Construction of Entangled Coordination Polymers Based on M2+

Article pubs.acs.org/crystal

Construction of Entangled Coordination Polymers Based on M2+ Ions, 4,4′-{[1,2-Phenylenebis(methylene)]bis(oxy)}dibenzoate and Different N‑Donor Ligands Fei-Long Hu,†,‡ Wei Wu,§ Peng Liang,§ Yun-Qiong Gu,† Li-Gang Zhu,† Han Wei,† and Jian-Ping Lang*,† †

College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People’s Republic of China ‡ College of Chemistry and Material, Yulin Normal University, Yulin, 537000, People’s Republic of China § College of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Nanning 530006, People’s Republic of China S Supporting Information *

ABSTRACT: Reactions of several transition metal [M = Mn(II), Cu(II), Zn(II), Co(II)] salts with 4,4′-{[1,2phenylenebis(methylene)]bis(oxy)}dibenzoic acid (H2L) and auxiliary N-donor ligands afforded a series of entangled coordination frameworks, [Mn2L2(4,4′-bpy)2][Mn2L2(H2O)2]·2H2O (1), [CuL(bbm)]·0.5H2O (2), [CuL(4,4′-bpy)0.5] (3), [Zn3L2(4,4′-bpy)2(HCOO)2] (4), [ZnL(4,4′-bpy)] 2 ·H 2 O (5), [Co 4 L 4 (bpp) 2 ]·DMF (6), [Co2L2(bbm)]2·2H2O (7), and [CoL(2,2′-bpy)] (8) [2,2′bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine; bbm =1,4di(1H-imidazol-1-yl)benzene; bpp = 1,3-bis(4-pyridyl)propane]. Their structures were characterized by elemental analysis, IR spectra, and TG analysis and further determined by single-crystal X-ray diffraction analysis. Compound 1 has an uncommon 2Dlayer + 1Dchain → 3D framework, while 2 displays a 2-fold interpenetrated 3D framework. Compounds 3−5 show different entangled networks though they adopt the same 4,4′-bpy as the auxiliary ligand. Compounds 3 and 5 show 2-fold interpenetrated 2D networks, showing both polycatenane and polyrotaxane characters. Compound 4 possesses a 2D → 3D polythreaded architecture. Compound 6 has a 3-fold interpenetrated 3D framework by using bpp as the second ligand. Compound 7 presents a 3D framework with a (44·62·88·12)(44·62)(8) topology. Compound 8 presents a 1D helical chain constructed by linking [Co(2,2′-bpy)]2+ units via L ligands. The results provided an interesting insight into how metal ions, auxiliary N-donor ligands, and molar ratios of the components exert great impact on the formation of these entangled networks. The thermal and luminescent properties of 1−8 in solid state at ambient temperature were also investigated.

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INTRODUCTION The design and synthesis of new entangled systems are of great interest due to their potential applications and intriguing topological structures.1−5 As an important subgroup of entangled systems, interpenetrating nets have provided a longstanding fascination for chemists.6 In recent years, the intense interest in coordination polymers has led to the discovery of more types of topological entanglements such as polycatenation, polythreading, and polyknotting that resemble molecular catenanes, rotaxanes, and knots.7−15 As an important member in the realm of entangled networks, polycatenated frameworks have a higher dimensionality than the component motifs.16 Polythreaded structure is characterized by the presence of closed loops, as well as of species that can thread through the loops.17a The polyrotaxane has a different motif that cannot be disentangled without breaking links, while the polypseudorotaxane is the infinite chains or finite components that can be slipped off from the threaded motif.17b To date, although some polycatenated coordination polymers have been © 2013 American Chemical Society

reported, the topological frameworks containing two kinds of entangled motifs in one compound are still quite rare. Only a few fascinating structures showing both polyrotaxane and polycatenane characters have been observed.17c,d It is a great challenge to synthesize entangled frameworks having both polyrotaxane and polycatenane characters that also achieve different topological structures in the entangled system. To achieve this aim, an important approach is the use of conformationally flexible components. In this work, we selected a conformationally flexible V-shaped long bicarboxylic acid ligand 4,4′-{[1,2-phenylenebis(methylene)]bis(oxy)}dibenzoic acid (H2L)18 based on the following considerations (Scheme 1). This bicarboxylic acid ligand is structurally not rigid and contains pairs of the flexible −O−, −CH2−, and −O−CH2− atoms and groups. Such a conformationally nonrigid ligand is Received: August 8, 2013 Revised: September 21, 2013 Published: September 24, 2013 5050

dx.doi.org/10.1021/cg401212s | Cryst. Growth Des. 2013, 13, 5050−5061

Crystal Growth & Design

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yield) and 5 (40% yield) and pink crystals of 6 (64% yield), 7 (60% yield), and 8 (36% yield). In the formation of 4, one in situ-formed HCOO− anion was observed. Since solvothermal treatment of H2L in DMF/H2O (v/v = 4:6) at 145 °C did not produce any HCOO− anion, the formation of this HCOO− anion may be due to the metal-induced hydrolysis of DMF under solvothermal conditions.19 As described later in this paper, compounds 1−8 possess eight different polydimensional frameworks. Such structural diversity may be attributed to the flexible ligand L, which showed six different coordination modes in these structures. Besides, these structural diversities may also be ascribed to metal ions with different coordination environments, geometries of the auxiliary N-donor ligands employed, reaction temperatures, molar ratio of the components, and so on. For example, since the same H2L and 4,4′-bpy ligands were employed in the formation of 1, 3, and 5, their different entangled structures may be due to the different metal ions and also their different coordination geometries, though the temperature factor could not be ruled out in the case of 1. For 2 and 3, the introduction of two different auxiliary N-donor ligands (bbm vs 4,4′-bpy) was likely to be the reason for the formation of their different topological arrays. For 4 and 5, their different outcomes may be attributed to the different molar ratios of the same components, suggesting that the molar ratio of the components could sometimes play an important role in the formation of coordination polymers. For the cobalt complexes 6−8, their structure diversity may be ascribed to the introduction of three different auxiliary N-donor ligands (bpp vs bbm vs 2,2′-bpy). These three ligands have three different geometries: chelating for 2,2′-bpy, rigid for bbm and flexible for bpp. It seems that chelating ligands like 2,2′-bpy tend to produce lower dimension structures such as the onedimensional (1D) helical chain of 8. Rigid ligands like bbm may produce higher dimension structures such as the threedimensional (3D) net of 7. The flexible ligands like bpp generate multifold interpenetrated frameworks like the 3D 3fold interpenetrated net of 6. Complexes 1−8 are air-stable and insoluble in common solvents. Their elemental analysis was consistent with the chemical formulas of 1−8. In order to check the phase purity of 1−8, the powder X-ray diffraction (PXRD) patterns were measured at room temperature. As shown in Figures S1 and S2 of the Supporting Information, the peak positions of the simulated and experimental PXRD patterns are in agreement with each other, suggesting the good phase purity of the title compounds. The IR spectra of 1−8 showed strong peaks in the range of 1526−1672 cm−1 and 1320−1470 cm−1, indicating that they all contain coordinated carboxylate groups. The broad medium intensity bands from about 3100 to 3500 cm−1 of 1, 2, 5, and 7 can be contributed to the water molecules. The band at 1699 cm−1 in 6 can be assigned to the solvent DMF molecule, while that at 1685 cm−1 may be ascribed to the existence of the HCOO− anion in 4. The strong peak at 1055 and 659 cm−1 means the existence of imidazolyl groups in 2 and 7. The identities of 1−8 were finally confirmed by singlecrystal X-ray crystallography. Crystal Structure of [Mn2L2(4,4′-bpy)2][Mn2L2(H2O)2]· 2H2O (1). Compound 1 crystallizes in the triclinic space group P1̅, and its asymmetric unit contains two independent molecules [Mn2L2(4,4′-bpy)2] and [Mn2L2(H2O)2] and two H2O solvent molecules. In the [Mn2L2(4,4′-bpy)2] molecule, Mn1 and Mn2 are linked by two carboxyl groups of two L ligands to form a dinuclear structure with a long Mn1···Mn2

Scheme 1. L Ligand and Auxiliary Ligands Used in This Work

anticipated to favor the formation of interesting motifs with peculiar features like new topologies and entanglements (including polycatenanes and polyrotaxanes). Therefore, the two phenyl rings can freely twist around the −O− atoms or −CH2− and −O−CH2− groups to meet the requirements of the coordination geometries of metal centers in the assembly process. Conformational changes of flexible ligands can more easily give unusual entanglements involving a molecular unit with loops and insertion of linear rod through those loops. Thus we carried out solvothermal reactions of H2L with various metal [M = Mn(II), Cu(II), Zn(II), Co(II)] salts in the presence of several N-donor auxiliary ligands, including 4,4′bipyridine (4,4′-bpy), 2,2′-bipyridine (2,2′-bpy), 1,4-di(1Himidazol-1-yl)benzene (bbm), and 1,3-bis(4-pyridyl)propane (bpp). Eight interesting entangled coordination polymers: [Mn2L2(4,4′-bpy)2][Mn2L2(H2O)2]·2H2O (1), [CuL(bbm)]· 0.5H 2 O (2), [CuL(4,4′-bpy) 0 . 5 ] (3), [Zn 3 L 2 (4,4′bpy) 2 (HCOO) 2 ] (4), [ZnL(4,4′-bpy)] 2 ·H 2 O (5), [Co4L4(bpp)2]·DMF (6), [Co2L2(bbm)]2·2H2O (7), and [CoL(2,2′-bpy)] (8) were isolated and structurally characterized. Herein, we report their syntheses, structures, and thermal and photoluminescent properties.

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RESULTS AND DISCUSSION Synthesis Aspects. The solvothermal reactions of MnCl2 with H2L and 4,4′-bpy in a 1:1:1 molar ratio in DMF/H2O (v/v = 4:6) at 160 °C for 2 days followed by a standard workup gave rise to yellow crystals of 1 in 53% yield. When the reactions were carried out at lower temperatures, only a large amount of insoluble solids were obtained, which could not be characterized due to its low solubility in common solvents. Treatment of CuSO4·5H2O with H2L and bbm in a 1:1:1 molar ratio in DMF/H2O (v/v = 4:6) at 145 °C for 2 days under solvothermal conditions followed by a standard workup afforded blue crystals of 2 in 41% yield. Analogous reactions of CuSO4·5H2O with H2L and 4,4′-bpy in a 1:1:1 molar ratio produced blue crystals of 3 in a 34% yield. Other similar reactions of Zn(OAc)2 + H2L + 4,4′-bpy (molar ratio = 1:1:2), Zn(OAc)2 + H2L + 4,4′-bpy (molar ratio = 1:1:1), CoSO4· 7H2O + H2L + bpp (molar ratio = 1:1:1), CoSO4·7H2O + H2L + bbm (molar ratio =1:1:1), or CoSO4·7H2O + H2L + 2,2′-bpy (molar ratio = 1:1:1) produced colorless crystals of 4 (43% 5051



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Figure 1. (a) View of the coordination environments of Mn1 and Mn2 centers in [Mn2(L)2(4,4′-bpy)2]. (b) View of the coordination environments of Mn3 and Mn4 centers in [Mn2(L)2(H2O)2]. (c) View of the 2D sheet formed by Mn1, Mn2, L, and 4,4′-bpy ligands. (d) View of the 1D chain formed by Mn3, Mn4, and L ligands. (e) Schematic illustration of the 2Dsheet + 1Dchain → 3D. (f) View of the 3D framework formed by the threading of the 1D chains into the rhombic windows of the 2D sheets.

ones by the L ligands, leading to a 1D chain. Pairs of 4,4′-bpy ligands further connect chains to develop a two-dimensional (2D) layer structure [Mn2L2(4,4′-bpy)2]n (Figure 1c). Adjacent layers are joined together by the π···π stacking interactions to form a 3D porous net with 1D channels (its dimension of the rectangular opening being 11.4 × 11.5 Å2), extending along the a axis (Figure S3a of the Supporting Information). The [Mn2L2(H2O)2] unit is further linked through L ligands to yield a 1D chain [Mn2L2(H2O)2]n (Figure 1d). The 1D channels in the above-mentioned 3D porous net are occupied by the 1D chain [Mn2L2(H2O)2]n, thereby generating an uncommon 2Dlayer + 1Dchain → 3D framework (Figure 1 (panels e and f) and Figure S3b of the Supporting Information). There existed only three examples [Cu(L)(solv)(NO3)2][Cu(L)1.5(NO3)2]· 2solv {L = 1,4-bis[(4′-pyridylethyny)benzene; solvent = EtOH or MeOH]} 21a and [Ag 0.52 Na 0.48 (β-Mo 8 O 26 )(H 2 O)][Ag3(Tipa)2] [Tipa = tri(4-imidazolylphenyl)amine],21b which showed similar frameworks. However, their entangled models are entirely different from that of 1. The latter two possessed a 1Dladder + 1Dchain → 3Dpolypseudorotaxane framework, and the windows between the rungs were threaded by two cationic chains. For 1, only neutral [Mn2L2(H2O)2]n chains pass

separation (4.161 Å) (Figure 1a). Both Mn(II) centers adopt a trigonal bipyramidal coordination geometry, coordinated by three O atoms from the three L ligands and two N atoms (in the axial positions) from two 4,4′-bpy ligands. In addition, there is a weak interaction between Mn1 and O21 (2.670 Å) or between Mn2 and O28 (2.664 Å). The two carboxyl groups of each L ligand linking this unit display different coordination modes: η,η-μ-bridging and monodentate. Each L ligand takes a twisted V-shaped conformation with a dihedral angle of 74.91° between two benzene rings. The [Mn2L2(H2O)2] molecule has a dinuclear paddle-wheel structure in which two Mn(II) centers (Mn3 and Mn4) are bridged by four carboxyl groups from four L ligands (Figure 1b). The square pyramidal geometry of each Mn(II) center is completed by one water molecule occupying its axial position. The two carboxyl groups of each L ligand linking this unit have the same η,η-μ-bridging coordination mode. The Mn−O(carboxyl) bond lengths are in the range of 2.08−2.14 Å, while the Mn···Mn separation is 3.098 Å, which are comparable to those reported previously.20 Each L ligand also has a twisted V-shaped conformation with a dihedral angle of 83.53° between the two benzene rings. For [Mn2L2(4,4′bpy)2], its [Mn2L2] species is linked with other four equivalent 5052



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mean Cu−O and Cu−N bond lengths (1.983 Å vs 1.977 Å) are slightly shorter than those of the corresponding ones found in [CuL(terehpthalato)]n·2nH2O (2.26 Å vs 2.01 Å, L = 6,15dimethyldocosahydrodibenzo[b,i][1,4,8,11]tetraazacyclotetradecine).25 In addition, there are two weak interactions between Cu1 and O1 from one carboxylate group (2.634 Å) and between Cu1 and O5 (H2O solvent molecule) (2.620 Å), which are shorter than that observed in [CuL(terehpthalato)]n·2nH2O (2.73 Å).25 It is noted that the L ligand displays a zigzag conformation due to the rotation of the −CH2− or −O−CH2− groups. With the introduction of the rigid ligand bbm, the whole structure presents a 3D porous channel-like net with (424·64) topology (Figure 3c). Two such nets are interwoven into a 2-fold interpenetrated 3D structure (Figure 3d). Crystal Structure of [CuL(4,4′-bpy)0.5] (3). Complex 3 crystallizes in the monoclinic space group P21/c, and its asymmetric unit consists of half a [Cu2L2(4,4′-bpy)] molecule. Cu1 is coordinated by one N atom from 4,4′-bpy and four O atoms from four L ligands to furnish a distorted squarepyramidal geometry (Figure 4a). Interestingly, the 4,4′-bpy ligand does not occupy the exact position of the axial position of the paddle-wheel, but it bends away by 26.3° (Figure S4 of the Supporting Information). Each V-shaped L ligand uses its two carboxylate groups to link two Cu atoms in a η,η-μbridging coordination mode, thereby forming a dinuclear paddle-wheel [Cu2L] subunit with a short Cu···Cu separation of 2.681 Å. Two such subunits combine into a rhombic [Cu4L2] unit. This unit is fused with other equivalent ones to form a 1D chain [Cu4L2]n. Such a chain is further bridged by 4,4′-bpy to afford a 2D network (Figure 4b). In this 2D sheet, each paddlewheel building unit is connected to four others, two of them by two 4,4′-bpy ligands, the others by two pairs of the V-shaped L ligands, which created a [Cu4L2] loop. Although the bimetallic

through the windows and the whole structure shows 2Dlayer + 1Dchain → 3D framework (Figure 1e). The most interesting structural feature of 1 is that since big side arms are formed by the L ligand with a twisted V-shaped conformation (Figure 2a), the middle benzene ring acting as

Figure 2. (a) View of the mutual polythreading of the three layers. (b) Schematic illustration of the mutual polythreading of three layers.

side arms thread into the rhombic voids of three adjacent layers up and down (Figure 2b). Each rhombic window is penetrated by three arms from the mutual opposite directions. Three adjacent 2D arrays are entangled into an intriguing 2D → 3D polythreaded architecture.22 To some extent, such a 2Dlayer + 1Dchain → 3D entangled framework of 1 displays both polythread and polycatenation characters, which are quite rare to the best of our konwledge.18,23,24 Crystal Structure of [CuL(bbm)]·0.5H2O (2). Complex 2 crystallizes in the orthorhombic space group Pbcn, and its asymmetric unit contains one discrete [Cu2L2(bbm)2] molecule and half a water molecule. The Cu1 center takes a normal square planar coordination geometry, coordinated by two O atoms from two carboxylate groups and two N atoms from two bbm ligands (Figure 3a). Each L ligand also has a Z-shaped conformation with a dihedral angle of 31.07° between two benzene rings. Its two carboxyl groups display two different coordination modes: monodentate and η,η-μ-bridging. The

Figure 3. (a) View of the coordination environment of Cu1 center in 2. (b) View of the 3D net of 2, which displays 1D channels extended along the a axis. (c) View of the 2-fold interpenetrated 3D structure of 2 looking along the a axis. 5053



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Figure 4. (a) View of the coordination environment of the Cu1 center in 3. (b) View of the single 2D sheet in 2. (c) View of two interpenetrating sheets in 3. (d) Schematic view of the parallel 2D → 2D 2-fold interpenetration in 3.

Figure 5. (a) View of the coordination environments of the Zn1 and Zn2 centers in 4. Symmetry code: A: −x, 1 − y, −z. (b) View of the mutual 3fold polythreading of three layers in 4. (c) View of the polythreading model in 4. (d) View of the π···π stacking interactions between the benzene rings of different layers in 4.

paddle-wheel subunit is a common and highly stable arrangement found in many coordination frameworks, it is rare that the bimetallic species have been systematically introduced into a polyrotaxane system.26,27 The structure of 3 is similar to that of the Zn(II) complex reported recently,26a but it is an important member in the family of entangled systems constructed by the

L ligands. The most interesting structural feature of 3 is that two such networks interpenetrate in a (2D → 2D) parallel fashion, but in a highly unusual way, to produce a 2D polyrotaxane layer (Figure 4c). The [Cu4L2] loop of each net are threaded through by one 4,4′-bpy rod of the other net and vice versa (Figure 4d). Such an entanglement represents an 5054



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Figure 6. (a) View of the coordination environment of the Zn1 center in 5. (b) View of the 2D (6,3) layer extending along the ab plane. (c) View of the 2-fold interpenetrating net in 5. (d) Schematic representation of the 3D polycatenated net in 5.

benzene ring of the L ligand (the central-to-central distances being 3.77−3.93 Å) (Figure 5d) and between the pyridyl groups of the 4,4′-bpy ligands (the central-to-central distances being 3.787 Å). A similar occurrence of a polythreaded net with mixed ligands was found in the previous structure.29 It is uncommon that threaded layers are extended by 4,4′-bpy as bridging spacers and decorated by the middle phenyl ring of the ligand as pendants. Crystal Structure of [ZnL(4,4′-bpy)]2·H2O (5). Compound 5 crystallizes in the monoclinic space group P21/c, and its asymmetric unit contains half a [ZnL(4,4′-bpy)]2 molecule and one lattice water molecule. Zn1 is coordinated by three O atoms from two L ligands and two N atoms from two 4,4′-bpy ligands to give a ZnO3N2 square pyramidal geometry (Figure 6a). A weak interaction (2.607 Å) between Zn1 and O2 from one L ligand is also observed. Each L ligand adopts a monodentate and chelating coordination mode, and a pair of L ligands bind two Zn(II) to form a [Zn2L2] rhombic unit with a window being a dimension of 11.7 × 11.6 Å2. Such a [Zn2L2] unit is interconnected to its neighboring ones via 4,4′-bpy ligands to afford a 2D layer structure extending along the ab plane (Figure 6b). If each [ZnO3N2] unit is considered as a 4connected node and 4,4′-bpy and L ligands are considered as linkages, the structure of 5 can be viewed as 2D (4,4) topology (Figure S6 of the Supporting Information). Two identical layers interpenetrate into each other in the vertical direction, thereby forming a 2D → 3D 2-fold interpenetrating network (Figure 6, panels c and d). The C−H···π unconventional interactions play important roles in the formation of the 3D network with the C(28)− H(28)···Cg distance of 2.77 Å, and the angle is 97.6° (Cg is the ring defined by the atoms of C19 to C24) as shown in Figure S7 of the Supporting Information. It is noted that this net also shows both polyraxane and polycatenane characters. The loop of [Zn2L2] in one sheet is threaded by another 4,4′-bpy ligands

unusual mode of parallel interpenetration of 2D sheets, which was described by Batten and Robson as examples containing both polyrotaxane and polycatenane characters. This kind of interpenetrating network is exceedingly rare.28 Crystal Structure of [Zn3L2(4,4′-bpy)2(HCOO)2] (4). Compound 4 crystallizes in the monoclinic space group P21/ c, and its asymmetric unit contains one [Zn3L 2(4,4′bpy)2(HCOO)2] molecule. As shown in Figure 5a, Zn1 adopts an uncommon square pyramidal geometry, coordinated by N1 from one 4,4′-bpy ligand, O3 and O4 from one L ligand, O5 (in one vertex position) from another L ligand, and O2 from one HCOO− anion. In addition, there is one weak interaction (2.673 Å) between Zn1 and O1 from this HCOO- anion (in the other axial position). Zn2 is octahedrally coordinated by two O atoms from two L ligands, two O atoms from two HCOO− anions, and two N atoms (occupying the axial positions) from two 4,4′-bpy ligands. The two carboxyl groups of each twisted V-shaped L ligand show the same chelating/η,ημ-bridging coordination mode. It is quite rare that the HCOO− anion works as a bridging ligand with a monodentate mode to bind two Zn atoms. Zn1, Zn2, and Zn1A hold together via two bridging HCOO− anions and two bridging L ligands to form a trinuclear linear Zn3 unit. This unit is further linked by four carboxyl groups of four L ligands, generating a 2D network (Figure S5 of the Supporting Information). To our knowledge, the rhombic subunit composed by Zn3 units has not previously been reported. When it is viewed along the b axis, both left- and right-hand helical chains appear alternatively by sharing the Zn3 units, resulting in the formation of the 1D helical nanochannels in this 2D sheet (Figure 5b). Each rhombic window is therefore penetrated by four side arms from the mutual opposite directions. Three adjacent 2D networks are threaded into the rhombic voids to form intriguing 2D → 3D polythreaded architecture (Figure 5c). Such a threading structure is reinforced by strong π···π stacking interactions between the 5055



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pyramidal geometry, coordinated by one N atom (in the axial position) from one bpp ligand and three O atoms from three L ligands. Co1 and Co2 (or Co3 and Co4) are joined together by sharing the three carboxyl groups to form a paddle-wheel dinuclear [Co2L2] subunit. Such two subunits are further connected by a bpp ligand to form a tetranuclear [Co4L4(bpp)] unit. The two carboxyl groups of the L ligands show different coordination modes: chelating/η,η-μ-bridging and η,η-μ-bridging/η,η-μ-bridging. In this case, two kinds of windows are formed by two kinds of L ligand (Figure S8 of the Supporting Information). A 2D double-layer structure with 1D channels (Figure 8b) is formed by the two kinds of windows which appear alternately (Figure S8 of the Supporting Information). The cis−trans windows arrange in a line and are further linked by the bpp ligand to form a layer structure. The driving force for the formation of this type of interpenetration may be due to the request, filling empty space in the structure as suggested by Batten and Robson. Therefore, three identical layers interpenetrate each other to form a 3D 3-fold interpenetrated net (Figure 8c). As shown in Figure 8d, two bpp ligands penetrate the window formed by the L ligand with mutual anti fashion. In a sequence of “cell” along the direction of catenation, only those of the same color are interlocked. Two bpp ligands are interlocked by the [Zn2L2] loop (Figure 8d). Crystal Structure of [Co2L2(bbm)]2·2H2O (7). Compound 7 crystallizes in the monoclinic space group P21/c, and its asymmetric unit contains one [Co2L2(bbm)] molecule and two lattice water molecules. Co1 is octahedral by coordination to four O atoms of four L ligands and two N atoms from two bbm ligands, while Co2 has a distorted trigonal bipyramidal geometry, coordinated by five O atoms from four ligands (Figure 9a). Co1 and Co2 are linked together by L ligands to form a Co2 paddle-wheel unit. The two carboxyl groups of the L ligands show different coordination modes: monodentate/ η,η2-μ-bridging versus η,η-μ-bridging/η,η-μ-bridging. The L ligands bearing the former coordination mode bind Co(II) centers to form an undulating 2D (4,4) net with a rhombic window (Figure 9b, brown). Other L ligands work as the latter coordination mode to bind Co(II) centers (Figure 9b). The

as rods from two adjacent layers (Figure 7a). A large ring of [Zn4(4,4′-bpy)2(L)2] from one layer is interlocked by two

Figure 7. (a) Schematic representation of the single layer of 5, which shows the windows formed by the L ligands and the 44′-bpy pillars. (b) Space filling model showing the rods representing the benzene− O−CH2−benzene groups of the L ligand.

[Zn2(L)2] loops from the other two identical layers. The polyrotaxane nature of this species is evident due to the presence of two kinds of loops. In accordance with the literature,9b it requires rods to thread through the center of loops in order to obtain a polyrotaxane. To a certain extent, the benzene−O−CH2−benzene groups of the L ligand serve as the rod which passes through the big loops formed by [M6(4,4′bpy)4L4] units, as shown in Figure 7b. Although the ligands adopted in 5 are similar to those of 3 and 4, complex 5 presents a completely different network. Both 3 and 5 show a 2D 2-fold interpenetrated network by using the [M2L2] unit as the loop and 4,4′-bpy as the rod. In 3, 4,4′-bpy links the loops up and down nearly in a line direction. But in 5, 4,4′-bpy is set in a nearly vertical direction with the angle of 82.5°. Crystal Structure of [Co4L4(bpp)2]·DMF (6). Compound 6 crystallizes in the triclinic space group P1̅, and its asymmetric unit contains one [Co4L4(bpp)2] molecule and one lattice DMF molecule. Co1 or Co3 is octahedrally coordinated by one N atom from one bpp ligand and five O atoms from four L ligands (Figure 8, panels a and b). Co2 or Co4 adopts a trigonal

Figure 8. (a) View of the coordination environments of Co1, Co2, Co3, and Co4 centers in 6. (b) View of the 2D layer of 6. (c) Space-filling model showing the 3D 3-fold interpenetrated net of 6. (d) View of interlocking the [Zn2L2] loop by the two bpp ligands in 6. 5056



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Figure 9. (a) View of the coordination environments of Co1 and Co2 centers in 7. (b) View of the 3D net of 7 showing channels along the a axis, which are filled by water molecules. (c) Schematic drawing of the 3D network with a (44·62·88·12)(44·62)(8) topology.

Figure 10. (a) View of the coordination environment of the Co1 center in 8. (b) View of one section of the 1D helical chain of 8. (c) View of the polythreading model in 8.

bbm ligands link the paddle-wheel units to yield a 3D net with a (44·62·88·12)(44·62)(8) topology (Figure 9c). It is noted that an unusual contact between a C−H group of the phenyl ring of the L ligand and the π system of the aromatic ring of the L ligand is observed, which is responsible for the strengthening of the 3D structure of 7. A close inspection of the structure reveals that the C−H···π and C−H···O interactions provide an extra source of stability (Figures S9a and S9b of the Supporting Information). The C46−H46 group points out to the center of the phenyl ring of the big arm directly with the distance of 2.461 Å (Figure S9a of the Supporting Information) (C46−H46···Cg = 2.461 Å, Cg is the centroid of the ring

defined by the atoms C37−C42), which suggests strong C− H···π interactions.30−32 Moreover, the C(49)−H(49) group points out to another phenyl ring center with the distance of 2.836 Å (Figure S9b of the Supporting Information) (C49− H49···Ch = 2.836 Å, Ch is the centroid of the ring defined by the atoms of C30−C35). Therefore, the structure is further stabilized by the strong unconventional interactions to form a 3D supramolecular architecture. Crystal Structure of [CoL(2,2′-bpy)] (8). Compound 8 crystallizes in the monoclinic space group P21/c, and its asymmetric unit has one [CoL(2,2′-bpy)] molecule. Co1 is octahedrally coordinated by four O atoms from two L ligands 5057



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CONCLUSIONS In the work reported here, we have demonstrated self-assembly of eight entangled coordination frameworks 1−8 from reactions of metal salts with one dicarboxylate ligand L and various auxiliary N-donor ligands (4,4′-bpy, 2,2′-bpy, bbm, and bpp) under solvothermal conditions. It is noted that structural diversities of these frameworks may be greatly affected by the flexible ligands with different geometries. Conformational changes of flexible ligands can more easily give entanglements involving a molecular unit with loops and insertion of linear rods through those loops. The flexible ligand L in this work served as a versatile building block by bridging the metal ions in diverse coordination modes. The two carboxyl groups of the L ligand in 1−8 show six different coordination modes: η,η-μbridging and η,η-μ-bridging (1, 3, 6, and 7), η,η-μ-bridging and monodentate (1, 2), η,η2-μ-bridging and monodentate (7), chelating and η,η-μ-bridging (4,6), chelating and chelating (8), monodentate and chelating (5). In addition, the structural diversity described above may also be related to the nature of metal ions with different coordination environments, geometry of the auxiliary N-donor ligands employed, reaction temperature, molar ratio of the components, and so on. These results indicate that novel extended entanglements containing both polyrotaxane and polycatenane character could be realized by combining metal nodes with flexible polycarboxylic ligands and auxiliary N-donor ligands along with controlling the suitable reaction conditions. Further studies in this respect are underway in this laboratory.

and two N atoms from the 2,2′-bpy molecule (Figure 10a). The two carboxyl groups of each L ligand take a chelating/chelating coordination mode. The L ligands bind Co(II) centers to form a 1D helical chain, extending along the b axis. Complex 8 features a 2D parallel polythreaded network with alternate leftand right-handed 21 helical motifs with the pitch of the helix being ca. 14.657 Å (Figure 10c). As a result of enough space, two such frameworks threaded into the space of each other by the π···π interactions as shown in Figure S10 of the Supporting Information. Compound 8 can also be viewed as the polythreaded conformation with the big benzene ring as the big arms threading into the channels formed by the helical model of the chain. It is noted that strong π···π stacking interactions are observed between the adjacent chains (Figure S10 of the Supporting Information). The benzene ring of the big arm and 2,2′-bpy molecule of the adjacent motif are stacked in a face-to-face model with the distance of 3.87 Å, suggesting strong π···π stacking interactions according to the literature.33,34 In addition, strong π···π stacking interactions are also observed between the pyridyl groups of 2,2′-bpy ligands of the adjacent motif and are observed along the c axis. Thermal and Photoluminescent Properties. Their thermal stability was studied by the TG-DTA technique (Figures S11 and S12 of the Supporting Information). The TGA analysis revealed that 1−8 were stable up to 300 °C. For 1, the first weight loss of 5% in the range of 100−200 °C corresponded to the loss of water molecules. The second weight loss of 7% in the range of 230−300 °C could be attributed to the release of one 4,4′-bpy ligand. When the temperature was elevated, the product lost 70% of the total weight in the range of 300−500 °C, corresponding to the removal of L and the rest of the 4,4′-bpy ligand. For 2 and 3, its weight loss of 60% (2) or 75% (3) in the range of 300−500 °C corresponded to the release of the L and bbm (2) or 4,4′-bpy (3) ligands. For 4, the first weight loss of 2% at ca. 50 °C could be the loss of the water molecule. The second weight loss of 50% in the range of 300−330 °C corresponded to the loss of the L ligand. The third weight loss of 25% in the range of 400− 550 °C could be ascribed to the release of 4,4′-bpy. For 5, 6, and 7, the first weight loss of 7% at ca. 220 °C (5), 3% at ca. 200 °C (6), or 2% at ca. 150 °C (7) could be formate (5), DMF (6), or H2O (7), which was followed by the release of the L ligand with a weight loss of 50% in the range of 200−300 °C (5), 55% in the range of 300−550 °C (6), or 58% in the range of 320−500 °C (7). The third weight loss of 22% in the range of 350−500 °C (5), 19% in the range of 520−530 °C (6), or 15% in the range of 520−540 °C (7) was assignable to the loss of the 4,4′-bpy (5), bpp (6), or bbm (7) ligand. For 8, it lost 2,2′-bpy in the range of 300−400 °C and the L ligand in the range of 420−550 °C. The photoluminescent properties of 1−8 in the solid state were investigated at ambient temperature (Figure S13 of the Supporting Information). Compounds 1, 2, and 8 did not exhibit any luminescence upon excitation at 250−310 nm while 3, 6, and 7 show emission maxima at 397 nm upon excitation at 280 nm. For 4 and 5, strong photoluminescence with emission maxima at 430 (4) or 440 nm (5) was observed upon excitation at 280 (4) or 303 nm (5). The emission peak of 4 or 5 was redshifted ca. 100 (4) or 110 nm (5) relative to that of the pure L ligand. The bands might be assigned as the metal-to-ligand charge transfer (MLCT).35

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EXPERIMENTAL SECTION

General Procedures. Ligands H2L and bbm were prepared according to the literature methods.18,36 All the analytical grade chemicals were obtained commercially and used without further purification. Elemental analyses (C, H, and N) were performed using a PE 2400 II elemental analyzer. The FT-IR spectra were recorded with a Nicolet Magna-IR 550 spectrometer in dry KBr disks in the 4000− 400 cm−1 range. Thermogravimetric analyses (TGA) were performed using a Mettler TGA/SDTA851 thermal analyzer under an N2 atmosphere with a heating rate of 10 °C/min in the temperature region of 20−1000 °C. Powder X-ray diffraction (XRD) patterns were collected on a Bruker D8 advance diffractometer using graphite monochromatized Cu Kα radiation (λ = 1.5406 Å). The emission/ excitation spectra were measured on a Varian Cary Elipse fluorescence spectrophotometer equipped with a continuous xenon lamp. Synthesis. [Mn2L2(4,4′-bpy)2][Mn2L2(H2O)2]·2H2O (1). To a thick Pyrex tube was loaded MnCl2 (13 mg, 0.1 mmol), H2L (32 mg, 0.1 mmol), 4,4′-bpy (16 mg, 0.1 mmol), and 2 mL of DMF/H2O (v/v = 4:6). The sealed tube was heated at 160 °C for 2 days and then cooled to room temperature at a rate of 5 °C/100 min to form yellow crystals of 1. Yield: 53% based on MnCl2. Anal. Calcd for C108H88Mn4N4O28: C, 61.49; H, 4.20; N, 2.66. Found: C, 61.38; H, 4.18; N, 2.65. IR (KBr disk): 3468 (s), 3049 (m), 1677 (s), 1602 (m), 1642 (w), 1248 (w), 1160 (w), 1001 (w), 860 (w), 772 (w), 626 (s) cm−1. [CuL(bbm)]·0.5H2O (2). To a thick Pyrex tube was loaded CuSO4· 5H2O (25 mg 0.1 mmol), H2L (32 mg, 0.1 mmol), bbm (21 mg, 0.1 mmol), and 2 mL of DMF/H2O (v/v = 4:6). The sealed tube was heated at 145 °C for 2 days and then cooled to room temperature at a rate of 5 °C/100 min to produce blue crystals of 2. Yield: 41% based on CuSO4·5H2O. Anal. Calcd for C34H27CuN4O6.5: C, 61.95; H, 4.13; N, 8.50. Found: C, 62.18; H, 4.09; N, 8.50. IR (KBr disk): 3440 (s), 3125 (m), 1614 (s), 1530 (m), 1369 (w), 1303 (w), 1219 (w), 1165 (w), 1069 (w), 1019 (w), 957 (w), 842 (w), 785 (w), 731 (w) cm−1. [CuL(4,4′-bpy)0.5] (3). To a thick Pyrex tube was loaded CuSO4· 5H2O (249 mg 0.1 mmol), H2L (32 mg, 0.1 mmol), 4,4′-bpy (156 mg, 0.1 mmol), and 2 mL of DMF/H2O (v/v = 4:6). A workup similar to 5058



Article

Table 1. Crystal Data and Structure Refinement Parameters for 1−8 empirical formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z T (K) Dcalcd (g cm−3) λ (Mo Kα) (Å) μ (mm−1) F(000) Ra wRb GOFc 5 C64H48N4O13Zn2 1211.80 monoclinic P21/c 13.9742(12) 15.7792(14) 14.0779(11) 116.132 2786.9(4) 2 296(2) 1.444 0.71073 0.932 1248 0.0842 0.2480 0.994

1

2

3

4

C108H88Mn4N4O28 2105.55 triclinic P1̅ 11.134(3) 17.06(14) 20.12(18) 103.7(5) 94.693(6) 92.822(5) 4866.5(8) 2 293(2) 1.437 0.71073 0.590 2168 0.0577 0.1281 0.989

C34H27CuN4O6.5 658.13 orthorhombic Pbcn 12.39(6) 21.00(11) 22.86(11)

C27H20CuNO6 517.98 monoclinic P21/c 8.001(3) 10.600(4) 28.861(10)

C66H50N4O16Zn3 1351.21 monoclinic P21/c 13.475(5) 12.797(5) 17.276(6)

103.98(2)

110.072(4)

5955.1(5) 4 296(2) 1.468 0.71073 0.789 2712 0.0437 0.0588 1.048

2375.2(15) 4 296(2) 1.449 0.71073 0.963 1064 0.0516 0.074 1.134

6

7

2798.2(17) 2 293(2) 1.604 0.71073 1.356 1384 0.0298 0.0752 1.031 8

C117H95Co4N5O25 2204.68 triclinic P1̅ 15.436(8) 17.511(9) 20.779(11) 84.825(6) 72.130(6) 83.602(7) 5303(5) 2 296(2) 1.381 0.71073 0.692 2276 0.0553 0.1352 1.016

C112H88Co4N8O24 2161.59 monoclinic P21/c 8.855(4) 17.267(8) 34.250(15)

C32H24CoN2O6 591.46 monoclinic P21/c 10.673(2) 14.657(3) 18.405(4)

102.274(12)

104.337(2)

5117(4) 2 293(2) 1.403 0.71073 0.716 2224 0.0730 0.1596 1.143

2789.4(9) 4 296(2) 0.664 0.71073 0.664 1220 0.0371 0.0823 1.015

R = Σ||Fo| − |Fc||/Σ|Fo|. bwR = {Σw(Fo2 − Fc2)2/Σw(Fo2)2}1/2. cGOF = {Σw[(Fo2 − Fc2)2]/(n − p)}1/2, where n = number of reflections and p = total number of parameters refined. a

that used for the isolation of 2 produced blue crystals of 3. Yield: 34% based on CuSO4·5H2O. Anal. Calcd for C27H20CuNO6: C, 62.60; H, 3.89; N, 2.70. Found: C, 62.68; H, 3.87; N, 2.70. IR (KBr disk): 1674 (m), 1596 (s), 1398 (m), 1241 (w), 1168 (w), 980 (w), 860 (w), 782 (w), 662 (w) cm−1. [Zn3L2(4,4′-bpy)2(HCOO)2] (4). To a thick Pyrex tube was loaded Zn(OAc)2 (183 mg, 0.1 mmol), H2L (32 mg, 0.1 mmol), 4,4′-bpy (312 mg, 0.2 mmol), and 2 mL of DMF/H2O (v/v = 4:6). A workup similar to that used for the isolation of 2 produced colorless crystals of 4. Yield: 43% based on Zn(OAc)2. Anal. Calcd for C66H50N4O16Zn3: C, 58.66; H, 3.73; N, 4.15. Found: C, 58.68; H, 3.77; N, 4.10. IR (KBr disk): 3446 (s), 3067 (m), 1640 (s), 1602 (m), 1550 (w), 1393 (w), 1220 (w), 1171 (w), 999 (w), 860 (w), 808 (w), 785 (w), 722 (w), 632 (w) cm−1. [ZnL(4,4′-bpy)]2·H2O (5). To a thick Pyrex tube was loaded Zn(OAc)2 (183 mg, 0.1 mmol), H2L (32 mg, 0.1 mmol), 4,4′-bpy (156 mg, 0.1 mmol), and 2 mL of DMF/H2O (v/v = 4:6). A workup similar to that used for the isolation of 2 produced colorless crystals of

5. Yield: 40% based on Zn(OAc)2. Anal. Calcd for C64H48N4O13Zn2: C, 63.43; H, 3.99; N, 4.62. Found: C, 63.42; H, 3.97; N, 4.60. IR (KBr disk): 1654 (s), 1552 (m), 1324 (w), 1368 (w), 1157 (w), 981 (w), 725 (w) cm−1. [Co4L4(bpp)2]·DMF (6). To a thick Pyrex tube was loaded CoSO4· 7H2O (16 mg 0.1 mmol), H2L (32 mg, 0.1 mmol), bpp (20 mg, 0.1 mmol), and 2 mL of DMF/H2O (v/v = 4:6). A workup similar to that used for the isolation of 2 produced pink crystals of 6. Yield: 64% based on CoSO4·7H2O. Anal. Calcd for C117H95Co4N5O25: C, 63.68; H, 4.34; N, 3.17. Found: C, 63.58; H, 4.37; N, 3.09. IR (KBr disk): 1699 (m), 1625 (s), 1511 (m), 1381 (w), 1248 (w), 1169 (w), 1059 (w), 989 (w), 816 (w), 741 (w), 643 (w), 517 (w) cm−1. [Co2L2(bbm)]2·2H2O (7). To a thick Pyrex tube was loaded CoSO4·7H2O (16 mg, 0.1 mmol), H2L (32 mg, 0.1 mmol), bbm (21 mg, 0.1 mmol), and 2 mL of DMF/H2O (v/v = 4:6). A workup similar to that used for the isolation of 2 produced pink crystals of 7. Yield: 60% based on CoSO4·7H2O. Anal. Calcd for C112H88Co4N8O24: C, 62.23; H, 3.92; N, 5.18. Found: C, 62.18; H, 3.87; N, 5.15. IR (KBr 5059



Article

disk): 3485 (s), 3072 (m), 1604 (s), 1531 (m), 1402 (w), 1243 (w), 1161 (w), 995 (w), 864 (w), 781 (w), 649 (w) cm−1. [CoL(2,2′-bpy)] (8). To a thick Pyrex tube was loaded CoSO4· 7H2O (16 mg 0.1 mmol), H2L (32 mg, 0.1 mmol), 2,2′-bpy (16 mg, 0.1 mmol), and 2 mL of DMF/H2O (v/v = 4: 6). A workup similar to that used for the isolation of 2 produced pink crystals of 8. Yield: 36% based on CoSO4·7H2O. Anal. Calcd for C32H24CoN2O6: C, 64.98; H, 4.09; N, 4.74. Found: C, 64.88; H, 4.07; N, 4.75. IR (KBr disk): 1642 (s), 1620 (m), 1575 (s), 1328 (m), 1242 (w), 1117 (w), 956 (w), 838 (w), 635 (w) cm−1. X-ray Structure Determinations. Single crystals of 1−8 suitable for X-ray analysis were obtained directly from the above preparations. All measurements were made on a ApexII smart using graphite monochromated Mo Kα (λ = 0.71073 Å). Single crystals of 1−8 were mounted with grease at the top of a glass fiber at 293 or 296 K. The collected data were reduced by the program ApexII, and an absorption correction (multiscan) was applied. The reflection data were also corrected for Lorentz and polarization effects. The crystal structures of 1−8 were solved by direct methods and refined on F2 by full-matrix least-squares methods with SHELXL-97.37 All of the non-H atoms were refined anisotropically. Hydrogen atoms of free water molecules in 1 and 7 are not located in the different Fourier maps but added in the formula. All other H atoms were placed in geometrically idealized positions (C−H = 0.96 Å for methyl groups, N−H = 0.86 Å for amino groups, O−H = 0.82 Å for hydroxyl groups, or C−H = 0.93 Å for phenyl groups) and constrained to ride on their parent atoms with Uiso(H) = 1.5Ueq(C) for methyl groups, 1.2Ueq(N) for amino groups, and 1.5Ueq(O) for hydroxyl groups. SIMU restraints prevent atoms from adopting different orientations. C93 in 6 is disordered over two positions with an occupancy factor of 0.66/0.34. The middle benzene ring of the L ligand in 5 is disordered over two positions with an occupancy factor of 0.6/0.4 occupancy. A summary of the important crystallographic information for 1−8 are summarized in Table 1.

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data of 1−8 (CIF), additional figures, and details of characterization (PDF). This material 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 and Tel: +86 512 65880089. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the National Natural Science Foundation of China (Grants 21171124 and 21373142) for financial support. J.P.L. also highly appreciated the support for the Qin-Lan Project and the “333” Project of the Jiangsu Province, the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the “SooChow Scholar” Program of Suzhou University. The authors also greatly thanked the helpful comments from the editor and the reviewers.

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REFERENCES

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Construction of Entangled Coordination Polymers Based on M2+

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