MetalâOrganic Frameworks Based on Different Benzimidazole

DOI: 10.1021/cg9010482

Metal-Organic Frameworks Based on Different Benzimidazole Derivatives: Effect of Length and Substituent Groups of the Ligands on the Structures

2010, Vol. 10 1161–1170

Shun-Li Li, Ya-Qian Lan, Ji-Cheng Ma, Jian-Fang Ma,* and Zhong-Min Su Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast Normal University, Changchun 130024, People’s Republic of China Received August 27, 2009; Revised Manuscript Received January 18, 2010

ABSTRACT: Seven coordination polymers constructed from structurally related ligands, namely, [Cd2(ODPT)(L1)(H2O)2] 3 H2O (1), [Cd2(ODPT)(L2)(H2O)2] (2), [Zn2(BPTC)(L3)] 3 (H2O)3 (3), [Cd(m-BDC)(L4)] (4), [CdL5] (5), [CdL6] 3 H2O (6), and [ZnL6] 3 H2O (7) (H4ODPT = 4,40 -oxidiphthalic acid, H4BPTC = 3,30 ,4,40 -benzophenone tetracarboxylate ligand, H2m-BDC = 1,4-benzenedicarboxylate acid, L1=1,4-di(1H-benzo[d]imidazol-2-yl)butane, L2=bis((1H-benzo[d]imidazol-2-yl)methyl)amine, L3=1,4-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)butane, L4=bis((1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)methyl)amine, H2L5 = 4,40 -(2,20 -(butane-1,4-diyl)bis(1H-benzo[d]imidazole-2,1-diyl))bis(methylene)dibenzoic acid, and H2L6 = 2,20 -(2,20 -azanediylbis(methylene)bis(1H-benzo[d]imidazole-2,1-diyl))diacetic acid) have been synthesized under hydrothermal conditions. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. In 1, one kind of phthalate group of ODPT4- links CdII cations to form a Cd-O helical chain which is connected by L1 ligand and the other kind of phthalate group to form a twodimensional (2D) layer. These layers are further connected by ether O atoms of ODPT4- anions to generate a three-dimensional (3D) network with (42 3 52 3 62)(42 3 52 3 64 3 72) topology. Each ODPT4- anion links all CdII cations to form a 3D framework with (45 3 65)(47 3 68) topological type, in which each L2 ligand coordinates to CdII with two imidazole nitrogen atoms and one imine nitrogen atom as a terminal ligand in 2. For 3, BPTC4- ligands link Zn1 and Zn2 cations to generate a right-handed helical chain. L3 ligands connect Zn cations from helical chains to extend to a 3D open framework, showing a (43 3 83)2(42 3 84)(4 3 85) topology. L4 as terminal ligands coordinate to metal centers in a tridentate mode, and the m-BDC anion coordinates to metal to generate an infinite chain, which is linked by π 3 3 3 π interactions, giving a 2D supramolecular layer in 4. Each L52- ligand shows a bis(monodentate) and bis(bidentate) coordination mode and connects four CdII cations to generate a PtS topological net in 5. Compounds 6 and 7 are isostructural and show 3D supramolecular nets constructed through π 3 3 3 π interactions between adjacent layers formed by L62and metal centers. By careful inspection of the structures of 1-7, we believe that the different lengths and substituent groups of Ndonor ligands adopting various coordination modes are crucial factors for the formation of the different structures. The photoluminescent properties of L1-H2L6 and 1-7 have been studied in the solid state at room temperature.

Introduction Current interest in coordination polymers on the basis of the assembly of metal ions and multifunctional organic ligands is rapidly expanding owing to their intriguing architectures and potential applications, although rational design and synthesis of metal-organic frameworks (MOFs) with unique structures and functions still remain a long-term challenge.1 The rational design of prospective structures with specific properties can be constructed based on a careful selection of the properties of the ligands, such as shape, functionality, flexibility, symmetry, length, and substituent group.2 The nitrogen-donor ligands have been intensely investigated for the construction of novel MOFs, and the use of nitrogen-donor ligands is an effective method because they can satisfy and even mediate the coordination needs of the metal centers and consequently generate more meaningful architectures.3 Benzimidazole is a typical heterocyclic ligand with nitrogen as the donor atom. It exhibits a wide variety of pharmacological activities like fungicides or anti-helminthics among others.4 Because of this, the coordination chemistry of related ligands has been the subject of numerous investigations.4,5 *Corresponding author. E-mail: [email protected]. r 2010 American Chemical Society

On the other hand, the rigid ligands (4,40 -bipyridine,6 pyrazine,7 etc.) have been extensively employed in the construction of a rich variety of intriguing architectures. However, there are an increasing number of recently characterized interesting interwoven frames incorporating flexible ligands.8 Systematic investigation of the influence of the substituent groups of N-donor ligands on the formation of coordination frameworks is scarce so far. Here we select neutral ligands 1,4-di(1H-benzo[d]imidazol2-yl)butane (L1) and bis((1H-benzo[d]imidazol-2-yl)methyl)amine (L2) by using -(CH2)4- and -(CH2NHCH2)- groups connecting two benzoimidazole based on the following consideration: The two benzoimidazole can freely twist around the -(CH2)4- and -(CH2NHCH2)- groups to meet the requirements of the coordination geometries of metal atoms in the assembly process. And conformational changes of flexible ligands generate the different but often related network architecture and can more easily produce these new classes of compounds. In order to systematically investigate the influence of the substituent groups of N-donor ligands on the formation of coordination frameworks, we focus our attention on a series of nitrogenous ligands and design four new N-donor ligands with different substituent groups. So L1-H2L6 (Chart S1, Supporting Information) with different substituent groups Published on Web 02/04/2010

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can display various coordination modes with two N atoms from 2-(2-pyridyl)imidazole and N and/or O atoms from substituent groups. The hindrance and competition among these functional groups can result in novel multidimensional frameworks. Experimental Section General Procedures. Chemicals were purchased from commercial sources and used without further purification. Ligands L1, L2, and L3 were prepared according to the literature.9 Synthesis of Bis((1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2yl)methyl)amine (L4). A mixture of L2 (13.85 g, 50 mmol) and NaOH (8.00 g, 200 mmol) in DMSO (40 mL) was stirred at 5 C for 2 h, and then 4-(chloromethyl)pyridine hydrochloride (16.30 g, 100 mmol) was added. The mixture was cooled to room temperature after stirring at 50 C for 24 h, and then poured into 200 mL of water. A yellow solid of L4 formed immediately, which was isolated by filtration in 81% yield after drying in air. Anal. Calcd for C28H25N7(459.55): C, 73.18; H, 5.48; N, 21.34. Found: C, 72.98; H, 5.58; N, 21.30%. MS(ESI) m/z 460[(M þ 1)]þ. Synthesis of 4,40 -(2,20 -(Butane-1,4-diyl)bis(1H-benzo[d]imidazole2,1-diyl))bis(methylene)dibenzoic acid (H2L5). A mixture of L1 (14.50 g, 50 mmol) and NaOH (2.00 g, 50 mmol) in DMSO (20 mL) was stirred at 5 C for 2 h, and then 4-(chloromethyl)benzonitrile (15.10 g, 100 mmol) was added. The mixture was cooled to room temperature after stirring at 50 C for 24 h, and then poured into 200 mL of water. A yellow solid of 4,40 -(2,20 -(butane-1,4diyl)bis(1H-benzo[d]imidazole-2,1-diyl))bis(methylene)dibenzonitrile formed immediately, which was isolated by filtration in 86% yield after drying in air. A mixture of 4,40 -(2,20 -(butane-1,4-diyl)bis(1H-benzo[d]imidazole-2,1-diyl))bis(methylene)dibenzonitrile (26.03 g, 50 mmol) and KOH (11.20 g, 200 mmol) in H2O (200 mL) was stirred at 100 C for 15 h, and was cooled to room temperature. Then the mixture was adjusted to pH ≈ 5 with HCl (1.0 mol 3 L-1), and a white solid of 4,40 -(2,20 -(butane-1,4-diyl)bis(1H-benzo[d]imidazole-2,1-diyl))bis(methylene)dibenzoic acid (H2L5) formed immediately, which was isolated by filtration in 57% yield after drying in air. Anal. Calcd for C34H30N4O4(558.62): C, 73.10; H, 5.41; N, 10.03. Found: C, 73.25; H, 5.48; N, 9.99%. MS(ESI) m/z 559[(M þ 1)]þ. Synthesis of 2,20 -(2,20 -Azanediylbis(methylene)bis(1H-benzo[d]imidazole-2,1-diyl))diacetic acid (H2L6). A mixture of L2 (13.85 g, 50 mmol) and NaOH (2.00 g, 50 mmol) in DMSO (20 mL) was stirred at 5 C for 2 h, and then methyl 2-chloroacetate (10.80 g, 100 mmol) was added. The mixture was cooled to room temperature after stirring at 50 C for 24 h, and then poured into 200 mL of water. A yellow solid of dimethyl 2,20 -(2,20 -azanediylbis(methylene)bis(1H-benzo[d]imidazole-2,1-diyl))diacetate formed immediately, which was isolated by filtration in 76% yield after drying in air. A mixture of 2,20 -(2,20 -azanediylbis(methylene)bis(1H-benzo[d]imidazole-2,1-diyl))diacetate (21.06 g, 50 mmol) and KOH (11.20 g, 200 mmol) in H2O (200 mL) was stirred at 100 C for 15 h, and was cooled to room temperature. Then the mixture was adjusted to pH ≈ 5 with HCl (1.0 mol 3 L-1), and a white solid of 2,20 -(2,20 -azanediylbis(methylene)bis(1H-benzo[d]imidazole-2,1-diyl))diacetic acid (H2L6) formed immediately, which was isolated by filtration in 63% yield after drying in air. Anal. Calcd for C20H19N5O4(393.40): C, 61.06; H, 4.87; N, 17.80. Found: C, 60.99; H, 4.88; N, 17.99%. MS(ESI) m/z 376[(M - 17)]þ. Synthesis of [Cd2(ODPT)(L1)(H2O)2] 3 H2O (1). A mixture of ODPTA (0.16 g, 0.50 mmol), L1 (0.15 g, 0.5 mmol), Cd(OAc)2 3 2H2O (0.27 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless steel container. The container was heated to 150 C and held at that temperature for 72 h, then cooled to 100 C at a rate of 5 C 3 h-1, and held for 8 h, followed by further cooling to 30 C at a rate of 3 C 3 h-1. Colorless crystals of 1 were collected in 69.4% yield based on Cd(OAc)2 3 2H2O. Anal. Calcd for C25H21Cd2N2O12 (766.24): C, 39.19; H, 2.76; N, 3.66. Found: C, 38.89; H, 2.88; N, 3.70%. IR (cm-1): 3433 (s), 3069 (m), 1555 (s), 1376 (s), 1267 (s), 1227 (s), 1144 (m), 1074 (w), 1012 (m), 968 (m), 837 (m), 768 (w), 657 (w), 616 (w).

Li et al. Synthesis of [Cd2(ODPT)(L2)(H2O)2] (2). A mixture of ODPTA (0.16 g, 0.50 mmol), L2 (0.14 g, 0.5 mmol), Cd(OAc)2 3 2H2O (0.27 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless steel container. The container was heated to 150 C and held at that temperature for 72 h, then cooled to 100 C at a rate of 5 C 3 h-1, and held for 8 h, followed by further cooling to 30 C at a rate of 3 C 3 h-1. Colorless crystals of 2 were collected in 62.7% yield based on Cd(OAc)2 3 2H2O. Anal. Calcd for C32H23Cd2N5O10 (862.35): C, 44.57; H, 2.69; N, 8.12. Found: C, 44.57; H, 2.76; N, 8.01%. IR (cm-1): 3065 (m), 1533 (s), 1403 (s), 1266 (s), 1227 (s), 1143 (m), 1074 (w), 967 (w), 836 (m), 793 (m),745 (w), 654 (w). Synthesis of [Zn2(BPTC)(L3)] 3 (H2O)3 (3). A mixture of 3,30 ,4,40 benzophenone tetracarboxylic dianhydride (BPTA) (0.16 g, 0.50 mmol), L3 (0.24 g, 0.50 mmol), Zn(OAc)2 3 2H2O (0.22 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless steel container. The container was heated to 150 C and held at that temperature for 72 h, then cooled to 100 C at a rate of 5 C 3 h-1, and held for 8 h, followed by further cooling to 30 C at a rate of 3 C 3 h-1. Colorless crystals of 3 were collected in 56.2% yield based on Zn(OAc)2 3 2H2O. Anal. Calcd for C47H40N6O12Zn2 (1011.59): C, 55.80; H, 3.89; N, 8.31. Found: C, 55.69; H, 4.00; N, 8.35%. IR (cm-1): 3413 (s), 1546 (s), 1410 (s), 1261 (s), 1226 (s), 1141 (m), 1073 (w), 965 (w), 891 (w), 841 (m), 786 (m), 667 (w), 618 (w). Synthesis of [Cd(m-BDC)(L4)] (4). A mixture of 3,30 ,4,40 -benzophenone tetracarboxylic dianhydride (0.16 g, 0.50 mmol), L4 (0.23 g, 0.50 mmol), Cd(OAc)2 3 2H2O (0.27 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless steel container. The container was heated to 150 C and held at that temperature for 72 h, then cooled to 100 C at a rate of 5 C 3 h-1, and held for 8 h, followed by further cooling to 30 C at a rate of 3 C 3 h-1. Colorless crystals of 4 were collected in 61.8% yield based on Cd(OAc)2 3 2H2O. Anal. Calcd for C36H29CdN7O4 (736.06): C, 58.74; H, 3.97; N, 13.32. Found: C, 58.71; H, 4.01; N, 13.22%. IR (cm-1): 3377 (s), 1605 (s), 1544 (s), 1477 (m), 1379 (s), 1160 (m), 1077 (w), 833 (w), 741 (m), 659 (w). Synthesis of [CdL5] (5). A mixture of ODPTA (0.16 g, 0.50 mmol) or 3,30 ,4,40 -benzophenone tetracarboxylic dianhydride (0.16 g, 0.50 mmol), H2L5 (0.28 g, 0.5 mmol), Cd(OAc)2 3 2H2O (0.27 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless steel container. The container was heated to 150 C and held at that temperature for 72 h, then cooled to 100 C at a rate of 5 C 3 h-1, and held for 8 h, followed by further cooling to 30 C at a rate of 3 C 3 h-1. Colorless crystals of 5 were collected in 55.3% yield based on Cd(OAc)2 3 2H2O. Anal. Calcd for C34H28CdN4O4 (669.00): C, 61.03; H, 4.22; N, 8.37. Found: C, 61.12; H, 4.19; N, 8.47%. IR (cm-1): 3342 (m), 1651 (s), 1542 (m), 1457 (s), 1406 (m), 1290 (s), 1247 (m), 1155 (w), 1013 (m), 949 (w), 741 (w). Synthesis of [CdL6] 3 H2O (6). A mixture of ODPTA (0.16 g, 0.50 mmol) or 3,30 ,4,40 -benzophenone tetracarboxylic dianhydride (0.16 g, 0.50 mmol), H2L6 (0.18 g, 0.5 mmol), Cd(OAc)2 3 2H2O (0.27 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless steel container. The container was heated to 150 C and held at that temperature for 72 h, then cooled to 100 C at a rate of 5 C 3 h-1, and held for 8 h, followed by further cooling to 30 C at a rate of 3 C 3 h-1. Colorless crystals of 6 were collected in 86.3% yield based on Cd(OAc)2 3 2H2O. Anal. Calcd for C20H14CdN5O5 (516.76): C, 46.48; H, 2.73; N, 13.55. Found: C, 46.55; H, 2.66; N, 13.46%. IR (cm-1): 3442 (m), 1620 (s), 1597 (s), 1478 (s), 1388 (m), 1297 (s), 1211 (s), 1140 (w), 988 (m), 898 (w), 845 (w), 759 (m), 678 (w). Synthesis of [ZnL6] 3 H2O (7). A mixture of ODPTA (0.16 g, 0.50 mmol) or 3,30 ,4,40 -benzophenone tetracarboxylic dianhydride (0.16 g, 0.50 mmol), H2L6 (0.18 g, 0.5 mmol), Zn(OAc)2 3 2H2O (0.22 g, 1.00 mmol), NaOH (0.08 g, 2.00 mmol), and H2O (10 mL) was stirred for 1 h and then sealed in a 25 mL Teflon-lined stainless steel container. The container was heated to 150 C and held at that temperature for 72 h, then cooled to 100 C at a rate of 5 C 3 h-1, and held for 8 h, followed by further cooling to 30 C at a rate of 3 C 3 h-1. Colorless crystals of 7 were collected in 49.3% yield based on Zn(OAc)2 3 2H2O. Anal. Calcd for C20H14N5O5Zn (469.73): C,

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Table 1. Crystal Data and Structure Refinements for Compounds 1-7 formula fw crystal system space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z Dcalcd [g cm-3] F(000) reflns collected/unique R(int) GOF on F2 R1a [I > 2σ(I)] wR2b largest residuals [e A˚-3]

formula fw crystal system space group a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z Dcalcd [g cm-3] F(000) reflns collected /unique R(int) GOF on F2 R1a [I > 2σ(I)] wR2b largest residuals [e A˚-3] a

1

2

3

C25H21Cd2N2O12 766.24 monoclinic P21/n 13.7370(2) 7.9310(4) 24.0220(7) 90 105.9590(10) 90 2516.28(15) 4 2.023 1508 16118/6830

C32H23Cd2N5O10 862.35 monoclinic P21/c 14.2375(18) 27.810(3) 7.6786(9) 90 100.399(2) 90 2990.4(6) 4 1.915 1704 14936/5273

C47H40N6O12Zn2 1011.59 monoclinic C2 11.218(2) 15.927(3) 12.965(3) 90 111.176(3) 90 2160.0(8) 2 1.555 1040 6086/4261

0.0282 1.032 0.0322 0.0677 0.756/-0.725

0.0670 1.042 0.0574 0.1311 1.371/-0.836

0.0511 1.008 0.0627 0.1591 0.942/-0.692

4

5

6

7

C36H29CdN7O4 736.06 monoclinic P21/n 8.0970(6) 20.4110(15) 19.5330(16) 90 99.436(2) 90 3184.5(4) 4 1.535 1496 19107/7468

C34H28CdN4O4 669.00 monoclinic C2/c 16.8292(8) 14.5542(8) 16.0123(9) 90 114.4320(10) 90 3570.8(3) 4 1.244 1360 8806/3154

C20H14CdN5O5 516.76 monoclinic C2/c 12.248(2) 10.340(2) 16.856(4) 90 95.295(5) 90 2125.6(8) 4 1.615 1028 6275/2455

C20H14N5O5Zn 469.73 monoclinic C2/c 11.1050(13) 10.179(3) 17.959(3) 90 92.532(3) 90 2028.1(7) 4 1.538 956 5995/2365

0.0451 1.008 0.0460 0.0866 0.443/-0.512

0.0348 1.006 0.0508 0.1280 0.796/-0.279

0.0977 0.954 0.0690 0.1644 0.968/-0.758

0.0649 0.944 0.0576 0.1334 0.619/-0.442

R1 = Σ||Fo| - |Fc||/Σ|Fo|. b wR2 = |Σw(|Fo|2 - |Fc|2)|/Σ|w(Fo2)2|1/2.

51.13; H, 3.00; N, 14.91. Found: C, 51.20; H, 3.09; N, 15.01%. IR (cm-1): 3414 (m), 1626 (s), 1521 (s), 1459 (s), 1388 (m), 1154 (s), 986 (s), 755 (w), 626 (m). Physical Measurements. The C, H, and N elemental analysis was conducted on a Perkin-Elmer 240C elemental analyzer. The FT-IR spectra were recorded from KBr pellets in the range 4000-400 cm-1 on a Mattson Alpha-Centauri spectrometer. Thermogravimetric analysis (TGA) was performed on a Perkin-Elmer TG-7 analyzer heated from 35 to 600 C under nitrogen. The emission/excitation spectra were recorded on a Varian Cary Eclipse spectrometer. X-ray Crystallography. Single-crystal X-ray diffraction data for compounds 1-7 were recorded on a Bruker Apex CCD diffractometer with graphite-monochromated MoKR radiation (λ = 0.71073 A˚) at 293 K. Absorption corrections were applied using multiscan technique. All the structures were solved by Direct Method of SHELXS-9710 and refined by full-matrix least-squares techniques using the SHELXL-97 program11 within WINGX.12 Non-hydrogen atoms were refined with anisotropic temperature parameters. The hydrogen atoms of the organic ligands were refined as rigid groups. H atoms of water molecules were located from different Fourier maps. The detailed crystallographic data and structure refinement parameters for 1-7 are summarized in Table 1. Structure Description of 1. As shown in Figure 1a, there are two kinds of CdII cations and one kind of L1 ligand and ODPT4- anion in the structure. Cd1 is coordinated by five carboxylate oxygen

atoms from four ODPT4- anions and one water molecule, showing a distorted {CdO6} octahedral coordination geometry. Cd2 cation shows a distorted {CdNO4} square pyramid coordination geometry which is coordinated by one nitrogen atom from one L1 ligand, three carboxylate oxygen atoms from different ODPT4- anions, and one water molecule. The Cd-O and Cd-N distances are quite similar to normal Cd-O and Cd-N distances.13 One kind of phthalate group of ODPT4- links CdII cations to form a Cd-O helical chain. And the adjacent chains are connected by L1 ligand (Chart 1a) and the other kind of phthalate group to form a 2D layer. These layers are further connected by ether O atoms of ODPT4anions to generate a 3D network. If each ODPT4- anion is considered as a four-connected node, and two kinds of CdII cations are considered as a five-connected node, the framework of compound 1 can be classified as a (42 3 52 3 62)(42 3 52 3 64 3 72) topology. Water clusters have been widely studied both theoretically and experimentally.14 A variety of water clusters, [(H2O)n, n = 2-18] found in a number of crystal hosts, have been characterized and display different configurations. Water molecules in 1 assemble themselves to form a hydrogen-bonded water trimer. As shown in Figure 1e, the water trimer consists of three water molecules with OW 3 3 3 OW distances of 2.829(5) and 2.779(5) A˚ (Table 2). Two coordinated water molecules O2W and O3W donate hydrogen bonds to lattice O1W which in turn donates a hydrogen bond to one carboxylate oxygen atom to form a hydrogen-bonded water trimer which is connected by carboxylate oxygen atom (O4) to

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Figure 1. (a) ORTEP diagram of the coordination environments for CdII atoms in 1. (b) View of a 2D sheet of 1 formed by CdII, L1 and phthalate groups of ODPT4- anions (blue and black balls showing two kinds of L1 ligands and red balls showing phthalate groups of ODPT4anions, respectively). (c) Ball-and-stick representation of 3D structure of 1 (green balls showing two kinds of L1 ligands and blue and red balls showing phthalate groups of ODPT4- anions in different layers, respectively). (d) Schematic view of the topological structure of 1 (blue and purple balls showing five and four connected nodes, respectively). (e) Water cluster in 1. generate a hydrogen-bonding chain. These hydrogen bonding interactions stabilize the 3D framework. Structure Description of 2. If the shorter connector with another coordinated node is selected instead of the -(CH2)4- group, L2 is used in the same condition with compound 1 showing a different structural type. In 2, there are two kinds of CdII cations, one kind of L2 ligand and ODPT4- anion. Cd1 shows an octahedral coordination geometry which is surrounded by three nitrogen atoms from one L2 ligand and three carboxylate oxygen atoms from different ODPT4- anions, while Cd2 is coordinated by six carboxylate oxygen atoms from four ODPT4- anions and one water molecule, showing a pentagonal bipyramidal coordinated geometry (Figure 2). Two kinds of phthalate groups of ODPT4- anions link all CdII cations to generate an interesting 2D layer, which includes a [CdII]2 unit. These 2D layers are connected by ether O atoms of ODPT4anions to generate a 3D network. Each L2 ligand (Chart 1b) coordinates to Cd1 with two imidazole nitrogen atoms and one

imine nitrogen atom as a terminal ligand. To further analyze the 3D structure, if the [CdII]2 unit and ODPT4- anion are considered as five and six connected nodes, the structure of 2 shows a (45 3 65)(47 3 68) topological type. In addition, coordinated water molecule and nitrogen atoms from imidazole groups donate hydrogen bonds to adjacent carboxylate oxygen atoms, which stabilize the 3D structure. Structure Description of 3. The asymmetric unit of 3 consists of one kind of ZnII cation, L3 ligand and BPTC4- ligand. As shown in Figure 3a, the Zn1 cation is a distorted tetrahedral coordination geometry {ZnN2O2} with two nitrogen atoms (Zn1-N 2.007(11) and 2.056(5) A˚) from two L3 ligands and two carboxylic oxygen atoms (Zn1-O 1.913(5) and 1.922(5) A˚) from different BPTC4ligands. The Zn-O and Zn-N bond lengths are all within the normal ranges.15 The BPTC4- ligand exhibits a quadri(monodentate) coordination mode. So BPTC4- ligands link Zn1 and Zn2 cations to generate a right-handed helical chain. L3 ligands

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show quadri-(monodentate) coordination mode (Chart 1c) and connect Zn cations from helical chains to extend to a 3D open framework. From the topological view, if the ZnII cation, each BPTC4- ligand, and L3 ligand are considered as three kinds of four-connected nodes, compound 3 shows a (43 3 83)2(42 3 84)(4 3 85) topology. In addition, one lattice water molecule O2W donates two hydrogen bonds to two O1W which in turn donates two hydrogen bonds to two carboxylate oxygen atoms to form a hydrogen-bonded water trimer. These hydrogen bonding interactions stabilize the lattice water molecules in the 3D framework. It is interesting that compound 3 is a chiral structure. To further investigate the reason, it may be that each ZnII cation is coordinated by two nitrogen atoms and two carboxylate oxygen atoms with different distances, which corresponds to a chiral center. And ZnBPTC helical chains transfer the chirality to the whole framework.

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Structure Description of 4. Similar to L3, when the pyridyl group is decorated to L2, a new nitrogen ligand (L4) is obtained. And the interesting 2D supromolecular structure of 4 has been synthesized by using L4, CdII, and m-BDC anion. Single-crystal X-ray diffraction reveals that compound 4 has a chainlike structure consisting of one CdII atom, L4 ligand, and one m-BDC anion. The crystallographically unique CdII atom is six coordinated by three nitrogen

Chart 1. The Coordination Modes of Six Kinds of Ligands

Figure 2. (a) ORTEP diagram of the coordination environments for CdII atoms in 2. (b) Ball-and-stick representation of a 2D layer formed by CdII and phthalate groups of ODPT4- anions. (c) Balland-stick representation of 3D structure of CdII and ODPT4anions. (d) Ball-and-stick and space filling representations of the 3D structure of 2. (e) Schematic view of the topological structure of 2 (blue and purple balls showing five and six connected nodes [CdII]2 and ODPT4- anions, respectively). Table 2. Hydrogen Bonds for mm [A and deg]a D-H 3 3 3 A Compound 1 O(1W)-H(1A) 3 3 3 O(7) O(2W)-H(2A) 3 3 3 O(1W)#5 O(2W)-H(2B) 3 3 3 O(4)#6 O(3W)-H(3A) 3 3 3 O(4)#5 N(2)-H(2N) 3 3 3 O(2)#4 O(3W)-H(3B) 3 3 3 O(1W)#5 Compound 2 O(1W)-H(1B) 3 3 3 O(8)#2 O(1W)-H(1A) 3 3 3 O(8)#8 N(4)-H(4A) 3 3 3 O(7)#9 N(5)-H(5) 3 3 3 O(6)#10 Compound 5 O(1W)-H(1A) 3 3 3 O(1)#1 O(2W)-H(2B) 3 3 3 O(1W)#5 O(2W)-H(2B) 3 3 3 O(1W)#6 O(1W)-H(1B) 3 3 3 O(3)

d(D-H)

d(H 3 3 3 A)

d(D 3 3 3 A)

— (DHA)

0.85(3) 0.85(3) 0.85(4) 0.85(2) 0.86 0.86(3)

1.91(3) 2.28(5) 2.06(4) 2.06(2) 1.99 1.954(18)

2.749(4) 2.829(5) 2.875(4) 2.848(4) 2.806(3) 2.779(5)

169(6) 123(5) 164(5) 155(5) 158.9 163(6)

0.851(10) 0.851(11) 0.86 0.86

2.00(6) 1.88(3) 2.22 2.02

2.786(9) 2.716(7) 2.932(9) 2.857(9)

153(13) 168(10) 140.2 163.5

0.85(16) 0.851(9) 0.851(9) 0.85(7)

2.4(2) 2.299(13) 2.299(13) 2.3(3)

2.930(11) 2.886(15) 2.886(15) 2.884(13)

121(21) 126.4(4) 126.4(4) 124.00

a Symmetry transformations used to generate equivalent atoms: for 1: #1 -x þ 1/2, y þ 1/2, -z þ 1/2; #2 -x þ 1, -y, -z þ 1; #3 -x, -y, -z þ 1; #4 -x þ 1, -y þ 1, -z þ 1; #5 -x þ 1/2, y - 1/2, -z þ 1/2; #6 x, y - 1, z; for 2: #1 x þ 1, y, z þ 1; #2 x þ 1, y, z; #3 -x þ 1, -y þ 1, -z þ 2; #4 x, -y þ 3/2, z þ 1/2; #5 x, -y þ 3/2, z - 1/2; #6 x - 1, y, z; #7 x - 1, y, z - 1; #8 -x, -y þ 1, -z þ 1; #9 x þ 1, -y þ 3/2, z þ 1/2; #10 -x, y þ 1/2, -z þ 3/2; for 5: #1 -x þ 1, y, -z þ 1; #2 x - 1/2, y þ 1/2, z; #3 -x þ 1, y, -z þ 2; #4 x þ 1/2, y - 1/2, z; #5 x, y - 1, z; #6 -x þ 1, y - 1, -z þ 1.

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Figure 3. (a) ORTEP diagram of the coordination environments for ZnII atoms in 3. (b) Ball-and-stick representation of a 1D helical chain formed by ZnII and BPTC4- anions. (c) Ball-and-stick representation of 3D structure of 3. (d) Schematic view of the topological structure of 3 (green, purple, and blue balls showing three kinds of four connected nodes ZnII, BPTC4-, and L3, respectively). (e) Water cluster in 3.

Figure 4. (a) ORTEP diagram of the coordination environments for CdII atoms in 4. (b) Ball-and-stick representation of a 1D chain of 4. (c) Ball-and-stick representation of 2D supromolecular structure. atoms from one L4 ligand, and three carboxylate oxygen atoms from two distinct m-BDC anions, showing a distorted octahedral geometry (Figure 4). All L4 as terminal ligands (Chart 1d) coordinate to metal centers in a tridentate mode. The m-BDC anion coordinates to metal in a bis-monodentate fashion to generate an

infinite chain. All chains are parallel in the structure. Adjacent chains are linked by π 3 3 3 π interactions16 between phenyl and pyridyl rings, and phenyl and phenyl rings with the mean centroid-centroid distances of 3.740, 3.740, and 3.488 A˚, and the mean plane-plane distances of 3.462, 3.548, and 3.395 A˚, respectively, giving a 2D supramolecular layer. Structure Description of 5. The asymmetric unit of 5 is shown in Figure 5a, which consists of one kind of CdII cation and one kind of L5- anion, respectively. Each Cd1 center is in a distorted octahedral coordination geometry which is completed by four carboxylate oxygen atoms (Cd-O = 2.285(4) and 2.432(4) A˚) from two L5anions and two nitrogen atoms (Cd-N = 2.266(4) A˚) from different L5- ligands. Each L5- ligand shows a bis(monodentate) and bis(bidentate) coordination mode (Chart 1e) and connects CdII cations with nitrogen atoms to generate a chain, which is further linked by carboxylate atoms coordinating to CdII atoms to form a 3D framework. From the topological view, if each CdII cation and L5- ligand are considered as two kinds of four-connected nodes, compound 5 shows a PtS (4284) topological net.17 Structure Description of 6. When H2L5 is replaced by H2L6, a particularly fascinating 3D supramolecular structure of 6 is obtained. As shown in Figure 6a, the structure of 6 contains one kind of CdII atom and one kind of unique L62- ligand. Cd1 is five coordinated by three nitrogen atoms from one L62- anion and two carboxylate oxygen atoms from different L62- anions, showing a distorted square pyramidal coordination geometry. Each L62- anion (Chart 1f) links two CdII cations with carboxylate groups to generate a 1D chain, and connects another CdII cation to form a 2D layer. Adjacent layers are linked by π 3 3 3 π interactions between phenyl and imidazole rings, and phenyl and phenyl rings with the mean centroid-centroid distances of 3.728 and 3.556 A˚, and the mean plane-plane distances of 3.372 and 3.388 A˚, respectively, giving a 3D supramolecular net. Structure Description of 7. Compound 7 is isostructural with 6 by only using ZnII ions instead of CdII ions (Figure S1, Supporting Information). Syntheses of the Compounds. As is well-known, the reactions of metal ions with carboxylates and/or neutral ligands in aqueous solution often result in the formation of insoluble substances, presumably because of the fast coordination of them to form

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Figure 5. (a) ORTEP diagram of the coordination environments for CdII atoms in 5. (b) Ball-and-stick representation of a 1D helical chain formed by CdII and L5- anions. (c) Ball-and-stick representation of 3D structure of 5. (d) Schematic view of the topological structure of 5 (green and purple balls showing two kinds of four connected nodes CdII and L5-, respectively).

Figure 6. (a) ORTEP diagram of the coordination environments for CdII atoms in 6. (b) Ball-and-stick representation of a 1D chain formed by CdII and L8- anions. (c) Ball-and-stick representation of 2D structure of 6. (d) Ball-and-stick representation of 3D supromolecular structure of 6. polymeric structures. In this paper, solvothermal synthesis has been used to synthesize the compounds. All compounds are stable in air and are insoluble in common solvents such as ethanol, benzene, acetone, and acetonitrile. From the structural descriptions above (Scheme 1), it can be seen that the N-donor ligands have a great influence on the frameworks

of the complexes. Because of their structural features, the linkers in L1, L3, and L52- are -(CH2)4- which is longer than that in L2, L4, and L62- (-(CH2-NH-CH2)-). So L1, L3, and L52- show TTT (T = trans) conformation and the distances of two N atoms of benzoimidazole groups coordinating metal centers are 8.193 A˚ for L1 in 1, 7.677 A˚ for L3 in 3, and 7.808 A˚ for L52- in 5, respectively.

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Scheme 1. View of Seven Compounds in This Work

Table 3. The Wavelengths of the Emission Maxima and Excitation (nm) ligand

L1

L2

L3

L4

H2L5

H2L6

λem λex

303 260

472 374

528 450

504 440

396 347

540 390

compound λem λex

1

2

3

4

5

6

7

416 340

450, 495 363

428 355

471, 497 409

458 376

466, 500 435

453, 481 420

Figure 7. Solid-state photoluminescent spectra of 1-7 at room temperature. L2, L4, and L62- show TT conformation and the distances of two N atoms of benzoimidazole groups coordinating metal centers are 4.347 A˚ for L2 in 2, 4.356 A˚ for L4 in 4, and 4.293 A˚ and 4.124 A˚ for L62- in 6 and 7, respectively. The linkers with different lengths play an important role in affecting the final structures. The shorter distances of two N atoms of benzoimidazole groups coordinating metal centers in L2, L4, and L62- benefit for chelating one metal center, and the similar tridentate coordination modes are shown, while L1, L3, and L52- with the longer linkers coordinate multi metal centers showing bis(monodentate) or quadric(monodentate) coordination modes. Because of the different coordination behaviors of L1-L62-, it is anticipated that the structures of 1-7 are various. Although L1, L3, and H2L5 ligands have similar lengths, the changes in the substituent groups can result in changes in the final frameworks for 1, 3, and 5. For L1 without a substituent group, it coordinates to two metal centers. And L3 with two pyridine groups can link four metal centers. Tetracarboxylate ligands and neutral ligands L1 or L3 connect metal centers to form different 3D frameworks of 1 and 3, while in 5, each L52- ligand links four metal centers to give an interesting 3D net of 5. L52- acts as not only an N-donor ligand but also a counteranion instead of other carboxylate ligands, although different tetracarboxylate ligands are introduced. L2, L4, and L62- ligands have similar lengths; the changes in the substituent groups can result in changes in the final frameworks for 2, 4, 6, and 7. In 2, tetracarboxylate ligand links metal centers to form a 3D framework, and L2 acts as a terminal ligand. Although L4 is decorated by pyridine groups, the pyridine group does not coordinate to metal centers and acts as a terminal ligand in 4. The

pyridine groups of L4 ligand show intermolecular π 3 3 3 π interaction. So compound 4 shows a 2D supramolecular structure. In 6 and 7, L62- acts as not only an N-donor ligand but also a counteranion, which is similar to L52- in 5. The six kinds of ligands with different long characters and substituent groups adopt various coordination modes and conformations. They also have a significant effect on the structures of the coordination polymers. It is possible to introduce ancillary ligands to construct coordination polymers of different structural types. Luminescent Properties. Luminescent compounds are of great current interest because of their various applications in chemical sensors, photochemistry, and electroluminescent display.18 The luminescent properties of zinc and cadmium carboxylate compounds have been investigated.19 The main emission peaks of L1-H2L6 being attributed to the π*/π and/or π*/n transition (Figure S2, Supporting Information) and compounds 1-7 (Figure 7) are listed in the Table 3, respectively. The carboxylate ligands mH2BDC (λem=370 nm), ODPTA (λem=406 nm), and 3,30 ,4,40 -benzophenone tetracarboxylic dianhydride (λem = 557 nm) can also exhibit fluorescence at room temperature. The emission bands of these carboxylate ligands can be assigned to the π*/n transition as previously reported.20 In comparison with the N-donor ligands and multicarboxylate ligand, the emission maxima of compounds 1-7 have changed. For compound 1, the emission maximum for compound 1 exhibits a shift (10 nm) with respect to the free multicarboxylate ligands, which may be assigned to the intraligand fluorescent emission of multicarboxylate ligands. The emission maxima for the compounds 2-7 may be attributed to a joint contribution of the intraligand transitions and/or charge transfer transitions between the coordinated ligands and the metal center. Thermal Analysis. In order to characterize the compounds more fully in terms of thermal stability, their thermal behaviors were studied by TGA. The experiments were performed on samples consisting of numerous single crystals of 1-7 under N2 atmosphere with a heating rate of 10 C/min. As shown in Figure S3, Supporting Information. The TGA curve of 1 shows that it loses the water molecules from room temperature to 135 C (obsd 6.7%, calcd 7.1%), and then the anhydrous compound begin to decompose, leading to the formation of CdO as the residue (obsd 33.9%, calcd 33.5%). For compounds 2 and 3, the weight loss in the range of 23-123 C for 2 and 18-120 C for 3 corresponds to the departure of water molecules (obsd 4.3%, calcd 4.2% for 2 and obsd 5.4%, calcd 5.3% for 3), the weight losses in the range of 166-413 C for 2 and 172-518 C for 3 correspond to the removal of the corresponding organic components, and the remaining weight corresponds to the formation of CdO (obsd 29.6%, calcd 29.8%) for 2 and ZnO (obsd 16.2%, calcd 16.1%) for 3. For compounds 4 and 5, the weight losses in the range of 176-543 C for 4 and 175-444 C for 5 correspond to the removal

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of the corresponding organic components, and the remaining weight corresponds to the formation of CdO in 4 (obsd 17.3%, calcd 17.5%) and CdO in 5 (obsd 18.7%, calcd 19.2%). For compound 6, the weight loss in the range of 11-128 C corresponds to the departure of lattice water molecules (obsd 3.3%, calcd 3.5%), the weight losses in the range of 211-517 C correspond to the removal of the corresponding organic components, and the remaining weight corresponds to the formation of CdO (obsd 24.3%, calcd 24.9%). The TGA curve of 7 shows that it loses the water molecules from room temperature to 155 C (obsd 3.5%, calcd 3.8%), and then the anhydrous compound begins to decompose, leading to the formation of ZnO as the residue (obsd 17.5%, calcd 17.3%).

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Conclusion In summary, seven novel complexes with different lengths and substituent groups of N-donor ligands have been synthesized under hydrothermal conditions. By careful inspections of these structures, metal cations, carboxylate anions, and Ndonor ligands have a great influence on the construction of different structures in the self-assembly process. Appropriate choices of novel N-donor ligands and multicarboxylate anions may offer new opportunities to construct new types of MOFs in the near future. Acknowledgment. We thank the Program for Changjiang Scholars and Innovative Research Teams in Chinese University, China Postdoctoral Science Foundation, the Specialized Research Fund for the Doctoral Program of Higher Education, the National Natural Science Foundation of China (No. 20901014), the Science Foundation for Young of Jilin Scientific Development Project (Nos. 20090125 and 20090129), the Science Foundation for Young Teachers of NENU (No. 20090407), the Training Fund of NENU’s Scientific Innovation Project (NENU-STC08019), Ph.D. Station Foundation of Ministry of Education for New Teachers (No. 20090043120004), the Postdoctoral Foundation of Northeast Normal University, and the Postdoctoral Foundation of China (No. 20090461029).

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Supporting Information Available: Photoluminescent spectra of L2-H2L6. TGA curves of compounds 1-7. This material is available free of charge via the Internet at http://pubs.acs.org.

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