Syntheses, Structures, and Photoluminescent Properties of 12 New

Apr 6, 2012 - Porntiva Suvanvapee , Jaursup Boonmak , Fatima Klongdee ..... Three novel metal–organic frameworks based on an unsymmetrical rigid ...
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Syntheses, Structures, and Photoluminescent Properties of 12 New Metal−Organic Frameworks Constructed by a Flexible Dicarboxylate and Various N-Donor Ligands Dan Niu,† Jin Yang,*,† Jiao Guo,† Wei-Qiu Kan,† Shu-Yan Song,*,‡ Peng Du,† and Jian-Fang Ma*,† †

Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast Normal University, Changchun 130024, People’s Republic of China ‡ State Key Laboratory of Rare Earth Resources Utilization, Changchun Institute of Applied Chemistry, Changchun 130022, People’s Republic of China S Supporting Information *

ABSTRACT: Twelve new metal−organic frameworks (MOFs), namely, [Cd(L)(H2O)] (1), [Cd(L)2Na2]·H2O (2), [Cd(L)(phen)] (3), [Cd(L)(phen)]·2H2O (4), [Cd2(L)2(biim-2)]·H2O (5), [Cd(L)(biim-4)]·2H2O (6), [Co(L)(biim-4)]·H2O (7), [Cd(L)(btp)] (8), [Cd(L)(btb)] (9), [Cd(HL)(bth)0.5(H2O)]·H2O (10), [Co(HL)(btb)0.5]·H2O (11), and [Cd(L)(btbp)1.5]·4H2O (12), where phen = 1,10-phenathroline, biim-2 = 1,2-bis(imidazol-1′-yl)ethane, biim-4 = 1,1′(1,4-butanediyl)bis(imidazole), btp = 1,3-bis(1,2,4-triazol-1-yl)propane, btb = 1,4-bis(1,2,4-triazol-1-yl)butane, bth = 1,6-bis(1,2,4-triazol-1yl)hexane, btbp = 4,4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl, and H2L = (3-carboxyl-phenyl)-(4-(2′-carboxyl-phenyl)-benzyl) ether, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Compound 1 features a two-dimensional (2D) layer, which is further stabilized by hydrogen bonds between the coordinated water molecules and adjacent carboxylate oxygen atoms. Compound 2 shows a 2D double layer with 36·46·53 topology. Compounds 3 and 4 exhibit similar one-dimensional (1D) double chains, which are further extended into 2D supramolecular sheets and three-dimensional (3D) supramolecular frameworks through π−π interactions between pyridyl rings and phenyl rings, respectively. Compound 5 furnishes a 1D double chain, which is further extended into a 2D supramolecular layer via two kinds of π−π interactions. Compounds 6 and 7 are isostructural and display the same 2D undulated sheets with 44·62 topology. Compound 8 possesses a 2D sheet structure. Compound 9 displays 3D (3,4)connected frameworks with (4·102)(4·103·122) topology. Compounds 10 and 11 possess similar 1D infinite chains, which are further linked via π−π interactions to generate 2D supramolecular layers. Compound 12 possesses a 2D double layer, which is further extended into a 3D supramolecular architecture through hydrogen-bonding interactions. The structural and topological differences of the 12 compounds indicate that the L anion and N-donor ligands play important roles in the formation of the final framework structures. The thermal behaviors of compounds 1, 3−4, 8−10, and 12 and luminescent properties of 1−6, 8−10, and 12 have also been investigated in detail.

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INTRODUCTION Recently, great attention has been focused on the rapidly growing field of crystal engineering of one-, two-, and threedimensional (1D, 2D, 3D) metal−organic frameworks (MOFs) not only for their structural and topological diversities but also for their potential application as functional materials in catalysis, optics, magnetism, molecular architectures, materials chemistry, etc.1,2 It is well established that the final structures of desired crystalline products are usually influenced by several factors in the self-assembly process, such as the solvent system, pH values, temperature, N-donor ligands, coordination geometry of central metal, organic anions, and so on.3−5 Among these factors, the organic anions play a key role in © 2012 American Chemical Society

directing the ultimate complex architectures. In this regard, (3carboxyl-phenyl)-(4-(2′-carboxyl-phenyl)-benzyl) ether (H2L), as a new dicarboxylate ligand, is a good candidate for the construction of MOFs with diverse architectures. Because of the presence of a flexible −O−CH2− group in the molecule, the phenyl and biphenyl rings can twist and rotate freely to conform to the requirements of the coordination geometries of metal cations in the self-assembly process.6 Up to now, although polycarboxylates are widely utilized in the conReceived: January 13, 2012 Revised: March 9, 2012 Published: April 6, 2012 2397

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struction of coordination polymers,3,7,8 MOFs built by H2L and flexible N-donor ligands, especially bis(imidazole) or bis(triazole) ligands, have not been investigated so far.9 On the other hand, among the N-donor bridging ligands, bis(imidazole) or bis(triazole) ligands with −CH2− spacers have received the intense interest of chemists.10 Compared with the rigid N-donor ligands, the flexible bis(imidazole) or bis(triazole) ligands have more possible conformational changes because of the flexible nature of −CH2− spacers allowing the ligands to bend and rotate freely when interacting with metal centers so as to conform to the coordination geometries of metal ions.11 In our previous work, we have synthesized a series of alkyl-based bis(imidazole) or bis(triazole) ligands and reported a number of fascinating complex architectures of these ligands.12 In order to further investigate the coordination chemistry of bis(imidazole) or bis(triazole) ligands, in this work, 12 new MOFs have been successfully synthesized under hydrothermal conditions, namely, [Cd(L)(H2O)] (1), [Cd(L)2Na2]·H2O (2), [Cd(L)(phen)] (3), [Cd(L)(phen)]·2H2O (4), [Cd2(L)2(biim-2)]·H2O (5), [Cd(L)(biim-4)]·2H2O (6), [Co(L)(biim-4)]·H2O (7), [Cd(L)(btp)] (8), [Cd(L)(btb)] (9), [Cd(HL)(bth)0.5(H2O)]·H2O (10), [Co(HL)(btb) 0 . 5 ]·H 2 O (11), and [Cd(L)(btbp)1.5]·4H2O (12), where phen =1,10-phenathroline, biim2 = 1,2-bis(imidazol-1′-yl)ethane, biim-4 = 1,1′-(1,4butanediyl)bis(imidazole), btp = 1,3-bis(1,2,4-triazol-1-yl)propane, btb = 1,4-bis(1,2,4-triazol-1-yl)butane, bth = 1,6bis(1,2,4-triazol-1-yl)hexane, and btbp = 4,4′-bis(1,2,4-triazol-1ylmethyl)biphenyl. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, and powder X-ray diffraction (PXRD). The crystal structures as well as the topological analysis of these compounds and the systematic investigation of the effects of L anion and N-donor ligands on the ultimate frameworks are discussed in detail. In addition, the thermal behaviors of compounds 1, 3−4, 8−10, and 12 and luminescent properties of 1−6, 8−10, and 12 have also been investigated in detail.

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for syntheses were purchased from commercial sources and used as received. General Characterization and Physical Measurements. The C, H, and N elemental analysis was conducted on a Perkin−Elmer 2400CHN elemental analyzer. The FT-IR spectra were recorded from KBr pellets in the range 4000−400 cm−1 on a Mattson Alpha-Centauri spectrometer. The photoluminescent properties of the ligands and compounds were measured on a Perkin-Elmer FLSP920 Edinburgh Fluorescence spectrometer at room temperature. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer TG-7 analyzer heated from 40 to 600 °C under nitrogen atmosphere. The powder Xray diffraction (PXRD) patterns of the samples were collected on a Rigaku Dmax 2000 X-ray diffractometer with graphite monochromatized Cu Kα radiation (λ = 0.154 nm) and 2θ ranging from 5 to 50° at room temperature. The experimental PXRD patterns are in good agreement with the corresponding simulated ones except for the relative intensity variation because of preferred orientations of the crystals. Therefore, the phase purity of the synthesized products is substantiated. Synthesis of H2L. A mixture of 3-hydroxy benzoic acid methyl ester (8.3 g, 20 mmol), anhydrous NaOH (2.0 g, 50 mmol), 4bromomethylbiphenyl-2′-carboxylic acid methyl ester (15.3 g, 20 mmol), and DMF (40 mL) were stirred at 60 °C for 2 h. After completion of the reaction, the solvent was removed by distillation in a water bath. Then the isolated products were heated and refluxed at 90 °C in ethanol (100 mL) and sodium hydroxide aqueous solution. After ethanol was removed by evaporation, the pH value was adjusted to 2− 3 via diluted hydrochloric acid solution as soon as the reaction was completed. Meanwhile, a large quantity of light yellow powder was deposited. After the sample was filtrated, washed by water, and dried, the target H2L ligand was obtained with a yield of 80%. Anal. Calcd (%) for C21H14O5 (Mr = 346.33): C, 72.82; H, 4.07. Found: C, 72.85; H, 4.01. Synthesis of [Cd(L)(H2O)] (1). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), DMF (2 mL), and water (6 mL) was placed in a Teflon reactor (15 mL) and heated at 120 °C for 3 days. After the mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 1 were obtained with a yield of 45% based on Cd(II). Anal. Calcd for C21H16CdO6 (Mr = 476.75): C, 52.90; H, 3.38. Found: C, 52.78; H, 3.22. IR data (KBr, cm−1): 3394 (m), 3139 (m), 3023 (m), 2882 (m), 2615 (s), 2090 (s), 1951 (s), 1693 (w), 1597 (w), 1485 (w), 1129 (m), 933 (s), 862 (s), 764 (w), 678 (m). Synthesis of [Cd(L)2Na2]·H2O (2). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), NaOH (4.0 mg, 0.1 mmol), and methanol (8 mL) was placed in a Teflon reactor (15 mL) and heated at 160 °C for 3 days. After the mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 2 were obtained with a yield of 30% based on Cd(II). Anal. Calcd for C42H30CdNa2O11 (Mr = 869.04): C, 58.04; H, 3.48. Found: C, 59.12; H, 3.53. IR data (KBr, cm−1): 3426 (w), 1561 (w), 1442 (w), 1397 (w), 1283 (w), 1233 (w), 1105 (s), 1030 (m), 914 (s), 859 (m), 682 (s). Synthesis of [Cd(L)(phen)] (3). The preparation of 3 was similar to that of 2 except that phen (19.0 mg, 0.1 mmol) was added to the reaction system. Colorless crystals of 3 were obtained with a yield of 38% based on Cd(II). Anal. Calcd for C33H22CdN2O5 (Mr = 638.93): C, 62.03; H, 3.47; N, 4.38. Found: C, 62.10; H, 3.52; N, 4.34. IR data (KBr, cm−1): 3420 (s), 3055 (s), 2917 (s), 2868 (s), 1553 (w), 1512 (w), 1464 (m), 1345 (w), 1240 (w), 1148 (m), 1076 (s), 960 (s), 877 (s), 763 (s), 684 (m). Synthesis of [Cd(L)(phen)]·2H2O (4). The preparation of 4 was similar to that of 3 except that water (8 mL) was used at 180 °C instead of methanol (8 mL) at 160 °C. Colorless crystals of 4 were obtained with a yield of 52% based on Cd(II). Anal. Calcd for C33H26CdN2O7 (Mr = 674.96): C, 58.72; H, 3.88; N, 4.15. Found: C, 58.75; H, 3.90; N, 4.26. IR data (KBr, cm−1): 3421 (s), 3055 (s), 2867 (s), 1929 (s), 1597 (w), 1512 (w), 1431 (w), 1388 (w), 1272 (m), 1147 (m), 1018 (m), 977 (s), 932 (s), 786 (s), 684 (m).

EXPERIMENTAL SECTION

Materials and Methods. The N-donor ligands were prepared by the procedures reported previously.10f,12 The ligand H2L was synthesized by the following method. All other reagents and solvents

Scheme 1. Structures of H2L and the N-Donor Ligands Used in This Work

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Table 1. Crystal Data and Structure Refinements for Compounds 1−12 formula fw space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd [g cm−3] F(000) R(int) GOF on F2 R1a [I > 2σ(I)] wR2b CCDC

a

1

2

3

4

C21H16CdO6 476.75 Pbca 12.701(5) 7.340(5) 39.243(5) 90 90 90 3658(3) 8 1.731 1904 0.0560 1.078 0.0416 0.0731 870695 5

C42H30CdNa2O11 869.04 P1̅ 6.5428(6) 13.4439(13) 22.2129(16) 101.771(7) 92.372(7) 100.630(8) 1873.6(3) 2 1.540 880 0.0386 0.778 0.0379 0.0733 870696 6

C33H22CdN2O5 638.93 P1̅ 10.1491(7) 11.2091(7) 12.6834(7) 103.803(5) 105.730(6) 95.165(6) 1330.15(14) 2 1.595 644 0.0374 0.641 0.0305 0.0381 870697 7

C33H26CdN2O7 674.96 P1̅ 9.9307(10) 11.8889(10) 12.7078(13) 79.514(8) 75.083(9) 79.507(8) 1411.1(2) 2 1.589 684 0.0509 0.899 0.0475 0.1085 870698 8

formula fw space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd [g cm−3] F(000) R(int) GOF on F2 R1a[I > 2σ (I)] wR2b CCDC

C50H40Cd2N4O10.5 1089.64 P1̅ 10.426(5) 14.228(5) 15.195(5) 101.070(5) 100.043(5) 92.132(5) 2172.4(15) 2 1.666 1096 0.0392 1.016 0.0435 0.0772 870699 9

formula fw space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd [g cm−3] F(000) R(int) GOF on F2 R1a [I > 2σ (I)] wR2b CCDC

C25H20CdN3O5 554.84 P2(1/c) 22.0506(8) 13.8182(5) 7.1851(3) 90 90.829(3) 90 2189.07(14) 4 1.684 1116 0.0428 1.029 0.0504 0.0950 870703

C31H32CdN4O7 685.01 P1̅ 9.282(5) 13.083(5) 13.145(5) 78.899(5) 76.087(5) 74.571(5) 1479.4(11) 2 1.538 700 0.0288 1.049 0.0412 0.0882 870700 10 C26H26Cd0.5N3O7 548.70 P1̅ 9.467(5) 10.099(5) 13.961(5) 77.044(5) 72.448(5) 85.341(5) 1240.1(10) 2 1.461 560 0.0213 1.096 0.0382 0.0994 870704

C31H30CoN4O6 613.52 P1̅ 9.2554(8) 12.3680(11) 13.2738(11) 75.178(8) 85.892(7) 75.422(8) 1421.6(2) 2 1.433 638 0.0430 1.016 0.0606 0.1490 870701 11

C28H24CdN6O5 636.93 P2(1)/c 13.655(5) 8.902(5) 21.908(5)) 90 92.364(5) 90 2660.8(19) 4 1.590 1288 0.0376 1.037 0.0412 0.0870 870702 12

C25H24Co0.5N3O7 507.94 P1̅ 9.4457(5) 9.8630(4) 14.2574(6) 71.897(4) 73.467(4) 85.931(4) 1210.09(10) 2 1.394 529 0.0224 1.029 0.0526 0.1502 870705

C48H46CdN9O9 1005.34 P1̅ 10.3440(4) 14.9830(6) 15.6820(5) 85.423(3) 71.030(3) 89.647(3) 2290.63(15) 2 1.458 1034 0.0256 1.049 0.0398 0.0848 870706

R1 = Σ||Fo| − |Fc||/Σ|Fo|. bwR2 = |Σw(|Fo|2 − |Fc|2)|/Σ|w(Fo2)2|1/2.

Synthesis of [Cd2(L)2(biim-2)]·H2O (5). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), biim-2

(16.2 mg, 0.1 mmol), NaOH (4.0 mg, 0.1 mmol), DMF (2 mL), and water (6 mL) was placed in a Teflon reactor (15 mL) and heated at 2399

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mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 12 were obtained with a yield of 63% based on Cd(II). Anal. Calcd for C48H46CdN9O9 (Mr = 1005.34): C, 57.34; H, 4.61; N, 12.54. Found: C, 57.40; H, 4.66; N, 12.51. IR data (KBr, cm−1): 3420 (w), 3130 (m), 3029 (m), 2857 (s), 1604 (w), 1556 (w), 1436 (w), 1386 (w), 1276 (w), 1130 (w), 904 (s), 800 (m), 756 (w), 678 (w). Crystal Structure Determination. Single-crystal X-ray diffraction data for compounds 1−12 were recorded on an Oxford Diffraction Gemini R Ultra diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Ǻ ) at 293 K. Absorption corrections were applied using a multiscan technique. All the structures were solved by Direct Method of SHELXS-9713 and refined by full-matrix leastsquares techniques using the SHELXL-97 program within WINGX.14 Non-hydrogen atoms of 1−12 were refined with anisotropic temperature parameters. The hydrogen atoms attached to carbons were generated geometrically. Some aqua hydrogen atoms of compounds 2, 4−6, and 12 were not included in the model. Other hydrogen atoms of water molecules were located from difference Fourier maps and refined with isotropic displacement parameters. O1W and O1W′ for 2 and C26 and C26′ for 10 were refined with isotropic temperature parameters. O1W for 2 and C26 for 10 are disordered. The disordered atoms were refined using isotropic C and O atoms split over two sites, with a total occupancy of 1. The hydrogen atoms of the disordered C atoms and O1W molecules were not included in the model. In order to refine the structures with reasonable bond lengths, the O−H and H−H distances of water molecules and hydroxyl groups for 7 and 10−12 were restrained to 0.90 and 1.44 Å, respectively. The detailed crystallographic data and structure refinement parameters for these compounds are summarized in Table 1. Selected bond distances and angles and hydrogen bonds are listed in Tables S1−S12.

110 °C for 3 days. After the mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 5 were obtained with a yield of 66% based on Cd(II). Anal. Calcd for C50H40Cd2N4O10.5 (Mr = 1089.64): C, 55.11; H, 3.70; N, 5.14. Found: C, 55.15; H, 3.76; N, 5.12. IR data (KBr, cm−1): 3426 (m), 3127 (m), 2951 (s), 2877 (s), 1552 (w), 1483 (w), 1397 (w), 1279 (w), 1130 (s), 1024 (w), 940 (s), 877 (s), 760 (w), 656 (m). Synthesis of [Cd(L)(biim-4)]·2H2O (6). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), biim-4 (19.0 mg, 0.1 mmol), NaOH (4.0 mg, 0.1 mmol), DMF (2 mL), and water (6 mL) was placed in a Teflon reactor (15 mL) and heated at 120 °C for 4 days. After the mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 6 were obtained with a yield of 52% based on Cd(II). Anal. Calcd for C31H32CdN4O7 (Mr = 685.01): C, 54.35; H, 4.71; N, 8.18. Found: C, 54.32; H, 4.75; N, 8.16. IR data (KBr, cm−1): 3419 (s), 3146 (s), 3062(s), 2924 (s), 2875 (s), 1681 (s), 1600 (m), 1536 (w), 1464 (m), 1307 (m), 1233 (w), 1153 (m), 1033 (m), 943 (s), 865 (w), 765 (w), 655 (w). Synthesis of [Co(L)(biim-4)]·H2O (7). The preparation of 7 was similar to that of 6 except that Co(CH3COO)2·4H2O was used instead of Cd(CH3COO)2·2H2O. Purple crystals of 7 were collected in a 65% yield based on Co(II). Anal. Calcd for C31H30CoN4O6 (Mr = 613.52): C, 60.69; H, 4.93; N, 9.13. Found: C, 61.00; H, 4.78; N, 9.12. IR data (KBr, cm−1): 3549 (w), 3415 (w), 3132 (s), 2930 (s), 1617 (s), 1566 (m), 1362 (m), 1232 (m), 1108 (m), 946 (s), 800 (m), 768 (w). Synthesis of [Cd(L)(btp)] (8). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), btp (17.8 mg, 0.1 mmol), DMF (2 mL), and water (6 mL) was placed in a Teflon reactor (15 mL) and heated at 120 °C for 3 days. After the mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 8 were obtained with a yield of 52% based on Cd(II). Anal. Calcd for C28H24CdN6O5 (Mr = 636.93): C, 52.80; H, 3.80; N, 13.19. Found: C, 52.75; H, 3.86; N, 13.25. IR data (KBr, cm−1): 3582 (m), 3269 (m), 2903 (s), 2857 (s), 1948 (s), 1542 (w), 1462 (w), 1445 (w), 1287 (w), 1166 (s), 964 (s), 897 (s), 763 (w), 679 (m). Synthesis of [Cd(L)(btb)] (9). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), btb (19.2 mg, 0.1 mmol), DMF (2 mL), and water (6 mL) was placed in a Teflon reactor (15 mL) and heated at 140 °C for 4 days. After the mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 9 were obtained with a yield of 65% based on Cd(II). Anal. Calcd for C25H20CdN3O5 (Mr = 554.84): C, 54.12; H, 3.63; N, 7.57. Found: C, 54.06; H, 3.68; N, 7.61. IR data (KBr, cm−1): 3440 (m), 3148 (s), 2939 (s), 2898 (s), 1598 (m), 1537 (w), 1474 (w), 1394 (w), 1320 (m), 1288 (m), 1160 (s), 1042 (w), 949 (s), 867 (m), 768 (w), 684 (m). Synthesis of [Cd(HL)(bth)0.5(H2O)]·H2O (10). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), bth (22.0 mg, 0.1 mmol), DMF (2 mL), and water (6 mL) was placed in a Teflon reactor (15 mL) and heated at 110 °C for 3 days. After the mixture had been cooled to room temperature at a rate of 10 °C·h−1, colorless crystals of 10 were obtained with a yield of 79% based on Cd(II). Anal. Calcd for C26H26Cd0.5N3O7 (Mr = 548.70): C, 56.91; H, 4.78; N, 7.66. Found: C, 56.85; H, 4.72; N, 7.46. IR data (KBr, cm−1): 3627 (m), 3348 (m), 3205 (m), 2934 (m), 2770 (s), 2498 (m), 1939 (s), 1698 (w), 1583 (w), 1550 (w), 1399 (w), 1212 (w), 981 (m), 826 (s), 764 (m). Synthesis of [Co(HL)(btb)0.5]·H2O (11). The preparation of 11 was similar to that of 7 except that btb was used instead of biim-4. Pink crystals of 11 were collected in a 65% yield based on Co(II). Anal. Calcd for C25H24Co0.5N3O7 (Mr = 507.94): C, 59.11; H, 4.76; N, 8.27. Found: C, 60.01; H, 4.78; N, 8.31. IR data (KBr, cm−1): 3575 (m), 3393 (w), 3128 (m), 2946 (m), 2767 (s), 2484 (s), 1945 (s), 1693 (m), 1658 (m), 1548 (s), 1450 (w), 1127 (m), 902 (s), 763 (w), 675 (m). Synthesis of [Cd(L)(btbp)1.5]·4H2O (12). A mixture of H2L (34.6 mg, 0.1 mmol), Cd(CH3COO)2·2H2O (27.0 mg, 0.1 mmol), btbp (31.6 mg, 0.1 mmol), DMF (2 mL), and water (6 mL) was placed in a Teflon reactor (15 mL) and heated at 120 °C for 3 days. After the

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RESULTS AND DISCUSSION Structure of [Cd(L)(H2O)] (1). Single-crystal X-ray structural analysis shows that the asymmetric unit of 1 contains one Cd(II) ion, one L anion, and one coordinated water molecule (Figure 1a). The Cd(II) center is six-coordinated by five carboxylate oxygen atoms from four individual L anions (Cd(1)−O(2)#1 = 2.221(3), Cd(1)−O(4)#2 = 2.240(3), Cd(1)−O(1) = 2.265(3), Cd(1)−O(4) #3 = 2.286(3), Cd(1)−O(5)#3 = 2.374(3) Å) and one water molecule (Cd(1)−O(1W) = 2.327(4) Å), displaying a slightly distorted octahedral coordination sphere. Each L anion acts as a μ3bridge to link three Cd(II) ions through its two carboxylate groups. One of the carboxylate groups possesses a μ2-η1:η1 mode, while the other one shows a μ3-η1:η2 coordination mode (mode I in Scheme 2). As shown in Figure 1b, the L anions bridge Cd(II) ions to form a 2D double-layer. Each doublelayer contains two monolayers, which share the same binuclear [Cd2(COO)4] unit. Two symmetry-related Cd1 atoms and four carboxylate groups from four L anions are involved in the construction of the binuclear unit, with the Cd···Cd distance of 3.807(7) Å. In addition, intramolecular O1W−H1A···O1 hydrogen-bonding interactions exist among the coordinated water molecules and carboxylate oxygen atoms, which further stabilized the 2D structure of 1 (Figure 1c). Structure of [Cd(L)2Na2]·H2O (2). As shown in Figure 2a, compound 2 contains one crystallographically independent Cd(II) ion, two Na(I) ions, one L anion, and one lattice water molecule. The Cd(II) center is seven-coordinated by seven carboxylate oxygen atoms from four individual L anions (Cd(1)−O(6) = 2.249(3), Cd(1)−O(1) = 2.294(3), Cd(1)− O(9)#1 = 2.321(2), Cd(1)−O(5)#2 = 2.352(3), Cd(1)−O(4)#2 = 2.437(3), Cd(1)−O(10)#1 = 2.526(3), Cd(1)−O(2) = 2.605(3) Å), displaying a pentagonal−bipyramidal coordination 2400

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Scheme 2. Coordination Modes of the Ligand L Found in Compounds 1−12

2.2652(18), Cd(1)−O(4)#2 = 2.2715(19), Cd(1)−O(5)#3 = 2.272(2) Å) and two nitrogen atoms from one phen ligand (Cd(1)−N(1) = 2.385(3) and Cd(1)−N(2) = 2.463(3) Å), showing a distorted [CdO4N2] octahedral geometry. The average Cd−O and Cd−N distances are 2.26 and 2.42 Å, respectively. As expected, each L anion bridges four Cd(II) ions with two carboxylate groups exhibiting μ2-η1:η1 coordination modes and showing a “U-shaped” conformation (mode III in Scheme 2). The phen ligands exhibit a bidentate chelating coordination mode attaching to the double chain of L anions and Cd(II) ions (Figure 3b). The chains are further extended into the 2D supramolecular layer through π−π interactions between pyridyl rings and phenyl rings of the phen ligands from neighboring chains with a face-to-face distance of 3.69 Å and centroid-to-centroid distance of 4.09 Å (Figure 3c). Structure of [Cd(L)(phen)]·2H2O (4). The asymmetric unit of 4 contains one crystallographically independent Cd(II) ion, one L anion, one phen ligand, and two lattice water molecules. As shown in Figure 4a, each Cd(II) center is sevencoordinated by five carboxylate oxygen atoms from three L anions (Cd(1)−O(1)#1 = 2.282(3), Cd(1)−O(4)#2 = 2.325(3), Cd(1)−O(5)#2 = 2.411(3), Cd(1)−O(2) = 2.521(3), Cd(1)− O(1) = 2.400(3) Å) and two nitrogen atoms from one phen ligand (Cd(1)−N(1) = 2.402(4) and Cd(1)−N(2) = 2.331(4) Å), displaying a slightly distorted pentagonal−bipyramidal geometry with O4#1 and O1#1 atoms located at the apical position. Like compound 3, the Cd(II) centers are linked by L anions to form a 1D double chain. However, the coordination mode of carboxylate groups is different from that of 3. In compound 4, one carboxylate group of the L anion displays a bidentate chelating mode (μ2-η1:η1), while the other one exhibits a tridentate coordination mode (μ3-η1:η2) as shown in mode IV. The phen ligands also exhibit a bidentate chelating coordination mode attaching to the double chain of L anions and Cd(II) ions (Figure 4b). In addition, three kinds of π−π stacking interactions exist associated with phenyl rings of L anions and pyridyl rings of phen ligands in the adjacent layers (face-to-face distances of 3.75, 3.43, and 3.48 Å; centroid-to-

Figure 1. (a) Coordination environment of the Cd(II) ion in 1 (30% probability displacement ellipsoids). Symmetry codes: #1 −x + 1/2, y + 1/2, z; #2 −x, −y, −z + 1; #3 x + 1/2, −y − 1/2, −z + 1. (b) The 2D sheet of 1 along the a axis. (c) View of the 2D structure formed by intramolecular hydrogen-bonding interactions.

geometry. In addition, O7 is weakly coordinated to Cd1 with a distance of 2.799(8) Å. Both Na1 and Na2 ions coordinate to four carboxylate oxygen atoms of three different L anions in a tetrahedral geometry. Cd(II) ions and Na(I) ions are linked by carboxylate oxygen atoms to form a 1D chain, and these chains are further joined by two kinds of L anions to generate a 2D double layer (Figure 2b). It is interesting to note that two carboxylate groups bridge two Cd(II) ions and four Na(I) ions in μ4-η1:η3 and μ4-η2:η2 coordination modes (mode II). As such, a trinuclear Cd(II) cluster is formed (Figure 2c). For convenience, from the topological point of view, this cluster can be defined as a 4connected node. Thus, the overall structure of 2 is a 2D uninodal 4-connected network with the short Point Symbol of 36·46·53 (Figure 2d). Structure of [Cd(L)(phen)] (3). When phen ligand was introduced into the reaction system of 1, a different structure of 3 was obtained. As shown in Figure 3a, the asymmetric unit of 3 contains one crystallographically independent Cd(II) ion, one L anion, and one phen ligand. Each Cd(II) center is sixcoordinated by four carboxylate oxygen atoms from four L anions (Cd(1)−O(1) = 2.235(2), Cd(1)−O(2) #1 = 2401

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Figure 3. (a) Coordination environment of the Cd(II) ion in 3 (30% probability displacement ellipsoids). Symmetry codes: #1 −x + 1, −y, − z + 1; #2 x + 1, y, z + 1; #3 −x, −y, −z. (b) View of the 1D double chain of 3. (c) The 2D supramolecular layer constructed via π−π interactions in 3.

coordinated by five carboxylate oxygen atoms from four L anions (Cd(1)−O(5) = 2.290(3), Cd(1)−O(9)#1 = 2.301(4), Cd(1)−O(6)#2 = 2.341(3), Cd(1)−O(4) = 2.360(3), Cd(1)− O(10)#1 = 2.449(3) Å) and one N atom from one biim-2 ligand (Cd(1)−N(1) = 2.226(4) Å). Cd2 cation is coordinated by five carboxylate oxygen atoms from three L anions (Cd(2)−O(2)#2 = 2.252(3), Cd(2)−O(6)#3 = 2.292(3), Cd(2)−O(9) = 2.374(3), Cd(2)−O(1)#2 = 2.491(3), Cd(2)−O(7)#1 = 2.561(3) Å), and one nitrogen atom from one biim-2 ligand (Cd(2)−N(4) =2.218(4) Å). It is interesting to note that the two types of L anions (La and b L ) show different coordination modes. La bridges two Cd(II) atoms with both two carboxylate groups in μ2-η1:η1 modes (mode VI), while Lb connects four Cd(II) atoms with one of two carboxylate groups in a μ3-η1:η2 coordination mode and the other one in a μ4-η2:η2 coordination mode (mode V). As such, two La and two Lb anions bridge two Cd(II) atoms to form a binuclear [Cd2(La)2(Lb)2] unit, which is further linked by biim2 ligands to generate a 1D double chain with [Cd2(La)(Lb)]2 loops (Figure 5a,b). Furthermore, adjacent chains are linked by two kinds of π−π interactions: one is between the two imidazole rings with the mean centroid-to-centroid distance of 3.97 Å (plane-to-plane distance of 3.52 Å); the other one is between imidazole and phenyl rings of L anions with the mean centroid-to-centroid distance of 3.81 Å (plane-to-plane distance of 3.23 Å) to give rise to a 2D supramolecular layer (Figure 5d). Structure of [Cd(L)(biim-4)]·2H2O (6). When the biim-2 ligand was replaced by the longer biim-4 ligand, a 2D undulated

Figure 2. (a) Coordination environment of the Cd(II) ion and Na(I) ions in 2 (30% probability displacement ellipsoids). Symmetry codes: #1 x, y − 1, z; #2 x + 1, y + 1, z; #3 x, y + 1, z; #4 x + 1, y, z; #6 x − 1, y − 1, z. (b) View of 2D sheet constructed by L anions and Cd(II) ions. (c) View of the trinuclear Cd(II) cluster. (d) Schematic representation of the 2D topology of 2 (the green spheres represent the trinuclear Cd(II) units and the blue lines represent the L anions).

centroid distances of 3.91, 3.86, and 3.68 Å, respectively). However, unlike compound 3, the intermolecular π−π interactions in 4 led these 1D double chains to a 3D supramolecular architecture (Figure 4c). Structure of [Cd2(L)2(biim-2)]·H2O (5). When phen ligand was replaced by biim-2 ligand, a quite different structure of 5 was obtained. As illustrated in Figure 5a, the structure of 5 contains Cd1 and Cd2 cations, both lying in general positions, two L anions, one biim-2 ligand, and one lattice water molecule. Both Cd1 and Cd2 ions are six-coordinated, displaying distorted [CdO5N] octahedral geometries. Cd1 cation is 2402

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Figure 5. (a) Coordination environment of the Cd(II) ions in 5 with solvent water molecules omitted for clarity (30% probability displacement ellipsoids). Symmetry codes: #1 x, y + 1, z; #2 −x, −y − 1, −z + 1; #3 −x, −y − 2, −z + 1. (b) View of the 1D single chain of 5 consructed by Cd(II) ions and biim-2 ligands. (c) View of the 1D double chain of 5. (d) The 2D supramolecular layer constructed via π−π interactions in 5.

Figure 4. (a) Coordination environment of the Cd(II) ion in 4 with solvent water molecules omitted for clarity (30% probability displacement ellipsoids). Symmetry codes: #1 −x + 2, −y + 1, −z; #2 −x + 1, −y + 2, −z; #3 −x + 2, −y + 2, −z + 1. (b) View of the 1D double chain of 4. (c) The 3D supramolecular architecture via π−π interactions in 4.

network has large rectangular windows with approximate dimensions of 13.8818(9) × 14.3670(1) Å2 built up by four Cd(II) atoms, two biim-4 ligands, and two L anions within the 2D motif (Figure 6d). For convenience, if Cd1 ions are viewed as uninodal 4-connected nodes, and L anions and biim-4 ligands are viewed as linkers, the undulated layer can be described as a 4-connected sql topology with the point Symbol of 44·62 (Figure 6e). In addition, there exist π−π stacking interactions associated with pyridyl rings and pyridyl rings of biim-4 ligands (face-toface distance of 3.57 Å and centroid-to-centroid distance of 3.45 Å) in the adjacent layers. These π−π interactions among layers led the 2D undulated layers to a 3D supramolecular architecture (Figure 6f). Structure of [Co(L)(biim-4)]·H2O (7). The structure of compound 7 is essentially isostructural with 6. But there are small differences between them. The coordination number of the metal center is different. Compound 7 consists of one Co(II) ion, one L anion, two half biim-4 ligands, and one

layer of 6 was obtained. As shown in Figure 6a, the asymmetric unit of 6 contains one crystallographically independent Cd(II) ion, one L anion, two half biim-4 ligands, and two lattice water molecules. The Cd(II) center is six-coordinated by four carboxylate oxygen atoms from two individual L anions (Cd(1)−O(1) = 2.295(3), Cd(1)−O(5) #1 = 2.312(3), Cd(1)−O(4)#1 = 2.406(3), Cd(1)−O(2) = 2.494(3) Å) and two nitrogen atom from two different biim-4 ligands (Cd(1)− N(3) = 2.237(3), Cd(1)−N(1) = 2.251(3) Å), displaying a distorted octahedral coordination geometry. Each L anion links two Cd(II) ions with its two carboxylate groups adopting bidentate chelating modes (mode VI). The biim-4 ligands connected adjacent Cd(II) ions to afford a 1D zigzag chain (Figure 6b). If biim-4 ligands are neglected, Cd(II) ions are bridged by L anions to form a 1D wavelike chain (Figure 6c). The two types of chains are linked to generate 2D undulated layers through sharing the central Cd(II) atoms. Notably, the 2403

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Figure 6. continued undulated layer constructed by Cd(II) ions, L anions, and biim-4 ligands. (e) Schematic representation of topology of 6 (the purple spheres represent the Cd(II) atoms and green and blue lines represent the biim-4 ligands and L anions, respectively). (f) The 3D supramolecular network constructed by π−π interactions in 6.

coordinated water molecule. As depicted in Figure 7, each Co(II) ion is four-coordinated in a tetrahedral coordination

Figure 7. Coordination environment of the Co(II) ion in 7 with solvent water molecules omitted for clarity (30% probability displacement ellipsoids). Symmetry codes: #1 x − 1, y + 1, z; #2 −x + 3, −y, −z + 1; #3 −x + 3, −y + 1, −z.

geometry defined by two nitrogen atoms from two biim-4 ligands and two oxygen atoms from two L anions. However, in compound 6, each Cd(II) is six-coordinated in an octahedral coordination environment. In addition, the coordination modes of the L anions in 6 and 7 are different. In 7, both of the two carboxylate groups of L anion display monodentate coordination modes (mode VIII). However, their frameworks of 6 and 7 show the same 4-connected topology with the point symbol of 44·62. Structure of [Cd(L)(btp)] (8). When biim-4 ligand was replaced with btp ligand, a 2D structure of compound 8 was obtained. As exhibited in Figure 8a, the asymmetric unit of 8 contains one crystallographically independent Cd(II) ion, one L anion, and one btp ligand. Each Cd(II) atom is sevencoordinated by five carboxylate oxygen atoms from three individual L anions (Cd(1)−O(1) = 2.316(3), Cd(1)−O(2) = 2.357(8), Cd(1)−O(5)#2 = 2.348(3), Cd(1)−O(2)#1 = 2.358(3), Cd(1)−O(4)#2 = 2.485(3) Å) and two nitrogen atom (Cd(1)−N(6)#1 = 2.283(3), Cd(1)−N(3) = 2.306(3) Å), displaying a slightly distorted pentagonal−bipyramidal geometry. Each L anions links two Cd(II) ions with one of the carboxylate groups in a μ2-η1:η1 mode, while the other one shows a μ3-η1:η2 coordination mode (mode IX in Scheme 2). Cd(II) ions are bridged by L anions to form a 2D layer (Figure 8b). As shown in Figure 8c, the 2D layer is further stabilized by two kinds of [Cd2(btp)2] rings in different directions. The two kinds of [Cd2(btp)2] rings are composed of two Cd(II) centers and two btp ligands with all the bth ligands adopting cisconformations (Figure 8c). It is easily noted that the btp

Figure 6. (a) Coordination environment of the Cd(II) ion in 6 with solvent water molecules omitted for clarity (30% probability displacement ellipsoids). Symmetry codes: #1 x + 1, y − 1, z; #3 −x + 2, −y + 1, −z − 1; #4 −x + 2, −y, −z. (b) View of the 1D chain of 6 constructed by Cd(II) ions and biim-4 ligands. (c) View of the 1D chain of 6 constructed by Cd(II) ions and L anions. (d) View of 2D 2404

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Figure 8. (a) Coordination environment of the Cd(II) ion in 8 (30% probability displacement ellipsoids). Symmetry codes: #1 −x + 1, −y + 1, −z; #2 −x + 1, y + 1/2, −z + 1/2. (b) View of 2D sheet constructed by Cd(II) ions and L anions along the a axis. (c) View of 2D structure formed by Cd(II) ions, btp ligands, and L anions.

ligands do not play a role in enhancing the dimension of the whole framework. Structure of [Cd(L)(btb)] (9). When the btb ligand was used instead of the btp ligand in compound 8, a completely different compound 9 was obtained. As illustrated in Figure 9a, the structure of 9 contains one unique Cd(II) atom, one L anion, and one btb ligand. The Cd(II) atom is six-coordinated by five carboxylate oxygen atoms from three different L anions (Cd(1)−O(4)#1 = 2.233(3), Cd(1)−O(1) = 2.256(3), Cd(1)− O(5)#2 = 2.297(3), Cd(1)−O(5)#1 = 2.446(3), Cd(1)−O(2) = 2.484(3) Å) and one nitrogen atom from one btb ligand (Cd(1)−N(1) = 2.243(3) Å) in a distorted octahedral environment. Each L anion coordinates to three Cd(II) atoms with one of the carboxylate groups in a μ2-η1:η1 mode,

Figure 9. (a) Coordination environment of the Cd(II) ion in 9 (30% probability displacement ellipsoids). Symmetry codes: #1 −x + 1, −y + 1, −z + 1; #2 −x + 1, y + 1/2, −z + 3/2; #3 −x, −y + 2, −z + 1. (b) View of the 2D sheet of 9 constructed by Cd(II) ions and L anions. (c) View of 3D structure of 9. (d) Schematic representation of topology of 9 (the green and blue spheres represent the Cd(II) atoms and L anions, respectively; the purple lines represent the btb ligands).

while the other one shows a μ3-η1:η2 coordination mode (mode IX). Two L anions connect two Cd(II) atoms to form a closed ring, and then these rings are connected by a μ3-O-bridge to give rise to a 2D layer viewing along the a-axis (Figure 9b). These layers are further bridged by crossed btb ligands to 2405

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Structure of [Cd(L)(btbp)1.5]·4H2O (12). The asymmetric unit of 12 contains one Cd(II) ion, one L anion, one and a half btbp ligands, and four lattice water molecules (Figure 11a). Each Cd(II) ion is surrounded by four carboxylate oxygen atoms from two independent L anions (Cd(1)−O(2) =

generate a 3D framework (Figure 9c). From the topological view, Cd(II) atoms can be viewed as 4-connected nodes, L anions can be viewed as 3-connected nodes, and the btb ligands can be considered as linkers, so the structure of 9 can be described as a 3D binodal (3,4)-connected framework with a point symbol of (4·102)(4·103·122) (Figure 9d). Structure of [Cd(HL)(bth)0.5(H2O)]·H2O (10). Compounds 10 and 11 show the similar chain structures (Figure S1, Supporting Information). Therefore, compound 10 is employed as a representative structure to be described in detail. As shown in Figure 10a, the asymmetric unit of 10 contains one

Figure 10. (a) Coordination environment of the Cd(II) ion in 10 with solvent water molecules omitted for clarity (30% probability displacement ellipsoids). Symmetry codes: #1 −x, −y, −z; #2 −x − 1, −y + 1, −z. (b) View of the 1D chain of 10. (c) The 2D supramolecular layer constructed via π−π interactions in 10.

crystallographically independent Cd(II) ion, one HL anion, half bth ligand, one coordinated water molecule, and one lattice water molecule. Different from compounds 1−9, only one carboxylate group of H2L is deprotonated in 10. Each Cd(II) center is six-coordinated by two carboxylate oxygen atoms from two HL anions, two water molecules (Cd−O = 2.318(2)− 2.354(3) Å), and two nitrogen atoms from two bth ligands (Cd−N = 2.312(2) Å), showing a distorted octahedral geometry with the two O1W molecules in the apical positions. Each bth ligand links two Cd(II) cations to form a 1D chain with its two triazole rings. However, the dangling HL anions adopt a monodentate coordination mode (mode VII), attaching to the 1D chains (Figure 10b). In addition, these chains are further stacked by π−π interactions between phenyl rings and phenyl rings from adjacent chains with a face-to-face distance of 3.62 Å and centroid-to-centroid distance of 3.88 Å, yielding a 2D supramolecular layer (Figure 10c).

Figure 11. (a) Coordination environment of the Cd(II) ion in 12 with solvent water molecules omitted for clarity (30% probability displacement ellipsoids). Symmetry codes: #1 x, y − 1, z; #2 x + 1, y − 1, z; #3 −x + 1, −y, −z + 1. (b) View of the 1D zigzag chain of 12 consructed by Cd(II) ions and btbp ligands. (c) View of the 1D chain of 12 constructed by Cd(II) ions and L anions. (d) The 2D sheet of 12 along the c axis. (e) View of 3D supramolecular network formed by hydrogen-bonding interactions. 2406

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2.281(2), Cd(1)−O(1) = 2.687(6), Cd(1)−O(5)#1 = 2.353(2), Cd(1)−O(4)#1 = 2.493(2) Å) and three nitrogen atoms from three different btbp ligands (Cd(1)−N(3) = 2.288(3), Cd(1)− N(6) = 2.334(2), Cd(1)−N(9)#2 = 2.382(2) Å) in a distorted pentagonal−bipyramidal geometry. Each L anion coordinates to two Cd(II) centers with both two carboxylate groups in bidentate chelating modes (mode VI). As shown in Figure 11b, btbp ligands connected Cd(II) ions to form a ladder-like chain. If the btbp ligands are ignored, L anions bridge the Cd(II) ions to generate a 1D chain (Figure 11c). The two kinds of chains are linked to yield a 2D double sheet through sharing the central Cd(II) atoms (Figure 11d). Furthermore, the lattice water molecules donate hydrogen bonds to water oxygen atoms and nitrogen atoms (O1W−H1B···O1W, O1W−H1B···O2W, O3W−H3A···N3, O3W−H3A···N6), which further extend the 2D sheets into a 3D supramolecular architecture (Figure 11e). Coordination Modes of the Ligand. From the structure descriptions above, we can see that the L anion can adopt a variety of coordination modes. It can connect one (compounds 10 and 11), two (compounds 6, 7, and 12), three (compounds 4, 8, and 9), four (compounds 1, 3, and 5), or six (compound 2) metals. In compound 1, one of the carboxylate groups possesses a μ2-η1:η1 mode, while the other one shows a μ3-η1:η2 coordination mode (mode I). In compound 2, two carboxylate groups bridge two Cd(II) ions and four Na(I) ions in μ4-η1:η3 and μ4-η2:η2 coordination modes (model II). In compound 3, both two carboxylate groups exhibit μ2-η1:η1 coordination modes (mode III). In compound 4, one of the carboxylate groups exhibits a μ3-η1:η2 coordination fashion and the other one shows a μ2-η1:η1 mode (mode IV). However, in compound 5, two types of L anions (La and Lb) show different coordination modes. La bridges two Cd(II) atoms with both two carboxylate groups in μ2-η1:η1 modes (mode VI), while Lb connects four Cd(II) atoms with one of two carboxylate groups in a μ3-η1:η2 coordination mode and the other one in a μ4-η2:η2 coordination mode (mode V). In compounds 6 and 12, the coordination modes of L anions are the same to that of La in compound 5. In compound 7, both two carboxylate groups of L anion display μ1-η1:η0 coordination modes (mode VIII). In compounds 8 and 9, each L anion coordinates to three Cd(II) atoms with one of the carboxylate groups in a μ2-η1:η1 mode and the other one in a μ3-η1:η2 coordination fashion (mode IX). In Compounds 10 and 11, the μ1-HL anions are partly deprotonated and link one metal atom in a μ 1 -η 1 :η 0 coordination mode (mode VII). The results indicate that the different coordination fashions of L anions have a remarkable effect on the structures of the MOFs. Effects of the N-Donor Ligands on the Frameworks. Compounds 5, 6, 8−10, and 12 show the effects of the flexible N-donor ligands on their structures. These effects are mainly related to the length of N-donor ligands and steric hindrance of the substituent groups. Compounds 5 and 6 show the effect of the length of N-donor ligand on their structures. Compared with biim-2, biim-4 has a slightly long alkyl spacer. In 5, two La and two Lb anions bridge two Cd(II) atoms to form a binuclear [Cd2(La)2(Lb)2] unit. These units are further linked by biim-2 ligands to generate a 1D double chain with [Cd2(La)(Lb)]2 loops. However, in 6, the biim-4 ligands connect the Cd(II) ions to form 1D ladder-like chains, which are further linked by L anions to furnish a 2D undulated layer. The effect of the length of N-donor ligand is further supported by compounds 8−10.

Compounds 9 and 12 exhibit the effects of steric hindrance of the substituent groups on their structures. Compared with btb ligand, the btbp ligand has an additional biphenyl group instead of -CH2−CH2- group at the center of the molecule. Obviously, the additional biphenyl groups of the btbp ligands will increase the steric hindrances when the btbp ligand coordinated with the metal atom. In 12, the btbp ligands connect the Cd(II) ions to furnish 1D ladder-like chains. These chains are further extended by the L anions to yield a 2D double layer. However, in 9, L anions connect Cd(II) atoms to generate 2D layers, which are further bridged by crossed btb ligands to give rise to a 3D binodal (3,4)-connected framework with point symbol of (4·102)(4·103·122). IR Spectra. In the IR spectra of compounds 1−2, 4−7, and 10−12, the broad absorption bands of 3394−3627 cm−1 are attributable to the O−H stretching vibrations of the water molecules.10h For compounds 1−9 and 12, the asymmetric and symmetric stretching vibrations of carboxylate groups are observed in the ranges of 1542−1600 and 1362−1485 cm−1, respectively. For compounds 10 and 11, the stretching vibration peaks at 1693 and 1698 cm−1 corresponds to the incomplete deprotonation of the H2L ligand.10f For compounds 3−12, the bands of 1536−1597 cm−1 can be assigned to the CN stretching vibrations of the N-donor ligands.12j Thermal Analysis and PXRD Patterns. In order to characterize the compounds more fully in terms of thermal stability, the thermal behaviors of 1, 3−4, 8−10, and 12 were examined by thermogravimetric analysis (TGA). The experiments were performed on samples consisting of numerous single crystals under N2 atmosphere with a heating rate of 10 °C/min (Figure S2, Supporting Information). For compound 1, the weight loss attributed to the release of one coordinated water molecule is observed from 20 to 137 °C (obsd 4.1%, calcd 4.8%). Decomposition of the residual composition occurs from 262 to 565 °C. The TGA curve of 3 shows that it is stable in the temperature range of 28−320 °C, and the structure decomposes in the range of 320−538 °C. The departure of the structure finally led to the formation of CdO (obsd 21.8%, calcd 20.0%). Compound 4 has two steps of weight losses. The first weight loss of 5.1% in the range of 20− 98 °C is consistent with the removal of two uncoordinated water molecules (calcd 5.3%). The second step from 325 to 501 °C can be attributed to the release of the organic ligands. The remaining weight is assigned to CdO (obsd 20.1%, calcd 19.0%). For compound 5, the weight loss of 2.5% from 20 to 103 °C is assigned to the loss of one noncoordinated water molecule (calcd 1.6%). There is no further weight loss from 103 to 326 °C, and after that temperature, the organic components start to decompose. For compound 6, the weight loss attributed to the release of free water molecules is observed below 103 °C (obsd 4.0%, calcd 5.2%), and the anhydrous compound starts decomposition after 310 °C. For compound 8, the weight loss corresponding to the release of organic ligands is observed from 267 to 502 °C. The remaining residue is assigned to the formation of CdO (obsd 19.2%, calcd 20.4%). The organic components of compound 9 decompose from 318 to 501 °C. The remaining residue corresponds to the formation of CdO (obsd 22.5%, calcd 23.1%). In compound 10, the weight loss in the range of 60−140 °C (obsd 6.0%, calcd 6.4%) can be attributed to the removal of one lattice and one coordinated water molecules. At 250−551 °C, the weight loss can be attributed to the decomposition of the organic ligand. The remaining weight corresponds to the formation of CdO 2407

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Figure 12. Solid-state emission spectra of compounds 1−6, 8−10, and 12 at room temperature.

(obsd 24.9%, calcd 23.3%). Compound 12 undergoes dehydration in the range of 60−112 °C (obsd 6.1%, calcd 7.2%), and the structure decomposes in the range of 285−543 °C. The departure of the structure finally led to the formation of CdO (obsd 13.3%, calcd 12.7%). To confirm whether the crystal structures are truly representative of the bulk materials, PXRD experiments were carried out for 1−12. The PXRD experimental and computersimulated patterns of the corresponding complexes are shown in Supporting Information. They show that the synthesized bulk materials and the measured single crystals are the same (Figure S3). Luminescent Properties. Luminescent properties of compounds containing d10 metal centers have attracted intense interest due to their potential applications, such as in chemical sensors, photochemistry, electroluminescent display, and so on.15 In this work, the solid-state photoluminescent spectra of H2L, the N-donor ligands, and the compounds 1−6, 8−10, and 12 have been carried out at room temperature (Figure 12). The main emission peaks of H2L, phen,10f biim-4,4e biim-2,10f bth,10f btb, btp,10f and btbp10f are at 448, 380, 443, 400, 414, 441, 408, and 443 nm, respectively, which can be attributed to the π* → n or π* → π transitions.16 On complexation of these ligands with Cd(II) atom, the emission peaks occur at 425 nm (λex = 400 nm) for 1, 438 nm (λex = 333 nm) for 2, 448 nm (λex = 373 nm) for 3, 418 nm (λex = 351 nm) for 4, 464 nm (λex = 352 nm) for 5, 448 nm (λex = 339 nm) for 6, 428 nm (λex = 348 nm) for 8, 425 nm (λex = 362 nm) for 9, 489 nm (λex = 351 nm) for 10, and 420 nm (λex = 357 nm) for 12. According to the literature, the Cd(II) ions are difficult to oxidize or reduce because of the d10 configuration. As a result, the emissions of these compounds are neither metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) in nature.17 The emission peaks of compounds 3 and 6 are the same as that of the free H2L. Thus the emission bands of the two compounds can probably be attributed to the intraligand fluorescent emission.18 The emission bands of compounds 1, 4, 8, 9, and 12 are slightly blue-shifted with respect to the bands shown by the H2L, which may be attributed to the coordination effects of the L ligands to Cd(II) cations.19 However, for compound 10, the main emission peak is highly red-shifted by 41 nm relative to the free H2L, which probably can be assigned to co-coordination of the partly deprotonated HL ligand and the bth ligand to metal center.20

Table 2. Wavelengths of the Emission Maxima and Excitation (nm) compounds

λem (nm)

λex (nm)

1 2 3 4 5 6

425 438 448 418 448/464 448

400 333 373 351 352 339

8 9 10 12

428 425 489 420

348 362 420 357

τ (ns)

ligand

λem (nm)

λex (nm)

1.99, 7.54 1.60, 7.47 1.74, 7.61 3.48 1.52, 7.76 2.00, 10.33 1.54, 6.81 1.63, 5.12 2.99, 6.83 0.78, 5.53

phen biim-2 biim-4 btp bth btbp

380 400 443 408 414 443

325 303 366 320 312 305

btb H2L

441 448

385 358

The luminescent decay curves of 1−3, 5−6, 8−10, and 12 at room temperature are well fitted into a double-exponential function as I = A + B1 × exp(−t/τ1) + B2 × exp(−t/τ2). The emission decay lifetimes are τ(1) = 1.99 (50.49%) ns and τ(2) = 7.54 ns (49.51%) for 1, τ(1) = 1.60 ns (39.33%) and τ(2) = 7.47 ns (60.67%) for 2, τ(1) = 1.74 ns (71.82%) and τ(2) = 7.61 ns (28.18%) for 3, τ(1) = 1.52 ns (50.44%) and τ(2) = 7.76 ns (49.56%) for 5, τ(1) = 2.00 ns (33.91%) and τ(2) = 10.33 ns (66.09%) for 6, τ(1) = 1.54 ns (73.21%) and τ(2) = 6.81 ns (26.79%) for 8, τ(1) = 1.63 ns (64.58%) and τ(2) = 5.12 ns (35.42%) for 9, τ(1) = 2.99 ns (66.62%) and τ(2) = 6.83 ns (33.38%) for 10, and τ(1) = 0.78 ns (97.57%) and τ(2) = 5.53 ns (2.43%) for 12, respectively. The decay curves of compound 4 can be fitted with a single-exponential decay function with τ1 = 3.48 ns. The luminescent lifetimes of these compounds are much shorter than the ones resulting from a triplet state (>10−3 s), so the emissions should arise from a singlet state.21,22 The nanosecond range of lifetime in the solid state at room temperature reveals that the emission is fluorescent in nature (Figure S4, Supporting Information).

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CONCLUSIONS In summary, 12 new MOFs based on H2L and flexible bis(imidazole) or bis(triazole) ligands have been successfully synthesized under hydrothermal conditions. The flexibility of N-donor ligands, the diversity of the coordination mode of H2L, and the different coordination preferences of the Cd(II) and Co(II) metal ions led cooperatively to the intriguing and versatile architectures from 1D chains to 3D frameworks (Table 3). The photoluminescent behaviors show that these complexes 2408

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Y.; Yan, S. G.; Wu, L. P.; Ion, I.; Kuroda-Sowa, T.; Maekawa, M. J. Chem. Soc., Dalton Trans. 1998, 1121. (c) Hirsch, K. A.; Wilson, S. R.; Moore, J. S. Inorg. Chem. 1997, 36, 2960. (d) Carlucci, L.; Ciani, G.; Macchi, P.; Proserpio, D. M.; Sironi, A. Chem. Commun. 1997, 631. (4) (a) Zhang, L. P.; Yang, J.; Ma, J. F.; Jia, Z. F.; Xie, Y. P.; Wei, G. H. CrystEngComm 2008, 10, 1410. (b) Yang, J.; Ma, J. F.; Liu, Y. Y.; Ma, J. C.; Batten, S. R. Cryst. Growth Des. 2008, 8, 4383. (c) Zhang, L. P.; Ma, J. F.; Pang, Y. Y.; Ma, J. C.; Yang, J. CrystEngComm 2010, 12, 4433. (d) Liu, B.; Yu, Z. T.; Yang, J.; Wu, H.; Liu, Y. Y.; Ma, J. F. Inorg. Chem. 2011, 50, 8967. (5) (a) Sun, J.-K.; Li, W.; Cai, L.-X.; Zhang, J. CrystEngComm 2011, 13, 1550. (b) Li, B.; Li, G.; Liu, D.; Peng, Y.; Zhou, X.; Hua, J.; Shi, Z.; Feng, S. CrystEngComm 2011, 13, 1291. (c) Yin, P.-X.; Zhang, J.; Qin, Y.-Y.; Cheng, J.-K.; Li, Z.-J.; Yao, Y.-G. CrystEngComm 2011, 13, 3536. (d) Pachfule, P.; Das, R.; Poddar, P.; Banerjee, R. Inorg. Chem. 2011, 50, 3855. (e) Chen, M.; Chen, S.-S.; Okamura, T.-a.; Su, Z.; Chen, M.S.; Zhao, Y.; Sun, W.-Y.; Ueyama, N. Cryst. Growth Des. 2011, 11, 1901. (f) Li, C.-P.; Du, M. Chem. Commun. 2011, 5958. (6) (a) Li, X. J.; Wang, X.-Y.; Gao, S.; Cao, R. Inorg. Chem. 2006, 45, 1508. (b) Lan, X. Y.; Li, S. L.; Fu, Y. M.; Xu, Y. H.; Li, L.; Su, Z. M.; Fu, Q. Dalton Trans. 2008, 6796. (7) (a) Yang, S. Y.; Long, L. S.; Jiang, Y. B.; Huang, R. B.; Zheng, L. S. Chem. Mater. 2002, 14, 3229. (b) Guo, X.; Zhu, G.; Li, Z.; Sun, F.; Yang, Z.; Qiu, S. Chem. Commun. 2006, 3172. (c) Chen, W.-X.; Wu, S.-T.; Long, L.-S.; Huang, R.-B.; Zheng, L.-S. Cryst. Growth Des. 2007, 7, 1171. (8) (a) Ye, B.-H.; Tong, M.-L.; Chen, X.-M. Coord. Chem. Rev. 2005, 249, 545. (b) Yang, J.; Yue, Q.; Li, J.-D.; Cao, J.-J.; Li, G.-H.; Chen, J.S. Inorg. Chem. 2006, 45, 2857. (c) Yao, J.; Huang, W.; Li, B.; Gou, S.; Xu, Y. Inorg. Chem. Commum. 2002, 5, 711. (d) Dalai, S.; Mukherjee, P. S.; Rogez, G.; Mallah, T.; Drew, M. G. B.; Chaudhuri, N. R. Eur. J. Inorg. Chem. 2002, 31, 3292. (e) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (f) Férey, G.; Serre, C.; Mellot-Draznieks, C.; Millange, F. Acc. Chem. Res. 2005, 38, 217. (9) (a) Chen, L.; Xu, G.-J.; Shao, K.-Z.; Zhao, Y.-H.; Yang, G.-S.; Lan, Y.-Q.; Wang, X.-L.; Xu, H.-B.; Su, Z.-M. CrystEngComm 2010, 12, 2157. (b) Zhang, X.; Yang, J.-X.; Zhang, J.; Cheng, J.-K.; Sun, M.-L.; Yao, Y.-G. Inorg. Chem. Commun. 2011, 14, 986. (10) (a) Duncan, P. C. M.; Goodgame, D. M. L.; Menzer, S.; Williams, D. J. Chem. Commun. 1996, 2127. (b) Dong, B.-X.; Peng, J.; Gómez-García, C. J.; Benmansour, S.; Jia, H.-Q.; Hu, N.-H. Inorg. Chem. 2007, 46, 5933. (c) Ma, J. F.; Liu, J.-F.; Jia, H.-Q.; Lin, Y.-H. J. Chem. Soc., Dalton Trans. 2000, 2403. (d) Wu, H.; Yang, J.; Su, Z. M.; Batten, S. R.; Ma, J. F. J. Am. Chem. Soc. 2011, 133, 11406. (e) Yang, J.; Ma, J. F.; Liu, Y.-Y.; Ma, J.-C.; Jia, H.-Q.; Hu, N.-H. Eur. J. Inorg. Chem. 2006, 6, 1208. (f) Liu, Y.-Y.; Li, J.; Ma, J.-F.; Yang, J.; Ma, J.-C. CrystEngComm 2012, 14, 169. (g) Mukherjee, S.; Lan, Y. H.; Kostakis, G. E.; Clérac, C. E. A.; Powell, A. K. Cryst. Growth Des. 2009, 9, 1577. (h) Kan, W.-Q.; Yang, J.; Liu, Y.-Y.; Ma, J.-F. Polyhedron 2011, 30, 2113. (11) (a) Hoskins, B. F.; Robson, R.; Slizys, D. A. J. Am. Chem. Soc. 1997, 119, 2952. (b) Hoskins, B. F.; Robson, R.; Slizys, D. A. Angew.Chem. Int. Ed. 1997, 36, 2336. (c) Hennigar, T. L.; MacQuarrie, D. C.; Losier, P.; Roger, R. D.; Zaworotko, M. J. Angew. Chem., Int. Ed. 1997, 36, 972. (d) Tong, M. L.; Chen, X. M.; Ye, B. H.; Ji, L. N. Angew. Chem., Int. Ed. 1999, 38, 2237. (e) Carlucci, L.; Ciani, G.; Moret, M.; Proserpio, D. M.; Rizzato, S. Angew. Chem., Int. Ed. 2000, 39, 1506. (f) Zhu, H. L.; Tong, Y. X.; Chen, X.-M. J. Chem. Soc., Dalton Trans. 2000, 4182. (g) Van Albada, G. A.; Guijt, G. A.; Haasnoot, R. C.; Lutz, J. G.; Spek, M.; Reedijk, J. Eur. J. Inorg. Chem. 2000, 121. (h) Bu, X. H.; Hou, W. F.; Du, M.; Chen, W.; Zhang, R. H. Cryst. Growth Des. 2002, 2, 303. (i) Carlucci, L.; Ciani, G.; Proserpio, D. M. Chem. Commun. 2004, 380. (j) Zhang, J.; Chen, Y. B.; Chen, S. M.; Li, Z. J.; Cheng, J. K.; Yao, Y. G. Inorg. Chem. 2006, 45, 3161. (12) (a) Ma, J. F.; Yang, J.; Zheng, G. L.; Li, L.; Zhang, Y. M.; Li, F. F.; Liu, J. F. Polyhedron 2004, 23, 553. (b) Li, S. L.; Lan, Y. Q.; Ma, J. F.; Yang, J.; Wei, J.; Zhang, L. P.; Su, Z. M. Cryst. Growth Des. 2008, 8, 675. (c) Yang, J.; Ma, J. F.; Liu, Y. Y.; Li, S. L.; Zheng, G. L. Eur. J.

Table 3. Coordination Modes of L Ligand and Dimensions of Compounds 1−12 compounds 1 2 3 4 5 6, (7) 8 9 10, (11) 12

metal ions Cd(II) Cd(II) Cd(II) Cd(II) Cd(II) Cd(II), (Co(II)) Cd(II) Cd(II) Cd(II), (Co(II)) Cd(II)

N-donor ligands

coordination modes (L)

dimensions

phen phen biim-2 biim-4

I II III IV V, VI VI, (VIII)

2D 2D 1D 1D 1D 2D

btp btb bth, (btb)

IX IX VII

2D 3D 1D

btbp

VI

2D

may be good candidates for optical materials. It is anticipated that other novel MOFs with various entertaining structures as well as physical properties will be synthesized.

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ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic data in CIF format, selected bond lengths and angles, structure illustrations for compounds 11, luminescent decay curves for compounds 1−6, 8−10, and 12, thermogravimetric analysis (TGA) for compounds 1, 3−4, 8− 10, and 12, PXRD patterns. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (J.Y.); [email protected] (S.-Y.S.); [email protected] (J.-F.M.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Program for the National Natural Science Foundation of China (Grant Nos. 21071028 and 21001023), the Science Foundation of Jilin Province (20090137 and 20100109), the Fundamental Research Funds for the Central Universities, the Specialized Research Fund for the Doctoral Program of Higher Education and the State Key Laboratory of Rare Earth Resources Utilization of Changchun Institute of Applied Chemistry (RERU2011017) for support.

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REFERENCES

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Crystal Growth & Design

Article

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dx.doi.org/10.1021/cg3000526 | Cryst. Growth Des. 2012, 12, 2397−2410