Three-Dimensional Metal (II)− Organic Coordination Polymers from

Mar 3, 2010 - ‡Department of Materials and Chemical Engineering, Taishan University, Taian 271021, P. R. China, and §Hefei National Laboratory for ...
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DOI: 10.1021/cg900579s

Three-Dimensional Metal(II)-Organic Coordination Polymers from Binuclear, Trinuclear, and Polynuclear Clusters Bridged by p-Benzenediacrylates: Syntheses, Topologies, Photosensitive Properties, and Hydrogen Uptake

2010, Vol. 10 1508–1515

Kun-Lin Huang,*,† Xi Liu,† Ji-Kun Li,‡ Yan-Wei Ding,§ Xin Chen,† Ming-Xing Zhang,† Xiao-Bo Xu,† and Xiao-Jun Song† †

College of Chemistry, Chongqing Normal University, Chongqing 400047, P. R. China, Department of Materials and Chemical Engineering, Taishan University, Taian 271021, P. R. China, and §Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, P. R. China

‡

Received May 29, 2009; Revised Manuscript Received December 17, 2009

ABSTRACT: The hydrothermal/solvothermal reactions of metal(II) nitrate hydrates with organic ligands (p-benzenediacrylic acid = H2pbda, 1,10-phenanthroline = phen) generate three three-dimensional (3-D) coordination polymers with (3,4)connected (4.8.10)(42.6.8  102) topology (1, {[Cd2(pbda)2(phen)2](H2O)}n), 2-fold interpenetrating CdSO4-type open framework (2, [Zn3(pbda)3(phen)2]n), and 3-fold interpenetrated sra net (3, [Pb(pbda)]n). The porous zinc open framework 2 has the typical type-I sorption curve with a H2 uptake of 31 cm3 3 g-1(STP) at 77 K, BET surface area of 65.84 m2 3 g-1, and meso-[Zn2(pbda)2] helical motifs. With strong luminescent emission at 504 nm, complex 2 may be suitable as an excellent candidate for solid-state photosensitive materials at room temperature.

Introduction The self-assembly of metal-organic frameworks (MOFs) from metal ions and organic moieties is of much current interest in crystal engineering because of their outstanding bulk properties (gas uptake, catalysis, photosensitivity, and so on), which are intimately related to their structures.1 For the construction of three-dimensional (3-D) MOFs with porous and regular/semiregular nets (pts, sod, dia, nbo, pcu, etc.), some functional organic ligands, for example, 4,40 -bipyridine, azolate, and aromatic acids, are usually chosen as rigid tectons.2 For the helical or interpenetrating architectures, the long or the flexible linkers are good candidates, such as 4,40 -oxybis(benzoate), 1,3-di(pyridin-4-yl)propane, and 1, 2-di(4-pyridyl) ethane.3 However, it is still a great challenge to synthesize a predicted structure because there are numerous influences that can have decisive roles in determining the structure and crystal packing. Fortunately, these uncertainties can be reduced by the use of well selected spacers that have the ability to aggregate metal ions into different secondary building units (SBUs).4 Moreover, as we know, 1,10-phenanthroline (phen) usually serves as an excellent chelate group in coordinate chemistry, and most of its derivatives are zerodimensional (0-D), one-dimensional (1-D), and two-dimensional (2-D), while its 3-D coordinate frameworks are relatively rare.5 In this work, we choose an elongated dicarboxylate ligand, p-benzenediacrylic acid (H2pbda), for building 3-D coordinate networks with diverse topologies and properties, on the basis of the following considerations: (i) Athough the ditopic symmetry H2pbda and its derivatives or analogues have wide applications in the field of solid-state photosensitive

*To whom correspondence should be addressed. Tel: 86-23-65910308. Fax: 86-23-65362770. E-mail: [email protected]. pubs.acs.org/crystal

Published on Web 03/03/2010

materials,6 H2pbda has not been well exploited in building MOFs, few metal complexes of H2pbda are reported,7 and only one 3-D MOF of H2pbda has been recently reported;8 (ii) H2pbda is a long ligand (12.4 A˚), which may lead to cavities, interpenetration, helical structures, and other novel motifs. Herein, we report our effort on 3-D metal(II) coordinate polymers with distinct topologies based on the H2pbda building block. Experimental Section General Materials and Methods. All reagents and solvents for synthesis and analysis were commercially available and used as received. Infrared spectra were recorded with a Nicolet ESP 460 FTIR spectrometer on KBr pellets in the range of 4000-400 cm-1. Carbon, hydrogen, and nitrogen analyses were performed on a PE2400II (Perkin-Elmer) analyzer. Luminescence spectra of the solid samples were recorded on a Varian Cary Eclipse spectrometer. Thermogravimetric analysis (TGA) experiments were carried out on a Dupont thermal analyzer from room temperature to 800 C under N2 atmosphere at a heating rate of 10 C /min. X-ray powder diffraction (XRPD) patterns were taken on a Rigaku D/max-2500 diffractometer at 40 kV and 300 mA for Cu KR radiation (λ = 1.5406 A˚), with a scan speed of 2o/min and a step size of 0.02 in a 2θ range of 4-40. Single-Crystal X-ray Diffraction Determination and Refinement. Single-crystal X-ray diffraction measurements of 1-3 were performed on a Bruker Apex II CCD diffractometer at the ambient temperature with Mo Ka radiation (λ = 0.71073 A˚). A semiempirical absorption correction was applied using SADABS, and the program SAINT was used for integration of the diffraction profiles.9 The structures were solved by direct methods using the SHELXS program of SHELXTL packages.9 The final refinement was performed by full-matrix least-squares methods on F2 with the SHELXL program. Hydrogen atoms bound to carbon were placed geometrically using a riding mode with the isotropic displacement parameters fixed at 1.2 times Ueq of the parent atoms. Further details for structural analysis are summarized in Table 1, and the selected bond lengths and angles are listed in Table 2. r 2010 American Chemical Society

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Table 1. Crystal Data and Structure Refinement for Compounds 1-3 data and refinement

1

Table 2. Selected Interatomic Distances (A˚) and Angles (Deg) for Compounds 1-3a Cd(1)-O(7) Cd(1)-O(4)#1 Cd(1)-N(2) Cd(2)-O(3) Cd(2)-N(3) Cd(2)-N(4) O(7)-Cd(1)-O(1) O(1)-Cd(1)-O(4)#1 O(1)-Cd(1)-N(1) O(7)-Cd(1)-N(2) N(2)-Cd(1)-O(5) O(3)-Cd(2)-O(2) O(2)-Cd(2)-N(3) O(2)-Cd(2)-O(5) O(3)-Cd(2)-N(4) N(3)-Cd(2)-N(4) O(3)-Cd(2)-O(6) N(3)-Cd(2)-O(6) Zn(1)-O(1) Zn(1)-O(5) Zn(2)-O(3) Zn(2)-N(2) O(1)-Zn(1)-O(3)#1 O(1)#1-Zn(1)-O(3) O(1)#1-Zn(1)-O(5) O(3)-Zn(1)-O(5) O(2)-Zn(2)-O(6) O(2)-Zn(2)-N(2) O(6)-Zn(2)-N(2) O(3)-Zn(2)-N(1) Pb(1)-O(1) Pb(1)-O(2)#2 O(1)-Pb(1)-O(2) O(2)-Pb(1)-O(2)#1 O(2)-Pb(1)-O(2)#2

2

3

Zn3C60H40N4O12 1205.13 298(2) 0.71073 monoclinic P2/n 12.321(3) 10.609(3) 25.816(7) 91.739(4) 3372.9(1) 2, 1.187 1.113 1228 1.58 to 25.01 16616/5947 [R(int) = 0.0725] 5947/0/358 1.001 R1 = 0.0591, wR2 = 0.1323 R1 = 0.1074, wR2 = 0.1611 0.843/-1.360

PbC12H8O4 423.38 298(2) 0.71073 monoclinic C2/c 24.800(8) 5.4672(1) 7.999(3) 96.237(5) 1078.1(6) 4, 2.609 15.647 1728 3.31 to 25.35 2717/987 [R(int) = 0.0217] 987/0/82 1.030 R1 = 0.0151, wR2 = 0.0326 R1 = 0.0160, wR2 = 0.0329 0.566/-0.534

)

)

empirical formula Cd2C48H34N4O9 formula weight 1035.61 temperature (K) 298(2) wavelength (A˚) 0.71073 crystal system monoclinic space group P21/c a (A˚) 11.0351(1) b (A˚) 23.458(2) c (A˚) 15.7276(1) β (deg) 101.759(2) 3 3985.8(6) V (A˚ ) 4, 1.726 Z, Fcalcd (g/cm3) 1.134 absorption coefficient (mm-1) F(000) 2072 theta range (deg) 1.58 to 25.01 reflections collected/unique 20003/7023 [R(int) = 0.0257] data/restraints/parameters 7015/12/568 GOF 1.004 R1 = 0.0348, wR2 = 0.0758 final R indices [I > 2σ(I)] a,b R indices (all data) R1 = 0.0504, wR2 = 0.0873 1.626/-2.001 peak/hole [e/A˚3 ] P P P P a R1 = Fo| - |Fc / |Fo| b wR2 = { [w(Fo2 - Fc2)2]/ [w(Fo2)]2}1/2.

Compound 1 2.196(3) Cd(1)-O(1) 2.408(3) Cd(1)-N(1) 2.448(3) Cd(1)-O(5) 2.251(2) Cd(2)-O(2) 2.354(4) Cd(2)-O(5) 2.422(4) Cd(2)-O(6) 168.98(11) O(7)-Cd(1)-O(4)#1 99.22(9) O(7)-Cd(1)-N(1) 95.90(10) N(1)-Cd(1)-O(4)#1 93.18(11) N(1)-Cd(1)-O(5) 168.80(10) O(1)-Cd(1)-N(2) 84.36(9) O(3)-Cd(2)-N(3) 130.38(11) O(3)-Cd(2)-O(5) 76.40(9) N(3)-Cd(2)-O(5) 88.69(10) O(2)-Cd(2)-N(4) 69.29(12) O(5)-Cd(2)-N(4) 157.64(11) O(2)-Cd(2)-O(6) 79.96(11) O(5)-Cd(2)-O(6) compound 2 2.047(4) Zn(1)-O(3) 2.119(4) Zn(2)-O(2) 2.011(4) Zn(2)-O(6) 2.076(5) Zn(2)-N(1) 88.34(15) O(1)-Zn(1)-O(3) 88.34(15) O(1)-Zn(1)-O(5) 88.85(15) O(3)#1-Zn(1)-O(5) 88.70(15) O(2)-Zn(2)-O(3) 94.03(17) O(3)-Zn(2)-O(6) 93.59(18) O(3)-Zn(2)-N(2) 109.67(18) O(2)-Zn(2)-N(1) 88.31(18) O(6)-Zn(2)-N(1) compound 3 2.455(3) Pb(1)-O(2) 2.722(3) O(1)-Pb(1)-O(1)#1 53.11(9) O(1)#1-Pb(1)-O(2) 78.29(13) O(1)-Pb(1)-O(2)#2 68.24(9) O(1)-Pb(1)-O(2)#3

2.226(3) 2.430(3) 2.499(3) 2.320(3) 2.366(3) 2.424(3) 82.54(10) 87.94(11) 147.95(10) 122.67(10) 97.84(11) 92.60(11) 139.88(10) 126.62(10) 159.30(11) 97.06(10) 84.60(10) 54.69(10) 2.074(4) 2.010(4) 2.011(4) 2.201(5) 91.66(15) 91.15(15) 91.30(15) 97.61(16) 110.58(17) 137.17(17) 170.5(2) 90.77(19) 2.458(3) 118.76(14) 79.07(10) 110.10(9) 77.75(9)

Symmetry transformations: 1: #1, x, -y þ 1/2, z þ 1/2. 2: #1, -x þ 1, -y þ 1, -z þ 1. 3: #1, -x þ 2, y, -z þ 1/2; #2, -x þ 2, -y þ 2, -z; #3, x, -y þ 2, z þ 1/2. a

CCDC-734249 to -734251 (for 1-3) containing the crystallographic data in this article can be obtained free of charge from The Cambridge Crystallographic Data Centre.

Scheme 1. Synthesis of 1-3

Syntheses of M(II) Complexes (Scheme 1. {[Cd2(pbda)2(phen)2](H2O)}n (1). A solution of water (10 mL) containing H2pbda (43 mg, 0.20 mmol), 1,10-phenanthroline (phen, 40 mg, 0.20 mmol), Cd(NO3)2 3 4H2O (62 mg, 0.20 mmol), and Et3N (0.02 mL) was sealed in a reactor of 23 mL and heated at 160 C for 72 h, then cooled to room temperature. The crystal samples were washed with ethanol (3  3 mL), DMF (3  3 mL), and DMSO (dimethyl sulphoxide= DMSO, 3  3 mL), respectively, to give compound 1 in yield of 72% (75 mg, on the basis of H2pbda). Element analysis for Cd2C48H34N4O9 (%), calcd: C 55.67, H 3.31, N 5.41; found, C 55.48, H 3.12, N 5.47. IR (KBr, ν/cm-1): 3400 m, 1636vs, 1537s, 1379s, 1082s, 983 m, 834 m, 715 m. [Zn3(pbda)3(phen)2]n (2). A solution of DMF (10 mL) containing H2pbda (43 mg, 0.20 mmol), 1,10-phenanthroline (phen, 40 mg, 0.20 mmol), Zn(NO3)2 3 6H2O (60 mg, 0.20 mmol), and N,N-dimethylbenzenamine (0.04 mL) was sealed in a reactor of 23 mL and heated at 75 C for 72 h, then cooled to room temperature. The crystals were washed with ethanol (3  3 mL), DMF (3  3 mL), and DMSO (3  3 mL), respectively, to give compound 2 in a yield of 65% (52.2 mg, based on the H2pbda). Element analysis for Zn3C60H40N4O12 (%), calcd: C 59.74, H 3.32, N 4.65; found, C 59.44, H 3.01, N 4.56. (KBr, ν/cm-1): 1634s, 1556s, 1427 m, 1381 m, 1030 m, 970 m, 725 m. [Pb(pbda)]n (3). A solution of DMF (10 mL) containing H2pbda (43 mg, 0.20 mmol) and Pb(NO3)2 3 6H2O (66 mg, 0.20 mmol) was sealed in a reactor of 23 mL and heated at 75 C for 120 h, then cooled to room temperature. The crystals were washed with DMF (3  3 mL) and DMSO (3  3 mL), respectively, to give compound 3 in a yield of 68% (57.6 mg, on the basis of H2pbda). Element analysis for PbC12H8O4 (%), calcd: C 34.01, H 1.89; found, C 34.10, H 1.78. IR (KBr): 1630 m, 1501s, 1378s, 1250 m, 994 m, 971 m, 848 m, 721s.

Results and Discussion Syntheses and Characterization. Coordination polymers 1-2 were obtained in different mix-solvent systems by

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Figure 1. (a) Portion of the crystal structure of 1 showing coordinate environments of Cd(II) ions and pbda ligands; phen groups and H atoms are omitted for clarity. (b) Simplified schematic representation of the same portion of the structure. The five pbda anions are represented by sticks. Dissimilar colors relate with crystallographically distinct metal ions or different coordinate modes.

assembling of H2pbda, M(II)(NO3)2, and phen in a molar ratio of 1:1:1 under solvthermal/hydrothermal considerations, while 3 was prepared with H2pbda and Pb(II)(NO3)2 in the molar ratio of 1:1. X-ray structural analyses of 1-3 reveal they have distinct structural topologies. Complexes 1-3 are stable under the ambient conditions and insoluble in common solvents such as water, alcohol, and acetonitrile. The crystalline phase purity of 1-3 was confirmed by the experimental XRPD patterns, which match well with the corresponding simulated ones obtained from the singlecrystal data (see the Supporting Information). In the IR spectra of 1-3, the absorption bands resulting from the skeletal vibrations of the aromatic ring are observed in the 1600-1400 cm-1 region. The asymmetric and symmetric stretching of carboxylate are indicated by strong bands appearing in the range of 1636-1630 cm-1 and 1427-1378 cm-1, respectively. The broad bands of 3400 cm-1 reveal the O-H stretching mode for water molecules in 1. Crystal Structure of {[Cd2(pbda)2(phen)2](H2O)}n (1). An X-ray single-crystal diffraction study reveals that 1 crystallizes in a monoclinic space group P21/c (no.14) and displays a 3-D coordinate framework. In the asymmetric unit of 1, there exist two crystallographically distinct Cd(II) centers (Cd1 and Cd2), two pbda ligands, two 1,10-phenanthroline (phen) molecules, and one solvent water molecule (Figure 1a). The Cd1 center adopts a six-coordinated octahedral geometry (CdO4N2) by coordinating to four oxygen donors (O1; O4A; O5; O7A) from four pbda anions with the Cd-O distances in the range of 2.196(3)-2.499(3) A˚ and two nitrogen atoms (N1; N2) from one phen molecule with the Cd-N distances of 2.430(3) and 2.448(3) A˚. The Cd2 center also adopts a six-coordinated mode (CdO4N2) by bonding to three oxygen donors (O2; O3A; O5; O6) from four pbda ligands with the Cd-O distances in the range of 2.252(2)-2.424(3) A˚ and two nitrogen atoms (N3; N4) from one phen molecule with the Cd-N distances of 2.355(4) and 2.421(4) A˚. The above-mentioned O5 atom has a μ3-connection mode (μ3 shows that the center atom is linked with three

Scheme 2. Four Coordinate Modes of p-Benzenediacrylate (pbda) Found in 1-3

other atoms);10 thus, two CdO4N2 octahedra share the O5 of the μ3-connection to form a binuclear (Cd2O7N4) cluster with a Cd1-Cd2 separation of 3.925 A˚. As illustrated in Scheme 2 (syn-I and trans-II), in 1 one crystallographically distinct pbda ligand adopts an exotridentate mode, and the other has an exo-quadridentate mode. In the crystal structure of the syn-pbda-I anion, two acrylate groups (CHdCH-COO-) are located at the benzene ring in a syn-position fashion. The two dihedral angles of the CHdCH-COO- groups are 2.5 and 6.2, and those of C6H4-CHdCH groups are 11.5 and 15.1, while in the trans-pbda-II anion, the two dihedral angles of CHdCHCOO- are 6.3 and 28.1, and those of C6H4-CHdCH are 10.4 and 12.6. The above-mentioned data indicate that there exist π-π electronic conjugations in the crystal structures of pbda moieties.11 The separation of 3.493 A˚ (C29 3 3 3 C39) indicates that the distance of corresponding phenyl rings is about 3.5 A˚. Therefore, there exist various nonconvalent interactions in 1, such as face-to-face π-π interactions and C-H 3 3 3 π contacts (Figure S1, the Supporting Information).12 The above-mentioned π-π conjugations and face-to-face π-π interactions in 1 can

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Figure 2. Schematic representation of the (3,4)-connected 4-nodal 3-D network of (4.8.10) (42.6.8  102) topology in 1 as viewed down the c axis. Red and yellow sticks represent the 3- and 4-connected pbda ligands, respectively. Green and azure ellipsoidal balls represent 3-c and 4-c Cd(II) nodes, respectively. Phen ligands are omitted for clarity.

be related with its stability and solid-state luminescent property. When the Cd1 and Cd2 centers are regarded as 4- and 3-connected nodes (Figure 1b), respectively, and the two crystallographically independent pbda building blocks serve as 4- and 3-connected points (denoted as L4-c, and L3-c), the resultant 3-D coordinate framework can be described as a (3,4)-connected 4-nodal network with a Schl€ afli symbol of (4.8.10)(42.6.8  102) (Figure 2). To our knowledge, this is an unprecedented topological net.13 Crystal Structure of [Zn3(pbda)3(phen)2]n (2). X-ray singlecrystal analysis reveals that 2 has a porous 3-D polymeric architecture in the monoclinic system and a P2/n (no.13) space group. In the structural unit of 2, there exist two crystallographically distinct zinc ions (Figure 3a). One Zn(II) center (Zn1) adopts a six-coordinated octahedral geometry (ZnO6) by coordinating to six oxygen donors (O1; O1A; O3; O3A; O5; O5A) from six trans-pbda anions with the Zn-O distances of 2.047(4)-2.119(4) A˚. The other Zn(II) center (Zn2) adopts a five-coordinated distorted trigonal bipyramidal geometry (ZnO3N2) by coordinating to two oxygen donors (O2; O3; O6) from three trans-pbda anions with the Zn-O lengths in the range of 2.010(4)-2.011(4) A˚ and two nitrogen atoms (N1; N2) from one phen molecule with the Zn-N distances of 2.076(5) and 2.201(5) A˚. The abovementioned O3 atom displays a μ3-connection (connecting two Zn(II) centers and a carbon atom). Thus, each ZnO6 octahedron shares its O3/O3A of the μ3-connection with two ZnO3N2 hexahedrons, forming a three nuclear (Zn3O10N4) cluster with a Zn1-Zn2 separation of 3.325 A˚. As we know, meso-helical motifs are relatively rare compared with common helical structures in metal-organic coordinate chemistry.14 Interestingly, compound 2 possesses the meso-helical motif [Zn2(pbda)2] with a Zn-Zn separation of 14.47 A˚, in which there a face-to-face π-π interaction of 3.6 A˚ (Figure 3b). It is obvious that the face-to-face π-π interaction is related to the outward bend of pbda anions, which also indicates that the H2pbda ligand elongated with CHdCH groups is more flexible than the terephthalic acid. Furthermore, these meso-helical units build up to an infinite 1-D [Zn(pbda)2]n chain by sharing the Zn centers.

Figure 3. (a) Coordinate environments of two crystallographic Zn(II) ions in 2. Zn1 is coordinated with six N atoms, while Zn2 is linked with three O atoms and two N atoms. (b) Presentation of the meso-helicate composed of Zn2(pbda)2. (c) Portion of the crystal structure showing coordinate environments of pbda ligands (H atoms are omitted for clarity) and the schematic representation of the nanosized coplanar 4-connected second building unit (SBU). (d) The 4-connected CdSO4-type network. (e) Representation of 2-fold interpenetrating in 2.

As depicted in Scheme 2 (II and III) and Figure 3c, there exist two crystallographically distinct pbda anions and pbda ligands adopting two distinct exo-quadridentate coordinate styles. The pbda-II anion is near coplanar and contains an eighteen-electron (18e) conjugate system of π-π (C6H4CHdCH) and p-π (CHdCH-COO-). pbda-III is slightly bent with an angle of ca. 168, the dihedral angle of CHdCH-COO- is ca. 9, and that of C6H4-CHdCH is ca.10. When each trinuclear Zn3L6 serves as a 4-connected SBU (Figure 3c), the 3-D network 2 has a CdSO4-type topology (Figure 3d), similar to those examples of MOFs in the literature.15 In order to effectively reduce the nanosized void space, 2 possesses a 2-fold interpenetration of architecture (Figure 3e). Even so, it exhibits a porous open framework containing intersected 1-D channels of ca. 6 A˚  6 A˚ in dimension rather than a close-packed structure (Figure 4a, Figure S2 (Supporting Information)). The porosity of 2 is expected because of the strategy of elongated bridging ligands.16 Although there exist obstructive phen entities, the 3-D porous architecture of 2 has a void of 32.9% (1111.4 A˚3 out of the unit cell of 3372.9 A˚3) as calculated by PLATON.17 Moreover, similar to 1, there also exist the face-to-face π-π interactions of 3.5-3.6 A˚ between pbda and phen/ pbda blocks, and the C-H 3 3 3 π weak contacts (C 3 3 3 C 3.8 A˚) in 2 (Figure 4b). The above-mentioned electronic structures of π-π conjugations and face-to-face π-π interactions may relate to its stability and photoluminescence.

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Crystal Structure of [Pb(pbda)]n(3). Coordinate polymer 3 was crystallized in a monoclinic system and C2/c (no.15) space group. Each asymmetric unit contains one crystallographically distinct pbda anion and one Pb(II) center. The Pb2þ ion is in a distorted octahedral environment, coordinated by six oxygen atoms (PbO6) from four different pbda anions (Figure 5a). Four O atoms display μ3-connections

Figure 4. (a) Representation of the intersected channels (denoted as artifical cylinders) in the porous structure of 2. (b) View of the square-shape channel of 6 A˚  7 A˚ (nuclear-to-nuclear) [010], the face-to-face π 3 3 3 π interactions of 3.5-3.6 A˚ between pbda and phen/pbda ligands, and the C-H 3 3 3 π contacts (C 3 3 3 C 3.8 A˚, nuclear-to-nuclear).

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(connecting two metal centers and a carbon atom). Thus, each distorted PbO6 octahedron shares its μ3-connections with other PbO6 octahedrons, forming an infinite zigzag PdO-Pd chain with the successive Pb-Pb separation of 4.291 A˚ ( — Pb-Pb-Pb 137.54) (Figure 5b and c). The Pb-O bond lengths are in the normal range of 2.355(3)-2.722(3) A˚. Noticeably, the lone electron pair18 of the Pb2þ ion causes its coordinate geometry to be distorted and hemidirected with the O2-Pb1-O2A angle of 165.16 (Figure 5b). All pbda anions of 3 adopt trans-exo-quadridentate coordinate modes, as illustrated in Scheme 2 (IV) (Figure 6a). In the structure of pbda2- two COO- groups are coplanar, the dihedral angle of the CHdCH-COO- group is ca. 10, and that of C6H4-CHdCH is ca. 13. Therefore, there also

Figure 6. (a) Portion of the crystal structure of 3 showing the coordinate environment of pbda ligands and schematic representation of the 4-connected SBU. (b) The sra net along the [001] direction.

Figure 5. (a) Coordinate environment of the Pb(II) ion in 3. (b) PbO6 polyhedra showing the hemidirected nature of lead atoms. (c) Octahedral polynuclear (PbO4)n chain.

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Figure 7. View of the 3-fold interpenetration in 3 [001].

exist p-π (CHdCH-COO-) and π-π (CHdCH-COO-, C6H4-CHdCH) electronic conjugations in 3, which is similar to those in 1 and 2. Bridged by the pbda anions, a 3-D structure is built up from infinite 1-D (PbO4)n chains, and each anionic pbda separates the metal ions by a distance of 15.9 A˚. As simplified in Figure 7, the resultant 3-D coordinate structure could be described as a uninodal 4-c network of rare sra topology with a Schl€afli symbol of (42.63.8), which is related to the structural prototype of zeolite ABW (Figure 6b).19 In order to avoid an extremely large void space, 3 displays a 3-fold interpenetrating structure (Figure 7).20 Moreover, compared with 1 and 2, no strong face-to-face π-π interactions (3.4-3.6 A˚) occur in 3. This phenomenon may be correlative with the appropriate arrangement of organic moieties in the 3-fold interpenetration network. Alternatively, when the Pb center acts as a tetrahedral 4-connected node and the pbda ligand serves as a 4-connected knot, 3 is a 3-D coordinate framework with a Schl€ afli symbol of (42.84) (Figure S3, in the Supporting Information), which is related to the topological prototype of PtS. Several MOFs with PtS topology have been reported.21 Thermogravimetric Analyses. The primary thermostability of the coordination polymers has been checked by recording thermogravimetric (TG) curves of the complexes 1-3 under N2 atmosphere. In the TG diagram of 1, a weight loss of 1.60% between 40 and 140 C is in accordance with the release of one free water molecule per formula unit (calcd 1.73%), and the complex remains undecomposed up to 210 C, where the second weight loss starts. For 2, the complex stabilizes up to 260 C, and complete decomposition finishes at about 700 C. Complex 3 has high decomposition temperature at 365 C, which is related with its 3-fold interpenetrating architecture. The above-mentioned decomposition temperatures of complexes 1-3 are in the range of 200-400 C, which are typical for most 3-D metalorganic coordinate frameworks.1Luminescent Properties. Figure 8 and Figure S4 (in the Supporting Information) present the photoluminescent spectra of compounds 1-3 in the solid state at room tem-

Figure 8. Solid-state photoluminescent spectra of 2 (λ em = 504 nm upon λ ex = 390 nm) at room temperature. ex = excitation (maximum), and em = emission (maximum). I = intensity.

perature. Free H2pbda has a bimodal emission maximum centering at 409 and 430 nm upon excitation at 299 nm, while the emission maximum of phen is at 409 nm upon excitation at 356 nm.7,22 Compound 1 exhibits a bimodal emission maximum located at 462 and 482 nm upon excitation at 336 nm. The emission peak of 1 is red-shifted by about 50 nm compared to that of the pure H2pbda ligand, but the spectrum curve of 1 is similar to that of free H2pbda. Together with the electronic structures of pbda after coordination to Cd(II) ions and the π-π conjugations and the faceto-face π-π interactions, the emission origin of 1 is probably due to the coordination of the ligands.23 Compound 3 presents an emission band at 408 nm with a shoulder sign at 422 nm upon excitation at 380 nm, which is like that of free H2pbda. Therefore, the emission origin of 3 is also probably due to the coordination of the ligands. Solid-state compound 2 displays a strong photoluminescence with an emission maximum at 504 nm upon excitation

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(No. 208116) and the Scientific and Technological Project of CQEC (No. KJ080829). Supporting Information Available: Crystallographic data in CIF format, additional figures, powder X-ray patterns, and TGA curves for 1-3. This material is available free of charge via the Internet at http://pubs.acs.org.

References

Figure 9. BET H2 and N2 sorption isotherms for 2 at 77 K.

at 390 nm, which is different from that of free H2pbda and phen. The emission peak of 2 is red-shifted by about 90 nm compared to that of the pure H2pbda ligand. The explanation is that the π-π electronic conjugations and the strong face-to-face π-π interactions can be related with the obvious red-shift phenomena in 2. The excited state is best described as ligand-to-metal charge transfer (LMCT) in nature.24 Complex 2 may be suitable as an excellent candidate for luminescent solid-state materials at room temperature. Gas Sorption Behavior of 2. The nitrogen and hydrogen uptake behaviors of 2 have been examined at 77 K (Figure 9). A known weight of the as-synthesized sample was placed in a quartz tube, which was dried prior to measurement under high vacuum at 150 C for 2 h. The H2 and N2 uptakes of 2 are approximately 31 and 28 cm3 3 g-1(STP) at P/P0 = 1.0, respectively, with the typical type-I curve.25 The N2 absorption isotherm reveals a Brunauer-Emmett-Teller (BET) surface area of 65.84 m2 3 g-1. We also have determined a pore size distribution of 2 by carbon dioxide adsorption. A known weight of the assynthesized sample was dried prior to measurement under high vacuum at 150 C for 2 h. The CO2 uptake is about 15 cm3 3 g-1 (STP, at 22 Torr) with the typical type-I curve at 273 K (Figure S5 in the Supporting Information). Compound 2 shows a pore size distribution centering at 5.1 A˚, which is consistent with its X-ray structure. Conclusions Three new metal(II)-organic complexes based on the elongated p-benzenediacrylic acid (H2pbda) building blocks are reported in this work. The dicarboxylate spacers link metal centers to form binuclear, trinuclear, and polynuclear units, which further lead to 3-D coordinate polymers with (3,4)connected (4.8.10)(42.6.8  102) topology (1), 2-fold interpenetrating CdSO4-tpye open framework (2), and a 3-fold interpenetrating sra net (3). The porous zinc open framework 2 has the typical type-I sorption curve with a H2 uptake of 31 cm3 3 g-1(STP) at 77 K, a BET surface area of 65.84 m2 3 g-1, meso-[Zn2(pbda)2] helical motifs, and strong solid-state luminescence with λ em at 504 nm. These experimental data also indicate that elongated H2pbda is an excellent building block for the construction of 3-D metal-organic coodinate frameworks with diverse topologies and properties. Acknowledgment. We gratefully acknowledge the financial support by the Key Project of Chinese Ministry of Education

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