Three Interpenetrated Frameworks Assembly from a Long

Jan 10, 2008 - Huan-Yu Wang, Shan Gao*, Li-Hua Huo, Seik Weng Ng and Jing-Gui Zhao. Laboratory of Functional Materials, School of Chemistry and ...
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CRYSTAL GROWTH & DESIGN

Three Interpenetrated Frameworks Assembly from a Long Multicarboxylate Ligand and Transition Metal Huan-Yu Wang,† Shan Gao,*,† Li-Hua Huo,† Seik Weng Ng,‡ and Jing-Gui Zhao† Laboratory of Functional Materials, School of Chemistry and Materials Science, Heilongjiang UniVersity, Harbin 150080, People’s Republic of China, and Department of Chemistry, UniVersity of Malaya, Kuala Lumpur 50603, Malaysia

2008 VOL. 8, NO. 2 665–670

ReceiVed September 16, 2007; ReVised Manuscript ReceiVed October 31, 2007

ABSTRACT: Three three-dimensional polymers, namely, [Zn(bpea)(H2O)]n (1), [Cd(bpea)(H2O)]n (2), and [Ni(bpea)(4,4′bipyridine)(pyridine)]n (3) have been synthesized by the hydrothermal reaction of ZnII, CdII, or NiII salts with biphenylethene-4,4′dicarboxylic acid. Complexes 1 and 2 have a 2-fold interpenetrating three-dimensional (3D) structure with Pts topology, and complex 1 exhibits strong fluorescent emission bands at 435 and 459 nm in the solid state at room temperature. Complex 3 is a 3D structure with an unprecedented 9-fold interpenetrated Ths topology. Introduction Current interest in polymeric coordination networks is rapidly expanding for their intriguing architectures1 and potential applications.2 The origin of interpenetration can be ascribed to the presence of large free voids in a single network, although it has been demonstrated that interpenetration does not prevent the possibility of obtaining open porous materials.3 As a type of entanglement, interpenetration has been the most investigated,4 and more merits of the interpenetrating network have been discovered.5 On the one hand, materials with interpenetrating lattices can have free volumes that exceed 80% of the total volume,3a and some researchers proved interpenetration could be utilized to strengthen the interaction between the gaseous molecule and the framework by an entrapment mechanism in which a hydrogen molecule is in close proximity with several aromatic rings from interpenetrating networks.6 On the other hand, peculiar magnetic and electrical properties have been also found in interpenetrated nets.7 Although interpenetration is now common, examination of interpenetration topology will increase our understanding of interpenetration and can have a significant effect on the overall properties of the structure,8 and the factors that control the observed degrees of interpenetration in these systems remain largely unknown and/or unproven. Generally, longer ligands will lead to larger voids. In a very loose and general sense it can be said that the larger the voids in a threedimensional (3D) net, the more likely interpenetration occurs and the higher the number of independent nets a particular void is passed through. The most outstanding examples are by using the long sebaconitrile and 1,12-dodecanedinitrile ligands; 4- to 10-fold interpenetrating diamondoid networks have been obtained by Ciani and co-workers.9 As a kind of long O-donor organic aromatic dicarboxylate ligand, biphenylethene-4,4′-dicarboxylic acid (bpea) has been regarded as a good candidate to construct metal-organic frameworks (MOFs) with novel topologies, such as the 9-fold interlocking homochiral helices, entanglement of 1D zigzag coordination polymers of a robust microporous framework, and intriguing 3D polycatenated arrays featuring an uneven “density of catenation”.10 To prepare novel materials with interpenetration * To whom correspondence should be addressed. E-mail: Shanga067@ yahoo.com. † Heilongjiang University. ‡ University of Malaya.

and good physical properties, we chose bpea as a bridging ligand to react with the d-block metal ions ZnII, CdII, and NiII and obtained three coordination polymers, namely, [Zn(bpea)(H2O)]n (1), [Cd(bpea)(H2O)]n (2), and [Ni(bpea)(4,4′-bipyridine)(pyridine)]n (3). Complexes 1 and 2 have a 2-fold interpenetrating 3D Pts structure. Complex 3 is a 3D structure with an unprecedented 9-fold interpenetrated Ths topology. Experimental Section All chemicals were reagent grade and used without further purification. Elemental analyses were performed on a CARLO ERBA 1106 analyzer. The IR spectra were recorded on a Bruker Equinox 55 FTIR spectrometer using KBr pellet. Luminescence spectra were measured on a Perkin Elmer LS 55 luminance meter. Thermogravimetry (TG) was measured on a Perkin Elmer TG 6300 thermal analyzer under flowing N2 atmosphere, with a heating rate of 10 °C/min. Synthesis of [Zn(bpea)(H2O)]n (1). A mixture of ZnSO4 · 7H2O (0.288 g, 1 mmol), H2bpea (0.268 g, 1 mmol), triethylamine (0.28 mL, 2 mmol), and water (10 mL) was sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 160 °C for 5 days, and then it was slowly cooled to room temperature. Colorless crystals were collected by hand, washed with distilled water, and dried in air. Yield: 84.1% based on Zn. Anal. Found C, 54.91, H, 3.54%. Calcd for C16H12O5Zn: C, 54.96, H, 3.46%. Synthesis of [Cd(bpea)(H2O)]n (2). An identical procedure with 1 was followed to prepare 2 except ZnSO4 · 7H2O was replaced by Cd(NO3)2 · 4H2O (1 mmol, 0.308 g). Yield: 71.7% based on Cd. Anal. Found C, 48.41, H, 3.46%. Calcd for C16H12O5Cd: C, 48.45, H, 3.05%. Synthesis of [Ni(bpea)(4,4′-bipyridine)(pyridine)]n (3). A mixture of Ni(NO3)2 · 6H2O (0.290 g, 1 mmol), H2bpea (0.268 g, 1 mmol), 4,4′bipyridine (0.156 g, 1 mmol), pyridine (2 mL), and water (10 mL) was placed in a 23-mL Teflon-lined stainless steel vessel, and the mixture was heated at 160 °C for 5 days and then slowly cooled to room temperature. Green crystals were collected by hand, washed with distilled water, and dried in air. Yield: 55.7% based on Ni. Anal. Found C, 64.73, H, 3.91 N 5.79%. Calcd for C26H19N2O4Ni: C, 64.77, H, 3.97, N 5.81%. X-ray Crystallographic Measurements. Table 1 provides a summary of the crystal data, data collection, and refinement parameters for complexes 1, 2, and 3. All diffraction data were collected at 295 K on a RIGAKU RAXIS-RAPID diffractometer with graphite monochromatized Mo-KR (λ ) 0.71073 Å) radiation in ω scan mode. All structures were solved by direct method and difference Fourier syntheses. All nonhydrogen atoms were refined by fullmatrix least-squares techniques on F2 with anisotropic thermal parameters. The H atoms on carbon were placed in calculated positions with C-H ) 0.93 Å (aromatic) or 0.97 Å (aliphatic) and U(H) ) 1.2Ueq(C) in the riding model approximation, and the H atoms of water molecules were located in difference Fourier

10.1021/cg700896j CCC: $40.75  2008 American Chemical Society Published on Web 01/10/2008

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Table 1. Crystallographic Data of 1, 2, and 3 complex

1

molecular formula formula weight space group a/Å b/Å c/Å β/o V/Å3 Z Dc/g m-3 µ (Mo KR)/mm-1 F(000) reflections collected unique reflections no. of params GOF on F2 final R indices [I g 2σ(I)] R (int) largest difference peak, hole /e Å-3

2

C16H12O5Zn 349.63 P2/c 14.799(3) 6.2738(13) 7.3671(15) 93.13(3) 683.0(2) 2 1.700 1.820 356 6455 1562 104 1.101 R1 ) 0.0253 wR2 ) 0.0596 wR2 ) 0.0596 0.0339 0.408, -0.234

3

C16H12O5Cd 396.66 P2/c 15.161(3) 6.4431(13) 7.1366(14) 91.87(3) 696.8(2) 2 1.891 1.589 392 6431 1605 104 1.097 R1 ) 0.0388 wR2 ) 0.0883

C26H18O4N2Ni 481.13 C2/c 23.067(2) 11.6485(7) 18.889(1) 119.375(2) 4422.7(15) 8 1.445 0.913 1984 20103 5029 322 1.06 R1 ) 0.051 wR2 ) 0.118

0.0382 1.405 and -1.186

0.0682 0.40, -0.730

Table 2. Selected Bond Lengths [Å] and Angles [°] for 1, 2, and 3a 1 Zn(1)-O(2)#1 Zn(1)-O(2) Zn(1)-O(1W) O(2)#1-Zn(1)-O(2) O(2)-Zn(1)-O(1W) O(2)#1-Zn(1)-O(1W) O(1W)-Zn(1)-O(1)#2 O(1W)-Zn(1)-O(1)#3 O(1W)-H(1W1) · · · O(1)#5

1.945(2) 1.945(2 1.972(2) 139.17(9) 110.42(5) 110.42(5) 87.12(3) 87.12(3) 163.4(18)

Cd(1)-O(1) Cd(1)-O(1)#1 Cd(1)-O(2)#3 O(1)-Cd(1)-O(1)#1 O(1)#1-Cd(1)-O(1W) O(1)#1-Cd(1)-O(2)#2 O(1)-Cd(1)-O(2)#3 O(1W)-Cd(1)-O(2)#3 O(1W)-H(1W1) · · · O(2)#5

2.191(3) 2.191(3) 2.384(3) 161.84(19) 99.08(9) 84.79(12) 84.79(12) 88.19(7) 159.4(18)

Ni(1)-N(2) Ni(1)-N(1) Ni(1)-O(4) N(2)-Ni(1)-N(1) N(2)-Ni(1)-O(4) N(1)-Ni(1)-O(4) N(2)-Ni(1)-O(2) N(1)-Ni(1)-O(2) O(4)-Ni(1)-O(2) N(2)-Ni(1)-O(1)

2.074(3) 2.068(3) 2.116(2) 93.3(1) 161.8(1) 90.8(1) 90.5(1) 163.7(1) 90.6(1) 93.9(1)

Zn(1)-O(1)#3 Zn(1)-O(1)#2 O(1W) · · · O(1)#5 O(2)#1-Zn(1)-O(1)#2 O(2)-Zn(1)-O(1)#2 O(2)#1-Zn(1)-O(1)#3 O(2)-Zn(1)-O(1)#3 O(1)#2-Zn(1)-O(1)#3

2.184(3) 2.184(3) 2.6423(19) 88.59(6) 93.42(6) 93.42(6) 88.59(6) 174.25(7)

Cd(1)-O(1W) Cd(1)-O(2)#2 O(1W) · · · O(2)#5 O(1)-Cd(1)-O(1W) O(1)-Cd(1)-O(2)#2 O(1W)-Cd(1)-O(2)#2 O(1)#1-Cd(1)-O(2)#3 O(2)#2-Cd(1)-O(2)#3

2.221(5) 2.384(3) 2.688(4) 99.08(9) 95.78(12) 88.19(7) 95.78(12) 176.38(15)

Ni(1)-O(2) Ni(1)-O(1) Ni(1)-O(3) N(1)-Ni(1)-O(1) O(4)-Ni(1)-O(1) O(2)-Ni(1)-O(1) N(2)-Ni(1)-O(3) N(1)-Ni(1)-O(3) O(4)-Ni(1)-O(3)

2.112(2) 2.088(2) 2.080(2) 101.1(1) 102.7(1) 62.8(1) 98.9(1) 95.9(1) 63.0(1)

2

3

a Symmetry codes (in 1): #1 -x + 1, y, -z + 1/2. #2 -x + 1, -y + 1, -z + 1. #3 x, -y + 1, z - 1/2. #4 -x, -y, -z + 1. #5 -x + 1, y + 1, -z + 1/2. Symmetry codes (in 2): #1 -x, y, -z + 3/2. #2 -x, -y + 1, -z + 1. #3 x, -y + 1, z + 1/2. #5 -x, y - 1, -z + 3/2.

synthesis maps and refined in the riding model approximation, with O-H distance restraint (0.85(1) Å) and U(H) ) 1.5Ueq (O). In complex 3 one of the bpea ligand is disordered. The two independent carboxylate groups and bipyridine ligands both lay on inversion centers. One of the carboxylate groups is disordered over this symmetry element; the constraint was relaxed, and the -C6H4-CHd CH-C6H4- portion was refined with half-occupancy atoms. Additionally, the two phenylene rings were each refined as rigid hexagons of 1.39 Å sides, and the anisotropic temperature factors of the 14 carbon atoms were restrained to be nearly isotropic. All calculations were carried out with the SHELXTL crystallographic software package.11 The CCDC reference numbers are 645153 for 1, 654261 for 2, and 645154 for 3. Selected bond lengths and angles are listed in Table 2.

Results and Discussion Crystal Structures of 1 and 2. Single-crystal X-ray structural analysis reveals that 1 and 2 are all constructed from rod-shaped secondary building units (SBUs).12 Compounds 1 and 2 are isostructural, so only the structure of 1 will be discussed herein. The ZnII atom is five-coordinated by four different carboxyl groups (Zn-O 1.9452(13)-2.1844(14) Å) and one water molecule (Zn-O1w 1.972(2) Å) exhibiting a slightly distorted trigonal-bipyramidal geometry. Two carboxyl groups of bpea ligand adopt bridging bis-bidentate coordination modes. This bridge of the carboxyl pattern results in infinite Zn-O-C rods

Frameworks from Long Multicarboxylate Ligand

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Figure 1. (a) View of one set of the 3D network. (b) Infinite rod-shaped building blocks: ball-and-stick representation of SBU. (c) A schematic of the 2-fold interpenetration. (d) Topological representation of 3 showing the Pts topology.

(SBUs) running along the [001] direction (Figure 1b). The rods are linked by the bpea arms that connect each rod to four neighboring rods in the directions of [110] and [11j0] (Figure 1a), and further extended 3D structure. Simultaneously, the coordinated water molecules form hydrogen-bonding interactions with carbolxylate O atoms (Table 2). A better insight into the nature of this intricate framework can be achieved by the application of topological approach, reducing multidimensional structures to simple node and connection nets. As discussed above, each five-coordinated Zn atom can be looked as a tetrahedral node, and every bpea ligand can be looked as a square planar node. Therefore, the whole structure can thus be represented to a cooperite Pts net, as displayed in Figure 1d. Furthermore, two such nets interpenetrate with catenation of just the larger rings (Figure 1c) for no bulky solvent molecules occupied in the crystal, and there are some examples of the interpenetrated Pts nets.13 This is in accord with the fact that tetrahedral, trigonal, and octahedral metal templates have a high

tendency to form interpenetrated or self-inclusion compounds, if the cavity generated in this way is more than 50% of the crystal by volume.14 Crystal Structure of 3. In complex 3, the NiII atom is coordinated by four carboxylate oxygen atoms from two different bpea ligand and two nitrogen atoms from a 4,4′bipyridine ligand, a pyridine ligand, respectively, showing a distorted octahedral geometry (Figure 2a). The extension of the structure into a 3D network is accomplished by the connecting bpea ligand of which the two-carboxyl groups all adopt chelating bis-bidentate coordination modes and a 4,4′-bipyridine ligand to the NiII center. The topological analysis of 3 reveals that it is better known in the context of coordination polymers, a Ths network, if the NiII atoms are looked as 3-connect nodes, 4,4′bipyridine and bpea ligands are both considered as same linkers, and the Vertex Symbol of this net is 102 · 104 · 1041e,f,4a (Figure 2b). This complicated network can be understood in this manner:

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Figure 2. (a) Portional view of 3 and metal coordination. (b) Schematic representation of the Ths topology. (c) A schematic of the 9-fold interpenetration. (d) View of the triple interweaving chains. (e) A set of 3D triple interpenetration. (f) Three sets of 3D triple interpenetration.

Frameworks from Long Multicarboxylate Ligand

the [Ni(pyridine)]2+ groups are connected by bpea ligands forming a tortuous zigzag chain with a period of 56.67 Å along the c-axis, and the three kind of chains are interweaved (Figure 2d). Two of the chains are not entwined as they can be separated without any bond breakage. It is only the addition of the third chain that inserts the interstice of the other chains and ties them all together. According to ref 15 this entanglement can be defined as a “braid”. Then the 4,4′-bipyridine ligands, which span two directions, connect the adjacent braid groups forming a set of nets that triply interpenetrate as shown in Figure 2e. And then this set in turn interpenetrates with two other sets, thereby generating 9-fold interpenetration (Figure 2c,f). Moreover, according to ref 16b the interpenetrated network belongs to the uncommon class Ib, where more than one interpenetration vector can be found. One Ths network is related to the other eight by the following four translational vectors. To the best of our knowledge, this is the highest level of interpenetration yet observed in a Ths net within coordination polymers.16 Compared with 1, 2, and 3, it can be deemed that the single metal center or SBUs may be important in forming the interpenetration network. If the size of the SBU is large enough as an optimal SBU for the linker, the interpenetration will be avoided or the structure will not be maximally interpenetrated. From our point of view, mononuclear metal nodes should be introduced instead of SBUs to get high level of interpenetration structure. IR Analysis. The absence of the expected characteristic band at 1689 cm-1 for the protonated carboxylate groups indicates the complete deprotonation of bpea ligand in the complexes 1, 2, and 3.17 In 1, a strong and broadband has been observed at 3154 cm-1 and assigned to ν(OH) absorption with the hydrogen bonds. Its characteristic bands of the dicarboxylate groups are shown at 1600 cm-1 for asymmetric vibrations and at 1399 cm-1 for symmetric vibrations. The ∆ value, which represents the separation between νasym(-COO) and νsym(-COO), is 201 cm-1 and suggests the presence of bridging bis-bidentate coordination modes. For 3, the characteristic bands of the dicarboxylate groups are shown at 1596 cm-1 for the asymmetric vibrations and at 1419 cm-1 for the symmetric vibrations. The ∆ value is 177 cm-1. The separation of ∆ value indicates that the carboxylate groups adopt chelating bis-bidentate coordination modes. Thermal Analyses. Complex 1 is stable up to 175 °C. A rapid weight loss can be detected from 175 to 213 °C, which is attributed to the dehydration of the coordinated molecule with a weight loss of 5.70% (calcd 5.15%). The weight loss occurring between 414 and 670 °C corresponds to decomposition of bpea ligand. The final residual is ZnO (calcd: 23.28%; found: 23.04%). In comparison with 1, complex 3 is slightly more stable up to 319 °C, where the decomposition of the framework starts, a rapid and significant weight loss of 85.15% in the temperature range of 312–580 °C, the resulting residue is NiO (calcd: 15.49%; found: 15.25%). Luminescent Property. Previous studies have shown that coordination polymers containing zinc and cadmium ions exhibit photoluminescent properties.18 The emission spectra of complex 1 in the solid state at room temperature were investigated, as depicted in Figure 3. Upon excitation at 387 nm, 1 exhibits strong fluorescent emission bands at 435 and 459 nm. The luminescent behavior of 1 is such that its high-dimensional condensed polymeric structure leads to significant enhancement of fluorescence intensity compared to the free ligand. The peaks of 435 and 459 nm for the compound 1 exhibit a blue-shift

Crystal Growth & Design, Vol. 8, No. 2, 2008 669

Figure 3. Solid-state photoluminescent spectra of 1 and free ligand at room temperature.

(about 6 nm) with respect to the free bpea ligand (441 and 465 nm). It is probably due to the (π*–π) transitions changing into the (π*-n) transitions after forming the coordination polymer. The enhanced luminescence efficiency is therefore attributed to bpea coordinated to ZnII ions resulting in a decrease in the nonradiative decay of intraligand excited states. Compared with the Zn complex, the emission of the Cd complex became weak, which is probably due to the differences of the metal ions. The density of electron cloud for oxygen atoms may be changed by the coordination of the metal ions.19 Conclusions Three novel 3D MOFs have been synthesized from a hydrothermal reaction. 1 and 2 are constructed of infinite M-O-C rods, which are linked by bpea units that connect each rod to four neighboring rods forming a 2-fold interpenetrated Pts structure. Complex 3 displays unprecedented 9-fold interpenetration, which has not been observed in a Ths net within coordination polymers. Some factors of the level of interpenetration in structure have been presented, and the luminescent properties of 1 and 2 have also been investigated. More efforts will focus on the construction of novel interpenetrated coordination polymers by reacting long spacer ligand and different metal ions. Acknowledgment. This work is supported by Natural Science Foundation of Heilongjiang Province (No. B200501) and the Scientific Fund for Remarkable Teachers of Heilongjiang Province (No. 1054 G036). We thank the University of Malaya for supporting this study. Supporting Information Available: X-ray crystallographic files in CIF format, infrared spectra of 1, 2, and 3, TGA of 1 and 3, excitation spectra for ligands 1 and 2, and emission spectrum for 2. This material is available free of charge via the Internet at http://pubs.acs.org.

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