Three New Coordination Polymers Based on One Reduced Symmetry

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Three New Coordination Polymers Based on One Reduced Symmetry Tripodal Linker Ling Qin, Jin-Song Hu, Yi-Zhi Li, and He-Gen Zheng* State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, P. R. China

bS Supporting Information ABSTRACT: Three novel metalorganic frameworks, namely, {[(Zn4O)1/2(Zn3OH)1/2L3/2O1/4(H2O)5/2(NO2)1/2] 3 (H2O)4}n (1), {[Cd3L2(H2O)4] 3 (H2O)9 3 DMA}n (2), and {[Co(HL)(4,40 -bibp)]}n (3; H3L = 50 -carboxyl[1,10 :30 ,100 -terphenyl]-4,400 -dicarboxylic acid, 4,40 -bibp = 4,40 -bisimidazolylbiphenyl, DMA = N,N-dimethylacetamide), have been synthesized under hydrothermal conditions. These compounds were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. Compound 1 reveals an unusual 3D structure with {4 3 52}{4 3 62}{42 3 52 3 68 3 83}{52 3 6}{53 3 65 3 82} topology based on Zn4O and Zn3OH clusters. In compound 2, the H3L ligand assembles with Cd(NO3)2 to a 3D framework with sqc27 {4 3 62}2{42 3 610 3 83} topology. They are both three-dimensional frameworks containing one-dimensional channels. In compound 3, the HL2 anion and 4,40 -bibp both act as bidentate ligands and coordinate to Co cations to form a three-dimensional 4-connected uninodal network. In addition, the thermal stabilities for 13 and luminescent properties for 1 and 2 are also discussed in detail.

’ INTRODUCTION Remarkable progress has been achieved in the study of metalorganic frameworks (MOFs), not only due to their variety of topologies and intriguing structures1 but also owing to their interesting physical and chemical properties, such as sensing materials,2 magnetism,3 gas adsorption,4 ion exchange,5 and catalysis.6 The use of multidentate organic ligands and suitable metal salts to construct metalorganic frameworks (MOFs) has been a major strategy of supramolecular chemistry in recent years.7 As far as we know, compared with flexible ligands, rigid ligands with desired geometry, have been more inclined to be used to specifically design topologies. However, predictive coordination chemistry is still a challenge and deserves our careful study, because there are many other facts that can affect the structure, such as the nature of the metal ions, the temperature, the solvent, and the counterions.8 Besides that, the coordinating competition of the metal center between ligands and water molecules can affect the structure. Recently, we synthesized a rigid tripodal ligand H3L = 50 carboxyl-[1,10 :30 ,100 -terphenyl]-4,400 -dicarboxylic acid (H3L).9 Matzger and co-workers thought reduced symmetry linkers could offer the potential to expose new regions of phase space and, finally, might discover novel materials.10 Besides, we consider the following aspects: First, multicarboxylate ligands are often employed as bridging ligands to construct coordination polymers because of their versatile coordination modes,11 and their ability to act as H-bond acceptors and donors. Second, H3L ligand has a planar structure and assembles with d10 metal ions to exhibit intriguing photoluminescent properties. Third, r 2011 American Chemical Society

interpenetration control is an important challenge in the synthesis of new materials; a potential benefit of using the reduced symmetry linkers is that they tend to be a noninterpenetrated structure. Last, but not least, porous materials have achieved considerable attention in the past decade due to the development of microporous coordination polymers (MCPs) as a potentially viable alternative to sorbents.12 The fact that the H3L ligand links metal clusters or metal oxide clusters may generate microporous coordination polymers. To test the ability of the ligand to give new architectures and topologies, we selected H3L ligand and different bivalent metal salts, and we solvothermally synthesized two new coordination polymers with intriguing structures and topologies, namely, {[(Zn4O)1/2(Zn3OH)1/2L3/2O1/4(H2O)5/2(NO2)1/2] 3 (H2O)4}n (1) and {[Cd3L2(H2O)4] 3 (H2O)9 3 DMA}n (2). In addition, we chose 4,40 -bibp based on its conformationally restraint as coligands to synthesize {[Co(HL)(4,40 -bibp)]}n (3). Among the previous reports, linear, rigid, and bifunctional bridging ligands have been found to be one of the most versatile building blocks. All compounds are characterized by elemental analysis, IR spectra, and X-ray crystallography. The crystal structures, topological analyses, photoluminescent properties, and thermal properties are studied in detail. Received: March 23, 2011 Revised: May 8, 2011 Published: May 11, 2011 3115

dx.doi.org/10.1021/cg2003673 | Cryst. Growth Des. 2011, 11, 3115–3121

Crystal Growth & Design

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Table 1. Crystallographic Data and Structure Refinement Details for 1-3 compound

1

2

3 C39H26N4O6Co

empirical formula

C126H120N2O71Zn14

C46H39Cd3NO17

formula weight

3713.4

1214.98

705.57

crystal system

orthorhombic

triclinic

monoclinic C2/c

space group

Pnnm

P1

a/Å

21.209(2)

7.1422(16)

24.636(3)

b/Å

22.825(2)

21.211(5)

12.0873(16)

c/Å

18.1999(18)

22.181(5)

24.464(3)

R/deg B/deg

90.00 90.00

62.412(4) 81.392(4)

90.00 115.818(2)

γ/deg

90.00

89.538(4)

90.00

V/Å3

8810.5(14)

2937.4(11)

6557.8(15)

Z

2

2

8

Dcalcd/g 3 cm3

1.429

1.400

1.374

μ/mm1

1.950

1.135

0.579

F(000)

3756

1204.0

2904

θminmax/deg tot., uniq data

1.92, 26.0 46128, 8946

1.83, 25.0 14654, 10173

1.84, 26.00 17331, 6387

R(int)

0.0715

0.032

0.0559

obsd data [I > 2σ(I)]

6072

5984

3886

Nref, Npar

8946, 581

10173, 607

6429, 446 0.0565, 0.0831

R1, wR2 [I > 2σ(I)]

0.0542, 0.1187

0.0518, 0.1696

GOF on F2

1.029

1.058

1.005

min. and max. resd dens (e 3 Å3)

0.58, 0.85

0.88, 1.54

0.58, 0.69

)

)

R1 = ∑ Fo| |Fc /|∑|Fo|. wR2 = {∑[w(Fo2 Fc2)2]/∑[w(Fo2)2]}1/2, where w = 1/[σ2(Fo2) þ (aP)2 þ bP], P = (Fo2 þ 2Fc2)/3.

’ EXPERIMENTAL SECTION Materials and Measurements. The reagents and solvents employed were commercially available. H3L and 4,40 -bibp ligand were prepared by literature methods.13,14 IR absorption spectra of the compounds were recorded in the range 4004000 cm1 on a Nicolet (Impact 410) spectrometer with KBr pellets (5 mg of sample in 500 mg of KBr). C, H, and N analyses were carried out with a Perkin-Elmer 240C elemental analyzer. Powder X-ray diffraction (PXRD) measurements were performed on a Bruker D8 Advance X-ray diffractometer using Mo KR radiation (λ = 0.71073 Å), in which the X-ray tube was operated at 40 kV and 40 mA. The as-synthesized samples were characterized by thermogravimetric analysis (TGA) on a Perkin-Elmer thermogravimetric analyzer Pyris 1 TGA up to 1023 K using a heating rate of 10 K min1 under a N2 atmosphere. Luminescent spectra were recorded with a SHIMAZU VF-320 X-ray fluorescence spectrophotometer at room temperature. Synthesis of {[(Zn4 O)1/2(Zn3OH)1/2L3/2O1/4(H2O)5/2(NO2)1/2] 3 (H2O)4}n (1). A mixture of Zn(NO3)2 3 6H2O (29.7 mg,

0.1 mmol) and H3L (33.3 mg, 0.1 mmol) was dissolved in 8 mL of DMA/H2O (1:1, v/v). The final mixture was placed in a Parr Teflonlined stainless steel vessel (15 mL) under autogenous pressure and heated at 95 °C for 3 days. Colorless-block crystals were obtained. The yield of the reaction was ca. 50% based on H3L ligand. Calcd for Zn14C126H120N2O71: C, 40.70%; H, 3.36%; N, 0.75%. Found: C, 40.75%; H, 3.26%; N, 0.75%. IR (KBr, cm1): 3382(s), 2926(m), 2362(m), 1942(w), 1826(w), 1609(s), 1547(s), 1400(s), 1312(s), 1186(m), 1111(m), 1053(w), 1012(m), 901(w), 859(m), 778(m), 745(m), 705(w), 674(w), 587(w), 487(m). Synthesis of {[Cd3L2(H2O)4] 3 (H2O)9 3 DMA}n (2). Compound 2 was prepared in the same way as 1 but using Cd(NO3)2 3 4H2O

(30.1 mg, 0.10 mmol) to replace Zn(NO3)2 3 6H2O, and colorless crystals of 2 were obtained in a 60% yield (based on H3L). Anal. Calcd for C46H57Cd3NO26: C, 40.12%; H, 4.17%; N, 1.02%. Found: C, 40.08%; H, 4.23%; N, 1.05%. IR (KBr, cm1): 3385(m), 2360(w), 1944(w), 1829(w), 1610(m), 1583(m), 1534(m), 1446(m), 1398(w), 1315(w), 1186(w), 1142(w), 1109(w), 1051(w), 1014(w), 922(w), 905(w), 862(w), 810(w), 779(m), 746(w), 709(w), 670(w), 635(w), 592(w), 526(w), 477(w), 426(w). Synthesis of {[Co(HL)(4,40 -bibp)]}n (3). A mixture of Co(NO3)2 3 6H2O (29.1 mg, 0.1 mmol), H3L (33.3 mg, 0.1 mmol), and bibp (28.6 mg, 0.1 mmol) ligand was dissolved in 8 mL of CH3CN/H2O (3:1, v/v). The final mixture was placed in a Parr Teflon-lined stainless steel vessel (15 mL) under autogenous pressure and heated at 95 °C for 3 days. Pink-block crystals were obtained. The yield of the reaction was ca. 75% based on H3L ligand. Calcd for C39H26N4O6Co: C, 66.39%; H, 3.71%; N, 7.94%. Found: C, 66.31%; H, 3.62%; N, 7.85%. IR (KBr, cm1): 3404(s), 2359(s), 2341(s), 1699(m), 1609(m), 1559(m), 1519(m), 1380(m), 1309(m), 1249(w), 1178(w), 1097(w), 1063(m), 963(w), 854(w), 819(w), 781(w), 770(w), 746(w), 669(w), 654(m). X-ray Crystallography. Single crystals of 13 were prepared by the methods described in the synthetic procedures. X-ray crystallographic data of 1 and 2 were collected at room temperature by way of sealing the better single crystals in a quartz tube with mother liquor, and X-ray crystallographic data of 3 was collected using epoxy-coated crystals mounted on glass fiber. X-ray crystallographic data of these compounds were collected on a Bruker Apex Smart CCD diffractometer with graphitemonochromated Mo KR radiation (λ = 0.71073 Å). Structure solutions were solved by direct methods, and the non-hydrogen atoms were located from the trial structure and then refined anisotropically with SHELXTL using full-matrix least-squares procedures based on F2 values.15 The hydrogen atom positions were fixed geometrically at 3116

dx.doi.org/10.1021/cg2003673 |Cryst. Growth Des. 2011, 11, 3115–3121


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Figure 2. (a) A Zn4O cluster coordinated to five H3L ligands. (b) A Zn3OH cluster coordinated to four H3L ligands (The Zn octahedral coordination polyhedron is light orange, the square pyramidal polyhedron is lime, and the tetrahedral polyhedron is blue).

Figure 1. (a) Coordination environment of the Zn(II) ion in 1. The hydrogen atoms are omitted for clarity. Symmetry codes: (#1) x, y, 1 z; (#2) 0.5 þ x, 0.5 y, 0.5 þ z; (#3) 0.5 þ x, 0.5 y, 0.5 z; (#4) 1.5 x, 0.5 þ y, 0.5 z; (#5) 1.5 x, 0.5 þ y, 0.5 þ z. (b) Zn3OH and Zn4O clusters in compound 1 (Zn4O clusters are turquoise, and Zn3O clusters are pink). calculated distances and allowed to ride on the parent atoms. The distribution of peaks in the channels of 2 was chemically featureless to refine using conventional discrete-atom models. To resolve these issues, the contribution of the electron density by the remaining water molecule was removed by the SQUEEZE routine in PLATON.16 The numbers of solvent water molecules in 2 were obtained by elemental analyses. The relevant crystallographic data are presented in Table 1, while the selected bond lengths and angles are given in the Supporting Information (Table S1). A semiempirical absorption correction was applied using SADABS.17

’ RESULTS AND DISCUSSION Crystal Structure {[(Zn4O)1/2(Zn3OH)1/2L3/2O1/4(H2O)5/2(NO2)1/2] 3 (H2O)4}n (1). The crystal structure determination

reveals that compound 1 crystallizes in the orthorhombic crystal system Pnnm. The asymmetric unit contains half a Zn4O cluster, half a Zn3OH cluster, half a nitrate anion,18 one and a half L3 ligands, two and a half coordinated water molecules, four free water molecules, and a quarter of a bridging oxygen atom. The remaining portion in Figure 1a is generated by inversion symmetry. Compound 1, with both independent Zn3OH and Zn4O clusters, has not been reported until now (Figure 1b),19a although many works reported MOFs with Zn3OH or Zn4O clusters.19 While, through the coordinating competition of water, the Zn4O clusters are different from these reported works,19e the μ4-oxo bridged Zn4O (Zn1, Zn2, Zn2#1, Zn3) cluster is edgebridged by five carboxylate groups from five L3 ligands and two coordinated water molecules and one O atom from nitrate anion to provide the Zn4O(L)5(H2O)2 unit (Figure 2a), while the μ3-OH bridged Zn3O (Zn4, Zn5, Zn5#1) cluster is edge-bridged by four carboxylate groups from four L3 ligands and four

coordinated water molecules and one O atom from nitrate anion to generate the (Zn3OH)(L)4(H2O)4 (Figure 2b). In previously reported work, the coordinated number of Zn is four or five, while, in compound 1, Zn cations have three coordinated numbers: Zn1 and Zn5 are five-coordinate, and the τ trigonality factors are 0.098 and 0.329, indicating that they are in the distorted square pyramidal coordination geometry.20 Zn1 is anchored by two carboxylate bridges, one coordinated water molecule, one bridging O atom, and the central μ4-oxygen atom, while the Zn5 center is bridged by three carboxylates, one coordinated water molecule, and the central μ3-O atom. Zn2 and Zn3 are tetrahedrally coordinated, Zn2 is anchored by three carboxylate bridges and the central μ4-oxygen atom, while the Zn3 center is bridged by two carboxylate ligands, one O atom from nitrate anion, and the central μ4-oxygen. Zn4 is octahedrally anchored by two carboxylate bridges, two coordinated waters, one O atom from nitrate anion, and the central μ3-oxygen, as shown in Figures 1b and 2. The ZnO lengths are in the range 1.832(3)2.4221(8) Å, and they are all similar to those found in other Zn(II) compounds.21 The Zn4O clusters and Zn3OH clusters connect by one nitrate anion, and the two Zn4O clusters connect by O bridging atoms; finally, they assemble L3 ligands to a 3D structure with 1D channels, running along the c axis (Figure 3a). The channels are occupied by water molecules (Figure 3b). The desolvated framework shows 34.4% void space to the total crystal volume, as calculated by PLATON. To better understand the nature of this intricate framework, a topological approach has been applied; we reduce multidimensional structures to simple nodes and connection nets. (Zn4O)(L)5(H2O)2 and (Zn3OH) (L)4(H2O)4 can be regarded as 7-connected and 5-connected nodes, respectively. All crystallographically independent L3 ligands act as 3-connected linkers. The L3 ligands have three connection modes: one connects three Zn4O clusters, another connects three Zn3OH clusters, and the last connects two Zn4O and one Zn3OH (Figure 3c). Therefore, the whole structure can be represented as a new 3,3,3,5,7-c network topology (with the Schl€afli symbol {4 3 5 2 }{4 3 6 2 } {42 3 52 3 613 3 7 3 83}{52 3 6}{53 3 66 3 7}) (Figure 3d). Crystal Structure {[Cd3L2(H2O)4] 3 (H2O)9 3 DMA}n (2). Single crystal X-ray analysis reveals compound 2 crystallizes in a triclinic crystal system of P1 space group. The asymmetric unit contains three cadmium cations, two L3 ligands, four coordinated waters, and one free DMA molecule and nine lattice water molecules (Figure 4a). In the asymmetric unit, the two L3 ligands take 3117



Figure 3. (a) Perspective views of the 3D framework of 1 without the guest water molecules. (b) Perspective views with the guest water molecules in the cavities. The hydrogen atoms are omitted for clarity. (c) The three connection modes of compound 1. (d) Schematic representation of the 3D framework of compound 1 with the H3L ligand shown in gray, Zn3OH clusters shown in pink, and Zn4O clusters shown in blue.

different coordination modes (modes II and III of Chart 1), and the difference sites in that one carboxylate group take the μ3chelating-bridging tridentate mode while those in the other L3 ligand adopt the bismonodentate coordination mode to bridge two Cd centers. The other two carboxylate groups both chelate in a bidentate mode and a μ3-chelating-bridging tridentate mode. Cd1 is seven-coordinate, and Cd2 is six-coordinate; they both bond to O atoms, of which one O atom is from a water molecule and the others are all from the L3 ligand. The bridging carboxylate groups of the L3 ligand link the Cd1 and Cd2 centers into an infinite 1D zigzag chain, as shown in Figure 4b, which contains nonbonded Cd 3 3 3 Cd contacts of 3.76 Å. The Cd3 cation in an octahedral coordination sphere bonds with six O atoms, of which four O atoms come from two carboxylates with chelating coordination to the same Cd centers. The other two O atoms are from two water molecules, respectively. In compound 2, the Cd cations also have two coordination numbers: seven and six coordination spheres (Figure 4c). The CdO lengths are in the range 2.135(11)2.587(10) Å, which are all similar to those found in other Cd(II) compounds.22 The 3D framework contains three kinds of channels, namely, A, B, and C, along the a axis, with DMA molecules in channel B (Figure 5a). The desolvated framework shows 39.9% void space to the total crystal volume, as calculated by the PLATON. A better insight into the nature of this intricate framework is provided by a topology analysis, reducing multidimensional structures to simple nodes and connection nets. The Cd2(CO2)4 units can be regarded as 6-connected nodes and all crystallographical independent L3 ligands act as 3-connected linkers. Therefore, the whole structure can thus be represented as a 3,3,6-c net sqc network topology, which is noninterpenetrated (with the Schl€afli symbol {4 3 62}2{42 3 610 3 83}) (Figure 5b).

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Figure 4. (a) Coordination environment of the Cd(II) ions in 2. Hydrogen atoms are omitted for clarity (30% ellipsoid probability). Symmetry codes: (#1) x, y, 1 z; (#2) x, 1 y, 1 z; (#3) 1 x, y, 1 z; (#4) 1 x, 1 y, 1 z; (#5) 3 þ x, y, 1 þ z. (b) Views of the 1D zigzag chain (denoted by the bold green line). (c) Two coordinated modes of Cd cations (Cd octahedral coordination polyhedrons are green; seven-coordinated Cd coordination polyhedrons are red).

Crystal Structure {[Co(HL)(4,40 -bibp)]}n (3). Compound 3

crystallizes in monoclinic space group C2/c, as shown in Figure 6a; the asymmetric unit contains one Co(II) ion, one partially deprotonated HL2 ligand, and one 4,40 -bibp ligand. The Co(II) ion is coordinated by two carboxylic O atoms from two HL2 ligands and two nitrogen atoms from two 4,40 -bibp ligands to form a distorted tetrahedron geometry. The bond lengths of Co1N1 and Co1N3 are 2.010(3) and 2.033(2), respectively, and the Co1O1 distance is 1.9443(2). They are reasonable compared with the values in reported work.23 It is obvious that the 4,40 -bibp ligands have two different configurations when coordinated with Co atoms, which is attributed to the rotational flexibility about the axis of the molecule. One is shown in turquoise, in which the biphenyl shows a coplanar mode. The dihedral angle between imidazole and phenyl is 23.829(1)°. The other in pink is a little twisted, in which the angle between the two phenyl rings is 27.777(1). The dihedral angles between imidazole and phenyl are 36.643(1)° and 36.129(1)°, respectively. The two kinds of 4,40 -bibp ligands connect Co atoms to form a 1D chain, alternately, resulting in a beautiful ruffling (Figure 6b). Then the HL2 ligands take mode IV (Chart 1) to join all infinite 1D chains into a 3D framework (Figure 6c). With the topological viewpoint, the Co can be viewed as 4-connecting nodes and the ligands as linkers, and the whole structure can be represented as a {42 3 6 3 83} sqc155 net, as displayed in Figure 6d. Effect of the Central Metals and Solvent on the Framework. The structures of coordination networks in MOFs have been found to be greatly influenced by the physical and chemical factors. Different metal ions have a great influence on the structural construction of MOFs as the ligands employed different 3118



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Chart 1. Coordination Modes of Carboxylic Groups in Compounds 13

Figure 5. (a) Perspective of the 3D framework along the a axis with 1D channels (guest DMA molecules are omitted). (b) Schematic view of the sqc27 topology of structure 2.

coordination modes in different polymers, as shown in Chart 1. The different coordination environments of the central metals are the main reasons for the structural differences in 1 and 2. In 1, the five kinds of Zn(II) ions adopt three kinds of coordinated numbers, and they compose two kinds of clusters. Furthermore, they are linked by the L3 to generate a novel (3,3,3,5,7)connected net. In 2, the three kinds of Cd(II) ions also display two coordination geometries, that is pentagonal-bipyramidal and distorted octahedral. They are bridged by the L3 to furnish a (3,3,6)-connected and 2-nodal sqc27 net, while, for compound 3, the solvent takes more important roles, since we cannot get the crystal in other similar solvent. Luminescent Properties. During the past few years, the coordination polymers with d10 metal centers have been investigated for fluorescence properties with potential applications in

photochemistry, chemical sensors, and light-emitting diodes (LEDs).24 Therefore, the solid-state photoluminescent spectra of compounds 1 and 2 and free ligands H3L were measured at room temperature, and the results are given in Figure S1. The main emission peaks are observed at 415 nm (λex = 356 nm) for H3L ligand, which can be assigned to the π 3 3 3 π* transitions, 389 nm (λex = 355 nm) for 1, and 450 nm (λex = 350 nm) for 2. Compared to the free H3L ligand, the emission band of 1 is 26 nm blue-shifted and the emission band of 2 is 35 nm red-shifted, respectively. For compound 1, abundant lattice water molecules fill the network, forming important weak forces, which stabilize the framework and enhance the rigid structure.25 However, since the d10 configuration ions are difficultly oxidized or reduced, these bands should be assigned to the intraligand fluorescent emissions. In addition, it is noteworthy that compounds 1 and 2 showed intense emissions compared with that of free H3L at room temperature, which may be attributed to the strength of rigidity in the solid state.26 Furthermore, the emission decay lifetimes of compounds 1 and 2 were monitored and the curves are best fitted by biexponentials in solid.27 The emission decay lifetimes of the compounds 1 and 2 are τ1 = 2.99 μs, τ2 = 17.11 μs (χ2 = 1.296, Figure S3) for compound 1, and τ1 = 3.17 μs, τ2 = 17.08 μs (χ2 = 1.1517, Figure S4) for compound 2. Thermal Analysis and XRD Results. To estimate the stability of the coordination architectures, their thermal behaviors were studied by TGA (Supporting Information, Figure S2). For compound 1, a gradual weight loss of 7.45% is observed from 40 to 260 °C, which is attributed to the loss of the lattice water (calcd 7.75%). The second weight loss of 10.05% (calcd 9.96%) corresponds to the loss of coordinated water molecules and nitrate anion. Then the structure is decomposed starting at 420 °C. In compound 2, a rapid weight loss of 6.74% 3119



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Figure 7. Simulated and experimental X-ray diffraction patterns for 1 and samples after thermal treatment at different temperatures.

Figure 6. (a) Coordination environment of the Co(II) ions in 3. The hydrogen atoms of carbon atoms are omitted for clarity (30% ellipsoid probability). (b). The infinite polymeric chain constructed by 4,40 -bibp ligands and Co ions. (c) A perspective of the 3D framework. (d) Schematic view of the sqc155 topology of structure 3.

(calcd 6.32%) is observed from 20 to 75 °C, corresponding to the loss of lattice DMA molecules. The second weight loss of 12.46% (calcd 11.76%) is attributed to the loss of the nine lattice water molecules, which were removed by the SQUEEZE routine in PLATON and were obtained by element analyses. The third weight loss was attributed to the loss of the four coordinated water molecules with a weight loss of 5.77% (calcd 5.23%); then the network subsequently collapsed at 420 °C. The TGA study of compound 3 shows no weight loss from room temperature to 400 °C, suggesting that the frameworks are thermally stable. Above 400 °C, a rapid weight loss is observed which is attributed to the burning of the organic ligands. To confirm whether the crystal structures are truly representative of the bulk materials, PXRD experiments were carried out for 13. The PXRD experimental and computer-simulated patterns of the corresponding compounds are shown in the Supporting Information (Figures S5S7). They show that the bulk synthesized materials and the measured single crystals are the same. To further examine the thermal stability of compounds 1 and 2, variable temperature PXRD patterns were obtained, and the sample was heated at different temperatures under N2 gas flow. These results reveal that the structures remain unchanged until at least 300 °C (Figure 7 and Figure S8).

’ CONCLUSIONS In summary, we have successfully synthesized and characterized three new compounds by the self-assembly of H3L, 4,40 -bibp ligands, and different bivalent metal salts under solvothermal conditions. The investigations not only illustrate that structural diversities of coordination polymers can be achieved by changing the central metals and the sovent but also provide a new example of the H3L ligand for the design of novel frameworks. Zn compound containing both Zn4O and Zn3OH clusters will enrich the field of MOFs based on multicarboxylate ligands. Reduced symmetry linker (H3L) offers a largely unknown approach to the synthesis of high-performance coordination polymers. And the H3L ligand tends to construct the coordination polymers exhibiting metal oxide clusters and high porosity. Subsequent works will be focused on the structures and properties of a series of coordination compounds constructed by the H3L ligand with more bis(imidazole) ligands and metal ions, to examine the influence of the flexibility, spacer length, and steric hindrance of the imidazole ligands on the assembly of supramolecular entities. ’ ASSOCIATED CONTENT

bS

Supporting Information. Crystallographic data in CIF format, and selected bond lengths and angles, patterns of photochemistry, TGA, and PXRD in PDF format. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Fax: 86-25-83314502.

’ ACKNOWLEDGMENT This work was supported by grants from the Natural Science Foundation of China (Nos. 20971065; 91022011; 21021062) and the National Basic Research Program of China (2007CB925103; 2010CB923303). 3120



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Three New Coordination Polymers Based on One Reduced Symmetry

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