Five Novel Coordination Polymers Based on a C-Centered Triangular

Article pubs.acs.org/crystal

Five Novel Coordination Polymers Based on a C-Centered Triangular Flexible Ligand Jiehu Cui,† Zhenzhong Lu,† Yizhi Li,† Zijian Guo,† and Hegen 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 ‡ State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, P. R. China S Supporting Information *

ABSTRACT: Five new complexes of the wholly deprotonated C-centered triangular flexible ligand tris(p-carboxyphenyl)methane (TCOPM), namely, {[Zn4O(TCOPM)2(H2O)2]·8H2O·3DMF}n (1), {[Mn3(TCOPM)2(H2O)2]}n (2), {[Cd3(TCOPM)2(DMF)(H2O)3]·3H2O}n (3), {[Cd3(TCOPM)2(4,4′bipy)]·2H2O·2DMF}n (4), and {[Cd4(TCOPM)2(dpyb)3(NO2)2·(H2O)2]·5H2O}n (5), are synthesized in the presence or absence of auxiliary 4,4′-bipyridine (4,4′-bipy) and 1,4-di(pyridine4-yl)benzene (dpyb) ligands by solvothermal reaction. The complexes were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and X-ray single-crystal diffraction. Compound 1 exhibits an unusual three-dimensional (3D) framework containing a one-dimensional (1D) channel based on a Zn4O cluster, with (4·82)(42·6)(43· 6· 810·10) net topology. 2 displays a 3D network structure with tfz-d topology type. Compound 3 reveals double-layered two-dimensional (2D) framework. Compound 4 possesses a 3D structure with a (3,3,10)-connected net. 5 is a 3D structure with (623·85)(63)2(65·8) topology. The photochemical properties and emission decay lifetimes were determined in the solid state at room temperature. The luminescent properties of compounds 1 and 3−5 are discussed in detail. The N2 gas adsorption of compound 1 exhibits type-I sorption behavior.

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INTRODUCTION The design of crystalline molecular porous materials has become an attractive prospect because of their potential applications in luminescence,1 chemical sensors,2,3 separation,4 and catalysis.5 An effective and facile method for the design of two-dimensional (2D) and three-dimensional (3D) metallosupramolecular species is still the appropriate choice of welldesigned organic ligands as bridges or terminal groups (building blocks) with metal ions or metal clusters as nodes.6 Among various organic ligands, multicarboxylate ligands are often selected as multifunctional organic linkers because of their abundant coordination modes to metal ions, allowing for various structural topologies, and also because of their ability to act as H-bond acceptors and donors to assemble supramolecular structures.7 For example, aromatic multicarboxylates (benzene dicarboxylate, benzene tricarboxylate, etc.) have been investigated widely for the design and synthesis of open framework complexes. Recently, nonrigid ligands are usually the typical building elements in the multidimensional networks. The conformational freedom nature of the flexible ligand may provide more possibilities for the construction of unusual topology structures and microporous coordination polymers. Therefore, tris-(p-carboxyphenyl)-methane (TCOPM)8 based C-centered triangular flexible ligand can be considered to be an excellent candidate for the preparation of nanoporous materials. © 2012 American Chemical Society

For attaining novel structures, mixed ligands are also a good choice for the construction of new polymeric structures. To date, a large number of mixed-ligand metal−organic frameworks (MOFs) have been reported, revealing that the combination of different ligands can result in greater tunability of structural frameworks than can single ligands.9,10 In addition, research on luminescence of polymers with mixed ligands still remains rarely explored so far.11 With the aim of understanding the coordination chemistry of this versatile ligand and preparing new porous materials with interesting structural topologies and physical properties, TCOPM was selected to react with the d-block metal ions Zn(II), Mn(II), Cd(II), and to successfully synthesize compounds 1−5, namely, {[Zn4O(TCOPM)2(H2O)2]·8H2O·3DMF}n (1), {[Mn3(TCOPM)2(H2O)2]}n (2), {[Cd3(TCOPM)2(DMF)(H 2 O) 3 ]·3H 2 O} n (3), {[Cd 3 (TCOPM) 2 (4,4′-bipy)]·2(4), and H2O·2DMF}n {[Cd4(TCOPM)2(dpyb)3(NO2)2·(H2O)2]·5(H2O)}n (5). The five new compounds have been characterized by elemental analysis, IR spectra, thermogravimetric analysis (TGA) and XReceived: November 24, 2011 Revised: December 18, 2011 Published: January 4, 2012 1022

dx.doi.org/10.1021/cg201552g | Cryst. Growth Des. 2012, 12, 1022−1031

Crystal Growth & Design

Article

loaded in a sample tube and dried under high vacuum (less than 10−5 Torr) at 85 °C overnight to remove CH2Cl2 and all residue solvents in the channels. About 70 mg of the desolvated sample was used for the entire adsorption measurement. For measurements at 77 K, a standard low-temperature liquid nitrogen dewar vessel was used. Syntheses of 1−5. {[Zn4O(TCOPM)2(H2O)2]·8H2O·3DMF}n (1). A mixture of Zn(NO3)2·6H2O (33.4 mg, 0.1 mmol) and TCOPM (37.6 mg, 0.1 mmol) was added to 8 mL of DMF/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 80 °C for 3 days; colorless crystals were obtained (yield: 40% based on Zn). Anal. Calcd for C53H67O26N3Zn4: C, 41.71, H, 4.74, N, 2.95; found C, 41.64, H, 4.85, N, 2.86. IR (KBr, cm−1): 3410(w), 1661(w), 1605(m), 1551(s), 1408(m), 1097(m), 1022(m), 776(m). {[Mn3(TCOPM)2(H2O)2]}n (2). A mixture of Mn(Ac)2·2H2O (26.8 mg, 0.1 mmol) and TCOPM (37.6 mg, 0.1 mmol) was added to in 8 mL of acetonitrile/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 80 °C for 3 days; colorless crystals were obtained (yield: 66% based on Mn). Anal. Calcd for C44H30Mn3O14: C, 55.77, H, 3.19; found C, 55.54, H, 3.31. IR (KBr, cm−1): 3414(w), 1604(w), 1537(m), 1396(s), 1174(m), 1108(m), 772(m). {[Cd3(TCOPM)2(DMF)(H2O)3]·3H 2O}n (3). A mixture of Cd(NO3)2·6H2O (33.4 mg, 0.1 mmol) and TCOPM (37.6 mg, 0.1 mmol) was dissolved in 8 mL of DMF/H2O (3:1, v/v). The final mixture was placed in a Parr Teflon-lined stainless steel vessel (10 mL) under autogenous pressure and heated at 85 °C for 3 days. A large quantity of colorless-plank crystals were obtained, which were washed with mother liquid, and dried under ambient conditions (yield: 73% based on Cd). Anal. Calcd for C47H45O19NCd3: C, 44.62, H, 3.58, N, 1.11; found C, 44.87, H, 3.41, N, 1.26. IR (KBr, cm−1): 3414(w), 3115(w), 1655(s), 1589(s), 1533(s), 1396(s), 1255(m), 1183(s), 1100(w), 839(w), 779(w), 665(m), 524(s). {[Cd3(TCOPM)2(4,4′-bipy)]·2H2O·2DMF}n (4). Compound 4 was prepared by a procedure similar to that for the preparation of compound 3 by using Cd(NO3)2·6H2O (33.4 mg, 0.1 mmol), TCOPM (37.6 mg, 0.1 mmol), and 4,4′-bipy (15.6 mg, 0.1 mmol) in 8 mL of DMF/H2O (3:1, v/v). Colorless-plank crystals were obtained (yield: 66% based on Cd). Anal. Calcd for C60H54Cd3N4O16: C, 50.59, H 3.82, N, 3.93; found C, 50.48, H, 3.75, N, 3.84. IR (KBr, cm−1): 3416(m), 1671(w), 1594(w), 1543(m), 1506(s), 1396(s), 1255(s), 1235(w), 1182(s), 1081(m), 1009(s), 839(w), 809(w), 779(m), 705(w), 659(s), 625(s), 516(m).

ray crystallography. The crystal structures, topological analyses, photoluminescent properties, and thermal properties are studied in detail. Scheme 1. Pyridine and Carboxylic-Substituted Triphenylmethyl Ligands

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EXPERIMENTAL SECTION

Materials and Methods. The reagents and solvents employed were commercially available and used as received. TCOPM was prepared by the literature methods.8 IR absorption spectra of the complexes 1−5 were recorded in the range of 400−4000 cm−1 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 Xray diffractometer using Cu−Kα radiation (λ = 1.5418 Å), in which the X-ray tube was operated at 40 kV and 40 mA. Solid-state UV−vis diffuse reflectance spectra were obtained at room temperature using a Shimadzu UV-3600 double monochromator spectrophotometer, and BaSO4 was used as a 100% reflectance standard for all materials. Luminescent spectra were recorded with a SHIMAZU VF-320 X-ray fluorescence spectrophotometer at room temperature. The emission decay lifetimes were measured on Edinburgh instruments FLS920 fluorescence spectrometer. The as-synthesized samples were characterized by TGA on a Perkin-Elmer thermogravimetric analyzer Pyris 1 TGA up to 1023 K using a heating rate of 10 K min−1 under N2 atmosphere. Gas Adsorption Measurements. N2 (0.0−1.0 bar) isotherms for compound 1 was recorded on a Micromeritics ASAP 2020 adsorption apparatus. UHP-grade gases were used in measurements. Before the measurement, the sample of 1 was soaked in dichloromethane (CH2Cl2) for 3 days to remove DMF and H2O solvent molecules, then filtrated, and dried at room temperature. Then, the sample was

Table 1. Crystallographic Data and Structure Refinement Details for Complexes 1−5 compound

1

2

3

4

5

empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) Z V (Å3) Dcalcd(g cm−3) μ(Mo Kα) (mm−1) F(000) R(int) observed data [I > 2σ(I)] R1, wR2 (I > 2σ(I)) S

C44H30O15Zn4 1060.24 orthorhombic Pbcn 33.291(7) 24.518(5) 16.748(4) 90.00 90.00 90.00 8 13670(5) 1.030 1.431 4272.0 0.0784 4973 0.1010/0.1796 1.099

C44H30Mn3O14 947.50 monoclinic C2/c 29.722(6) 13.552(2) 18.680(4) 90.00 124.540(6) 90.00 4 6198(2) 1.015 0.648 1924.0 0.0774 3688 0.0447/0.0884 1.029

C47H42Cd3NO18 1246.05 monoclinic P2/c 14.132(3) 25.112(5) 19.910(3) 90 121.51(1) 90 4 6024(2) 1.374 1.110 2476.0 0.0855 6660 0.0660/0.1925 1.170

C60H52Cd3N4O16 1422.29 monoclinic P2/c 13.3185(13) 9.4298(9) 25.8321(19) 90.00 116.342(4) 90.00 2 2907.4(5) 1.625 1.160 1424.0 0.0449 5000 0.0447/0.1205 1.054

C92H68Cd4N8O23 2103.19 monoclinic C2/c 29.1269(17) 12.9184(8) 25.2889(14) 90.00 103.408(1) 90.00 4 9256.2(9) 1.509 0.982 4208.0 0.0240 5885 0.0607/0.1813 1.084

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Figure 1. (a) View of the [Zn4(μ4-O)] cluster in 1. (b) 1D micropore along the a axis. (c) Schematic representation of the (3, 6) topological net. (d) The angles through the central C atom in 1.

Scheme 2. Crystallographically Established Coordination Modes of Carboxylic Groups in Compounds 1−5

{[Cd4(TCOPM)2(dpyb)3(NO2)2·(H2O)2]·5H2O}n (5). Compound 5 was prepared by a procedure similar to that for the preparation of compound 3 by using Cd(NO3)2·6H2O (33.4 mg, 0.1 mmol), TCOPM (37.6 mg, 0.1 mmol), and dpyb (23.3 mg, 0.1 mmol). A large quanitity of colorless plank crystals were obtained (yield: 53% based on Cd). Calcd for C92H76Cd4N8O23: C, 52.33, H 3.62, N, 5.31; found C, 52.48, H, 3.56, N 5.46. IR (KBr, cm−1): 3379(m), 3045(s), 2925(m), 1668(s), 1607(s), 1596(m), 1537(s), 1483(m), 1397(s), 1329(m), 1221(m), 1101(m), 1063(m), 1018(w), 851(m), 815(m), 783(s), 715(s), 673(m), 501(m). X-ray Data Collection and Structure Determinations. Single crystals of 1−5 were prepared in single crystal form. X-ray crystallographic data of 1−5 were collected at room temperature using epoxy-coated crystals mounted on glass fiber. All measurements were made on a Bruker Apex Smart CCD diffractometer with graphitemonochromated Mo−Kα radiation (λ = 0.71073 Å). The structures of complexes 1−5 were solved by direct methods, and the non-hydrogen atoms were located from the trial structure and then refined

anisotropically with SHELXTL using a full-matrix least-squares procedures based on F2 values.12a The hydrogen atom positions were fixed geometrically at calculated distances and allowed to ride on the parent atoms. The distribution of peaks in the channels of 1−3 was chemically featureless to refine using conventional discrete-atom models. To resolve these issues, the contribution of the electron density by the remaining watermolecule was removed by the SQUEEZE routine in PLATON.12b The relevant crystallographic data are presented in Table 1, while the selected bond lengths and angles are given in Supporting Information, Table S1.

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RESULTS AND DISCUSSION Synthesis and Spectral Characterization. Compounds 1−5 are prepared in single crystalline through the hydrothermal reaction of cadmium nitrate, zinc nitrate, manganese acetate, TCOPM acid, 4,4′-bipy, and dpyb. It should be pointed out that syntheses of compounds 1−5 are highly reproducible for

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Figure 2. (a) Coordination environment of the Mn(II) ion in 2. The hydrogen atoms are omitted for clarity. Symmetry codes: A = x, −1 + y, z. B = 0.5 − x, −0.5 + y, 0.5 − z. C = −0.5 − x, 1.5 − y, −0.5 + z. D = x, −1 + y, z. F = 0.5 − x, 1.5 − y, −z. (b) Views of the 2D net structure and Mn (II) ions along the c axis. (c) Views of the 1D chain structure along the b axis. (d) Views of the 2D net structure and Mn(II) ions along the a axis. (e) View of the topological type (tfz) of 2. (f) The angles through the central C atom in 2.

(TCOPM)2(H2O)2]·8H2O·3DMF}n based on IR, TGA, elemental analysis, and single-crystal X-ray diffraction studies. X-ray analysis reveals that 1 crystallized in orthorhombic space group Pbcn. As shown in Figure 1a, 1 consists of four crystallographically independent Zn(II) ions, two TCOPM ligands, two coordinated water molecules, and one μ4-O atom. The TCOPM anions all adopt a bidentate coordination mode to bridge two Zn centers (Scheme 2a). Zn1, Zn2, and Zn3 reside in tetrahedral environments, and each coordinates by three carboxylate oxygen atoms from different TCOPM ligands and one μ4-O atom at the center of the cluster. The Zn4 ion adopts an octahedral coordination geometry surrounded by the μ4-O atom, three carboxylate oxygen atoms, and another two oxygen atoms from two water molecules. The four Zn ions form a distorted tetrahedron around μ4-O, and the distances of μ4-O and Zn range from 1.918 to 2.001 Å, with the distances of Zn···Zn from 3.148 to 3.229 Å, which falls in the usual range for similar clusters.14 The Zn−O−Zn angles for μ4-O are revealed to range from 109.45 to 110.94° and deviate slightly from the ideal value for the tetrahedral [Zn4O] motif. We note that the

repeated synthesis under the reaction conditions employed in this work. The infrared spectra of all of the compounds are consistent with their crystal structures (Figures S1−S5, Supporting Information). For all complexes, the absorption bands in the 1400−1600 cm−1 region and in 1454−1348 cm−1 show the skeletal vibrations of the aromatic ring for asymmetric vibration and for the symmetric vibration, respectively. The vibrations bands at 3400 cm−1, 1671−1660 cm−1, and 1607− 1602 cm−1 indicate the presence of H2O, DMF, and −COO−, respectively. The vibrations bands at 1329 cm−1 and 1221 cm−1 indicate the presence of NO2− in compound 5, which is consistent with the X-ray structural analysis.13 Phase purity was verified by elemental analysis and PXRD (Figures S6 and 8−10, Supporting Information). All compounds do not dissolve in water and common organic solvents. As can be seen from the Supporting Information (Figure S7), crystal 2 loses solvent molecules very rapidly at room temperature, becoming amorphous materials. Crystal Structure of {[Zn4O(TCOPM)2(H2O)2]·8H2O·3DMF}n (1). 1 is formulated as {[Zn4O1025



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Figure 3. (a) Coordination environment of the Cd(II) ion in 3. The hydrogen atoms are omitted for clarity. W represents water molecule. Symmetry codes: # = −1 + x, 1 − y, −0.5 + z. (b) Views of the 2D net structure and Cd(II) ions along the c axis. (c) Views of the 2D net structure and Cd(II) ions along the a axis. (d) Views of the 2D net structure and Cd(II) ions along the b axis. (e) The angles through the central C atom in 3.

connection nets. The TCOPM ligand acts as a 3-connected node. A μ4-oxo bridged Zn4O cluster is bridged by six carboxylate groups from six TCOPM3− units to provide the octahedron-shaped secondary building unit (SBU), which extends infinitely to give to 6-connected nets. So, the total topology of 1 can be considered to be a 3-nodal (3, 3, 6)connected net, and the Schläfli symbol is (4.82)(42.6)(43.6·810.10), as displayed in Figure 1c. Crystal Structure of {[Mn3(TCOPM)2(H2O)2]}n (2). X-ray analysis reveals that 2 crystallizes in monoclinic space group C2/c. As shown in Figure 2a, 2 consists of one and a half crystallographically Mn(II) ions, one TCOPM ligand, and one coordinated water. The TCOPM anions adopt two coordination modes: two carboxyl groups adopt a chelating coordination mode to bridge two Mn centers, and the other carboxylate group coordinates to two Mn centers by adopting a monodentate coordination mode (Scheme 2b). The Mn1 is octahedrally coordinated, bound to two oxygen atoms from two TCOPM ligands (Mn1−O: 2.117(5), 2.119(2) Å) in the apical positions and four oxygen atoms from four TCOPM ligands (Mn1−O: 2.117(5)−2.231(2) Å) in the equatorial positions. The Mn2 is also octahedrally coordinated, bound to five oxygen

clusters in 1 are different from the usual [Zn4O(CO2)6] clusters in the previous IRMOF-n series. In these previous series, all Zn ions are tetrahedrally coordinated by three carboxylate oxygens and a central μ4-O atom, as found for Zn1, Zn2, and Zn3 in 1, and each pair is bridged by a μ4-O atom and a μ2-carboxylate, with no solvent molecules involved in coordination. In 1, however, the solvent molecules are incorporated into a cluster leading to distortion of the cluster from tetrahedral.14c Compound 1 generates a 3D framework with a onedimensional (1D) channel through such coordination mode (Figure 1b), and the void volume calculated by PLATON15a is 49.5%. The central C atom undergoes significant positional and rotational rearrangements for the triangular carboxylate arms and flexible structures. As shown in Figure 1d, in 1, there are two kinds of different positional and rotational rearrangements around the central C atom; their angles are 111.4°, 110.3°, 113.1°, 110.5°, 109.6°, 109.6°, respectively, and those rotations will further result in changes in topology. A better insight into the nature of this intricate framework can be achieved by the application of a topological approach, reducing multidimensional structures to simple node and 1026



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Figure 4. (a) Coordination environment of the Cd(II) ion in 4. The hydrogen atoms are omitted for clarity. (b) Views of the net structure and Cd(II) ions along the b axis. (c) Views of the 2D net structure and Cd(II) ions along the b axis. (d) Views of the 1D net structure of 4 along the a axis. (e) Views of the 3D net structure of 4 along the b axis. (f) Views of the (3, 3, 10) net structure of 4. (g) The angles through the central C atom in 4.

atoms from four TCOPM anions (Mn2−O: 2.055(2)− 2.520(8) Å) and one oxygen atom from one water molecule (Mn2−O: 2.218(8) Å). In compound 2, the two Mn(II) atoms are bridged by one carboxylate to form a binuclear cluster with Mn(1)···Mn(2) separation of 3.472(8) Å. Each binuclear cluster is connected by O atoms to form a 1D wave-shaped chain (Figure 2c). The TCOPM ligands are connected by binuclear Mn clusters to attain an infinite 2D network (Figure

2b) and then further generate a 3D structure with a 1D channel (Figure 2d). Compared with 1, there is one kind of positional and rotational rearrangement based on the central C atom; their angles are 115.3°, 110.2°, 115.1° (Figure 2f), respectively. According to the literature, the intrinsic packing arrangement of 1D SBUs can prevent interpenetration to guarantee a porous MOF.15b,c Interconnection of the large polyhedral SBUs generates two different quadrangle channels (larger as A and 1027



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Figure 5. (a) Coordination environment of the Cd(II) ion in 5. The hydrogen atoms are omitted for clarity. (b) Views of the 2D net structure and Cd(II) ions along the c axis. (c) Coordination environment of dpyb ligands. (d) Views of the 2D net structure and Cd(II) ions along the b axis. (e) The binodal net with (623·85)(63)2(65·8) topology net. (f) The angles through the central C atom in 5.

Crystal Structure of {[Cd3(TCOPM)2(DMF)(H2O)3]·3H2O}n (3). X-ray analysis reveals that 3 crystallizes in monoclinic space group P2/c. The asymmetric unit of 3 contains three independent Cd(II) cations, two TCOPM3− anions, three H2O, one DMF, and three free H2O. As shown in Figure 3a, both Cd2 and Cd4 centers are six coordinated by six carboxylic O atoms from TCOPM ligands to form a slight distorted octahedral geometry. While Cd1 is six coordinated with one water molecule, one DMF molecule, and four carboxylic O atoms from three TCOPM ligands, Cd3 is six coordinated with two O atoms of water molecules and four carboxylic O atoms from three TCOPM ligands. The Cd−O lengths are in the range of 2.212(3)−2.587(3) Å, which are all similar to the values found in other Cd(II) complexes.16 Each completely deprotonated TCOPM3− anion coordinates to six Cd atoms by adopting different chelating bidentate coordination modes (Scheme 2c). As shown in Figure 3e, although possessing two kinds of different rearrangements of the central C atom which is similar to 1, their angles through the central C atom are different with 109.9°, 113.9°, 113.6°, 110.2°, 112.9°, 113.6°, respectively.

small as B, respectively) along the a axes (with apertures of 12.7460, 8.6302 Å). From Figure 2b, it can be seen that rhombus channels are large with a total potential solvent accessible void volume of 47.5% of the cell volume by PLATON. When it lost solvent molecules, 2 became opacity and turned into powder finally. The PXRD pattern shows a very broad peak, which indicates that 2 does not retain its structure. Thereby, such open structures do not have permanent porosity because collapse occurs upon removal of solvent guest molecules. To fully appreciate the structure and its topology, it is necessary to consider that the Mn1 atom can be regarded as one kind of linker because the Mn1 atom is located in a symmetrical position to link four Mn2 atoms, and the TCOPM ligand is considered as another kind of linker. Thus, TCOPM ligands and four Mn2 atoms surrounding a Mn1 center constitute an eight-connected octahedral SBU. According to this simplification, the topology of this 3D network can be described as a (43)2(46.618.84), and the topological type is tfz-d (Figure 2e). 1028



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TCOPM anions adopt three coordination modes: one carboxyl group adopts a bis(monodentate) coordination mode to bridge two Cd centers, one carboxylate group adopts a chelating coordination mode, and another adopts a monodentate coordination mode (Scheme 2e). The Cd1 is an octahedral coordination geometry coordinated by two nitrogen atoms from two dpyb ligands (Cd1−N: 2.312(6) Å) in the apical positions, two oxygen atoms from two TCOPM anions (Cd1− O: 2.285(7) Å) and two oxygen atoms from NO2− in the equatorial positions. The Cd2 is seven coordinated by two nitrogen atoms from two dpyb ligands (Cd1−N: 2.284(6) Å), three oxygen atoms from two TCOPM anions (Cd2−O: 2.255 (4)-2.408(6) Å), and two oxygen atoms from NO2− (Cd2−O: 2.422 (8), 2.582(8) Å). The Cd3 is also seven coordinated by two oxygen atoms from two NO2−, two oxygen atoms from two TCOPM anions and three oxygen atoms from three water molecules. It is noted that C34 and C35 atoms (pyridine ring) of the dpyb ligand are disordered. If dpyb ligands are omitted, as shown in Figure 5b, the structure of 5 is different from 3 and 4. The connection of 5 is very complex such that every two TCOPM ligands are coordinated with Cd atoms in the same aspect while adjacent two TCOPM ligands adopt opposite directions to coordinate with Cd atoms. Thus, the connection among TCOPM makes the cavities more huddled and the channels small (15.5%). As shown in Figure 5c, although three dpyb ligands are arranged in parallel, they are not coplanar and show a certain distortion. Comparing with 4, there is a little difference in that their angles through the central C atom are 115.4°, 114.6°, 107.1°, respectively, owing to the presence of the longer auxiliary dpyb ligand (Figure 5f). In compound 5, the Cd(II) atoms are bridged by carboxylate and N ligands to form a trinuclear cluster with Cd1···Cd2 and Cd2···Cd3 separation of 4.211(2) and 4.586(9) Å, respectively. Each trinuclear Cd is connected by O and N atoms to form a 1D wave-shaped chain (Figure 5d). The TCOPM ligands share the trinuclear Cd cluster with dpyb ligands and NO2− to attain an infinite 2D network (Figure 5b) and then further generate a 3D structure by the connection of a 1D wave-shaped chain. Because the Cd1 atom is located in a symmetrical position to link two Cd2 atoms and the Cd3 atom is also located in a symmetrical position, they can be regarded as two kinds of linkers, with the TCOPM3− and dpyb ligands considered as the other two linkers. Thus, the Cd1 acts as 8-conncting node, Cd3 acts as 4-connecting node, and TCOPM3− are simplified as 3connecting nodes. Therefore, as determined by TOPOS software, the topology for this 3D network can be described as a (623.85)(63)2(65.8) net. From the structural descriptions above, it can be seen that the neutral ligands have an influence on the frameworks of the complexes. As shown in Scheme 2, the TCOPM with flexibilities in 3, 4, and 5 display different bridging coordination modes (a, b, and c in Scheme 2, respectively) and play an important role in affecting the final structures. 3 exhibits two bis(monodentate) bridging and a tridentate chelating bridging modes through oxygen atoms of TCOPM, water, and DMF, 4 possesses a bis(monodentate) chelating bridging, a quadridentate and a tridentate chelating bridging modes, while 5 shows a monodentate, a bis(monodentate) chelating bridging, and a bidentate chelating bridging mode. Comparing with 3, although possessing the same ligand, 1 and 2 are a 3D structure with large pores. In 1, TCOPM all adopt bis(monodentate) bridging modes, while in 2, TCOPM adopts one bis(monodentate) bridging and two tridentate chelating bridging

Interconnection of the large polyhedral SBUs generates two different quadrangle channels (large as A and small as B, respectively) along the c axes (with apertures of 12.1491 and 6.86 Å, respectively) and one quadrangle channel along the a axs (with apertures of 11.308 Å) because of the rotational orientation of the flexible ligand phenyl rings. From Figure 3c, it can be seen that a quadrangle channel (D) is jammed by DMF molecules. Although possessing different channels, these cavities are not large with a total potential solvent accessible void volume of 32.4% of the cell volume. A 2D layered structure with channels is attained by the connection among the Cd center and O atom of TCOPM3− (Figure 3b), while it is interesting that this 2D is composed of a double-layered structure through the connection of two TCOPM3− and Cd atoms (Figure 3d). Crystal Structure of {[Cd3(TCOPM)2(4,4′-bipy)]·2DMF·2H2O}n (4). X-ray analysis reveals that compound 4 is solved in monoclinic space group P2/c. The fundamental building unit of 4 contains one and a half independent Cd(II) cations, one TCOPM3− anion, half a 4′4-bipy ligand, one free DMF molecule, and one free water molecule. The TCOPM3− ions take different coordination modes (Scheme 2d). As shown in Figure 4a, Cd1 is seven coordinated by six carboxylic O atoms from four TCOPM and one nitrogen atom from one 4′4-bipy ligand to form a distort trigonal bipyramidal geometry, while the Cd2 is an octahedral coordination environment of six carboxylic O atoms from five TCOPM. The Cd−O lengths are in the range of 2.27(6)−2.491(5) Å and Cd−N length is 2.312(5) Å. To avoid overlap in compound 4, the 4′4-bipy ligand is omitted in order to clarify and simplify the structure (Figure 4c). As shown in Figure 4c, there is a clear difference that complex 3 consists of a 2D layered structure with two different channels, while 4 possesses a homogeneous channel with a 3D structure. The 2D net structure in 4 is made up of TCOPM, 4′4-bipy, and Cd atoms, and then the O atoms of TCOPM ligands link a large number of Cd atoms to further generate an infinite 3D framework in the axial position of the coordination (Figure 4d). In addition, it is interesting that 4′4-bipy as pillar is connected with Cd atoms and divided quadrangle into two groups, while in the nearest quadrangle 4′4-bipy is not coordinated with Cd atoms (Figures 4b,e). These cavities in 4 (with a total potential solvent accessible void volume of 29.9% of the cell volume) are smaller than that of 3. In 4′4-bipy, two pyridine rings are not coplanar with a dihedral angle of 42.109 Å. In addition, the presence of auxiliary 4,4′-bipy cannot affect greatly their angles through the central C atom; there are similar angles of 111.3°, 111.5°, 114.9°, respectively. In 4, if the Cd2 atoms, TCOPM and 4′4-bipy ligands are considered as linkers to connect two Cd1 atoms, then based on the SBU concept, the four Cd2 atoms, TCOPM and 4′4-bipy ligands around one Cd1 center generate a 10-connected octahedral SBU. On the basis of this simplification, the whole structure can be described as a (3, 3, 10)-connected net (Figure 4c). If omitting the 4′4-bipy ligand, the topological type of 4 is tfz-d which is the same as 2. Crystal Structure of {[Cd4(TCOPM)2(dpyb)3(NO2)2·(H2O)2]·5(H2O)}n (5). When 4′4bipy is replaced by dpyb, a structurally different complex 5 is obtained. As shown in Figure 5a, the asymmetric unit of 5 contains two crystallographically independent Cd(II) ions, one TCOPM ligand, one NO2−, one, and a half dpyb ligand, one water molecule, and two and a half free water molecules. The 1029



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modes. Because of the different coordination modes and angular features from 1−5, they show different structural types, as expected. PXRD and TG Results. To confirm whether the crystal structures are truly representative of the bulk materials, PXRD experiments were carried out for 1 and 3−5. The PXRD experimental and computer-simulated patterns of the corresponding complexes are shown in Supporting Information (Figures S6 and 8−10). They show that the synthesized bulk materials and the measured single crystals are the same. To estimate the stability of the coordination architectures, 1, 3, 4, and 5 thermal behaviors were studied by TGA (Supporting Information, Figure S11). Complex 1, a weight loss of 28.1% (calcd 28.04%) are observed from 50 to 248 °C, which is attributed to the loss of the coordinated water, free water (50−170 °C), and the free DMF molecules (170−248 °C), and decomposed quickly after 431 °C, suggesting that the framework is more thermally stable than 3−5. For complex 3, a weight loss of 14.4% is observed from 133.1 to 231 °C, which is attributed to the loss of the coordinated water, free water, and the coordinated DMF molecules, and then it is decomposed quickly after 360 °C, suggesting that the framework is thermally stable. For complex 4, the TGA curve is similar to that of 3; a weight loss of 12.7% (calcd 12.8%) is observed from 110 to 247 °C, which is attributed to the loss of the coordinated water and the free DMF molecules, and next the structure collapses at 240 °C. For complex 5, a weight loss of 5.8% (calcd 5.9%) is observed from 177 to 266 °C, which is attributed to the loss of coordinated water and the free water molecules, and next the structure collapses at 315 °C. Photochemical Properties. Luminescent compounds are of great interest for their various applications in chemical sensors and photochemistry. Therefore, in the solid state luminescent properties of free ligands TCOPM, 4′4-bipy, dpyb, complexes 1, 3, 4, and 5 at room temperature were investigated, as depicted in Figure 6 and Supporting Information (Figures S12−16). The emissions of the free ligands are observed with wavelengths from 446 to 570 nm (λmax = 469 nm) for TCOPM, from 371 to 497 nm (λmax = 410 nm) for dpyb, and from 361 to 486 nm (λmax = 380 and 400 nm) for 4′4-bipy, which could be attributed to the π* → π or π* → n transitions. Complex 3 exhibits the same emission characteristics as the free TCOPM ligands, and the emission peak is 467 nm. 4 shows a clearly blue-shift 18 nm compared with that of TCOPM ligand, and 5 is exhibits emission characteristics similar to that of the dpyb ligand. More important is that 1 shows an uncommon red-shift in emission compared to TCOPM, displays an intense emission peak band at λem = 579 and 610 nm, and emits a bright salmon pink color upon ultraviolet radiation. The excitation scan suggests the luminescence intensity is maximized around λex = 390 nm. The emission decay lifetimes of compounds 1, 3, 4, and 5 are monitored, and the curves are best fitted by biexponentials in the solid. The emission decay lifetimes of compounds 1, 3, 4 and 5 are complex 1, τ1 = 58.87 ns (92.9%) and τ2 = 4.004 ns (7.07%) (χ2 = 1.024, Figure S17); complex 3, τ1 = 2.429 ns (33.07%) and τ2 = 9.709 ns (66.93%) (χ2 = 1.179, Figure S18); complex 4, τ1 = 1.954 ns (31.99%) and τ2 = 7.507 ns (68.01%) (χ2 = 1.275, Figure S19); complex 5, τ1 = 1.017 ns (43.4%) and τ2 = 3.425 ns (56.60%) (χ2 = 1.024, Figure S20). In the solid state, molecular interactions can bring lumophores close together, enabling electronic interactions between the lumophores (ligand-to-ligand charge transfer

Figure 6. Difference of solid-state, room-temperature emission photoemission spectra for TCOPM, 4′4-bipy, dpyb, 1, 3, 4, and 5.

(LLCT)), which can cause spectral shifts and broadening in the emission, so controlling ligand−ligand interactions is important. In this paper, with tuning from single ligand to mixed ligand, the luminescent properties have correspondingly changed. In comparison with the free TCOPM ligands, the emission maxima of compounds 4 and 5 show a clear blue-shift, which is probably caused by a change in the HOMO and LUMO energy levels of deprotonated TCOPM anions and neutral ligands coordinating to metal centers, a charge-transfer transition between ligands and metal centers, and a joint contribution of the intraligand transitions or charge-transfer transitions between the coordinated ligands and the metal centers.11 It is also connected with not coplanar and different distortion among benzene rings, preventing efficient electron transfer in 4 and 5. With the changes of single ligand to mixed ligand, emission decay lifetimes of 3, 4, and 5 decrease step by step, a phenomenon which may also be connected with the electronic interactions of ligands. While 1 shows a red-shift for an efficient energy transfer from the organic part of the framework to cluster, which is in agreement with the [Zn4O] cluster in IRMOF-1 (with BDC as linkers) as a ZnO-like quantum dot (QD) and an efficient energy transfers from the BDC linker as a photon trap to the cluster as a photon emitter.14c,17 The UV−vis absorption spectra of compounds 1, 3, 4, and 5 were also obtained in the crystalline state at room temperature (TCOPM in the solid state). As shown in Figure S21, TCOPM shows intense absorption peaks at 220−320 nm, which can be ascribed to π−π* transitions of the ligands. Energy bands of 1, 3, 4, and 5 from 500−600 nm are assigned as d−d transitions, while lower energy bands from 340 to 500 nm are probably assigned as metal-to-ligand charge-transfer (MLCT) transitions.9a The absorption spectrum bands of complexes 1, 3, 4, and 5 descrease in turn, which is in accordance with the changes of fluorescence. N2 Adsorption Properties. To assess the porosity of 1, N2 gas sorption measurement was carried out, and the adsorption isotherm is depicted in Supporting Information (Figure S22). The N2 isotherm at 77 K reveals that 1 exhibits typical type I adsorption behavior: the adsorption and desorption branches are closed without hysteresis. Compound 1 adsorbs 29.6 cm3 g−1 of N2 at 77 K, corresponding to a Brunauer−Emmett− Teller (BET) surface area of 88.9 m2 g−1 (within the range 0.06 < p/p0 < 0.2). The N2 adsorption shows very good reversibility. However, the gas uptakes are not as high as the pore volume 1030



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(7) (a) Pan, Z. R.; Zheng, H. G.; Wang, T. W.; Song, Y.; Li, Y. Z.; Guo, Z. J.; Batten, S. R. Inorg. Chem. 2008, 47, 9528. (b) Wang, J.; Lin, Z. J.; Ou, Y. C.; Yang, N. L.; Zhang, Y. H.; Tong, M. L. Inorg. Chem. 2008, 47, 190. (c) Ockwig, N. W.; Delgado-Friedrichs, O.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2005, 38, 176. (d) Abourahma, H.; Moulton, B.; Kravtsov, V.; Zaworotko, M. J. J. Am. Chem. Soc. 2002, 124, 9990. (8) Xu, Y. Q.; Lu, J. M.; Li, N. J.; Yan, F.; Xia, X. W.; Xu, Q. F. Eur. Polym. J. 2008, 44, 2404. (9) (a) Hu, J. S.; Huang, L. F.; Yao, X. Q.; Qin, L.; Li, Y. Z.; Guo, Z. J.; Zheng, H. G.; Xue, Z. L. Inorg. Chem. 2011, 50, 2404. (b) Qi, Y.; Che, Y. X.; Zheng, J. M. CrystEngComm 2008, 10, 1137. (c) Henninger, S. K.; Habib, H. A.; Janiak, C. J. Am. Chem. Soc. 2009, 131, 2776. (d) Ma, L. F.; Wang, L. Y.; Wang, Y. Y.; Du, M.; Wang, J. G. CrystEngComm 2009, 11, 109. (10) (a) Habib, H. A.; Sanchiz, J.; Janiak, C. Inorg. Chim. Acta 2009, 362, 2452. (b) Habib, H. A.; Hoffmann, A.; Höppe, H. A.; Janiak, C. Dalton. Trans. 2009, 1742. (c) Habib, H. A.; Sanchiz, J.; Janiak, C. Dalton. Trans. 2008, 1734. (d) Zhang, L. P.; Yang, J.; Ma, J. F.; Jia, Z. F.; Xie, Y. P.; Wei, G. H. CrystEngComm 2008, 10, 1410. (e) Wisser, B.; Lu, Y.; Janiak, C. Z. Anorg. Allg. Chem. 2007, 633, 1189. (f) Manna, S. C.; Okamoto, K. I.; Zangrando, E.; Chaudhuri, N. R. CrystEngComm 2007, 9, 199. (g) Chen, Z. F.; Zhang, S. F.; Luo, H. S.; Abrahams, B. F.; Liang, H. CrystEngComm 2007, 9, 27. (11) (a) Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Chem. Soc. Rev. 2009, 38, 1330. (b) Guo, H. D.; Guo, X. M.; Batten, S. R.; Song, J. F.; Song, S. Y.; Dang, S.; Zheng, G. L.; Tang, J. K.; Zhang, H. J. Cryst. Growth Des. 2009, 9, 1394. (12) (a) Bruker (2000), SMART (Version 5.0), SAINT-plus (Version 6), SHELXTL (Version 6.1), and SADABS (Version 2.03); Bruker AXS Inc.: Madison, WI. (b) Platon Program:Spek, A. L. Acta Crystallogr., Sect. A 1990, 46,194. (13) (a) Zhao, Q. H.; Wang, Q. H.; Fang, R. B. Transition Met. Chem. 2004, 29, 144. (b) Xu, J.; Yao, X. Q.; Huang, L. F.; Li, Y. Z.; Zheng, H. G. CrystEngComm 2011, 13, 857. (14) (a) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469. (b) Kesanli, B.; Cui, Y.; Smith, M. R.; Bittner, E. W.; Bockrath, B. C.; Lin, W. B. Angew. Chem., Int. Ed. 2005, 44, 72. (c) Yue, Q.; Sun, Q.; Cheng, A. L.; Gao, E. Q. Cryst. Growth Des. 2010, 10, 44. (15) (a) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (b) Devic, T.; Serre, C.; Audebrand, N.; Marrot, J.; Férey, G. J. Am. Chem. Soc. 2005, 127, 12788. (c) Zhang, J. P.; Lin, Y. Y.; Zhang, W. X.; Chen, X. M. J. Am. Chem. Soc. 2005, 127, 14162. (16) Dai, J. C.; Wu, X. T.; Fu, Z. Y.; Cui, C. P.; Hu, S. M.; Du, W. X.; Wu, L. M.; Zhang, H. H.; Sun, R. Q. Inorg. Chem. 2002, 41, 1391. (17) Bordiga, S.; Lamberti, C.; Ricchiardi, G.; Regli, L.; Bonino, F.; Damin, A.; Lillerud, K. P.; Bjorgen, M.; Zecchina, A. Chem. Commun. 2004, 2300. (18) (a) Cheon, Y. E.; Suh, M. P. Chem. Commun. 2009, 2296. (b) Chang, Z.; Zhang, D. S.; Hu, T. L.; Bu, X. H. Cryst. Growth Des. 2011, 11, 2050.

derived from the crystal structure, which suggests that the framework of 1 is significantly collapsed or shrunk by the removal of the guests.18

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CONCLUSION Under hydrothermal conditions, the reaction of Cd/Mn/Zn salt with TCOPM, 4′4-bipy, or dpyb generates five novel coordination polymers with different structures. The photochemical properties and emission decay lifetimes in the solid state at room temperature were performed. With the changes of coordination of metal with ligand (from single-ligand to mixedligand), the size of the channels have also correspondingly changed from big to small. 3 exhibits emission characteristics similar to the free TCOPM ligands, 4 and 5 show a clear blueshift, while 1 displays two intense emission peak bands at λem = 579 and 620 nm. The gas uptakes of 1 are not as high as the pore volume derived from the crystal structure, which suggests that the framework of 1 is significantly collapsed or shrunk by the removal of the guests.

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ASSOCIATED CONTENT

S Supporting Information *

Five X-ray crystallographic files in CIF format, selected bond lengths, angles, UV absorbance, luminescence spectra, TGA, PXRD, and IR in PDF format. This information is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

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

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

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REFERENCES

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Five Novel Coordination Polymers Based on a C-Centered Triangular

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