Structural Diversity, Luminescence, and Magnetic Properties of Eight

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Structural Diversity, Luminescence, and Magnetic Properties of Eight Co(II)/Zn(II) Coordination Polymers Constructed from Semirigid Ether-Linked Tetracarboxylates and Bend Dipyridyl-Triazole Ligands Tian Ma,† Ming-Xing Li,*,† Zhao-Xi Wang,† Jin-Cang Zhang,§ Min Shao,‡ and Xiang He*,† †

Department of Chemistry, and §Department of Physics, College of Sciences, Shanghai University, Shanghai 200444, People’s Republic of China ‡ Laboratory for Microstructures, Shanghai University, Shanghai 200444, People’s Republic of China S Supporting Information *

ABSTRACT: Eight coordination polymers based on H4L1/H4L2 (5,5′-(1,4/1,3-phenylenebis(methoxy))diisophthalic acid) and 3/4abpt (4-amino-3,5-bis(3/4-pyridyl)-1,2,4-triazole) ligands were synthesized: [Co4(L1)2(4-abpt)(H2O)10.5]n (1), {[Zn2(L1)(4-abpt)(H2O)3]·5H2O}n (2), {[Co(H2L1)(3-abpt)(H2O)2]·0.5H4L1}n (3), {[Co2(L1)(4-abpt)2 ]·4H2O}n (4), {[Zn2(L2)(4-abpt)(H2 O)]· 2.5H 2 O} n (5), {[Zn 2 (L 2 )(4-abpt)(H 2 O)]·3H 2 O} n (6), {[Co1.5(HL2)(3-abpt)(H2O)]·H2O}n (7), and {[Zn1.5(HL2)(3abpt)(H2O)]·H2O}n (8). Their structures were characterized by EA, IR, powder X-ray diffraction, thermogravimetric analysis (TGA), and single crystal X-ray diffraction. Complex 1 exhibits a three-dimensional (3D) metal−organic framework (MOF) composed of an interesting tetranuclear Co4(μ2-H2O)3(μ2-COO)4 cluster and 76-membered ring. Complex 2 shows a two-dimensional (2D) sheetlike network assembled by a one-dimensional (1D) [Zn2(L1)(H2O)3]n ribbon and 4-abpt linker. Complex 3 is a 1D nanotube coordination polymer constructed from parallel Co2(H2L1)2 rings pillared by two rows of 3-abpt spacers, which contains H4L1 guest molecule. Complex 4 displays a beautiful 3D porous MOF built by 2D sheetlike [Co2(L1)]n networks pillared by 4-abpt spacers. Complex 5 features a porous 3D MOF with regular nanosized rectangle tunnel. Complex 6 exhibits a 3D structure constructed from a double-layered [Zn2(L2)(H2O)]n network and 4-abpt linker. Complexes 7 and 8 are isostructural 3D polymers completed by 2D [Co1.5/Zn1.5(HL2)(H2O)]n networks pillared by 3-abpt spacers. H4L1 and H4L2 are fully or partly deprotonated in these complexes and exhibit six types of coordination modes. The 3/4-abpt ligands act as bidentate linkers. TGA shows that both tetracarboxylates ligands are thermally stable to 300 °C. Zn(II) complexes 2 and 8 are strong luminescent emitters. Variable-temperature magnetic studies indicate that complexes 1, 4, and 7 exhibit antiferromagnetic coupling between carboxyl-bridging CoII ions.

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INTRODUCTION The rational design and assembly of coordination polymers (CPs) and metal−organic frameworks (MOFs) have made rapid progress due to their intriguing structural variety and interesting functional properties, such as luminescence, magnetism, ferroelectric, chirality, catalysis, and porous absorption.1 Over the past decade, much effort has been invested in the purposeful design and controllable synthesis of these functional complexes.2 However, it is still a great challenge to construct target coordination polymers with desired structures and functional properties because many factors, such as metal ion, organic ligand, reagent ratio, solvent, pH value, temperature, and so on, affect the final results.3 Among the many strategies for constructing coordination polymers, the self-assembly of polycarboxylate anions and N-heterocyclic neutral ligands with metal ions under hydro(solvo)thermal conditions has become one of the most effective approaches.4 Plenty of rigid polycarboxylates, such as phthalic acid, trimesic acid and © 2014 American Chemical Society

pyromellitic acid, are widely used to afford vast coordination polymers.5 In recent years, flexible and semirigid polycarboxylates are frequently employed to construct coordination polymers.6 Relative to rigid ligands, flexible and semirigid polycarboxylates have more advantages, because their flexibility and conformational freedom allow them to conform to the coordination environment of metal ions and afford various coordination polymers with interesting structures and functional properties. Recently, ether-linked aromatic polycarboxylate ligands have attracted much attention in constructing coordination polymers because the freely rotating ether bond can bring flexibility and structural devisity.7 In this work, we chose two semirigid etherlinked tetracarboxylic acids, 5,5′-(1,4/1,3-phenylenebisReceived: May 23, 2014 Revised: July 2, 2014 Published: July 7, 2014 4155

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Quantum Design MPMS-XL7 SQUID magnetometer at an applied field of 1000 Oe. The diamagnetic corrections were applied by using Pascal’s constants. Synthesis of [Co4(L1)2(4-abpt)(H2O)10.5]n (1). A mixture of Co(NO3)2·6H2O (58 mg, 0.20 mmol), H4L1 (23 mg, 0.05 mmol), 4-abpt (12 mg, 0.05 mmol), H2O (7.5 mL), and DMF (0.5 mL) was sealed in a 15 mL Teflon-lined reactor and heated at 100 °C for 72 h. Pink crystals of 1 were obtained with 35.2% yield (14.0 mg, 0.009 mmol) based on H4L1. Anal. Calcd for C60H59Co4N6O30.5: C, 45.39; H, 3.75; N, 5.29. Found: C, 46.59; H, 3.64; N, 5.86. IR (KBr, cm−1): 3357w, 3052w, 2854w, 1633m, 1587s, 1550s, 1453m, 1382s, 1267m, 1046m, 822w, 770s, 712m. Synthesis of {[Zn2(L1)(4-abpt)(H2O)3]·5H2O}n (2). A mixture of Zn(NO3)2·6H2O (60 mg, 0.20 mmol), H4L1 (23 mg, 0.05 mmol), 4abpt (12 mg, 0.05 mmol), H2O (7.5 mL), and DMF (1.5 mL) was sealed in a 15 mL Teflon-lined reactor and heated at 120 °C for 72 h. Colorless crystals of 2 were obtained with 46.7% yield (22.8 mg, 0.023 mmol) based on H4L1. Anal. Calcd for C36H40N6O18Zn2: C, 44.60; H, 3.54; N, 8.66. Found: C, 44.43; H, 3.95; N, 8.51. IR (KBr, cm−1): 3419m, 3093w, 2870w, 1620s, 1572s, 1454m, 1371s, 1265m, 1036s, 778s, 728m. Synthesis of {[Co(H2L1)(3-abpt)(H2O)2]·0.5H4L1}n (3). A mixture of Co(NO3)2·6H2O (58 mg, 0.20 mmol), H4L1 (23 mg, 0.05 mmol), 3abpt (12 mg, 0.05 mmol), H2O (7.5 mL), and DMF (1.5 mL) was sealed in a 15 mL Teflon-lined reactor and heated at 100 °C for 72 h. Pink crystals of 3 were obtained in 58.2% yield (30.0 mg, 0.029 mmol) based on H4L1. Anal. Calcd for C48H39CoN6O17: C, 55.93; H, 3.81; N, 8.15. Found: C, 56.21; H, 3.82; N, 8.20. IR (KBr, cm−1): 3279w, 3127w, 1690s, 1593s, 1461m, 1413m, 1368s, 1279s, 1127m, 1040s, 822m, 761s, 705m. Synthesis of {[Co2(L1)(4-abpt)2]·4H2O}n (4). A mixture of Co(NO3)2· 6H2O (58 mg, 0.20 mmol), H4L1 (12 mg, 0.025 mmol), 4-abpt (12 mg, 0.05 mmol), H2O (7.5 mL), DMF (1.5 mL), and three drops of HNO3 (2.0 mol·L−1) was sealed in a 15 mL Teflon-lined reactor and heated at 120 °C for 48 h. Purple crystals of 4 were obtained in 60.0% yield (16.9 mg, 0.015 mmol) based on H4L1. Anal. Calcd for C48H42Co2N12O14: C, 51.07; H, 3.75; N, 14.89. Found: 51.72; H, 4.40; N, 16.19. IR (KBr, cm−1): 3333w, 3077w, 2870w, 1615s, 1580s, 1545s, 1458s, 1383s, 1036m, 833m, 781s, 724s. Synthesis of {[Zn2(L2)(4-abpt)(H2O)]·2.5H2O}n (5). A mixture of Zn(NO3)2·6H2O (60 mg, 0.20 mmol), H4L2 (23 mg, 0.05 mmol), 4abpt (24 mg, 0.10 mmol), H2O (5.0 mL), and DMF (1.0 mL) was sealed in a 15 mL Teflon-lined reactor and heated at 85 °C for 72 h. Colorless crystals of 5 were obtained with 49.0% yield (21.7 mg, 0.025 mmol) based on H4L2. Anal. Calcd for C36H31N6O13.5Zn2: C, 48.33; H, 3.55; N, 9.40. Found: C, 46.08; H, 4.12; N, 9.48. IR (KBr, cm−1): 3450m, 3357w, 3072w, 2929w, 1655m, 1618s, 1556s, 1453m, 1413m, 1361s, 1261m, 1034s, 779s, 735s. Synthesis of {[Zn2(L2)(4-abpt)(H2O)]·3H2O}n (6). A mixture of Zn(NO3)2·6H2O (60 mg, 0.20 mmol), H4L2 (23 mg, 0.05 mmol), 4abpt (12 mg, 0.05 mmol), H2O (4.0 mL), and DMF (2.0 mL) was sealed in a 15 mL Teflon-lined reactor and heated at 85 °C for 72 h. Colorless crystals of 6 were obtained with 40.1% yield (18.1 mg, 0.02 mmol) based on H4L2. Anal. Calcd for C36H32N6O14Zn2: C, 47.86; H, 3.57; N, 9.30. Found: C, 46.30; H, 3.65; N, 9.17. IR (KBr, cm−1): 3414m, 3372w, 2943w, 1653w, 1618s, 1571s, 1456m, 1410w, 1372s, 1260m, 1043m, 781s, 745s. Synthesis of {[Co1.5(HL2)(3-abpt)(H2O)]·H2O}n (7). A mixture of Co(NO3)2·6H2O (58 mg, 0.20 mmol), H4L2 (23 mg, 0.05 mmol), 3abpt (12 mg, 0.05 mmol), H2O (7.5 mL), and DMF (0.5 mL) was sealed in a 15 mL Teflon-lined reactor and heated at 120 °C for 72 h. Purple crystals of 7 were obtained with 61.8% yield (25.5 mg, 0.031 mmol) based on H4L2. Anal. Calcd for C36H29Co1.5N6O12: C, 52.35; H, 3.54; N, 10.17. Found: C, 53.07; H, 3.65; N, 10.45. IR (KBr, cm−1): 3392m, 3078w, 2890w, 1690s, 1558s, 1528s, 1460m, 1377s, 1227m, 1036s, 814m, 786s, 701s. Synthesis of {[Zn1.5(HL2)(3-abpt)(H2O)]·H2O}n (8). A mixture of Zn(NO3)2·6H2O (60 mg, 0.20 mmol), H4L2 (23 mg, 0.05 mmol), 3abpt (12 mg, 0.05 mmol), H2O (5.0 mL), DMF (1.0 mL), and three drops of HNO3 (2.0 mol·L−1) was sealed in a 15 mL Teflon-lined reactor and heated at 120 °C for 72 h. Colorless crystals of 8 were

(methoxy))diisophthalic acids (H4L1 and H4L2, Scheme 1), for our synthetic strategy. Both 5-substituted isophthalic acid Scheme 1. Coordination Modes of H4L1, H4L2, and 3/4-Abpt in 1−8

derivatives contain a central phenyl group and two rigid isophthalic acid arms combined by intervening flexible methoxy groups. The cooperation of four rotating carboxyl groups and two freely twisting methoxy groups would afford a directional control at three-dimensional (3D) extensions. Both versatile tetracarboxylates can act as valuable multidentate connectors to produce porous CPs and MOFs with unique structural motifs and functional properties. The carboxyl groups can propagate magnetic coupling between paramagnetic metal ions. Zaworotko characterized the first L2-coordinated 3D net [Cu24(L2)12(H2O)16(DMSO)8]n.8 Zheng and Du et al. constructed several 2D and 3D CPs from H4L1 and H4L2 ligands.9 We recently reported a series of H4L1 CPs with entangled networks and luminescent properties.10 Both tetracarboxylic acids have good ligating ability to metal ions, and their fully deprotonated forms display more negative charge (−4 valence). It is a good strategy to use neutral rigid Nheterocyclic spacers, such as 4-amino-3,5-bis(3/4-pyridyl)-1,2,4triazole (3/4-abpt, Scheme 1), as auxiliary ligands to pillar the tetracarboxylate-metal networks and promote structural diversity in constructing porous MOFs. The exo-dipyridyl 3/4-abpt ligands have a bent backbone which can generate onedimensional (1D) zigzag and helical chains, even bring out chirality.11 Now we combine both tetracarboxylates and 3/4abpt ligands with Co(II)/Zn(II) ions and successfully prepared eight coordination polymers. The dimensionality of these CPs varies from 1D to 3D, and H4L1 and H4L2 exhibit versatile coordination modes. Herein, we report their synthesis, crystal structures, thermal stability, luminescence, and magnetic properties.

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EXPERIMENTAL SECTION

Materials and Methods. H4L1 and H4L2 were prepared according to literature procedures.12 Other reagents were of reagent grade and used as received without further purification. Elemental analyses (C, H, and N) were performed on a Vario EL III elemental analyzer. Infrared spectra were recorded with a Nicolet A370 FT-IR spectrometer using KBr pellets in 4000−400 cm−1 range. Powder X-ray diffractions were measured at a scanning rate of 5° min−1 on a Rigaku DLMAX-2550 diffractometer using Cu−Kα radiation (λ = 1.5418 Å). Thermal analyses were completed on a Netzsch STA 449C thermal analyzer at a heating rate of 10 °C min−1 in air. Luminescent spectra of crystalline samples were recorded on a Shimadzu RF-5301 spectrophotometer. Variabletemperature (2−300 K) magnetic susceptibilities were measured on a 4156

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Table 1. Crystallographic Data and Structure Refinement for Complexes 1−8 1

2

3

4

formula fw cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V [Å3] Z Dc (g cm−3) μ (mm−1) reflections/unique Rint data/restraints/params GOF on F2 R1, wR2 (I >2σ(I)) R1, wR2 (all data) largest diff. peak and hole (e Å−3)

C60H59Co4N6O30.5 1587.85 orthorhombic Pmmn 20.423(5) 43.214(10) 7.0518(16) 90 90 90 6224(2) 4 1.695 1.149 36787/7406 0.1134 7406/0/ 516 1.043 0.0887, 0.2056 0.1536, 0.2389 2.526, −0.920 5

C36H40N6O18Zn2 975.48 monoclinic P2/c 20.103(3) 9.645(2) 21.915(4) 90 107.832(2) 90 4045.1(12) 4 1.602 1.272 23864/9094 0.0580 9094/0/561 0.986 0.0671, 0.1542 0.1198, 0.1797 0.751, −0.590 6

C48H39CoN6O17 1030.78 triclinic P1̅ 9.2048(9) 10.511(1) 26.568(3) 100.844(1) 91.573(1) 109.123(1) 2374.4(4) 2 1.442 0.443 15023/10533 0.0314 10533/0/654 1.021 0.0760, 0.1704 0.1150, 0.2131 0.717, −0.577 7

C48H42Co2N12O14 1128.80 triclinic P1̅ 10.079(4) 14.817(5) 20.165(7) 98.577(5) 103.941(4) 91.757(4) 2883.1(18) 2 1.300 0.644 17312/12462 0.0226 12462/0/685 1.588 0.1230, 0.3911 0.1529, 0.4109 2.605, −1.355 8

formula fw cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V [Å3] Z Dc (g cm−3) μ (mm−1) reflections/unique Rint data/restraints/params GOF on F2 R1, wR2 (I >2σ(I)) R1, wR2 (all data) largest diff. peak and hole (e Å−3)

C36H24N6O13.5Zn2 887.35 monoclinic C2/c 30.933(3) 14.715(1) 19.056(2) 90 111.440(1) 90 8073.4(12) 8 1.460 1.259 25129/9318 0.0486 9318/0/516 0.911 0.0733, 0.2081 0.1175, 0.2358 2.467, −0.615

C36H25Co1.5N6O12 822.02 monoclinic P21/c 15.166(4) 18.627(5) 12.018(3) 90 96.446(3) 90 3373.6(16) 4 1.618 0.824 20910/7717 0.0494 7717/0/503 1.067 0.0674, 0.1752 0.0986, 0.2034 0.850, −0.978

C36H29N6O12Zn1.5 835.71 monoclinic P21/c 15.244(4) 18.562(5) 12.019(3) 90 96.527(4) 90 3378.8(15) 4 1.643 1.152 20877/7669 0.0672 7669/0/504 1.038 0.0669, 0.1566 0.1143, 0.1954 1.014, −0.710

C36H32N6O14Zn2 903.42 monoclinic C2/c 38.030(4) 10.010(1) 26.423(3) 90 125.589(1) 90 8179.8(13) 8 1.467 1.245 25025/9328 0.0412 9328/0 /523 1.087 0.0812, 0.2641 0.1171, 0.2972 2.822, −0.778

Scheme 2. Synthetic Conditions for 1−8

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For 1, 2, 4, 5 and 6, the absence of νas(COOH) absorption in 1720−1680 cm−1 range indicates that H4L1/H4L2 adopt completely deprotonated forms.17 Whereas the presence of a strong peak at about 1690 cm−1 for 3, 7, and 8 indicates that H4L1/H4L2 are partly deprotonated, even 3 contains H4L1 guest molecule. Complexes 5 and 6 have similar formulas and different 3D structures. Their asymmetric and symmetric stretching vibrations of carboxylates are somewhat different, 1556 and 1361 cm−1 for 5, while 1571 and 1372 cm−1 for 6. The bands near 3080, 2890, 1260, 1035, and 780 cm−1 are respectively assigned to ν(Ar−H), ν(−CH2−), ν(C−O), ν(C− C), and γ(Ar−H) vibrations. The weak band near 3350 cm−1 and stong peak at 1550 cm−1 are respectively assigned to ν(N−H) and ν(CN) stretching vibrations of 3/4-abpt. The broad band near 3450 cm−1 corresponds to the ν(O−H) vibration of coordinated and lattice water molecules. Structure of [Co4(L1)2(4-abpt)(H2O)10.5]n (1). Single crystal Xray diffraction analysis reveals that complex 1 is an interesting 3D MOF. The asymmetric unit consists of four crystallographically independent Co(II) ions, two (L1)4− ligands, one 4-abpt ligand, 10 and a half aqua ligands as well as one lattice water molecule. As depicted in Figure 1a, four distinct Co(II) ions all adopt a distorted octahedral geometry. Co1 is coordinated by four carboxyl oxygen atoms on equatorial plane, and pyridyl N1 atom and water O1W atom in the axial positions. Co2 is coordinated by water O2W, O3W, O4W, and pyridyl N6 atoms on equatorial plane, and two carboxyl oxygens in the axial positions. Co3 is surrounded by two carboxyl oxygen atoms (O2, O2A) and two water molecules (O7W, O7WA) on equatorial plane, and two water molecules (O5W, O6W) in the axial positions. Co4 is surrounded by four water molecules on equatorial plane, and two carboxyl oxygens in the axial positions. All of the Co−O bond distances fall in the range of 1.945(14)−2.217(5) Å, and the average Co−N distance is 2.164(8) Å. Interestingly, Co3 and Co3A are bridged by three μ2-H2O molecules to form a Co2(μ2-H2O)3 dimer with a Co3···Co3A separation of 3.040(2) Å. To our best knowledge, no complex containing Co2(μ2-H2O)3 building block was reported to date. Previously, several complexes containing Co2(μ2-OH)3 dimer were structurally characterized.18 The Co2(μ2-H2O)3 dimer is further connected to Co1 and Co1A via four bridging carboxyl groups to generate an unique Co 4 (μ2 -H 2 O) 3 (μ 2 -COO) 4 tetranuclear cluster (Figure 1b). Four carboxyl groups of H4L1 are completely deprotonated and coplanar with two terminal phenyl groups. Due to the flexibility of ether linkage, two terminal phenyl groups can adopt syn- or anticonformation.8 In 1, the (L1)4− ligand adopts a synconformation. Both terminal phenyl rings are parallel (dihedral angle 1.62°) and twist about 66° with respect to the central phenyl ring (Table S2, Supporting Information). The (L1)4− ligand is pentadentate and adopts a coordination mode I (Scheme 1). One bis-monodentate carboxyl group links Co1 and Co3, and three monodentate carboxyl groups bind to Co1A, Co2, and Co4. In aid of the monodentate carboxyl groups, four (L1)4− ligands connect two Co2 and two Co4 ions to form an interesting 76-membered planar macrocycle (Figure 1b). As shown in Figure 1c, each pentadentate (L1)4− ligand connects five Co(II) ions to form a 2D [Co4(L1)2]n doublelayered network, which is also an assembly of the Co4(μ2H2O)3(μ2-COO)4 tetranuclear cluster and the 76-membered macrocycle. The neutral 4-abpt ligand acting as a bidentate bridge links Co1 and Co2 ions in adjacent [Co4(L1)2]n networks via two terminal pyridyl groups. Thus, the 2D [Co2(L1)]n

obtained with 46.0% yield (19.2 mg, 0.023 mmol) based on H4L2. Anal. Calcd for C36H29N6O12Zn1.5: C, 51.74; H, 3.50; N, 10.06. Found: C, 51.59; H, 3.44; N, 9.72. IR (KBr, cm−1): 3402m, 3305w, 3078w, 2952w, 2890w, 1691s, 1606m, 1567s, 14590m, 1442s, 1368s, 1256m, 1229s, 1037s, 786s, 767m, 702s. X-ray Crystallography. The single crystal X-ray diffractional data of 1−8 were collected on a Bruker Smart Apex-II CCD diffractometer with graphite monochromatic Mo Kα radiation (λ = 0.71073 Å) at room temperature. Determinations of the crystal system, orientation matrix, and cell dimensions were performed according to the established procedures. The structures were solved by the direct methods and refined on F2 by full-matrix least-square techniques using the SHELXTL program.13 The non-hydrogen atoms were refined anisotropically, and hydrogen atoms were placed geometrically and refined using the riding model. Crystallographic data and structural refinement parameters are summarized in Table 1. Selected bond distances and angles are listed in Table S1 (Supporting Information).

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RESULTS AND DISCUSSION Synthesis and Infrared Spectra. Hydro(solvo)thermal synthesis has been proven to be an effective method in preparing functional coordination polymers and growing single crystals for structural studies, despite reacting in a “black box” and being somewhat complicated.14 The crystal complexes 1−8 are successfully prepared by hydrothermal reactions in H2O−DMF mixed solvents at temperature 85−120 °C (Scheme 2). The molar ratio of metal salts to H4L1/H4L2 and 3/4-abpt ligands was kept in 4:1:1 in their preparation reactions, except complexes 4 and 5 prepared in the ratio of 8:1:2 and 4:1:2, respectively. Compared to the preparation of cobalt complex 1, the molar amount of H4L1 in preparing 4 was reduced by half. Meanwhile, three drops of dilute HNO3 solution was added. It is noticed that the reactor was kept at 120 °C for 48 h. If the reactor was heated for 72 h, only a {[Co(L1)0.5]·2H2O}n complex was produced, which was reported previously.9a The zinc complex 6 is an isomer of 5. The former was prepared by adding 0.05 mmol 4-abpt in a 2:1 H2O−DMF mixed solvent, the later was prepared by adding 0.10 mmol of 4-abpt in a 5:1 H2O−DMF solvent. Both complexes show obviously different 3D structures. Complexes 7 and 8 are two isostructural 3D coordination polymers. However, their preparation methods are somewhat different. The reaction system of 8 need be added three drops of dilute HNO3 solution. From previous studies, we know that different pH values attributed to not only the deprotonation of polycarboxylic acids but also their related connection modes.10b It is well-known that metal-hydroxide precipitates are easily formed when preparing carboxylate complexes using NaOH or triethylamine as base in water solution. Recently, H2O−DMF mixed solvent was frequently used in preparing carboxylate complexes without basic additive.15 At hydrothermal condition, DMF can hydrolyze to produce Me 2 NH that can act as a weak base to deprotonation.16 In this work, we used H2O−DMF mixed solvent without basic additive; even three drops of dilute HNO3 solution was added to the reaction systems of 4 and 8. The H4L1/ H4L2 ligands were successfully deprotonated and participated in coordination. In addition, neutral 3/4-abpt ligands possess two pyridyl terminals and an amino group, which also play a role in regulating the pH values of reacting systems. The existence of tetracarboxylates and 3/4-abpt ligands in the above eight complexes was confirmed by infrared spectra (Figure S1, Supporting Information). The asymmetric and symmetric stretching vibrations of carboxylate groups are observed in the ranges of 1626−1572 cm−1 and 1417−1329 cm−1, respectively. 4158

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Figure 2. (a) Asymmetric unit of 2. (b) The 2D sheetlike network. (c) The packing diagram.

H4L1 are fully deprotonated. The (L1)4− anion adopts an anticonformation. Two terminal phenyl rings are almost parallel (10.22°) and respectively twist 15.46° and 18.64° with the central phenyl ring. The (L1)4− anion is a nearly planar tetradentate ligand which adopts a coordination mode II (Scheme 1). Four monodentate carboxyl groups bind to two Zn1 ions and two Zn2 ions. Each (L1)4− ligand connects four zinc ions to form a 1D ladderlike ribbon. The 1D ribbons are further linked by bidentate 4-abpt spacers to generate a 2D sheetlike coordination network (Figure 2b). Previously, we have prepared a 2D sheetlike coordination network {[Zn2(L1)(btmbb)(H2O)4]·2H2O}n.20 Furthermore, the 2D networks are stacked together in a parallel fashion via face-to-face π···π interactions (Figure 2c). Six centroid-to-centroid distances between parallel aromatic rings range from 3.41 to 3.97 Å (Figure S2, Supporting Information). Structure of {[Co(H2L1)(3-abpt)(H2O)2]·0.5H4L1}n (3). Complex 3 is a 1D nanotube coordination polymer. The asymmetric unit contains one Co(II) ion, one (H2L1)2− ligand, one 3-abpt ligand, two aqua ligands, and half H4L1 guest molecule (Figure 3a). Co1 adopts a cis octahedral geometry, six-coordinated by two carboxyl oxygens, two water oxygens (O1W, O2W), and two pyridyl nitrogens. The O1W and N6 atoms occupy the axial positions with an O1W−Co1−N6 bond angle of 178.7(1)°. The Co−O bond distances vary from 2.037(3) to 2.211(3) Å, and the average Co−N distance is 2.144(3) Å. H4L1 is partly deprotonated, in which two carboxyl groups maintains protonated. The (H2L1)2− anion adopts a synconformation. Both terminal phenyl rings are parallel (dihedral angle 1.35°) and twist about 70° with the central phenyl ring. The (H2L1)2− anion is a bidentate ligand and adopts a coordination mode III (Scheme 1). Each (H2L1)2− ligand combines two Co(II) ions via two monodentate carboxyl groups. Co1 and Co1A are bridged by two (H2L1)2− ligands to form a

Figure 1. (a) Coordination structure of 1. (b) The tetranuclear Co4(μ2H2O)3(μ2-COO)4 cluster (left) and the 76-membered macrocycle (right). (c) 2D [Co2(L1)]n double-layered network viewed along the c axis (left) and the a axis (right). (d) 3D MOF structure of 1 viewed along the c axis (left) and the a axis (right).

networks are cross-linked by bidentate 4-abpt spacers to generate a final 3D metal−organic framework (Figure 1d). Structure of {[Zn2(L1)(4-abpt)(H2O)3]·5H2O}n (2). Complex 2 is a 2D sheetlike coordination polymer. The asymmetric unit contains two independent Zn(II) ions, one (L1)4− ligand, one 4abpt ligand, three aqua ligands, and five lattice water molecules (Figure 2a). Zn1 adopts a distorted tetrahedral geometry, coordinated by two carboxyl oxygens, pyridyl N1, and water O1W. Zn2 is five-coordinated by two carboxyl oxygens, two water oxygens (O2W, O3W), and pyridyl N4 to form a distorted trigonal-bipyramidal geometry with a τ value of 0.75.19 Water O2W and O3W occupy the apical sites with an O2W−Zn2− O3W bond angle of 178.0(1)°. All of the Zn−O bond distances range from 1.892(4) to 2.144(4) Å, except a weak coordination bond Zn2−O13 (2.466(5) Å). Zn1−N1 and Zn2−N4 bond distances are 2.013(4) and 2.023(4) Å, respectively. 4159

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Figure 4. (a) Asymmetric unit of 4. (b) 2D sheetlike [Co2(L1)]n network. (c) 3D porous MOF pillared by 4-abpt spacers. (d) 2-fold interpenetrating 3D framework. Figure 3. (a) Asymmetric unit of 3. (b) The Co2(H2L1)2 ring. (c) The 1D nanotube polymer. (d) The supramolecular architecture containing H4L1 guest molecules (blue).

and angles around Co1 and Co2 are somewhat different (Table S1, Supporting Information). All of the Co−O bond distances vary from 2.006(5) to 2.283(5) Å, and the Co−N bond distances range from 2.131(6) to 2.170(7) Å. H4L1 is fully deprotonated. The (L1)4− anion adopts an anticonformation. Both terminal phenyl rings are almost parallel (6.06°) to each other and perpendicular to the central phenyl ring with 87° twisting angle. The (L1)4− ligand is octadentate and adopts a coordination mode IV (Scheme 1), which possesses two chelating carboxyl groups and two bis-monodentate carboxyl groups. The Co1 and Co2 are linked by two bridging carboxyl groups to form a Co2(μ2-COO)2 dimer with a Co···Co separation of 2.946(3) Å. Each (L1)4− ligand chelates to Co1 and Co2 ions and bridges two pairs of Co1/Co2 ions to afford a 2D sheetlike [Co2(L1)]n network (Figure 4b). Two independent 4-abpt ligands act as bidentate spacers to link Co1/Co1A and Co2/Co2A, respectively. The 2D [Co2(L1)]n networks are pillared by the bidentate 4-abpt spacers to generate a beautiful 3D porous MOF (Figure 4c). In order to stabilize the porous structure, two such 3D single nets are further interlocked with each other to produce a 2-fold interpenetrating 3D framework (Figure 4d). Structure of {[Zn2(L2)(4-abpt)(H2O)]·2.5H2O}n (5). Complex 5 features a 3D metal−organic framework. The asymmetric unit consists of two independent Zn(II) ions, one (L2)4− ligand, one 4-abpt ligand, one aqua ligand together with two and a half lattice water molecules. As depicted in Figure 5a, Zn1 is six-coordinated

Co2(H2L1)2 ring (Figure 3b). Due to the flexible methoxy group and weak face-to-face π−π interaction, two central phenyl rings are closed to each other parallely with a centroid-to-centroid distance of 4.009(1) Å. The 3-abpt ligand acts as a bidentate spacer and links Co1 and Co1B via two pyridyl terminals. Two pyridyl groups display anticonformation (Scheme 1). The Co2(H2L1)2 rings are parallely arranged and linked by two rows of 3-abpt spacers to generate a 1D nanotube coordination polymer (Figure 3c). The 1D nanotubes are further stacked parallely to form a porous supramolecular architecture (Figure 3d). Interestingly, complex 3 contains H4L1 guest molecule in the tunnel. The guest H4L1 adopts an anticonformation. There exist two strong π···π interactions (centroid-to-centroid distances 3.585 and 3.621 Å) between parallel H4L1 guest molecule and (H2L1)2− ligand (Figure S3, Supporting Information). Structure of {[Co2(L1)(4-abpt)2]·4H2O}n (4). Complex 4 features a 3D metal−organic framework. As depicted in Figure 4a, the asymmetric unit consists of two independent Co(II) ions, one (L1)4− ligand, two 4-abpt ligands, and four lattice water molecules. Co1 and Co2 ions both adopt a trans octahedral geometry, six-coordinated by four carboxyl oxygens from three different (L1)4− ligands on equatorial plane, and two pyridyl nitrogens in the axial positions. The coordination bond distances 4160

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Figure 6. (a) Asymmetric unit of 6. (b) 2D double-layered [Zn2(L2)(H2O)]n network (left), and 3D porous MOF connected by 4-abpt spacer (right).

oxygens and pyridyl N1. The axial positions are occupied by carboxyl O2 and water O1W with an O2−Zn1−O1W bond angle of 177.8(2)°. The Zn1−O bond distances vary from 2.028(4) to 2.253(6) Å, and the Zn1−N1 distance is 2.114(5) Å. Zn2 adopts a distorted tetrahedral geometry, coordinated by three carboxyl oxygens and pyridyl N6. The Zn2−O bond distances range from 1.921(4) to 1.955(4) Å. The Zn2−N6 distance is 2.009(5) Å. H4L2 is fully deprotonated. The (L2)4− anion adopts a synconformation. Two terminal phenyl rings show a larger dihedral angle (62.27°), and respectively twist 53.84° and 12.07° with the central phenyl ring. Similar to 5, the (L2)4− ligand is heptadentate and adopts a coordination mode V (Scheme 1). Each (L2)4− ligand connects six zinc ions to form a wavelike 2D doublelayered network [Zn2(L2)(H2O)]n (Figure 6b), which is unlike the 3D rectangle framework of [Zn2(L2)(H2O)]n in 5. The wavelike double-layered networks are further connected by bidentate 4-abpt spacer to generate a porous 3D MOF (Figure 6b). Three lattice water molecules are perched in the pores. Although the complexes 5 and 6 have similar formulas and heptadentate (L2)4− ligand, the coordination fashions of 4-abpt are obviously different. In the structure of 5, the octahedral Zn1 center combines with two pyridyl nitrogens, and the tetrahedral Zn2 is coordinated only by four carboxyl oxygens. Whereas in the structure of 6, the octahedral Zn1 and tetrahedral Zn2 centers both combine one pyridyl nitrogen. Obviously, the variation of 4abpt connection fashions results in the structural difference. Structures of {[Co1.5(HL2)(3-abpt)(H2O)]·H2O}n (7), and {[Zn1.5(HL2)(3-abpt)(H2O)]·H2O}n (8). Complexes 7 and 8 are two isostructural 3D coordination polymers. We can study the magnetic property of Co(II) complex 7 and the luminescence of Zn(II) complex 8. Here only the structure of 7 is described in detail. As shown in Figure 7a, the asymmetric unit of 7 consists of a half Co1 ion, one Co2 ion, one (HL2)3− ligand, one 3-abpt ligand, one aqua ligand, and one lattice water molecule. Co1 adopts a centrosymmetic trans octahedral geometry. The equatorial plane is completed by two carboxyl oxygens and two water oxygens. The axial positions are occupied by two pyridyl nitrogens. Three bond angles along opposite positions are idealized 180°. Co2 is five-coordinated by four carboxyl oxygens

Figure 5. (a) Coordination structure of 5. (b) 3D porous [Zn2(L2)(H2O)]n framework. (c) 3D MOF structure of 5.

and adopts a distorted trans octahedral geometry. The equatorial plane is completed by three carboxyl oxygens and water O1W. The axial positions are occupied by two pyridyl nitrogens with a N1−Zn1−N6 bond angle of 171.8(2)°. The Zn1−O bond distances vary from 1.994(4) to 2.350(4) Å. Average Zn2−N distance is 2.160(4) Å. Zn2 adopts a distorted tetrahedral geometry, coordinated by four carboxyl oxygens from four different (L2)4− ligands. The Zn2−O bond distances vary from 1.931(4) to 1.974(4) Å. H4L2 is fully deprotonated. The (L2)4− anion adopts a synconformation. Similar to (L1)4− ligand in 1−4, four carboxyl groups of (L2)4− are coplanar with two terminal phenyl groups. Due to the flexibile methoxy group, two terminal phenyl rings are almost perpendicular to each other (dihedral angle 88.13°), and respectively twist 85.76° and 24.00° with the central phenyl ring. The (L2)4− ligand is heptadentate and adopts a coordination mode V (Scheme 1). Two carboxyl groups adopt bismonodentate coordination and link two pairs of Zn1/Zn2 ions. The other two carboxyl groups show monodentate and chelating coordinations, respectively. Each (L2)4− ligand connects six zinc ions to form a regular 3D porous [Zn2(L2)(H2O)]n framework (Figure 5b), which exhibits a nanosized rectangle tunnel with the dimensions of 1.5 × 0.8 nm2. Further observation found that this 3D framework can be regarded as an assembly of a 3D Zn1-L2 network and isolate Zn2L2 binuclear piece (Figure S4, Supporting Information). The bidentate 4-abpt ligand combines Zn2 and Zn2A via two pyridyl terminals, which inserts the rectangle tunnel and shares the cavity to two halves (Figure 5c). This affords the final 3D MOF. The lattice water molecules are perched in the pores. Structure of {[Zn2(L2)(4-abpt)(H2O)]·3H2O}n (6). As an isomer of 5, complex 6 exhibits obviously different 3D MOF. The asymmetric unit contains two independent Zn(II) ions. As depicted in Figure 6a, Zn1 locates in a distorted octahedral sphere. The equatorial plane is completed by three carboxyl 4161

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tion). The 2D [Co1.5(HL2)(H2O)]n network combines with the Co3(3-abpt)2 piece via sharing Co(II) ions to generate a complicated 3D coordination polymer (Figure 7c). Comparison of H4L1/H4L2 Coordination Modes and Structural Diversity. H4L1 is fully deprotonated in 1, 2 and 4, and partly deprotonated as (H2L1)2− in 3. H4L2 is fully deprotonated in 5 and 6, and partly deprotonated as (HL2)3− in 7 and 8. Two tetracarboxylate ligands adopt synconformation (1, 3, 5, 6) or anticonformation (2, 4, 7, 8), while H4L1 guest molecule in 3 displays anticonformation. Their asymmetric units contain only one tetracarboxylate, except 1 contains two independent (L1)4− ligands. Each H4L1 or H4L2 ligand connects two (3), four (2, 7, 8), five (1), or six (4, 5, 6) metal ions in their 1D (3), 2D (2), and 3D (1, 4−8) polymeric structures. As illustrated in Scheme 1, H4L1/H4L2 ligands adopt a total of six types of coordination modes, and act as bi-, tetra-, penta-, hepta-, and octa-dentate ligands in 1−8. The coordination mode I (1) has three monodentate and one bis-monodentate carboxyl groups. The mode II (2) or III (3) possesses four or two monodentate carboxyl groups, respectively. The mode IV (4) contains two chelating and two bis-monodentate carboxyl groups. The modes V (5, 6) and VI (7, 8) consist of monodentate, chelating, and bis-monodentate carboxyl groups together. Meanwhile, the 3/4-abpt ligands act as bidentate spacers in these complexes. Two pyridyl terminals of 3-abpt display anticonformation in 3, 7, and 8. In 1−8, four carboxyl groups of H4L1 and H4L2 are all coplanar with two terminal phenyl groups. Due to the flexibility of ether linkage, two terminal phenyl groups and the central phenyl ring can freely rotate to display various dihedral angles, as summarized in Table S2 (Supporting Information). Varied coordination geometries around metal centers are observed. All of Co(II) ions in 1, 3, 4, and 7 (Co1) adopt octahedral geometry, except a five-coordinated Co2 in 7. Complex 2 possesses a tetrahedral and trigonal-bipyramidal Zn(II) ions, while 5 and 6 both have a tetrahedral and an octahedral Zn(II) ion. Complex 8 has an octahedral Zn1 and a five-coordinated Zn2. Although 1 and 2 are prepared under similar reaction conditions, 1 is a 3D MOF, whereas 2 shows a 2D sheetlike network. This structural difference originates because four distinct Co(II) ions in 1 all adopt octahedral geometry, while two Zn(II) ions in 2 adopt tetrahedral and trigonal-bipyramidal geometries. Obviously, the coordination geometries influence the final structures of 1−8. Thermal Analyses and PXRD Patterns. Powder X-ray diffraction (PXRD) experiments have been carried out for 1−8. As shown in Figure S6 (Supporting Information), the peak positions of the experimental and simulated PXRD patterns are in good agreement with each other, indicating that the crystal structures are truly representative of the bulk crystal products. The differences in intensity may be owing to the preferred orientation of the crystal samples. In order to investigate the thermal stabilities of these tetracarboxylate complexes, the thermal behaviors of 1−8 were tested by TG-DSC (Figure S7, Supporting Information). Complex 1 successively lost weight in the 30−350 °C range, corresponding to the removal of 10 and a half coordinated water molecules (obsd 10.27%, calcd 11.90%). After 360 °C, the (L1)4− and 4-abpt ligands decomposed rapidly. A final residue at 800 °C was Co2O3 (obsd 24.26%, calcd 20.84%). Complex 2 lost five lattice water molecules in 40−100 °C (obsd 8.71%, calcd 9.28%) and three coordinated water molecules in 120−180 °C (obsd 3.31%, calcd 5.57%) with two endothermic peaks at 85 and 165

Figure 7. (a) Asymmetric unit of 7. (b) The 2D [Co1.5(HL2)(H2O)]n network. (c) The 3D structure of 7.

from three different (HL2)3− ligands and pyridyl N6. The coordination geometry is situated between trigonal-bipyramid and square-pyramid with a τ value of 0.51. Generally, the distortion of coordination geometry around Co1 can be expressed in terms of τ, which has a value of 0 and 1 for an ideal square-pyramidal and ideal trigonal-bipyramidal geometry, respectively.19 All of the Co−O bond distances fall in the range of 1.954(3)−2.122(3) Å, except a longer Co2−O4 bond distance (2.343(3) Å). Average Co−N bond distance is 2.144(4) Å. Three carboxyl groups of H4L2 are deprotonated, while one carboxyl group maintains protonated. The (HL2)3− anion displays an anticonformation. Two terminal phenyl rings show a larger dihedral angle (58.66°), and respectively twist 85.82° and 84.10° with the central phenyl ring. The (HL2)3− anion is a pentadentate ligand and adopts a coordination mode VI (Scheme 1). Three carboxylate groups are different and respectively adopt monodentate, chelating, and bis-monodentate coordination fashions. Each (HL2)3− ligand connects four Co(II) ions to form a 2D [Co1.5(HL2)(H2O)]n network lying on the ac plane (Figure 7b). Co2 and Co2A are linked by two bridging carboxyl groups to form a Co2(COO)2 dimer with a Co2···Co2A separation of 3.604(1) Å. The isolated Co1 is surrounded by large (HL2)3− ligands with a nearest Co1···Co2 separation of 8.817(2) Å. The 3-abpt ligand acts as a bidentate spacer to link Co1 and Co2 via two pyridyl terminals. Two pyridyl groups display anticonformation. Further observation found that Co1 links two Co2 ions via two 3-abpt ligands to form an isolate linear trinuclear Co3(3-abpt)2 piece (Figure S5, Supporting Informa4162

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°C, respectively. The anhydrous compound was stable to 330 °C and then successively decomposed to 800 °C without stopping. Complex 3 was stable up to 200 °C and then released two coordinated water molecules in 200−245 °C with an endothermic peak at 230 °C (obsd 3.92%, calcd 3.49%). The dehydrate compound successively decomposed from 300 to 800 °C without stopping. Complex 4 lost four lattice water molecules in the 20−100 °C range with an endothermic peak at 62 °C (obsd 6.20%, calcd 6.30%). After 320 °C, the (L1)4− and 4-abpt ligands decomposed continuously to 800 °C without stopping. Complex 5 lost three and a half lattice and coordinated water molecules in 30−100 °C with a total weight loss of 9.62% (calcd 7.10%). After 310 °C, the (L2)4− and 4-abpt ligands successively decomposed to 800 °C without stopping. Complex 6 lost four lattice and coordinated water molecules in the 30−100 °C range with a total weight loss of 8.26% (calcd 8.00%). The anhydrous framework was stable to 310 °C, and then successively decomposed to 800 °C without stopping. Complexes 7 and 8 are isostructural and exhibit similar thermal behaviors. For 7, a weight loss of 2.34% in 180−230 °C range is consistent with the removal of one coordinated water molecule (calcd 2.17%). The dehydrate compound was stable to 350 °C, and then decomposed continuously. The final residue at 800 °C was Co2O3 (obsd 25.25%, calcd 22.70%). Similarly, complex 8 lost one coordinated water molecule in 160−240 °C (obsd 3.36%, calcd 2.15%). After 320 °C, the dehydrate compound successively decomposed to 800 °C without stopping. The above thermogravimetric results indicate that the dehydrate frameworks are thermally stable until 300 °C, and then tetracarboxylates and 3/4-abpt ligands decompose successively. The intermediates would be CoCO3 or ZnCO3,21 which were decomposed fully or partly at 800 °C, and left the final Co2O3 or ZnO residues. Photoluminescence. The luminescent behaviors of four Zn(II) complexes 2, 5, 6, and 8 as well as free H4L1 and H4L2 ligands were investigated in the solid state at room temperature

emission mechanism of 2 originates from ligand-to-metal charge transfer (LMCT). The significantly enhanced luminescent efficiency can be attributed to the fact that (L1)4− and (HL2)3− ligands coordinated to zinc ions would impose rigidity and hence decrease the nonradiative decay of excited state.9a,22 The d10 Zn(II) ion is difficult to oxidize. It is rarely in the nature of metal-to-ligand charge transfer (MLCT). Zn(II) complexes often exhibit ligand-centered emission. However, the LMCT phenomenon can be observed sometimes in reported Zn(II) complexes.23 LMCT may compete with ligand-centered luminescence. We suppose that Zn(II) coordination geometry would influence the emission mechanism. In 8, two distinct Zn(II) ions adopt an octahedral and a five-coordinated geometries, which emit at 347 nm that can be assigned to ligand-centered emission. In 2, two Zn(II) ions adopt tetrahedral and trigonal-bipyramidal geometries which emit at 449 nm (LMCT). Complexes 5 and 6 both possess an octahedral Zn(II) and a tetrahedral Zn(II). Under excited with 275 nm light, 5 and 6 display similar luminescent spectra, and each shows two weak broad bands with maxima at about 369 and 452 nm, respectively, contributed to ligand-centered emission and LMCT. The further study for Zn(II) luminescent system is underway. Magnetic Property. Generally, the carboxylate group can propagate magnetic exchange between paramagnetic metal ions. Co(II) complexes 1, 4, and 7 contain carboxylate-bridging Co2 dimers. Their temperature dependences of magnetic susceptibilities were measured in 2−300 K temperature range. The data

Figure 8. Emission spectra of Zn(II) complexes 2, 5, 6, 8, and free H4L1/ H4L2 ligands.

(Figure 8). When excited with 275 nm light, free H4L1 and H4L2 ligands exhibit similar luminescent spectra with emission maximum at 359 and 356 nm, respectively. Under similar excitation condition, complex 8 displays an intense emission peak at 347 nm, whereas complex 2 shows a strong blue luminescence with an emission maximum at 449 nm. In contrast to the emission energy of free H4L1/H4L2 ligands, the similar emission wavelength indicates that the luminescence of 8 originates from ligand-centered emission, whereas the obviously red-shift emission energy suggests that the most possible

Figure 9. Plots of χMT and χM−1 vs T for CoII complexes 1 (a), 4 (b), and 7 (c). 4163

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are shown in Figure 9 as plots of χMT and χM−1 versus T. For 1, the χMT value is 9.35 cm3 K mol−1 at 300 K, which is higher than the value expected for four isolated high-spin CoII ions (7.50 cm3 K mol−1 with g = 2.0, and S1 = S2 = S3 = S4 = 3/2).24 This is due to the large orbital contribution of CoII ion, which is well-known to be significant for a CoII ion located in an octahedral geometry with the 4T1g ground state, and it is difficult to apply an exact theoretical model for fitting the magnetic susceptibility data.25 Upon cooling the sample, the χMT value decreases gradually and reaches a value of 4.81 cm3 K mol−1 at 2 K. The inverse magnetic susceptibility curve shows a linear behavior in 18−300 K range and obeys the Curie−Weiss law, χM = C/(T − θ), with C = 9.77 cm3 K mol−1 and θ = −12.1 K. The negative θ value suggests an antiferromagnetic coupling between CoII ions, especially in the Co4(μ2-H2O)3(μ2-COO)4 tetranuclear cluster. For 4, the χMT value is 5.38 cm3 K mol−1 at 300 K, which is higher than the value expected for two isolated high-spin CoII ions (3.75 cm3 K mol−1).26 Similarly, this is due to the large orbital contribution of CoII. Upon cooling of the sample, the χMT keeps almost a constant value until 88 K and then decreases rapidly to 1.93 cm3 K mol−1 upon further cooling to 2 K. The data can be fitted to the Curie−Weiss law, yielding C = 5.4 cm3 K mol−1 and θ = −2.5 K, which is consistent with a weak antiferromagnetic coupling existing in CoII2(μ2-COO)2 dimer. Considering the CoII2(μ2-COO)2 dimer is isolated by surrounding large-sized (L1)4− ligand, we try to fit the χMT versus T plot using a dimeric model based on spin Hamiltonian (H = −2J S1· S2). This gives the parameters J = −0.6 cm−1 and g = 2.41. For 7, the χMT value is 4.63 cm3 K mol−1 at 300 K, which is higher than the value expected for isolated high-spin value of one and a half CoII ions (2.81 cm3 K mol−1).27 Upon cooling the sample, the χMT value decreases gradually and reaches a value of 1.73 cm3 K mol−1 at 2 K. The data can be fitted to the Curie− Weiss law, yielding C = 4.8 cm3 K mol−1 and θ = −8.6 K, which indicates an antiferromagnetic coupling in the CoII2(μ2-COO)2 dimer.

charge via the Internet at http://pubs.acs.org. Crystallographic data have been deposited at the Cambridge Crystallographic Data Center, CCDC 1003953−1003960. These data can be obtained from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB21EZ, U.K.

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*(M.-X.L.) E-mail: [email protected]. *(X.H.) E-mail: [email protected]. Notes

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 (21171115, 21203117) and the Innovation Program (12ZZ089) of Shanghai Municipal Education Commission.

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REFERENCES

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CONCLUSIONS On the basis of two semirigid tetracarboxylic acids and bent 3/4abpt ligands, eight coordination polymers with various structures were synthesized and characterized. Complex 1 is a 3D MOF composed of an interesting Co4(μ2-H2O)3(μ2-COO)4 tetranuclear cluster and 76-membered ring. Complex 4 displays a beautiful 3D porous MOF built by sheetlike [Co2(L1)]n networks pillared by 4-abpt spacers. Complex 5 features a porous 3D MOF with a regular nanosized rectangle tunnel. The H4L1/H4L2 ligands are fully or partly deprotonated and adopt six types of coordination modes. The 3/4-abpt ligands act as bidentate spacers. Different reaction conditions can influence the deprotonation of tetracarboxylic acids and affect the overall structures of complexes. Thermal analyses show that both tetracarboxylate ligands are thermally stable to 300 °C. Zn(II) complexes 2 and 8 are strong luminescent emitters. Complexes 1, 4, and 7 exhibit antiferromagnetic coupling between carboxylbridging CoII ions. These research results reveal that ether-linked tetracarboxylates are valuable large-sized semirigid multidentate ligands. The further study for H4L1/H4L2 coordination systems is underway.

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S Supporting Information *

Bond distances and angles, IR spectra, structural figures, PXRD patterns, and TG−DSC curves. This material is available free of 4164

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Crystal Growth & Design

Article

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