One Chiral and Two Achiral 3-D Coordination Polymers Constructed

DOI: 10.1021/cg100736x

One Chiral and Two Achiral 3-D Coordination Polymers Constructed by 2-Phenyl Imidazole Dicarboxylate

2010, Vol. 10 4050–4059

Wenyue Wang, Xiling Niu, Yongchao Gao, Yanyan Zhu, Gang Li,* Huijie Lu, and Mingsheng Tang Department of Chemistry, Zhengzhou University, Henan 450052, P. R. China Received June 2, 2010; Revised Manuscript Received July 16, 2010

ABSTRACT: Two chiral three-dimensional (3-D) coordination polymers, [Cd4(μ3-HPhIDC)2(μ4-HPhIDC)2(H2O)] (1) and two achiral 3-D coordination polymers, [Mn1.5(μ3-PhIDC)(H2O)3] (2) and [Mn(μ3-HPhIDC)(H2O)]2} (3), have been synthesized by hydro(solvo)thermal reaction, employing 2-phenyl-1H-imidazole-4,5-dicarboxylic acid (H3PhIDC) as organic ligand, and characterized by single-crystal X-ray diffraction, elemental analyses, and IR spectra. Polymer 1 crystallizes in the orthorhombic chiral space group P2(1)2(1)2(1) and exhibits a 3-D framework, in which two-dimensional (2-D) layers are composed of right-handed helices along the b-axis and are further pillared by μ4-HPhIDC2- linkages. Polymer 2 crystallizes in trigonal chiral space group R3 and presents a novel 3-D structure, which is generated from 2-D honeycomb-like layers, containing similar righthanded helical chains along the a or b axes, respectively. Polymer 3 also has a 3-D architecture and is composed of novel 2-D stairlike layers in the bc plane. The theoretical prediction of the phenyl substituent effect of the H3PhIDC ligand has first been presented.

Introduction There is currently much interest in adopting heterocyclic dicarboxylate ligands to prepare intriguing structural metalorganic frameworks (MOFs) with potential applications.1 Particular attention has been paid to the imidazole-4,5-dicarboxylic acid (H3IDC) ligand,2 for its outstanding features of flexible coordination fashions under hydrothermal conditions. Prompted by these interesting findings, people have synthesized three analogue ligands of H3IDC, 2-methyl-1Himidazole-4,5-dicarboxylic acid (H3MIDC), 2-ethyl-1H-imidazole-4,5-dicarboxylic acid (H3EIDC), and 2-propyl-1Himidazole-4,5-dicarboxylic acid (H3PIDC) with methyl, ethyl, or propyl substituents on the 2-position of the imidazole group, to build up novel complexes. There are some reports of MOFs bearing H3MIDC,3 H3EIDC,4 or H3PIDC.5 But, to date, there are no reports concerning the structural factors of the ligands H3MIDC, H3EIDC, or H3PIDC for dominating the self-assembly by theory analysis. More recently, we have given the primary prediction about the ethyl substituent effect in the ligand H3EIDC and reported some interesting results.4a In this paper, we chose another new analogue ligand of H3IDC, 2-phenyl-1H-imidazole-4,5-dicarboxylic acid (H3PhIDC), to prepare novel MOFs. More importantly, we continuously explore useful information about the phenyl substituent effect in the H3PhIDC ligand by quantum-chemical calculation. To the best of our knowledge, the architectures of MOFs or supramolecular compounds constructed from the achiral H3PhIDC ligand have never been reported until now, especially the theoretical prediction of the phenyl substituent effect. Herein, we first report the hydro(solvo)thermal syntheses and structural determinations of one chiral three-dimensional (3-D) coordination polymers, [Cd 4 ( μ 3 -HPhIDC)2 ( μ 4 HPhIDC)2(H2O)] (1) and two achiral 3-D coordination polymers, [Mn1.5(μ3-PhIDC)(H2O)3] (2) and {[Mn(μ3-HPhIDC)*To whom correspondence should be addressed. E-mail: gangli@ zzu.edu.cn. Fax: þ86-371-67766109. pubs.acs.org/crystal

Published on Web 07/30/2010

(H2O)2]} (3) (see Scheme 1), which exhibit various layered and pillared motifs. Single-crystal X-ray diffractions reveal that the H3PhIDC ligand shows various coordination fashions (see Scheme 2) and strong coordination abilities. This is an interesting finding and gives useful guidance in the preparation of novel imidazole dicarboxylate-based MOFs. The thermal properties of the three complexes and solid-state photoluminescent properties of the polymer 1 have been determined as well. Experimental Section Materials. The organic ligand H3PhIDC was prepared according to a literature procedure.6 All the reagents were grade quality obtained from commercial sources and used without further purification. The C, H, and N microanalyses were carried out on a FLASH EA 1112 analyzer. IR spectra were recorded on a Nicolet NEXUS 470-FTIR spectrophotometer as KBr pellets in the 400-4000 cm-1 region. TG-DSC measurements were performed by heating the crystalline sample from 20 to 700 °C at a rate of 10 °C 3 min-1 in air on a Netzsch STA 409PC differential thermal analyzer. The optimized geometries, natural bond orbital (NBO) charge distributions, and energies of the frontier molecular orbitals of the free ligands were given by the GAUSSIAN 03 suite of programs.7 And all calculations were carried out at the B3LYP/ 6-311þþG(d,p) level of theory. Preparation of [Cd4(μ3-HPhIDC)2(μ4-HPhIDC)2(H2O)] (1). A mixture of Cd(NO3)2 3 4H2O (61.2 mg, 0.2 mmol), H3PhIDC (46.3 mg, 0.2 mmol), and CH3CN/H2O (3/4, 7 mL), Et3N (0.056 mL, 0.4 mmol) was sealed in a 25 mL Teflon-lined stainless steel autoclave, heated at 160 °C for 4 days, and then cooled to room temperature. The pH values of the solution before and after reaction were ca. 8 and 6, respectively. The block-shaped buff crystals of 1 were isolated, washed with distilled water, and dried in air (76% yield). Decomposition temperature: 320 °C. Anal. Calcd for C44H26N8O17Cd4: C, 38.76; H, 1.92; N, 8.15. Found: C, 38.46; H, 1.68; N, 7.77. IR (cm-1, KBr): 3574 (w), 1687 (m), 1552 (s), 1466 (s), 1384 (w), 1255 (w), 1121 (s), 996 (w), 853 (w), 788 (m), 731 (m), 545 (w). Preparation of [Mn1.5(μ3-PhIDC)(H2O)3] (2) and {[Mn(μ3-HPhIDC)(H2O)2]} (3). A mixture of MnCl2 3 4H2O (39.6 mg, 0.2 mmol), H3PhIDC (46.3 mg, 0.2 mmol), and CH3CN/H2O (3/4, 7 mL), Et3N (0.056 mL, 0.4 mmol) was sealed in a 25 mL Teflon-lined stainless r 2010 American Chemical Society

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Scheme 1. Syntheses of Polymers 1-3

Scheme 2. Coordination Modes of H3-nPhIDCn- Anions (n = 2 or 3)

steel autoclave, heated at 160 °C for 4 days, and then cooled to room temperature. The initial and final pH values of the reaction mixture were 8 and 6, respectively. Colorless cube-shaped crystals of 2 and colorless club-shaped crystals of 3 were formed simultaneously. Both crystals were of adequate size and quality for X-ray studies and easily separated manually. Polymer 2: (47% yield based on Mn). Decomposition temperature: 330 °C. Anal. Calcd for C11H11N2O7Mn1.5: C, 36.14; H, 3.03; N, 7.66. Found: C, 36.48; H, 3.32; N, 7.27. IR (cm-1, KBr): 3423 (m), 1560 (m), 1539 (s), 1456 (s), 1409 (m), 1352 (s), 1276 (m), 1254 (m), 1116 (s), 838 (w), 738 (m), 706 (w), 549 (w). Polymer 3: (43% yield). Decomposition temperature: 290 °C. Anal. Calcd for C22H16N4O10Mn2: C, 43.58; H, 2.66; N, 9.24. Found: C, 43.62; H, 2.69; N, 9.27. IR (cm-1, KBr): 3421 (m), 1592 (m), 1539 (s), 1465 (s), 1384 (m), 1274 (m), 1125 (s), 977 (m), 848 (w), 787 (s), 723 (s), 526 (m). We repeated the above reactions by hydrothermal reaction instead of solvothermal reaction, and only a few small crystalline powders were obtained, and the yield was less than 5%. So, compounds 1-3 are more suitable for growth in CH3CN/H2O solvent through the careful control of reaction condition. The final pH values of the solutions are another crucial factor for the formation of crystalline products, as the crystals could not be obtained at a final pH value higher than 7 or lower than 6, which can be perfectly controlled by Et3N instead of NaOH, KOH, py, etc. Crystal Structure Determinations. Suitable single crystals of compounds 1-3 were selected for single-crystal X-ray diffraction analyses. The intensity data were measured on a Bruker smart APEXII CCD imaging plate area detector with graphite monochromated Mo KR radiation (λ = 0.71073 A˚). Single crystals of 1-3 were selected and mounted on a glass fiber. All data were collected at room temperature using the ω-2θ scan technique and corrected for Lorenz-polarization effects. A correction for secondary extinction was applied. The three structures were solved by direct methods and expanded using the Fourier technique. The non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were included but not refined. All calculations were performed using the SHELX-97 crystallographic software package.8 The crystallographic data of the three complexes are given in Table 1. Selected bond lengths and angles are listed in Table 2.

Results and Discussion Synthesis. 2-Phenyl-1H-imidazole-4,5-dicarboxylic acid has six potential donor atoms, and consequently, the depro-

tonated ligands exhibit flexible coordination modes. It is to be noticed that the stoichiometry of the starting materials is important for the formations of complexes 1-3. The reactions of metal salts and H3PhIDC in a molar ratio of 1:1, 1:1, and 1:1 have respectively produced crystals of 1-3 successfully, while another stoichiometry has failed to produce suitable crystals or has given products with very low yields (about 3.7%). During the reactions, slightly excessive or less Et3N would cause failure, and the pH values of the solution before and after reaction are ca. 8 and 6, respectively, for each of the compounds.9c The reaction of Cd(NO3)2 3 4H2O (or MnCl2 3 4H2O) with H3PhIDC, Et3N, and CH3CN/H2O under hydro(solvo)thermal conditions successfully gave compounds 1-3. Polymer 1 is a novel chiral 3-D coordination polymer, while polymers 2 and 3 are two achiral 3-D compounds. It is to be noticed that polymers 2 and 3 were obtained from the same Teflon-lined stainless steel autoclave. That is to say, under the same reaction conditions, two different structural 3-D Mn(II) polymers could be obtained. This confirms the complexity of the hydrothermal reaction and the complicated coordination modes of H3PhIDC. In addition, it is noteworthy that the anion of the metal salt may affect the crystal shape of the final product.9,13a If the Cd(NO3)2 is changed to Cd(OAc)2 or CdSO4 in the synthesis of 1, only a small crystalline powder can be generated, which suggests that the anion NO3- plays an important role in the formation of 1. Similar cases can be found in the syntheses of 2 and 3. However, the anion effect in the construction of coordination complexes is ambiguous. In conclusion, by fine tuning the synthetic conditions, such as the nature of the organic ligand, solvent, pH values, metal/ ligand molar ratio, etc.,10 the reproducibility of our experiments is good. It is believed that more metal complexes with interesting structures as well as physical properties will be synthesized from this sort of ligand, and this work is underway in our laboratory now. [Cd4(μ3-HPhIDC)2(μ4-HPhIDC)2(H2O)] (1). Single crystal X-ray diffraction shows that complex 1 crystallizes in the

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Table 1. Crystal Data and Structure Refinement Information for Compounds 1-3 1 C44H26N8O17Cd4 296(2) 1388.33 orthorhombic 0.28 0.25 0.21 P2(1)2(1)2(1) 16.224(3) 16.644(3) 18.176(3) 90 90 90 4908.1(16) 1.879 4 1.789 36786/9132 R(int) = 0.0267 data/restraints/parameters 9132/0/658 0.0236 Ra 0.0547 Rw b 2 1.060 GOF on F -3 -0.6343 and 0.7051 ΔFmin and ΔFmax, e A˚ P P P P a R = [|Fo| - |Fc|]/ |Fo|. b Rw = [ (|Fo| - |Fc|)2/ |Fo|2]1/2.

formula temp, K fw crystal system crystal size, mm3 space group a, A˚ B, A˚ C, A˚ R, deg β, deg γ, deg V, A˚3 Dc, Mg m-3 Z μ, mm-1 reflns collected/unique

2

3

C11H11N2O7Mn1.5 296(2) 365.63 trigonal 0.19 0.18 0.18 R3 25.5178(3) 25.5178(3) 14.2324(4) 90 90 120 8025.9(3) 1.362 18 1.106 14580/4088 R(int) = 0.0225 4088/0/196 0.0407 0.1150 1.087 -0.8174 and 0.8258

C22H16N4O10Mn2 296(2) 606.27 rhombohedral 0.32 0.15 0.11 R3c 28.5972(6) 28.5972(6) 8.7442(5) 90 90 120 6192.9(4) 1.463 9 0.975 9826/2544 R(int) = 0.1130 2544/1/172 0.0515 0.0706 0.879 -0.7456 and 0.9004

Table 2. Selected Bond Distances (A˚) and Angles (deg) for Complexes 1-3a

Cd(1)-O(1) Cd(1)-O(16)#1 Cd(2)-O(5) Cd(2)-N(5) Cd(3)-O(1) Cd(3)-O(16)#1 Cd(4)-O(4)#4 Cd(4)-O(17) N(1)-Cd(1)-O(16)#1 N(1)-Cd(1)-N(3) N(7)-Cd(2)-N(5) N(7)-Cd(2)-O(9) N(4)#2-Cd(3)-O(1) N(8)#1-Cd(3)-O(1) O(8)-Cd(4)-O(12)#5 O(17)-Cd(4)-O(8)

2.501(3) 2.251(3) 2.306(2) 2.283(3) 2.301(3) 2.363(3) 2.411(3) 2.306(4) 137.41(11) 96.72(11) 116.22(12) 151.32(11) 97.01(11) 141.07(10) 67.03(9) 84.15(12)

1 Cd(1)-O(5) Cd(1)-N(1) Cd(2)-O(9) Cd(2)-N(7) Cd(3)-O(8)#2 Cd(3)-N(4)#2 Cd(4)-O(8) Cd(4)-N(2)#4 N(1)-Cd(1)-O(9) O(16)#1-Cd(1)-N(3) N(7)-Cd(2)-O(5) N(5)-Cd(2)-O(9) O(1)-Cd(3)-O(8)#2 O(12)#3-Cd(3)-O(1) O(17)-Cd(4)-O(4)#4 N(6)#5-Cd(4)-O(8)

2.390(3) 2.223(3) 2.372(3) 2.263(3) 2.408(3) 2.267(3) 2.344(3) 2.239(3) 97.51(11) 108.56(10) 97.96(10) 72.56(10) 96.97(10) 83.49(11) 173.59(13) 138.61(11)

Cd(1)-O(9) Cd(1)-N(3) Cd(2)-O(13) Cd(3)-O(12)#3 Cd(3)-N(8)#1 Cd(4)-O(12)#5 Cd(4)-N(6)#5

2.312(3) 2.316(3) 2.381(3) 2.277(3) 2.291(3) 2.367(3) 2.308(3)

O(16)#1-Cd(1)-O(9) O(9)-Cd(1)-N(3) N(5)-Cd(2)-O(5) O(5)-Cd(2)-O(9) O(1)-Cd(3)-O(16)#1 N(8)#1-Cd(3)-O(8)#2 N(6)#5-Cd(4)-O(17) N(2)#4-Cd(4)-O(17)

85.33(11) 139.27(10) 141.43(11) 68.87(9) 69.65(9) 117.70(11) 99.76(14) 100.41(14)

Mn(1)-O(2)#1 Mn(1)-N(1) Mn(2)-O(1)#2 Mn(2)-O(3) O(2)#1-Mn(1)-O(4) O(2)#1-Mn(1)-N(2)#1 O(1)#2-Mn(2)-O(1) O(1)#2-Mn(2)-O(3) O(1)#2-Mn(2)-O(7)#2

2.1560(15) 2.2223(19) 2.1095(16) 2.1129(17) 173.06(6) 74.68(6) 180.00(8) 91.44(7) 90.49(9)

2 Mn(1)-O(4) Mn(1)-N(2)#1 Mn(2)-O(1) Mn(2)-O(7)#2 O(2)#1-Mn(1)-O(6) O(4)-Mn(1)-N(1) O(1)#2-Mn(2)-O(3)#2 O(1)-Mn(2)-O(3) O(1)-Mn(2)-O(7)#2

2.1691(15) 2.2249(18) 2.1095(16) 2.203(2) 95.24(7) 75.09(6) 88.56(7) 88.56(7) 89.51(9)

Mn(1)-O(6) Mn(1)-O(5) Mn(2)-O(3)#2 Mn(2)-O(7) O(4)-Mn(1)-O(6) O(6)-Mn(1)-N(1) O(1)-Mn(2)-O(3)#2 O(3)#2-Mn(2)-O(3) O(3)#2-Mn(2)-O(7)#2

2.2177(19) 2.226(2) 2.1129(17) 2.203(2) 84.36(7) 158.74(7) 91.44(7) 180.00(13) 89.80(8)

Mn(1)-O(3)#1 Mn(1)-O(1) O(3)#1-Mn(1)-O(4)#2 O(3)#1-Mn(1)-O(1) O(4)#2-Mn(1)-N(1)

2.119(5) 2.173(4) 86.53(19) 178.1(2) 165.13(19)

3 Mn(1)-O(4)#2 Mn(1)-O(5) O(3)#1-Mn(1)-O(2)#1 O(2)#1-Mn(1)-O(1) O(1)-Mn(1)-N(1)

2.160(4) 2.191(4) 86.47(19) 91.79(18) 73.18(19)

Mn(1)-O(2)#1 Mn(1)-N(1) O(4)#2-Mn(1)-O(2)#1 O(4)#2-Mn(1)-O(5) O(5)-Mn(1)-N(1)

2.161(5) 2.321(6) 84.45(18) 90.02(17) 97.71(18)

a Symmetry transformations used to generate equivalent atoms for 1: (#1) -x þ 3/2, -y, z - 1/2; (#2) x þ 1/2, -y þ 1/2, -z; (#3) x - 1/2, -y þ 1/2, -z; (#4) -x þ 1, y - 1/2, -z þ 1/2; (#5) x - 1, y, z. For 2: (#1) y þ 1/3, -x þ y þ 2/3, -z þ 5/3; (#2) x þ 1, -y, -z þ 1. For 3: (#1) -y þ 1, -x þ 1, z þ 1/2; (#2) x þ 1 /3, x - y - 13, z þ 1/6.

chiral orthorhombic space group P2(1)2(1)2(1) and is composed of hexanuclear cadmium clusters. The asymmetric unit of the compound contains four crystallographically independent Cd(II) ions, four HPhIDC2- units with two distinctly different coordination modes, and one coordination water molecule (Figure 1a). The Cd1, Cd3, and Cd4 ions are

all six-coordinated, with each forming a distorted octahedron [CdN2O4] unit. The Cd1 atom is surrounded by two nitrogen atoms and four carboxylate oxygen atoms from two chelating μ3-HPhIDC2- and μ4-HPhIDC2-, and two individual μ3-HPhIDC2- and μ4-HPhIDC2-. The surrounding of atom Cd3 is similar to that of Cd1. The Cd4 is also six-coordinated

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Figure 1. (a) Coordination environments of Cd(II) ions in 1. (b) View of right-handed helical chains and a 2-D layer constructed via the helix in the b axis. (The part of HPhIDC2- units was omitted for clarity.) (c) Perspective view of the 3-D framework for 1 along the a-axis built from 2-D layers and HPhIDC2- bridges (H atoms and water molecules omitted for clarity. Color code: Cd, cyan; O, red; N, blue; C, gray).

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with two chelating μ3-HPhIDC2- and μ4-HPhIDC2- ligands, one carboxylate oxygen atom O8 from one individual μ4HPhIDC2- ligand, and one oxygen atom O17 from a water molecule, while Cd2 is five-coordinated with two chelating μ3-HPhIDC2- and μ4-HPhIDC2- ligands, and one carboxylate oxygen atom O5 from one individual μ4-HPhIDC2ligand, forming a slightly distorted trigonal-bipyramidal geometry [CdN2O3]. The Cd-L (L = O or N) distances are in the range 2.223(3)-2.501(3) A˚, and the trans L-Cd-L bond angles vary from 67.03(9)° to 173.59(13)°, all of which are comparable to those reported for other imidazole-based dicarboxyate Cd(II) complexes.11 The HPhIDC2- units in complex 1 show two kinds of complicated coordination fashions: μ3-kN,O: kN0 ,O0 : kO00 mode (Scheme 2a) and μ4kN,O: kO0 : kN0 ,O0 : kO00 mode (Scheme 2b).4a,11 Complex 1 indicates a novel 3-D structure with different types of channels running in the same direction. There are two types of 2-fold screw axes along the crystallographic b axis, containing right-handed helixes around the crystallographic 21 axis, with pitches of 16.644(3) A˚. The two types of helical chains are interconnected to each other through the O atoms (O1, O16) center to produce an interesting 2-D layered structure in the bc-plane (Figure 1b).13 The 2-D layer exhibits a unique Kagome’ net topology when the O atoms are viewed as the connected nodes between Cd1 and Cd3. Each of the Cd-O lengths is not identical, forming a deformational tetrahedron, and the mode is connected along the c-axis in an -ABAB- sequence. Furthermore, the adjacent parallel 2-D layers are further linked together to construct a 3-D framework by bridging μ4-HPhIDC2- ligands (Figure 1c). The layers are also stacked along the a-axis in an -ABABsequence. [Mn1.5(μ3-PhIDC)(H2O)3] (2). Complex 2 crystallizes in trigonal R3 space group and exhibits a 3-D framework constructed by 2-D honeycomb-like sheets of [Mn3(PhIDC)2(H2O)6]n, which is further linked by the 1-D right-hand helical chains [Mn3(PhIDC)2(H2O)6]n. As shown in Figure 2a, two crystallographically independent Mn(II) atoms are located in two different distorted octahedral coordination environments, [MnO4N2 ] or [MnO6]. Mn1 is six-coordinated by two imidazolate N atoms and two carboxylato O atoms from two individual μ3-PhIDC3ions; the other two O atoms come from two coordinated water molecules. Mn2 is six-coordinated by four carboxylato O atoms from two individual μ3-PhIDC3- ions in the equatorial plane, and two oxygen atoms from two coordinated water molecules in axial positions. The Mn-L distances are in the range 2.223(3)-2.501(3) A˚, and the trans L-Mn-L bond angles range from 67.03(9)° to 173.59(13)°. Each PhIDC3ligand adopts the same coordination mode, namely μ3-kN,O: kN0 ,O0 : kO,O0 (Scheme 2c) and links neighboring Mn(II) ions to form a 1D right-handed helix around the crystallographic 21 axis, with pitches of 25.5178(3) A˚, in the a/b axis (Figure 2b). For simplicity, one of three possible orientations of PhIDC3- is considered. The 2D layer is connected through the adjacent right-handed helical chains, which are linked by [Mn3(PhIDC)2(H2O)6]n bridges in the ac-plane (Figure 2c). The layer consists of one type of distorted hexagonal 54membered rings: Mn14(PhIDC3-)8, and each Mn14(PhIDC3-)8 ring is surrounded by six Mn14(PhIDC3-)8 rings. It is noteworthy that the hexagonal [Mn14(PhIDC3-)8] layers are ideally connected by the other hexagonal ring along the baxis. The layers contain 1D right-hand helical chains and are stacked in an AAA fashion (Figure 2b). In the ab-plane, the

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other hexagonal ring presents clearly, including 24-members of six Mn(II) cations and six PhIDC3- trianions [Mn6(PhIDC3-)6] (Figure 2c), and each Mn6(PhIDC3-)6 ring is surrounded by six Mn6(PhIDC3-)6 rings. The honeycomblike sheet of 2 is similar to the reported structural motifs.12 Two kinds of orientational helices are bridged by [Mn3(PhIDC)2(H2O)6]n linkages to lead to a novel annular interpenetrating 3-D framework (Figure 2d). {[Mn(μ3-HPhIDC)(H2O)2]} (3). Polymer 3 crystallizes in the rhombohedral space group R3c with one crystallographically independent Mn(II) ion in the crystal lattice, as shown in Figure 3a. Mn(II) ion lies in a distorted octahedral environment, which is completed by one nitrogen atom (N1) and three carboxylate oxygen atoms (O1, O2A, and O3A) from two chelating μ3-HPhIDC2- ions, O4B from one individual μ3-HPhIDC2- ligand, and one oxygen atom O5 from a water molecule. The μ3-HPhIDC2- ligand adopts a μ3-kN, O: kO,O0 : kO coordination mode to bridge three Mn(II) ions in N,O-chelating, O,O0 -chelating, and monodentate fashions (Scheme 2d). The Mn-N bond length is 2.321(6) A˚, and that of Mn-O is in the range 2.119(5)-2.191(4) A˚, with an average value of 2.161(2) A˚. The trans L-Mn-L bond angles are in the range 73.18(19)-178.1(2)°. Each μ3-HPhIDC2ligand further bridges the crystallographically identical Mn(II) ions to form a 1-D zigzag chain through the fusing of five- and seven-membered rings in the c direction. Furthermore, these chains linked by O4 atoms are further assembled into a novel 2-D stairlike network in the bc plane (Figure 3b),14 while a similar structure also exists in the ac plane. This particular supramolecular structure is rather rare among known molecular frameworks. Furthermore, the 2-D networks are connected by O4 atoms to form a 3-D supramolecular architecture in the ab plane (Figure 3c). Infrared Spectra, Thermal Analyses, Luminescent Properties, and Geometries of the Free Ligands. The IR spectra display characteristic absorption bands for water molecules, carboxylate, imidazolyl units, and phenyl units. Compounds 1-3 show strong and broad absorption bands in the range 3400 - 3500 cm-1, which indicate the presence of the νN-H and the νO-H stretching frequencies of the imidazole ring and coordinated water molecules, respectively. Complexes 1-3 exhibit strong characteristic absorptions around 1550-1561 cm-1 (νas(COO-)) and 1400-1466 cm-1 (νs(COO-)), respectively. The frame vibration of the phenyl ring is observed at 1466 cm-1 for 1, 1456 cm-1 for 2, and 1465 cm-1 for 3. The characteristic bands at 705-871 cm-1 imply bending vibration (δ=C-H) bands of the phenyl ring in the three compounds. The TG curves have been obtained under flowing air for crystalline samples of 1-3 in the temperature range 20-700 °C (Figure 4). For polymer 1, it is stable up to 127.7 °C and then reveals a weight loss of 10.46% (calcd 12.96%) from 127.7 to 312.4 °C for the removal of one coordinated water molecule. It keeps losing weight from 312.4 to 523.7 °C, corresponding to the decomposition of the HPhIDC2(observed 53.83%, calculated 50.02%). Finally, a plateau region is observed from 523.5 to 700 °C. A white amorphous residue is CdO (observed 35.71%, calculated 37.02%). TG data show that polymer 2 is stable up to 65.5 °C and then loses weight from 65.5 to 329.9 °C (observed 14.32%, calculated 14.77%), corresponding to losses of coordinated water molecules. It keeps losing weight from 329.9 to 456.3 °C, corresponding to the decomposition of the PhIDC3- units (observed 57.94%, calculated 56.11%). Subsequently, a plateau

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Figure 2. (a) Local coordination environments of Mn(II) ions in 2. (b) View of right-handed helical chains and the 2-D honeycomb-like with 54-membered hexagonal rings (phenyl units and coordinated water molecules omitted for clarity). (c) The 2-D layer containing 24-membered hexagonal rings. (d) View of 3-D network for 2 (H atoms omitted for clarity. Color code: Cd, cyan; O, red; N, blue; C, gray).

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Figure 3. (a) Coordination environment of the Mn atom in 3. (b) 1-D zigzag chain viewed along the b axis, and 2-D stairlike structure of 3 in the bc plane (partial HPhIDC2- units and coordinated water molecules omitted for clarity). (c) View of 3-D network for 3. (H atoms and guest water molecules omitted for clarity. Color code: Mn, cyan; O, red; N, blue; C, gray.)

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region is observed from 456.3 to 700 °C. A white amorphous residue is 1.5MnO (observed 27.74%, calculated 29.12%). The TG analysis of 3 revealed that the first weight loss of 21.72 wt % is between 72.7 and 282.4 °C, which could be attributed to the loss of two H2O molecules and a partial unit of the organic HPhIDC2- ligand (calculated 20.45%). When the temperature is higher than 282.4 °C, the remaining HPhIDC2- units could be removed (observed 54.79%, calculated 56.13%). Then the collapse of the 3-D framework of polymer 3 could be found. The final residue is 2MnO (observed 23.49%, calculated 23.42%). Previous studies have shown that coordination polymers containing cadmium exhibit photoluminescent properties. The photoluminescent properties of free H3PhIDC ligand and polymers 1, 2, and 3 have been investigated in the solid state at room temperature. Unfortunately, complexes 2 and 3 exhibit very weak emissions. The emission spectra of polymer 1 and free H3PhIDC ligand are illustrated in Figure 5.

Figure 4. TG analysis profiles of polymers 1-3.


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The free H3PhIDC ligand displays luminescence, with the emission maximum at 473 and 345 nm, respectively, which is attributed to the π* f n transition. Compared with the free H3PhIDC ligand, compound 1 shows different luminescent properties; it exhibits a broad emission at 367 nm when excited at 300 nm. The emission can be assigned to the ligand-to-metal charge transfer (LMCT), rather than the π* f n transition of the ligand. Recently, we have investigated the ethyl substituent effect of H3EIDC ligand in the hydrothermal preparation process.4a It was found that the position and type of functional groups on the ligand are crucial for the generation of resulting frameworks. Herein, we continuously explore useful information of the phenyl substituent effect in H3PhIDC ligand by theoretical calculation. The optimized geometries and natural bond orbital (NBO) charge distributions of the free ligand H3PhIDC and H3IDC have been calculated by the B3LYP/6-311þþG(d,p) level of theory. The computed results (Scheme 3 and Table 3) reveal that the free ligands H3PhIDC and H3IDC have two interesting features: (1) The negative NBO charges mainly distribute on the oxygen and nitrogen atoms. The NBO charges are -0.66499 for O1, -0.65854 for O2, -0.68904 for O3, -0.64712 for O4, -0.52367 for N5, and -0.49327 for N6 in the free ligand H3IDC, and -0.66493 for O1, -0.65884 for O6, -0.69007 for O2, -0.64991 for O13, -0.51400 for N7, and -0.49039 for N4 in the free ligand H3PhIDC (Table 3). Compared with the case of the free ligand H3IDC, the introduction of phenyl group into H3PhIDC has a slight effect on the NBO charge distributions of oxygen and nitrogen atoms. As discussed above, the NBO charge distributions of O atoms all increase and those of N atoms all decrease slightly in H3PhIDC. These values indicate that the oxygen and nitrogen atoms of the two ligands all have the potential ability of coordination to metal ions. So H3PhIDC can show various coordination modes under appropriate reaction conditions, such as use of H3IDC ligand. This finding can be confirmed by our present experimental results. In 1 and 3, the imidazole-H and COO-H are removed

Figure 5. Solid-state photoluminescent spectra of the free H3PhIDC ligand and polymer 1 at room temperature.

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Scheme 3. Optimized Geometries of the Free Ligands H3IDC and H3PhIDC (the blue ball represents N atom, the red ball represents O atom, and the gray ball represents C atom)

Table 3. Natural Bond Orbital Charge Distributions of the Free Ligands H3PhIDC and H3IDC H3IDC

H3PhIDC

atom number

NBO charge

atom number

NBO charge

O1 O2 O3 O4 N5 N6 C7 C8 C9 C10 C11 H12 H13 H14 H15

-0.66499 -0.65854 -0.68904 -0.64712 -0.52367 -0.49327 0.80744 0.01044 0.05658 0.78105 0.24933 0.50665 0.48765 0.23673 0.54074

O1 O6 O2 O13 N7 N4 C10 C8 C9 C12 C11 C15 C16 C17 C18 C20 C22 H3 H5 H14 H19 H21 H23 H24 H25

-0.66493 -0.65884 -0.69007 -0.64991 -0.51400 -0.49039 0.80755 0.02176 0.06282 0.77880 0.40655 -0.08825 -0.18271 -0.19503 -0.20781 -0.20658 -0.19635 0.50658 0.48002 0.54077 0.23323 0.22633 0.22685 0.22757 0.22604

from the ligand H3PhIDC to form a HPhIDC2- unit. The imidazole-H and two COO-H are deprotonated in 2, also leading to the triply deprotonated PhIDC3- units. (2) The coordination ability of N and O atoms in the H3PhIDC ligand is enhanced remarkably. This can be concluded by the calculation result of the highest occupied molecular orbital (HOMO) energies of the free ligands H3IDC (Ehomo= -0.279 au) and H3PhIDC (Ehomo = -0.247 au). It was found that the HOMO energy of H3PhIDC is larger than that of H3IDC. Surprisingly, the steric effect of the bulky phenyl unit in H3PhIDC is not remarkable. Usually the steric hindrance of the bulky phenyl group may prevent the H3PhIDC from linking more metal ions. Nevertheless, we have successfully obtained three 3-D polymeric frameworks 1-3. Obviously, the strong coordination ability of the N and O atoms in the ligand overrides the steric effect of the phenyl unit.

Acknowledgment. We gratefully acknowledge the financial support by the National Natural Science Foundation of China (20501017 and J0830412) and by the Key Project of the Chinese Ministry of Education (207067), the Project Sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars of the Chinese Ministry of Education, and the Natural Science Foundation of the Henan Education Department (2007150040; 2009A150028). Supporting Information Available: Crystallographic data in CIF and PDF formats. This material is available free of charge via the Internet at http://pubs.acs.org. Note Added after ASAP Publication. A previous web version of this paper published on July 30, 2010 stated incorrectly that polymer 2 is a chiral compound in space group R3. All instances of “chiral” pertaining to polymer 2 were corrected to “achiral” in this new version published on August 16, 2010.

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One Chiral and Two Achiral 3-D Coordination Polymers Constructed

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