) Å, Co(1)−O(5) #1 = 2.0329(12) Å], two pyridyl N atoms [Co(1)−N(1) = 2.1202(15) Å, Co(1)−N(4)#3 = 2.2070(16) Å] from two L5 ligands, exhibiting a distorted {CoN2O3} square-pyramidal geometry (Figure 5a). Two Co(II) ions are bridged by two carboxyl groups from two 5-AIP anions giving a binuclear {Co2} SBU [Co···Co = 4.365 Å]. Each {Co2} SBU is linked to the four neighboring {Co2} SBUs by two pairs of L5 ligands in the b axis and two pairs of 5-AIP ligands in c axis, respectively (Figure 5b). The distances between the cores of adjacent {Co2} SBUs are 19.468 and 9.910 Å, respectively. The 5-AIP adopts a monodentate-bis(monodentate) coordination mode with its carboxyl groups and links neighboring Co(II) ions forming a 1D [Co(5-AIP)]n double chain (Figure S6a). The amino group

Figure 5. (a) View of coordination environment of Co(II) ion in 5 with 50% thermal ellipsoids. (b) View of the linkage of the binuclear SBU with four adjacent SBUs by 5-AIP and L5 ligands. (c) The 3D framework of 5. (d) Schematic view of 3-fold interpenetrating CdSO4 topology in 5.

of 5-AIP is noncoordinated. In compound 5, the L5 ligand coordinates with two Co1 ions by its two pyridyl nitrogen G



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atoms to build a binuclear [Co2(L5)2] loop unit (Figure S6b), in which the nonbonding Co···Co separation is 16.659 Å. The dihedral angle between two pyridine rings of L5 ligand is 60.86°. The combination of 1D [Co(5-AIP)]n chains and [Co2(L5)2] loop units leads to the formation of an intriguing 3D framework containing a large rectangular cavity with the size of 21.10 × 22.30 Å2 (Figure 5c). The void space within the 3D network is occupied by two identical 3D networks, resulting in a 3-fold interpenetrating framework (Figure 5d). In 5, considering the {Co2} SBUs as nodes and the two types of bridging ligands (5-AIP and L5) as linkers, the 3D network is described as a CdSO4-like topological structure. Structural Description of [Co(HBTC)(L3)]·H2O (6). Single crystal structure analysis reveals that compound 6 is a doublelayer network and crystallizes in triclinic system P1̅ space group, whose asymmetric unit consists of one crystallographically independent Co(II) ion, a L3 molecule, one HBTC anion, and a lattice water molecule. As depicted in Figure 6a, the Co(II) ion is coordinated by four O atoms (O3, O4#1, O7#3, O8#3) from three carboxyl groups belonging to three HBTC anions [Co(1)−O(3) = 2.0153(16) Å, Co(1)−O(4)#1 = 2.0260(17) Å, Co(1)−O(7)#3 = 2.3021(18) Å, and Co(1)−O(8)#3 = 2.1577(17) Å] and two pyridyl nitrogen atoms (N1, N4#2) from two L3 ligands [Co(1)−N(1) = 2.170(2) Å, Co(1)−N(4) #2 = 2.147(2) Å] to finish a distorted octahedral coordination geometry. In 6, two carboxyl groups from the HBTC anion connect three Co(II) ions with the chelating-bis(monodetate) bridging mode (Table 2), generating a [Co(HBTC)]2n ladderlike chain (Figure S7a). The third carboxyl of HBTC is protonated (Table 2). In addition, L3 ligand adopting a bidentate mode connects two Co(II) ions [the Co···Co distance: 16.645 Å, the dihedral angle of two pyridyl rings: 12.37°], leading to the construction of a 1D [Co(L3)]n zigzag chain (Figure S7b). The alternating connection of 1D [Co(HBTC)]2n ladder-like chains and [Co(L3)]n chains builds a 2D double-layer network, which is different from that of compound 4 (Figure 6b). Each Co(II) ion is linked by three HBTC anions and two L3 ligands, which can be simplified as a 5-connected node. Each HBTC links three Co(II) ions, which is defined as a 3-connected node, and the L3 ligands can be viewed as linkers. Thus, the double-layer network is regarded as a binodal (3,5)-connected {42·67·8}{42·6} topology (Figure 6c). Finally, the N−H···O hydrogen bonds [N(3)−H(3B)··· O(7) = 2.969(5) Å] extended the double-layer network to a 3D supramolecular framework (Figure S7c). Structural Description of [Co(HBTC)(L6)(H2O)]·3H2O (7). Crystallographic analysis demonstrates that 7 is a 2D grid layer and crystallizes in triclinic system and P1̅ space group, whose asymmetric unit includes a Co(II) ion, a L6 ligand, a HBTC anion, a coordination water, and three noncoordinated water molecules. In Figure 7a, the Co(II) ion is six-coordinated by three carboxyl O atoms of two HBTC ligands (Co1−O(6) = 2.025(2) Å, Co1−O(1)#2 = 2.136(2) Å, Co(1)−O(2)#2 = 2.207(2) Å), two N atoms from two L6 molecules (Co1−N(1) = 2.163(3) Å, Co1−N(2) = 2.151(3) Å), and one O atom of a water molecule (Co1−O(1W) = 2.083(3) Å). For HBTC anion, two carboxyl groups are coordinated to two Co(II) ions with the chelating-monodentate mode, which is different from that in complex 6. In this manner, the HBTC anions bridge adjacent two Co(II) ions generating a [Co(HBTC)]n straightchain (Figure S8a). In addition, the L6 as bidentate bridging ligands link the neighboring two Co(II) centers forming a [Co(L6)]n zigzag chain with the nonbonding Co···Co distances

Figure 6. (a) The coordination environment for Co(II) ion in 6 with 50% thermal ellipsoids. (b) The 2D polymeric double-layer formed by ligands L3 and HBTC for complex 6. (c) The schematic of 2D doublelayer in complex 6.

of 21.629 Å, the dihedral angle between two pyridine rings is 18.19° (Figure S8b). The adjacent [Co(L6)]n chains are bridged by HBTC ligands forming a (4,4) grid layer (shown in Figure 7b,c). These neighboring layers are finally extended into a 3D supramolecular network through hydrogen bonds between the carbonyl oxygen atoms (O(8)) from L6 ligands and the O(1W) from the coordination water molecules [O(1W)−H(1WB)···O(8) = 2.717(2) Å] (Figure S8c). Structural Description of [Co2(L3)2(1,3-BDC)2]·4H2O (9). Single crystal X-ray analysis reveals that 9 crystallizes in triclinic crystal system and P1̅ space group. Similar to compound 2, there are two crystallographic different Co(II) ions, and their coordination environments are depicted in Figure 8a. The Co(1) ion exhibits a distorted {CoN2O4} octahedral geometry and is coordinated by two pyridyl N atoms of two L3 molecules and four carboxyl O atoms of three 1,3BDC ligands [Co(1)−N(1) = 2.170(4) Å, Co(1)−N(8)#1 = 2.161(4) Å, Co(1)−O(10) = 2.025(3) Å, Co(1)−O(5) = H



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Figure 7. (a) The coordination environment of Co(II) ion in complex 7 with 50% thermal ellipsoids. (b) The 2D grid layer of complex 7. (c) The schematic of 2D layer in complex 7.

2.040(3) Å, Co(1)−O(8)#2 = 2.225(3) Å, Co(1)−O(7)#2 = 2.166(3) Å]. The Co(2) ion is also six-coordinated by four O atoms from three 1,3-BDC anions and two N atoms of two L3 molecules to give a {CoN2O4} distorted octahedron. The bond distances for Co(2)−N and Co(2)−O are in the ranges of 2.161(4)−2.175(4) Å and 2.009(3)−2.039(3) Å, respectively. Different from those in compound 8, two carboxyl groups of 1,3-BDC anion adopt two distinct coordination fashions: one is a bis(monodentate) mode, and the other is a chelating coordination mode (Table 2). The carboxyl groups from two separated 1,3-BDC anions with the bis(monodentate) bridging mode link two Co(II) ions to construct a dinuclear {Co2} SBU [Co(1)···Co(2) distance: 4.1245(11) Å]. Each {Co2} SBU is connected to the neighboring six {Co2} SBUs by two pairs of 1,3-BDC anions and four L3 ligands constructing a 3D [Co2(L3)2(1,3-BDC)2]n network (Figure 8b,c) (Distances between the cores of SBUs: 10.11, 16.76, and 17.10 Å). In the 3D framework, the 1,3-BDC ligands link Co(II) centers to build a neutral [Co2(1,3-BDC)2]n ladder-like chain (Figure S9a). The L3 ligands adopting a bidentate bridging coordination fashion connect the neighboring Co(1) and Co(2) ions generating a [Co(L3)]n wave-like chain (Figure S9b), in which the L3 shows two kinds of conformations and bridges two Co(II) centers with the Co(1)···Co(2) distance of 16.881 Å (A-type) and Co(1)···Co(2A) distance of 16.788 Å (B-type) (Table 2). The related dihedral angles of two pyridyl groups are 5.933° (A-type) and 10.167° (B-type), respectively. From the topological view, if the dinuclear {Co2} SBU serves as a 6connected node and ligands 1,3-BDC and L3 act as linear linkers, the final 3D framework of compound 9 represents a

Figure 8. (a) The coordination environments of the Co(II) ions in compound 9 with 50% thermal ellipsoids. (b) View of the linkage of the binuclear SBU with six SBUs by 1,3-BDC and L3 ligands. (c) The 3D network with channels shown by yellow in 9. (d) Schematic representation of 2-fold interpenetrating α-Po net of 9.

distorted α-Po topology (10.11 Å × 16.76 Å × 17.10 Å). To minimize the voids and consolidate the coordination framework, two same 3D frameworks interpenetrate with each other, generating a 2-fold interpenetrated 3D architecture (Figure 8d). I



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Structural Description of [Co2(L4)1.5(1,2-BDC)(μ2-OH)(μ3-OH)(H2O)]·H2O (10). Crystal structural analysis displays that compound 10 crystallizing in triclinic P1̅ space group possesses a 3D polymeric framework. The fundamental building unit consists of two Co(II) ions [Co(1) and Co(2)], a 1,2-BDC anion, one and a half L4 ligands, one μ2-hydroxyl group, one μ3-hydroxyl group, a coordination water molecule, and a lattice water molecule. As illustrated in Figure 9a, Co(1) is five-coordinated by one carboxyl oxygen atom from a 1,2BDC anion [Co(1)−O(7) = 2.006(3) Å], one μ2-hydroxyl oxygen atom [Co(1)−O(12) = 1.956(3) Å], two μ3-hydroxyl oxygen atoms [bond lengths: Co(1)−O(11) = 1.969(3) Å, Co(1)−O(11)#1 = 2.246(3) Å], and one pyridyl nitrogen atom from one L4 ligand [Co(1)−N(1) = 2.121(3) Å] to complete a distorted square-pyramidal coordination geometry. While Co(2) is hexa-coordinated in a distorted octahedral configuration by one carboxyl O atom belonging to a 1,2-BDC ligand [Co(2)−O(8) = 2.112(3) Å], one μ2-hydroxyl oxygen atom [Co(2)−O(12)#1 = 2.042(3) Å], one μ3-hydroxyl oxygen atom [Co(2)−O(11) = 2.089(3) Å], two pyridyl N atoms of two L4 molecules [Co(2)−N(5) = 2.182(3) Å and Co(2)−N(7) = 2.157(3) Å], and a coordination water molecule [Co(2)− O(1W) = 2.212(3) Å]. In 10, only one carboxyl group from 1,2-BDC coordinated to two Co(II) ions with the bis(monodentate) mode. Two Co(1) and two Co(2) ions are bridged by two bis(monodentate) carboxyl groups and four hydroxyl groups with μ2-/μ3-bridging modes forming a tetranuclear cobalt cluster {Co4} SBU, in which the [Co4(μ3OH)4] unit demonstrates a chair-shaped structure (Figure S10).17 The Co···Co separations are 3.118(7) Å [Co(1)··· Co(2)#1], 3.5568(7) Å [Co(1)···Co(2), Co(1)#1···Co(2)#1], 3.1690(7) Å [Co(1)−Co(1)#1], and 5.8917(8) Å [Co(2)− Co(2)#1], respectively. In compound 10, the ligand L4 adopts a bidentate bridging coordination mode, exhibiting three conformations: (i) it bridges two Co(II) ions with the Co(1)···Co(1) distance of 18.716 Å (A-type); (ii) it connects two Co(II) ions and the Co(2)···Co(2) distance is 17.673 Å (B-type); (iii) it connects two Co(II) ions with the Co(2)··· Co(2) separation of 16.745 Å (C-type). For three different conformations of L4 ligands, their pyridyl rings are parallel and the corresponding dihedral angles are 0°. Each tetranuclear {Co4} SBU connects with the neighboring six tetranuclear {Co4} SUBs by six L4 ligands, which results in the construction of a 3D network of compound 10 (Figure 9b,c). The distances between the adjacent {Co4} SUBs are 22.89, 20.26, 21.65 Å, respectively. Each tetranuclear {Co4} SBU is linked to six tetranuclear {Co4} SBUs and can simply be viewed as a 6connected node. Each L4 coordinating to two {Co4} SBUs just serves as the linear linker. Hence, the topology of 10 can be demonstrated as a 6-connected coordination network and its Schläfli symbol is {412.63}, as can be seen in Figure 9d. Influence of the Flexible Bis(pyridylamide) with Different Spacers and Polycarboxylates on the Architectures of Compounds 1−10. In this study, six flexible bis(pyridylamide) ligands (L1, L2, L3, L4, L5, and L6) with different −(CH2)n− spacers (n = 0, 1, 2, 4, 5, 8) were prepared to react with Co(II) ion and four aromatic polycarboxylates, and 10 compounds with diverse structures were obtained. Our research indicates that polycarboxylates and bis(pyridylamide) ligands with different −(CH2)n− backbones have a significant effect on the architectures of compounds 1−10. From the structure description above, it can be clearly seen that these flexible bis(pyridylamide) ligands with −(CH2)n−

Figure 9. (a) The coordination environments of Co(II) ions in 10 with 50% thermal ellipsoids. (b) View of the linkage of the tetranuclear {Co4} SBU with six SBUs by L4 ligands. (c) The 3D framework of 10. (d) Schematic view of 6-connected 3D network of 10.

spacers play a crucial role in forming the Co-polycarboxylates subunits as well as the final polymeric frameworks. Compounds 1−5 based on the same bridging 5-AIP ligand have been synthesized by changing the bis(pyridylamide) ligands with J



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−(CH2)n− bridges (n = 0, 1, 2, 4, 5), which show structural changes from a 2D double layer (for 1) to a 1D polymeric chain (for 2), to a 3D coordination framework (for 3), to 2D layer (for 4), and to 3-fold interpenetrating 3D network (for 5). In compounds 1−5, the bridging 5-AIP anions display five different coordination modes (Table 2): tri(monodentate) mode for 1, bis(monodentate) mode for 2, monodentatemonodentate-bis(monodentate) bridging mode for 3, monodentate-monodentate-chelating mode for 4, and monodentatebis(monodentate) bridging mode for 5, which connect adjacent Co(II) ions resulting in various Co-5-AIP subunits: the polymeric layer in 1, the wavelike chain in 2, the 3D MOF in 3, the railroad-like chain in 4, and the double chain in 5, respectively. For 1−5, all the bis(pyridylamide) ligands adopt the bidentate bridging mode (Table 2), which connect Co(II) ions leading to various Co···Co distances: 12.767 Å for 1, 9.682 Å for 2, 15.356 Å for 3, 16.348 Å for 4, and 16.659 Å for 5, respectively. It is worth pointing out that only L2 ligand bridges Co(II) ions constructing a [Co(L2)]n “Ω”-like chain for 2. However, other four bis(pyridylamide) ligands (L1, L3, L4, and L5) link two adjacent Co(II) ions to produce discrete dinuclear subunits in other four compounds 1, 3, 4, and 5. Finally, the combination of bridging 5-AIP and bis(pyridylamide) ligands leads to the construction of five different topological structures: a 2D 3,4-connected {63}{66} double-layer network (for 1), a chain (for 2), a 3,8-connected 3D coordination network with {42.6}2{44.610.79.85} topology (for 3), a 2D ladder layer with 3,4-connected {62.10}{6} topology (for 4), and a 3-fold interpenetrating CdSO4-like coordination network (for 5). Likewise, compounds 6 and 7 are based on the same polycarboxylic acid H 3 BTC and different flexible bis(pyridylamide) ligands with -(CH2)n- (n = 2 and 8) backbones. In 6 and 7, the adjacent Co(II) centers are connected by the L3 or L6 bridging ligand, leading to zigzag chains with different Co···Co distances: 16.645 Å for 6 and 21.629 Å for 7. In these two compounds, HBTC anions exhibit two different coordination modes (Table 2): a chelating-bis(monodentate) bridging mode in 6, a chelating-monodentate mode in 7, which connect adjacent Co(II) ions to construct the [Co(HBTC)]2n doublechain in 6 and the [Co(HBTC)]n linear chain in 7, respectively. Finally, two different 2D networks were obtained: a (3,5)connected {42·67·8}{42·6} 2D double-layer structure in 6 and a (4,4) 2D grid layer in 7. Using the same 1,3-BDC ligand, we have prepared compounds 8 and 9 by changing the -(CH2)n- (n = 1 and 2) backbones of flexible bis(pyridylamide) ligands. The 1,3-BDC displays two types of bridging fashions in 8 and 9 (Table 2): a monodentate-monodentate mode and a bis(monodentate)-chelating mode, resulting in the [Co(1,3BDC)]n ‘V’−like chain in 8 and the [Co2(1,3-BDC) 2]n ladder-like chain in 9. For 8 and 9, both ligands L2 and L3 display the bidentate mode and bridge Co(II) centers generating the 1D [Co(L2)]n “Ω”-like chain (Co···Co separation: 9.722 Å) and a 1D [Co(L3)]n wave-like chain. Different from L2 in 8, the L3 in 9 shows two different conformations and bridge neighboring Co(II) ions with the Co···Co distances of 16.881 Å (A-type) and 16.788 Å (B-type), respectively (Table 2). Thus, a 1D chain-like structure for 8 and a 6-connected 2-fold interpenetrated 3D α-Po-related network for 9 were obtained. Our experimental research also reveals that different polycarboxylates play important roles in constructing different architectures derived from the same flexible bis(pyridylamide) ligand. When L3 is used as the N-donor bridging ligand and

three different polycarboxylates (5-AIP, 1,3,5-BTC, 1,3-BDC) are employed as the O-donor bridging ligands, three compounds with different structures were obtained: a 3D coordination framework for 3, a 2D double-layer for 6, and the 2-fold interpenetrated 3D architecture for 9. The various structures indicate that the polycarboxylate anions play an important role in constructing the final frameworks, which can be attributed to their differences in the amino substituent group and number of the carboxyl groups. Compared with 1,3-BDC, the 5-AIP has an extra amino substituent group and 1,3,5-BTC owns an additional carboxyl group, which generally may increase the connection numbers of these two polycarboxylates and further result in diverse structures. In compound 3, each 5AIP anion adopts a monodentate-monodentate-bis(monodentate) bridging mode by its one amino group and two carboxyl groups coordinating with Co(II) ions, which results in a 3D [Co(5-AIP)]n framework. While in 6, one carboxyl group of 1,3,5-BTC anion is protonated, and only other two carboxyl groups are coordinated to Co(II) ions with a bis(monodentate)-chelating mode, resulting in a 1D [Co(HBTC)]2n ladder-like chain. In 9, the bridging mode of 1,3BDC is same as that of HBTC in 6, which bridges Co(II) centers constructing the [Co2(1,3-BDC)2]n ladder-like chain. Though the L3 ligand adopts only one bidentate bridging mode, it shows four different conformations in these three compounds and connects Co(II) centers with diverse Co···Co distances (Table 2), resulting in different structures for 3, 6, and 9. Similarly, compounds 4 and 10 are prepared in the mixedligand systems based on the same L4 ligand and two different polycarboxylates (5-AIP and 1,2-BDC). In 4, the 5-AIP ligand with a monodentate-monodentate-chelating mode connects Co(II) centers to build the railroad-like chain. For 10, the 1,2BDC ligand displays a bis(monodentate) fashion and only a carboxyl coordinates to two Co(II) ions. Then, under the auxiliary role of hydroxyl group, the four Co(II) centers are integrated by 1,2-BDC anions to construct the {Co4} SBU. In two compounds, the L4 ligand adopts a bidentate mode and further bridges Co(II)-polycarboxylate subunits to form two diverse structures: a 2D ladder layer and a 3D 6-connected {412.63} topological framework, in which the L4 links two Co(II) ions with only one Co···Co distance of 16.348 Å for 4 and three different Co···Co distances (18.716, 17.673, and 16.745 Å) for 10. The results indicate that the different substituent groups, as well as the number and position of the carboxylic groups in polycarboxylates, have crucial influences on the final architectures for compounds 1−10. Powder X-ray Diffraction Analyses and Thermogravimetric Analyses. To characterize the phase purities of compounds 1−10, powder X-ray diffraction (PXRD) patterns have been checked at ambient temperature (Figure S12). For 1−10, the measured PXRD patterns agree with those calculated from the X-ray single crystal diffraction data, manifesting the purities of these crystals. By contrast, the slight differences in intensities may be attributed to the preferred orientation of the crystalline powder samples.18 In addition, the tiny peak shifts may be assigned to the baseline drift of the PXRD diffractometer and different measuring temperatures for single-crystal and powder diffraction. To estimate the stabilities of compounds 1−10, thermogravimetric analysis (TGA) experiments in 20−800 °C (heating rate: 10 °C min−1) under nitrogen atmosphere were performed (Figure S13). Compounds 1, 2, 4, 6−10 exhibit two evident K



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weight losses: the first corresponds to the loss of water molecules; the second occurs at 361−706 °C for 1, 233−737 °C for 2, 340−620 °C for 4, 280−524 °C for 6, 275−616 °C for 7, 234−648 °C for 8, 295−515 °C for 9, and 231−550 °C for 10, respectively, corresponding to decomposition of the ligands. In compounds 3 and 5, only one weight loss of 19.18% at 397−755 °C for 3 and 13.63% at 346−511 °C for 5 can be observed, accompanying the loss of organic ligands. The final residues of all the title compounds correspond to CoO. The results indicate that all the title compounds exhibit good thermal stabilities. Photocatalytic Activity. Methylene blue (MB), as a model of dye contaminant, is usually utilized to evaluate the photocatalytic activities of catalysts in the purification of wastewater. As is well-known, it is very hard to decompose the dye under visible light. As far as we know, the examples of the metal−organic complexes exhibiting obvious photocatalytic properties for degrading MB under visible light are very limited.19 Herein, we study the photocatalytic activities of compounds 1−10 toward the degradation of MB in visible light to detect the photocatalytic efficiencies in the wastewater treatment. The photocatalytic performance of each compound for the decomposition of MB was measured in typical processes: a 150 mg crystal sample of each title compound was mixed with 90 mL of MB aqueous solution (10.0 mg L−1), which was magnetically stirred about 30 min in the dark to obtain the uniform working solution. Then the resulting solution was irradiated with visible light from an xenon lamp under stirring. A 5.0 mL sample was taken out every 30 min and subsequently analyzed by UV−vis spectroscopy. In addition, the control experiment for MB degradation was also performed at the same condition without catalyst. The photocatalytic activities of compounds 1−10 are shown in Figure 10 and Figure S14.

compounds were plotted, as shown in Figure 11. The calculation results show that the MB degrades approximately

Figure 11. Photocatalytic decomposition rates of MB solution under visible light irradiation with the use of the title compounds and no crystal in the same conditions.

62% for compound 1, 82% for compound 2, 72% for compound 3, 68% for compound 4, 64% for compound 5, 53% for compound 6, 65% for compound 7, 46% for compound 8, 81% for compound 9, and 61% for compound 10 after 210 min, respectively. The differences of catalytic activity under visible light irradiation for 1−10 may trace back to the different structures of the 10 compounds.20 As illustrated in Figure 10 and Figure S14, using compounds 2 and 9 as photocatalysts, the absorption intensities of MB reduced gradually with the increase of reaction time. Furthermore, control experiments toward the degradation of MB molecules were also carried out under visible light. No significant change in the degradation of MB was observed in the following reaction conditions: (1) in the dark; (2) without catalyst; (3) only CoCl2·6H2O; (4) only six flexible bis(pyridylamide) ligands (L1, L2, L3, L4, L5, and L6); (5) only four aromatic polycarboxylates. The results show that compounds 2 and 9 possess high photodegradation efficiencies for MB contaminant under visible light irradiation, which may become potential photocatalysts in degrading some dye molecules. Recently, Ma’s group has reported four isomorphous metal− organic complexes, which exhibited photodegradation activities for MB molecules under UV light, and the degradation rates of MB were approximately 81%, 88%, 78%, and 87% after 1.5 h UV light irradiation, respectively.21 In this work, compounds 1−10 exhibit obviously photocatalytic activity under visible light. Though the photocatalytic activity of some title complexes is a little lower than that of Ma’s, photocatalytic degradation of organic dye under visible light is more significant than those of under UV irradiation. During the photocatalytic reactions, the stabilities of compounds 1−10 were monitored by PXRD, which demonstrated that the coordination networks were unchanged after the photocatalytic experiments, indicating the crystals were stable under the testing conditions (Figure S12). The repeated photocatalysis experiments were carried out with a constant MB concentration for evaluating reproducibility of compounds 1−10. Taking complex 9 as an example, after each round of photocatalysis experiment, the photocatalyst was filtered, kept stirring for 120 min in distilled water, and then filtered again. After being dried at room temperature, the

Figure 10. Absorption spectra of the MB solution during the decomposition reaction under visible light irradiation in the presence of compound 9.

No significant change in the degradation of MB was observed without any catalyst under visible light irradiation. However, it can be clearly observed that the absorption intensities of MB reduced gradually with increasing reaction time for the title compounds as photocatalysts, which indicates that all of compounds 1−10 show photocatalytic activity for the degradation of MB molecules under visible light. The concentrations of MB (C) versus reaction time (t) of the title L



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voltammetric behaviors for 1−10 bulk-modified carbon paste electrodes (1−10-CPE) under diverse scan rates were monitored in the different potential ranges of 400 to −400 mV for 1-CPE, 400 to −300 mV for 2-CPE, 500 to −200 mV for 3-CPE, 1000−400 mV for 4-CPE, 300 to −200 mV for 5CPE, 500 to −500 mV for 6-CPE, 200 to −400 mV for 7-CPE, 600 to −200 mV for 8-CPE, 1000−0 mV for 9-CPE, and 650 to −250 mV for 10-CPE; a pair of redox peak can be observed at the above modified CPEs, respectively, corresponding to the redox of CoIII/CoII.22 Their mean peak potentials [E1/2 = (Epa + Epc)/2] are −34 mV for 1-CPE, −10 mV for 2-CPE, −20 mV for 3-CPE, 660 mV for 4-CPE, 47 mV for 5-CPE, 0 mV for 6CPE, −135 mV for 7-CPE, 286 mV for 8-CPE, 350 mV for 9CPE, and 340 mV for 10-CPE, respectively. The differences in the mean peak potentials assigned to the CoIII/CoII redox couple for the title compounds might be attributed to the various coordination environments for Co(II) centers, different structures, and kinetic factors in the electron mediation processes.23 Herein, we investigate the influence of scan rates on the electrochemical property of the 9-CPE as an example. When the scan rates varied in the range of 60 to 200 mVs−1, the redox peak potentials gradually shifted (Figure 13): the reduction peak potentials shifted to the negative direction and the relevant oxidation peak potentials shifted to the positive direction. The redox peak currents are proportional to the scan rates (Figure S18), indicating that the redox of 9-CPE is a surface-confined process. It is well-known that nitrite is a hazardous circumstance pollutant, so its detection is very significative. Nevertheless, direct electrochemical reduction of nitrite demands a big overpotential at the surfaces of some electrodes, and no evident response can be seen at a bare CPE. In this paper, we investigated the electrochemical reduction of nitrite at the 1− 10-CPEs. As shown in Figure S19, at 1-CPE, 6-CPE, 9-CPE, and 10-CPE, when nitrite was gradually added, the reduction peak currents augmented, and the related oxidation peak currents reduced, indicating that 1-, 6-, 9-, and 10-CPE display electrocatalytic activities for the reduction of nitrite in 0.01 M H2SO4 + 0.5 M Na2SO4 aqueous solution. No electrocatalytic activities can be observed for the reduction of nitrite at other complexes modified CPEs. The different electrocatalytic activities for the title compounds could be assigned to their various components and diverse structures. Magnetic Behavior. Variable temperature magnetic susceptibilities for compounds 3, 5, 9, and 10 have been measured in the range of 1.8−300 K (magnetic field: 1000 Oe), due to the multiple superexchange paths in the dinuclear CoII clusters for 3, 5, 9, and the tetranuclear cluster [Co4(μ2OH)2(μ3-OH)2(O2C-)4] for 10. The magnetic behaviors of 3, 5, 9, and 10 under the model of both χmT and χm vs T graphs are displayed in Figures 14−17. In compounds 3 and 5, the χmT values at 300 K are 3.45 and 3.44 emu mol−1 K, which are slightly less than the calculated spin-only value (3.75 emu mol−1 K) for two Co(II) ions with uncoupled modes (S = 3/2, g = 2), respectively. As for 9, the χmT value at 300 K is 7.32 emu mol−1 K and much higher than the calculated spin-only value of 3.75 emu mol−1 K for two uncoupled Co(II) ion (S = 3/2, g = 2). The higher C and χmT values demonstrate the important orbital contribution for the Co(II) ions.24 The susceptibility (χm) of 3, 5, and 9 showed a sharp maximum at ca. 8 K, 16 K, 4 K as the temperature decreased, indicating the occurrence of an overall antiferromagnetic coupling among the Co(II) ions.25 In 10, at 300 K, the χmT value of 5.82 emu mol−1

recyclable samples were collected and reutilized. As shown in Figure S15, after the five same photodegradation processes, the decolorization rate for the photocatalyst shows no obvious decline. The result suggests that complex 9 shows a high photocatalysis reproducibility. After five photocatalysis cycles, the PXRD pattern of 9 was almost identical to the original one (Figure S12), revealing that compound 9 is a stable and reproducible photocatalyst. In addition, the similar experiments were performed to investigate the photocatalytic activities of 9 for the degradation of methyl orange (MO) or rhodamine B (RhB). After 210 min, the degradation rates of RhB and MO were only 28% and 12%, respectively (Figure 12 and Figure S16). This result indicates

Figure 12. Time dependent UV/vis spectra of three dyes (blue pillar: MB; orange pillar: MO; pink pillar: RhB) for compound 9.

that the compound 9 is a good selective photocatalyst for the degradations of MB. After the photodegradation of RhB and MO, the PXRD patterns are almost identical to the as-prepared sample (Figure S12). In this work, we have explored new waterinsoluble and easily recycled materials with photocatalytic activities. Especially, compound 9 represents a rare example of coordination polymers that exhibit high, reproducible, and selective photocatalysis activity for the degradation of organic dye molecules under visible light. Electrochemical Behaviors of 1−10-CPEs. The electrochemical properties of compounds 1−10 were measured by cyclic voltammetry in 0.01 M H2SO4 + 0.5 M Na2SO4 aqueous solution. As shown in Figure 13 and Figure S17, the cyclic

Figure 13. Cyclic voltammograms of the 9-CPE in 0.01 M H2SO4 + 0.5 M Na2SO4 aqueous solution at different scan rates (from inner to outer: 60, 80, 100, 120, 140, 160, 180, 200 mV·s−1). M



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from 300 K to 1.8 K, the χmT values decrease gradually from 3.45 to 0.018 emu mol−1 K, 3.44 to 0.014 emu mol−1 K, 7.32 to 0.032 emu mol−1 K, 5.82 to 0.02 emu mol−1 K, respectively. For 3, 5, 9, and 10, the susceptibility data of 1/χm versus T (Figures S20a−S23a) are fitted by Curie−Weiss law [χm = C/(T − θ)] over 100 K, giving the Curie constant values C = 3.81, 3.99, 9.05, 7.17 emu mol−1 K and the Weiss constants θ = −37.8, −43.9, −75.5, −79.2 K, respectively. The trend of χmT versus T and the negative values of θ indicate the antiferromagnetic interactions within the dinuclear CoII2 or the tetranuclear CoII4 cluster.26,27 The antiferromagnetic behavior of 10 may originate from the multiple superexchange interactions between the CoII ions within the CoII4 cluster by the mixed μ2-η1:η1-COO−, and part of μ2-OH, μ3-OH pathways. The field dependent magnetization curves (Figures S20b−S23b) of 3, 5, 9, and 10 at 1.8 K show that the magnetization values gradually augment along with the field up to 2.0, 1.3, 5.1, 2.1 Nβ at 55, 70.61, 70.46, 70.42 kOe, respectively, but without reaching saturation (6.00 Nβ for two CoII ions of 3, 5, 9, 12.00 Nβ for four CoII ions of 10). Recently, Zeng’s group reported two cobalt-based CPs [Co II 3 (lac) 2 (pybz) 2 ]·3DMF and [Co 4 (pico) 4 (4,4′-bpy) 3 (H2O)2]n·2nH2O, which exhibited magnetic transformation and metamagnetism.26,27 There are fragments containing M− O−M connections or interchain magnetic interactions within the frameworks. In this work, compounds 3, 5, 9, and 10 exhibit antiferromagnetic magnetic behaviors, which only possess dinuclear CoII clusters and/or chair-shaped tetranuclear clusters. The results indicate that the different magnetic behaviors may be ascribed to their different structures.

Figure 14. Temperature dependence of χm and χmT for complex 3.


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CONCLUSION Ten new CoII coordination polymers with different dimensionalities and structures by using four different polycarboxylates as the main ligands and six bis(pyridylamide) as the coligands were purposefully synthesized by the hydrothermal technique. These compounds exhibit various dimension and structural features. Four polycarboxylate anions play crucial roles in constructing polynuclear SBUs and show great influence on the structural diversities of compounds 1−10. The flexible bis(pyridylamide) with variable spacer length shows various conformations and has great impact on the ultimate networks of compounds 1−10. Compounds 2 and 9 display remarkable catalytic activities for the photodegradation of organic dye MB under the visible light, implying that these compounds might be potential photocatalysts. The magnetic properties of compounds 3, 5, 9, and 10 indicate that the four compounds may be potential magnetic materials. Further works for the designed construction of multifunctional crystal materials based on bis(pyridylamide) and polycarboxylates are ongoing in our laboratory.


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ASSOCIATED CONTENT

S Supporting Information *

Ten X-ray crystallographic files (CIF); selected bond distances and angles and figures for compounds 1−10. This material is available free of charge via the Internet at http://pubs.acs.org.

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Figure 17. Temperature dependence of χm and χmT for complex 10. −1

AUTHOR INFORMATION

Corresponding Author

K is much less than the theoretical value of 7.50 emu mol K for four spin-only CoII ions (S = 3/2, g = 2). For 3, 5, 9, and 10, the four χmT versus T plots exhibit the same trend, namely,

*Tel: +86-416-3400158. Fax: +86-416-3400158. E-mail: [email protected]. N



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Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 21171025, 21201021), Program of New Century Excellent Talents in University (NCET-09-0853), and Program of Innovative Research Team in University of Liaoning Province (LT2012020).

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