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ABSTRACT: This paper presents two 2-fold parallel interpenetrated polymers, namely ZnCo(bpp)(m-BDC)2 (1) and Co(bpp)(p-. BDC)(2), based on isomerous 1...
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CRYSTAL GROWTH & DESIGN

Two 2-Fold Interpenetrated Frameworks Showing Different Topologies Based on the Isomerous Benzenedicarboxylate Mixed with a Flexible N,N′-Type Ligand

2006 VOL. 6, NO. 11 2517-2522

Pang-Kuan Chen, Yun-Xia Che, Lin Xue, and Ji-Min Zheng* Department of Chemistry, Nankai UniVersity, Tianjin 300071, China ReceiVed May 10, 2006; ReVised Manuscript ReceiVed August 29, 2006

ABSTRACT: This paper presents two 2-fold parallel interpenetrated polymers, namely ZnCo(bpp)(m-BDC)2 (1) and Co(bpp)(pBDC)(2), based on isomerous 1,3-benzenedicarboxylate (m-BDC) and 1,4-benzenedicarboxylate (p-BDC). Compounds 1 and 2 have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, IR, ICP, TGA, DSC, and element analysis. 1 crystallizes in the triclinic space group P1h and affords a three-dimensional (3D) six-connected R-Po network, whereas 2 crystallizes in the orthorhombic space group Pbca and gives an usual 2D four-connected 44 grid. These interpenetrated topologies should be attributed to the high functionality and adaptability of the 1,3-bis(4-pyridyl)propane (bpp) ligand. Introduction The design and construction of the entangled system have received a wide range of attention in the field of supramolecular chemistry and crystal engineering during the past several years because of its intriguing aesthetic structure and topological features as well as its promising applications as functional solid materials and in host-guest chemistry, catalysis, ion exchange, and optical devices.1,2 One of the common phenomena related to the entanglement is the presence of a number of individual nets participating in interpenetration with each other, which evidently differs from the self-penetration networks (molecule knots) in a strict sense.3 Recently, a series of systematic studies on this subject have demonstrated that an interpenetrated array cannot prevent porosity, but enhances the porous functionlities of the supramolecular frameworks.4 More importantly, the research upsurge in the interpenetration structure was promoted by the fact that interpenetrated nets have been considered as potential super-hard materials 5 and possess peculiar magnetic and electrical properties.6 Moreover, the experimental and theoretical analysis of the network topology provides a powerful tool in directing the synthesis and discussion of the resulting crystal structures. Numerous classical examples have been deeply investigated because of the fundamental importance in the understanding of structure-function correlations, such as diamond (6,6),7 (10,3)-a,8 (10,3)-b,9 (10,3)-d,10 (6482)-b,11 and (4284).12 Usually, it is widely acknowledged that long spacer ligands often favor the formation of interpenetrated motifs.13-16 As the 4,4′-bipyridine analogue, bpp has proven to be a good candidate for the organization of polymeric interpenetrated systems because of its length and flexibility, which can assume different conformations such as TT, TG, GG, and GG′ (considering the relative orientations of the three CH2 groups, T ) trans, G ) gauche),17 and because a variety of network topologies can occur. Benzenedicarboxylic acids have been extensively employed to construct carboxylate bridged coordination polymers exhibiting high porosity and topological diversity with different dimensions.18 On the basis of aforementioned points, our synthetical strategy is to select isomerous benzenedicarboxylate as organic linkers in the presence of bpp as flexible spacers. * Corresponding author. Tel: 86-22-23501942. Fax: 86-22-23502458. E-mail: [email protected].

Herein in this paper, we describe the detailed preparation and present two 2-fold parallel interpenetrated frameworks. One of these compounds has self-assembled into a 3D superstructure with R-Po structural topology (1) while the other displays a 2D puckered 44 grid (2). Experimental Section Materials and General Procedures. All chemicals were of reagent grade and were used as received without further purification. The IR spectrum was recorded as KBr pellets on a Nicolet Magna-FT-IR 560 spectrometer in the 4000-400 cm-1 region. Elemental analysis for C, H, and N was performed on a Perkin-Elmer 240 analyzer. Inductively coupled plasma (ICP) analysis was carried out on a Perkin-Elmer Optima 3300 DV spectrometer. The thermogravimetric analysis (TGA) was investigated on a standard TG-DTA analyzer under a nitrogen flow at a heating rate of 20 °C/min for all measurements. The differential scanning calorimetry (DSC) measurements were performed on a NETZSCH DSC 204 with a heating rate of 10 °C/min in the temperature range of 25-550 °C. Synthesis of ZnCo(bpp)(m-BDC)2 (1). The mixture of CoCl2‚6H2O (0.12 g, 0.5 mmol), Zn(NO3)2‚6H2O (0.15 g, 0.5 mmol), bpp(0.10 g, 0.5 mmol), and m-H2BDC (0.17 g, 1.0 mmol) in the molar ratio of 1:1:1:2 was dissolved in 8 mL of distilled water. The pH value was then adjusted to 6 with 2 M KOH. Consequently, the resulting solution was transferred and sealed in a 25 mL Teflon-lined stainless steel vessel, which was heated at 140 °C for 2 days. After the reactor was slowly cooled to room temperature at a rate of 5 °C/h, light-purple needle crystals were filtered off, washed with water, and dried in air. Yield: 56%. ICP analysis of compound 1 gave the contents of Zn and Co as 10.23 and 9.28 wt %, respectively (calcd: Zn, 10.05; Co, 9.06 wt %), indicating a Zn:Co ratio of 1:1. Anal. Calcd for ZnCo(bpp)(m-BDC)2: C, 53.52; H, 3.41; N, 4.30. Found: C, 53.38; H, 3.64; N, 4.19. Selected IR (cm-1): ν 1614(s), 1577(s), 1450(m), 1407(m), 1337(m), 743 (s), 721(s). Synthesis of Co(bpp)(p-BDC) (2). The pink column-shaped single crystal of 2 was obtained by adopting the same synthetic procedure only with use of p-BDC instead of m-BDC and the removal of Zn(NO3)2‚6H2O. Yield: 24%. Anal. Calcd for Co(bpp)(p-BDC): C, 59.90; H, 4.31; N, 6.65. Found: C,59.73; H, 4.53; N, 6.51. Selected IR (cm-1): ν 1618(s), 1587(s), 1432(m), 1367(s), 834(s), 751(s). X-ray Crystallographic Measurements for 1 and 2. Crystal data and experimental details are summarized in Table 1. Single-crystal analyses were performed on a Bruker SMART 1000 CCD diffractometer with Mo-Ka radiation (λ ) 0.71073 Å) by the ω-2θ scan technique. All data were collected for absorption by semiempirical method using the SADABS program. The program SAINT19 was applied for integration of the diffraction profiles. Data analyses were carried out with the program XPREP. The structures were solved with the direct method using SHELXS-97 followed by structure refinement

10.1021/cg0602717 CCC: $33.50 © 2006 American Chemical Society Published on Web 09/28/2006

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Table 1. Crystal Data and Structure Refinement for 1 and 2 1 empirical formula fw T (K) cryst syst Space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (mg m-3) µ (mm-1) F (000) cryst size (mm) Θ range (deg) limiting indices no. of reflns collected/unique completeness GOF on F2 final R indices (I > 2σ(I))a largest diff. peak and hole (e Å-3) a

2

C29H22Co N2O8Zn 650.79 294(2) triclinic P1h 9.4045(15) 9.9465(16) 15.150(2) 80.939(3) 72.968(3) 75.745(2) 1307.7(4) 2 1.653 1.608 662 0.24 × 0.20 × 0.16 1.41-25.01 -10 e h e 11, -10 e k e 11, -18 e l e 17 6676/4569 [R(int) ) 0.0246] 99.4% 1.027 R1 ) 0.0375, wR2 ) 0.0826 0.463, -0.559

C21H18CoN2O4 421.30 293(2) orthorhombic Pbca 11.722(2) 16.609(3) 19.650(4)

3825.6(13) 8 1.463 0.927 1736 0.23 × 0.15 × 0.07 3.18-25.50 -14 e h e 14, -20 e k e 20, -23 e l e 23 28299/3501 [R(int) ) 0.0546] 98.2% 1.063 R1 ) 0.0410, wR2 ) 0.1112 0.619, -0.536

R1 ) ∑(|F0| - |Fc|)/∑|F0|; wR2) [∑w(F02 - Fc2)2/∑w(F02)2]1/2.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 and 2a 1 Co(1)-O(1) Co(1)-O(3)#2 Co(1)-O(4)#2 Zn(1)-O(5) Zn(1)-N(1) O(1)-Co(1)-O(3)#2 O(1)-Co(1)-N(2)#3 O(3)#2-Co(1)-N(2)#3 O(8)#1-Co(1)-O(4)#2 N(2)#3-Co(1)-O(4)#2 O(2)-Zn(1)-O(7)#1 O(2)-Zn(1)-N(1) O(7)#1-Zn(1)-N(1)

2.017(2) 2.099(3) 2.212(3) 1.990(3) 2.023(3) 148.73(11) 92.70(11) 96.46(12) 154.39(10) 93.39(12) 105.85(11) 94.79(11) 98.62(11)

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

2.000(2) 2.074(2) 2.400(5) 2.400(5) 114.91(14) 101.55(12) 130.67(14) 165.62(17) 96.29(16)

Co(1)-O(8)#1 Co(1)-N(2)#3 Zn(1)-O(2) Zn(1)-O(7)#1 O(1)-Co(1)-O(8)#1 O(8)#1-Co(1)-O(3)#2 O(8)#1-Co(1)-N(2)#3 O(1)-Co(1)-O(4)#2 O(3)#2-Co(1)-O(4)#2 O(2)-Zn(1)-O(5) O(5)-Zn(1)-O(7)#1 O(5)-Zn(1)-N(1)

2.035(2) 2.115(3) 1.982(3) 1.993(2) 116.18(10) 93.91(10) 88.71(11) 89.24(10) 60.49(10) 109.64(11) 102.45(10) 141.53(12)

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

2.008(3) 2.076(2) 2.008(3) 2.074(2) 96.17(9) 104.71(9) 102.17(9) 55.28(15) 79.57(12)

2

a Symmetry transformations used to generate equivalent atoms (in 1): #1 ) x + 1, y, z; #2 ) x, y - 1, z; #3 ) x, y - 1, z + 1. Symmetry transformations used to generate equivalent atoms (in 2): #1 ) x, -y + 1/2, z + 1/2; #2 ) x + 1, y, z; #3 ) x, -y + 1/2, z - 1/2; #4) x - 1, y, z.

on F2 with the program SHELXL-97.20 All non-hydrogen atoms were refined anisotropically. Aromatic hydrogen atoms were assigned to calculated positions with isotropic thermal parameters. The CCDC reference numbers are 288898 (1) and 605746 (2). Selected bond lengths and angles are listed in Table 2.

Results and Discussion Crystal Structure of ZnCo(bpp)(m-BDC)2 (1). Singlecrystal structure analysis reveals that complex 1 crystallizes in the triclinic space group P1h and features a 2-fold parallel interpenetrated 3Df3D network motif. The asymmetrical unit contains one Co(II) atom, one Zn atom (the Co:Zn ratio of 1:1 based on ICP analysis), one bpp ligand and two m-BDC

Figure 1. Polyhedral presentation of the heterodinuclear unit as a sixconnected node linked by the bpp and m-BDC ligands. Zn tetrahedron, blue; Co square-pyramid, pink.

molecules. The coordination number around the Co(II) ion is 4+1 with the CoO4N chromophore, and the coordination geometry is best described as an elongated square-pyramid defined by a trigonality parameter τ ) 0.34 (τ ) [θ-Φ]/60, where θ is the largest basal angel and Φ is the second one; τ ) 0 and 1 for the ideal square-pyramidal and trigonal-bipyramidal geometries, respectively),21 which comprises the basal positions occupied by four carboxylic oxygen atoms (Co-O ) 2.017(2)-2.212(3) Å) from three m-BDC and the elongated apical position occupied by one µ2-bpp nitrogen donor (Co-N2 ) 2.115(3) Å). A least-squares plane calculation shows that the CoO4 base unit is essentially planar with an inappreciable deviation (0.082 Å) from the corresponding mean plane. Each Zn ion in the center of a tetrahedral geometry is surrounded by three carboxylic oxygen atoms (Zn-O ) 1.982(3)-1.993(2) Å) from three m-BDC ligands and one µ2-bpp nitrogen atom (N1) with the Zn-N distance of 2.023(3) Å which is slightly longer than that observed (2.011(4) Å) in the complex [Zn2(BDC)(BPP)Cl2]n,22 but shorter than the value 2.063(6) Å of terminal Zn-N.10

Interpenetrated Frameworks Based on Benzenedicarboxylate

Crystal Growth & Design, Vol. 6, No. 11, 2006 2519

Figure 2. (a) View of the 1D ladder-type appearance of 1 showing the TT conformation of the arc-shaped bpp ligand. (b) Polyhedral presentation of one set of the 3D network. (c) Conceptual diagram showing the 2-fold parallel interpenetrating 3Df3D R-Po network. (d) Schematic representation of the interpenetration observed in 1, showing the structural topology.

All the bpp ligands adopt TT conformation with the N-to-N distance of 9.909 Å and a dihedral angle of the two pyridyl rings of 66.00° (see Figure 2a). There exist two types of m-BDC found in 1 (see Scheme 1, parts a and b), namely, monobidentate

bridging (µ3) and bi-bidentate chelating (µ3) coordination modes.The bpp and bi-bidentate chelating m-BDC connect mixed metals (the smallest Co‚‚‚Zn ) 3.359 Å) to form a ladder (see Figure 2a), which is further extended by monobidentate

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Figure 3. View of the coordination environment of the Co(II) atom in 2.

Scheme 1.

Coordination Mode of the m-BDC and p-BDC Ligands in 1 and 2

bridging m-BDC into a single 3D framework (see Figure 2b). From another viewpoint, two carboxylate groups bridge one Co and Zn atom to complete a six-connected heterodinuclear cluster that is jointly coordinated by four m-BDC and two bpp molecules (Figure 1). On the basis of the concept of chemical topology, the overall structure can be simplified to an elongated primitive cubic (R-Po) network if we define the dinuclear unit CoZn as a node. Of particular interest, the most striking feature of complex 1 is that a pair of identical 3D single nets is interlocked with each other, thus directly leading to the formation of a 2-fold interpenetrated 3Df3D architecture (see Figure 2c). Recently, a complete analysis of the 3D coordination networks shows that more than 50 interpenetrated pcu (R-Po) frames have been documented in the CSD database,23 including 2-fold, 3-fold,24 and 4-fold 25 interpenetration. In addition, several noninterpenetration motifs with R-Po topology have been reported to date. 26 Co(bpp)(p-BDC) (2). Complex 2 crystallizes in the orthorhombic space group Pbca and features a 2-fold parallel interpenetrated 2Df2D puckered rectangle grid. The asymmetrical unit is composed of one Co(II) ion, one p-BDC, and one bpp molecule. The Co(II) ion is also five-coordinated and close to a square-pyramidal CoN2O3 geometry (τ ) 0.17 is smaller than the corresponding value of 0.34 in 1). As shown in Figure 3, three oxygen atoms (O1, O3, and O4) belonging to two m-BDC and one bpp nitrogen atom (N1) are ligated to the Co center in the equatorial plane, with another nitrogen atom (N2) arising from the second bpp molecule situated in the axial position. Each Co(II) approximately lies in the equatorial position with a maximum deviation (0.320 Å) from the basal plane. In the structure, Co-O and Co-N bond distances are in the range of 2.000(2)-2.400(5) and 2.074(2)-2.076(2) Å, respectively. Unlike in 1, the bpp ligand in the TG conformation presents a N-to-N distance of 8.595 Å and a dihedral angle of 79.58° between the two pyridyl rings (see Figure 4a). Two Co atoms are interlinked by the µ2-bpp and monobidentate

Figure 4. (a) View of the 1D ladder-type motif of 1 showing the TG conformation of the bpp ligand. (b) View of a single 2D puckered grid representing the four-connected 44 topology. (c) Conceptual diagram showing the 2-fold parallel interpenetrating 2Df2D network. (d) Schematic representation of the interpenetration of (c).

chelating (µ2) p-BDC ligands (see Scheme 1c), thus affording a square grid with a large window of 11.7 × 10.8 Å, which are further connected together into a 2D puckered 44 net (see Figure 4b). The interesting feature of 2 is the occurrence of a parallel interpenetrating motif consisting of two identical single nets (see Figure 4c,d). Upon interpenetration, the PLATON calculation27 shows that the effective void volume has been drastically reduced to 58.3 Å3, which approximately corresponds to 1.5% of the crystal volume (3825.7 Å3). Compared with 1 and 2, it is important to note that the close structural relationship should be attributed to the following

Interpenetrated Frameworks Based on Benzenedicarboxylate

contributions: (1) The semirigid bpp ligand, in which three methylene (CH2) molecules between the pyridyl rings can rotate freely, endows itself with high flexibility to take on a variety of conformation and finally gives two interpenetrated frameworks here. (2) The different dispositions of the two carboxylate groups, i.e., the values of dispersion angles being 120 and 180°, respectively, in the m-BDC and p-BDC isomers, may give rise to different geometric effects and dimensional variations. IR Spectra of 1 and 2. The IR spectrum of compound 1 shows the typical antisymmetric (1614 cm-1) and symmetric (1577, 1450 and 1407 cm-1) stretching bands of carboxylate groups. The respective values of (νasym(CO2)-νsym(CO2)) clearly suggest the presence of chelating (37 cm-1), bridging (164 cm-1), and monodentate coordination modes (207 cm-1) of the carboxylate groups. The absence of the expected absorption band at around 1700 cm-1 for the protonated carboxylic groups indicates the complete deprotonation of the m-BDC ligand. The peak in the IR spectrum of compound 2 centered at 1618 cm-1 should be assigned to the antisymmetric stretching for carboxylate groups. The bands between 1587 and 1432 cm-1 correspond to the symmetric stretching of carboxyl groups. The respective values of (νasym(CO2)-νsym(CO2)) indicate the existence of chelating (31 cm-1) and monodentate coordination modes (186 cm-1) of carboxyl. These spectral information are consistent with the results of the single-crystal X-ray diffraction analyses. Thermal Analyses. To estimate the stability of the supramolecular architectures, thermogravimetric analyses experiments were carried out in the temperature range of 50-800 °C. As shown in Figure S1a of the Supporting Information, complex 1 is stable up to 415 °C. A rapid weight loss can be detected from 415 to 499 °C that is attributed to the complete decomposition of the bpp and m-BDC ligand, and one strong exothermic peak is observed at 459 °C. The remaining residue is presumed to be CoO and ZnO (calcd: 24.0%; found: 22.8%). In comparison with 1, compound 2 is slightly more stable up to 435 °C, where the decomposition of the framework starts (see Figure S1b of the Supporting Information), a very strong exothermic peak is found at 465 °C, and the resulting residue remains as CoCO3 (calcd: 28.3%; found: 30.0%). The DSC curves for 1 and 2 were presented in Figure S2 of the Supporting Information. For 1, a strong exothermic peak at 443.2 °C can be observed, which corresponds to the breakdown of the supramolecular framework, whereas for 2, the strongest exothermic peak centers at about 436.7 °C (lower than 443.2 °C in 1), which suggests the thermal stability of 1 is slightly higher than 2, being in good agreement with the TGA result. The presence of two visible shoulders indicates the decomposition of 2 in several steps. On the other hand, both 1 and 2 clearly show the absence of endothermic melting peaks. In conclusion, we have successfully synthesized and characterized two 2-fold parallel interpenetrated entanglement systems based on the connectivity co-effect between the isomerous benzenedicarboxylate and the semirigid bpp ligand. The use of V-shaped m-BDC affords an 3D R-Po topological network, whereas the linear p-BDC yields a typical 2D puckered 44 grid. This work will undoubtedly deepen our systemic understanding on the structural functionality of the benzenedicarboxylic acids and the conformational flexibility of long bpp molecule. Furthermore, our interest in the chemical topology is unprecedentedly excited by the practical examples. Acknowledgment. This work was supported by the National Natural Science Foundation of China (50572040).

Crystal Growth & Design, Vol. 6, No. 11, 2006 2521 Supporting Information Available: X-ray crystallographic files in CIF format and TGA and DSC curves of 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.

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