Three 3D Coordination Polymers Constructed by Cd(II) and Zn(II) with Imidazole-4,5-Dicarboxylate and 4,4′-Bipyridyl Building Blocks Wen-Guan
Lu,†,‡
Long
Jiang,†
Xiao-Long
Feng,†
and Tong-Bu
Lu*,†
School of Chemistry and Chemical Engineering, and Instrumentation Analysis & Research Center, Sun Yat-Sen UniVersity, Guangzhou 510275, China, and Department of Chemistry, Shaoguan UniVersity, Shaoguan, 512005 China
CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 2 564-571
ReceiVed October 4, 2005
ABSTRACT: Three 3D coordination polymers of {(H2bpy)[Cd9(HIDC)4(IDC)4(bpy)4]‚8H2O}n (1), [Zn3(IDC)2(bpy)(H2O)2]n (2), and {[Zn3(IDC)2(bpy)3]‚(bpy)‚8H2O}n (3) (H3IDC ) imidazole-4,5-dicarboxylic acid, bpy ) 4,4′-bipyridyl) were hydrothermally synthesized by controlling the final pH values of the solutions of ca. 6, and characterized by single-crystal X-ray diffraction. In compound 1, unprecedented “double-square” units of [Cd4(µ3-HIDC)2(µ4-IDC)(µ5-IDC)]24- are linked by [Cd(bpy)2]2+ to generate a 1D chain of {[Cd8(µ3-HIDC)4(µ4-IDC)2(µ5-IDC)2]Cd(bpy)2}n2n-, and the 1D chains are further bridged by µ2-bpy to form a 2D brick-wall-like network of {[Cd8(µ3-HIDC)4(µ4-IDC)2(µ5-IDC)2(µ2-bpy)2]Cd(bpy)2}n2n- (≡ [Cd9(HIDC)4(IDC)4(bpy)4]n2n-). Each “brick” contains one protonated bpy ion of H2bpy2+ to get a neutral compound of {(H2bpy)[Cd9(HIDC)4(IDC)4(bpy)4]‚8H2O}n. The adjacent 2D brick walls are perpendicularly packed and interlinked by µ4-IDC3- and µ5-IDC3- bridges to generate a 3D open framework of 1. The species of µ3-HIDC2-, µ4-IDC3-, µ5-IDC3-, H2bpy2+, µ2-bpy, and monodentate bpy coexist in compound 1. Compound 2 consists of 2D wavelike sheets of [Zn3(µ3-IDC)2(H2O)2], which are further linked through µ2-bpy to generate a 3D structure. In 3, the 2D honeycomb-like sheets of [Zn3(IDC)2]n are bridged by µ2-bpy to result in a 3D open framework with hexagonal and tetragonal channels. Compounds 1 and 2 are stable up to 320 and 400 °C, respectively, and display strong blue fluorescent emission at room temperature. Introduction In the past decade, coordination polymers have gained considerable attention due to their attractive structures and promising applications for catalysis, gas storage, magnetic materials, and optoelectronics.1 Recently, increasing investigations have been focused on the constructions of coordination polymers using heterocyclic carboxylic acids such as pyridine-,2 pyrazole-,3 and imidazole-carboxylic acids 4 as building blocks. These building blocks contain multi-oxygen and nitrogen atoms and can coordinate with metal ions in different ways, resulting in the formations of various metal-organic frameworks (MOFs) with specific topologies and useful properties. We are interested in the coordination chemistry of imidazole4,5-dicarboxylic acid (H3IDC), since it can be partially or fully deprotonated to generate H2IDC-, HIDC2-, and IDC3- anions (Scheme 1) at different pH values. Therefore, it can coordinate with metal ions in multi-coordinated ways (Scheme 1) to form a series of MOFs with different structures and interesting topologies and properties.4 Herein we report on the hydrothermal synthesis and structures of three 3D coordination polymers of {(H2bpy)[Cd9(HIDC)4(IDC)4(bpy)4]‚8H2O}n (1), [Zn3(IDC)2(bpy)(H2O)2]n (2), and {[Zn3(IDC)2(bpy)3]‚(bpy)‚8H2O}n (3) (H3IDC ) imidazole-4,5-dicarboxylic acid, bpy ) 4,4′-bipyridyl), which are constructed by cadmium and zinc ions with imidazole-4,5-dicarboxylate and 4,4′-bipyridyl (bpy) building blocks. Experimental Section General Remarks. Imidazole-4,5-dicarboxylic acid (H3IDC) was prepared from benzoimidazole in 65-75% yield. All of other chemicals are commercially available and used without further purification. * Corresponding author.
[email protected]. † Sun Yat-Sen University. ‡ Shaoguan University.
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Elemental analyses were determined using Elementar Vario EL elemental analyzer. The IR spectra were recorded in the 4000-400 cm-1 region using KBr pellets and a Bruker EQUINOX 55 spectrometer. Excitation and emission spectra were recorded on a Shimadzu RF-5301PC fluorescence spectrophotometer, using band pathways of 5 nm excitation and 5 nm emission at room temperature for the solid samples. Thermogravimetric analysis (TG) data were collected on a Netzsch TG-209 instrument under air atmosphere in the temperature range 20-800 °C with a heating rate of 10 °C /min. The variation temperature X-ray powder diffraction (XRPD) measurements were recorded on a RIGAKU D/MAX 2200 VPC diffractometer. {(H2bpy)[Cd9(HIDC)4(IDC)4(bpy)4]‚8H2O}n (1). A mixture of Cd(NO3)2‚4H2O (0.154 g, 0.50 mmol), H3IDC (0.078 g, 0.50 mmol), bpy (0.078 g, 0.50 mmol), pyridine (py, 0.50 mL), and water (10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 180 °C for 3 days, followed by cooling to 100 °C at a rate of 10 °C /h, and held at this temperature for 10 h, then cooled to room temperature. The pH values of the solution before and after reactions are ca. 8 and 6, respectively. Colorless block crystals were collected by hand, washed with distilled water, and dried in air. Yield: 43.8% based on Cd(NO3)2‚ 4H2O. Anal. found: C, 34.47, H, 1.96, N, 11.82%. Calcd for C90H62N26O36Cd9: C, 34.92, H, 2.02, N, 11.76%. IR (KBr, cm-1): 3426 (m), 1602 (vs), 1475 (vs), 1378 (s), 1243 (s), 1107 (m), 805 (m), 664 (w), 630 (w). Compound 1 could also be obtained in various yields under the following hydrothermal conditions: (1) Cd(NO3)2‚4H2O (0.50 mmol) + H3IDC (0.50 mmol) + bpy (0.50 mmol) + py (0.50 mL) + water (10 mL), 150 °C, 3 days; (2) Cd(NO3)2‚4H2O (0.25 mmol) + H3IDC (0.50 mmol) + bpy (0.50 mmol) + py (0.50 mL) + water (10 mL), 180 °C, 3 days; (3) Cd(NO3)2‚4H2O (0.50 mmol) + H3IDC (0.50 mmol) + bpy (1.0 mmol) + py (0.50 mL) + water (10 mL), 180 °C, 3 days; (4) Cd(Ac)2‚2H2O (0.50 mmol) + H3IDC (0.50 mmol) + bpy (1.0 mmol) + py (0.50 mL) + water (10 mL), 180 °C, 3 days; (5) Cd(Ac)2‚2H2O (1.0 mmol) + H3IDC (0.50 mmol) + bpy (1.0 mmol) + py (0.50 mL) + water (10 mL), 180 °C, 3 days; (6) Cd(NO3)2‚4H2O (0.50 mmol) + H3IDC (0.50 mmol) + bpy (0.50 mmol) + water (10 mL), adjusted to pH ) 8 with 1 mol/L NaOH, 180 °C, 3 days; (7) Cd(NO3)2‚4H2O (0.50 mmol) + H3IDC (0.50 mmol) + bpy (0.50 mmol) + NaOH (0.50 mmol) + water (10 mL) 180 °C, 3 days. The yields reacted at 180 °C are higher than that reacted at 150 °C, and the yields using Cd/H3IDC/bpy ) 1:1:1 molar ratio and NaOH to adjust pH value are also higher than those using Cd/H3IDC/bpy ) 1:1:2 or 1:2:2 molar
10.1021/cg0505158 CCC: $33.50 © 2006 American Chemical Society Published on Web 12/09/2005
Coordination Polymers Constructed by Cd(II) and Zn(II)
Crystal Growth & Design, Vol. 6, No. 2, 2006 565 Scheme 1
ratios and pyridine to adjust pH value. In all the cases, the pH values of the solutions before and after reactions are ca. 8 and 6, respectively. [Zn3(IDC)2(bpy)(H2O)2]n (2). A mixture of ZnSO4‚7H2O (0.144 g, 0.50 mmol), H3IDC (0.078 g, 0.50 mmol), bpy (0.078 g, 0.50 mmol), py (0.50 mL), and water (10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 180 °C for 3 days, followed by cooling to 100 °C at a rate of 10 °C /h and held at this temperature for 10 h and then cooled to room temperature. Colorless prism-shaped crystals were collected by hand, washed with distilled water, and dried in air. Yield: 54.0% based on Zn(SO4)2‚7H2O. Anal. found C, 34.41, H, 2.18, N, 12.15%. Calcd for C20H14N6O10Zn3: C, 34.56, H, 2.02, N, 12.10%. IR (KBr, cm-1): 3109 (m), 1621 (vs), 1592 (vs), 1551 (s), 1475 (s), 1425 (s), 1389 (s), 1245 (m), 1106 (m), 1079 (m), 1012 (m), 865 (m), 836 w, 794 (m), 670 (m), 643 (m). This compound could also be obtained in various yields by the hydrothermal reactions of Zn salts, H3IDC, and bpy with the following different molar ratios in 10 mL of water and 0.5 mL of py (or adjust pH value to 8 with NaOH) at 180 °C for 3 days: ZnSO4/IDC/bpy ) 1:0.5:1 (py as a base), Zn(NO3)2/IDC/bpy ) 1:0.5:1 (py as a base), ZnSO4/IDC/bpy ) 1:1:2 (NaOH as a base), and ZnSO4/IDC/bpy ) 1:0.5:1 (NaOH as a base). In all the cases, the starting and final pH values of the solutions are ca. 8 and 6, respectively. {[Zn3(IDC)2(bpy)3]‚(bpy)‚8H2O}n (3). This compound was prepared by a similar procedure to 2 from a mixture of Zn(NO3)2‚6H2O (0.149 g, 0.50 mmol), H3IDC (0.078 g, 0.50 mmol), bpy (0.078 g, 0.50 mmol), py (0.5 mL), and water (6 mL) in low yield. Anal. Calcd for C50H52N12O17Zn3 (3‚H2O): C, 46.58, H, 4.06, N, 13.04%. Found C, 46.19, H, 4.31, N, 13.06%. IR (KBr cm-1): 3410 (m), 3056 (m), 1591 (vs), 1469 (m), 1387 (s), 1246 (m), 1102 (m), 824 (w), 663 (w). Compound 3 could also be obtained in low yields (
