Chiral [Mo8O26]4– Polyoxoanion-Induced Three-Dimensional

Article pubs.acs.org/IC

Chiral [Mo8O26]4− Polyoxoanion-Induced Three-Dimensional Architectures With Homochiral Eight-Fold Interpenetrated Metal− Organic Frameworks Mengjie Zhou,† Dawei Yan,† Yayu Dong,† Xingxiang He,† and Yan Xu*,†,‡ †

College of Chemical Engineering, State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210009, P. R. China ‡ Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. China S Supporting Information *

ABSTRACT: A pair of novel chiral compounds based on homochiral 8-fold interpenetrated metal−organic frameworks (MOFs) and chiral polyoxometalates (POMs), formulated as D -[Cu(4,4′-bipy) 1.5 ] 4 [Mo 8 O 26 ] ( D -1) and L -[Cu(4,4′bipy)1.5]4[Mo8O26] (L-1) (4,4′-bipy = 4,4′-bipyridine), have been successfully synthesized and characterized by single crystal X-ray diffraction, infrared, thermogravimetric analysis, elemental analysis, and solid circular dichroism spectra. Structural analysis indicates that two compounds are enantiomers. The connection of copper cations and 4,4′-bipy ligands generates helical infinite chains, while adjacent chains are further linked by Cu−N bonds to form a three-dimensional interpenetrating framework with a (10,3)-a topology. Interestingly, the chiral [Mo8O26]4− polyanions are encapsulated in the chiral MOFs via sharing the oxygen atoms. Both D- and L-[Cu(4,4′-bipy)1.5]4[Mo8O26] crystallize in chiral space group C2221. Additionally, two compounds represent new examples of chiral self-assembly.

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INTRODUCTION

endowing them with new features and multiple functionalities distinctively different from the POMs or MOFs alone.9 In view of the superiority of MOFs, POMs and the significance of chirality, many researchers have worked on developing chiral inorganic−organic hybrid compounds.10−12 Up to now, two main strategies are used to synthesize these chiral inorganic−organic hybrid frameworks: one method is directly introducing chiral additives or structure-directing agents, such as chiral organic ligands or chiral metal−organic moiety linkers. Therefore, the chirality can transfer from these additives or structure-directing agent to the inorganic−organic hybrid framework. The other one is preparing chiral materials through self-assembled methods including the alteration of bond length and angles, the replacement of other metals, the formation of lacunae in POMs, or decorating POMs with achiral fragments to break the symmetric center.13,14 For the first strategy, it has a high cost and the types of enantiopure ligands are limited. With the second strategy, the chirality is derived from the spatial arrangement of achiral building blocks. More importantly, the achiral ligands are more common, which is more promising.

Metal−organic frameworks (MOFs) have drawn a great deal of attention from chemists due to not only their intriguing versatile structures, but also importantly their potential applications.1 In recent years, chiral metal−organic frameworks, especially chiral MOFs with entangled systems, have shown special appeal and significance on account of their unique properties for applications including chiral separations, enantioselective sorption, asymmetric catalysis, and so forth.2 On the other hand, introducing an entangled system into such frameworks could help to reinforce the interplay between structural motifs on some level and finally increase the stability of the whole network.3 Polyoxometalates (POMs) not only possess constituent diversity, excellent thermal and oxidative stability, but also have unique properties for applications as diverse as catalysis, magnetism, photochemistry, and material in many research fields.4−8 The introduction of POMs into MOFs will contribute to the complexity, stability, and the rational design of single-site solid catalysts, chemical sensors, bioimaging agents, anticancer therapeutics, and other materials with great potential. POMs can provide MOFs with various charges, symmetries, and sizes for assembly of diverse compounds. Furthermore, MOFs will be adjusted to possess more specialized functionalities, thus © 2017 American Chemical Society

Received: April 26, 2017 Published: July 18, 2017 9036

DOI: 10.1021/acs.inorgchem.7b01057 Inorg. Chem. 2017, 56, 9036−9043

Article

Inorganic Chemistry Table 1. Crystal Data and Structure Refinements for Compounds D-1 and L-1 compound empirical formula formula weight crystal system space group unit cell dimensions (Å)

volume (Å3) Z calculated density (g·cm−3) absorption coefficient F(000) crystal size limiting indices

reflections collected/unique max and min transmission Flack data/parameters goodness-of-fit on |F|2 final R indices [I > 2σ(I)]a R indices (all data) a

D-1

L-1

C60H48Cu4Mo8N12O26 2374.78 orthorhombic C222(1) a = 11.809(2) b = 24.703(4) c = 48.627(8) 14186(4) 8 2.224 2.623 9216 0.15 × 0.13 × 0.10 −14 ≤ h ≤ 14 −29 ≤ k ≤ 29 −56 ≤ l ≤ 58 52145/13118 [R(int) = 0.0500] 0.778 and 0.693 0.007(9) 13118/994 1.023 R1 = 0.0307 wR2 = 0.0634 R1 = 0.0351 wR2 = 0.0684

C60H48Cu4Mo8N12O26 2374.78 orthorhombic C222(1) a = 11.735(4) b = 24.608(9) c = 48.463(17) 13995(9) 8 2.254 2.659 9216 0.16 × 0.14 × 0.12 −14 ≤ h ≤ 14 −29 ≤ k ≤ 26 −58 ≤ l ≤ 58 48345/12770 [R(int) = 0.0838] 0.7405 and 0.6760 0.008(10) 12770/994 1.004 R1 = 0.0383, wR2 = 0.0676 R1 = 0.0588, wR2 = 0.0792

R1 = ∑∥Fo| − |Fc∥/∑|Fo|; wR2 = ∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]1/2. Å) radiation, and in the range of 5° ≤ 2θ ≤ 50°. The enantiomers were separated manually by using a XP-550C polarized light microscope, and the CD spectra were obtained on a JASCOJ-810 spectropolarimeter using pressed KBr pellets. Preparation of L- and D-[Cu(4,4′-bipy)1.5]4[Mo8O26] (L-1 and D1). The synthesis procedure for D-1 and L-1, the mixture of MoO3 (0.1473 g, 1.02 mmol), Cu(CH3COO)2·H2O (0.0985 g, 0.49 mmol), 4,4′-bipy (0.2006 g, 1.28 mmol), and 5 mL of deionized water was stirred for 20 min. The pH of suspension was adjusted to approximately 5 with acetic acid and stirred for additional 20 min. Then it was transferred in a 25 mL Teflon-lined stainless steel reaction kettle and kept in a 170 °C drying oven for 7 days. Cooled to ambient temperature, bronzing block crystals were collected, which were washed and filtered with deionized water (0.1128g, yield 38% based on Mo; L-1 and D-1 were separated by a polarizing microscope). The elemental analysis calcd (%): C 30.22; H 2.13; N 7.15. (Found) (%): C 30.37; H 1.88; N 6.99. X-ray Crystallography. Bruker Apex II CCD collected the diffraction data using the ω-2θ scan method, and it was equipped with Mo−Kα radiation (λ = 0.71073 Å) at 296 K. Direct methods were used to solve crystal structures, and the SHELXTL-2014 program package were employed to refine crystal structures by the full-matrix least-squares techniques on F2. H atoms of CH groups were placed in calculated positions and permitted to ride on their parent C atoms, while all the non-hydrogen atoms were refined with anisotropic temperature parameters. Table 1 summarizes detailed information on the two compounds including crystallographic data and structure determination (CCDC-1527363−1527364). Selected bond distances (Å) and angles (deg) for compound D-1 and L-1 are provided in Tables S1 and S2.

Inspired by the above-mentioned work, we in detail describe here the synthesis and characterization of two novel chiral compounds: D-[Cu(4,4′-bipy)1.5]4[Mo8O26] (D-1) and L-[Cu(4,4′-bipy)1.5]4[Mo8O26] (L-1). Structural analysis indicates that both compounds are enantiomers. Compound D-1 is composed of homochiral polymolybdate anions and MOFs. The only difference between D-1 and L-1 is the chirality. It is worth mentioning that the homochiral MOF is a threedimensional (3D) 8-fold interpenetrating framework with a (10, 3)-connected topological net. The [Mo8O26]4− polyoxoanion is a novel chiral octamolybdate cluster, which is different from the reported classical [Mo8O26]4− polyoxoanion isomers.15 The chiral [Mo8O26]4− polyoxoanion can be viewed as a chiral template; it can transfer the chirality to the whole framework through the bonds between ligands and metal centers. Although some chiral compounds have been reported in pertinent literature over the last several decades,16 chiral compounds containing chiral POMs-induced chiral MOFs are very rare. And as far as we know, the chiral [Mo8O26]4− polyoxoanion has not been reported previously.

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EXPERIMENTAL SECTION

Materials and Methods. All chemicals purchased were of reagent grade. Final products were washed with deionized water then dried and collected in open air. Elemental analysis (C, H, N) was conducted on an element analyzer and the model is PerkinElmer 2400 CHN. IR spectra of all compounds were obtained from a Nicolet Impact 410 FTIR spectrometer in the 450−4000 cm−1 region. Thermogravimetric (TG) measurement was performed on a Diamond thermogravimetric analyzer under N2 atmosphere, and the temperature in the range of 25−700 °C goes with a heating rate of 10 °C min−1. Powder X-ray diffraction (XRD) patterns were recorded on a Bruker D8X diffractometer equipped with monochromatized Cu−Kα (λ = 1.5418

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RESULTS AND DISCUSSION Crystal Structures of D- and L-[Cu(4,4′bipy)1.5]4[Mo8O26](D-1 and L-1). Single-crystal X-ray structural analysis indicated that D-1 and L-1 are enantiomers. 9037

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results distinctly from the synergy of the reactive oxidation− reduction properties of the copper atoms and the organic ligands as well as the unique hydrothermal conditions.17a Strikingly, the novel chiral [Mo8O26]4− polyoxoanion in compound D-1 has an unprecedented structure configuration, which is clearly different from classical [Mo8O26]4− polyoxoanion isomers α, β, γ, δ, ε, ζ, ξ, η, and θ (Figure S1− S3).15,18,19 Compared with classical [Mo8O26]4− polyoxoanions, novel [Mo8O26]4− polyoxoanion is asymmetric, and it is a chiral polyoxoanion. As shown in Figure 2 and Figure S1, the novel [Mo8O26]4− polyoxoanion composes a Mo6 ring capped on opposite faces by two {MoO4} tetrahedra. In the Mo6 ring, one capping {MoO4} tetrahedron is connected to two {MoO6} octahedra by corner sharing, while the other is linked to five {MoO6} octahedra by corner sharing. The most distinguishing feature of the novel [Mo8O26]4− is five {MoO6} octahedra and one {MoO4} tetrahedron in the equatorial plane Mo6 ring; this is equivalent to the replacement of {MoO6} octahedra from the Mo6 ring of the [α-Mo8O26]4− polyoxoanion, the {MoO4} tetrahedron destroy high symmetry of the polyoxoanion, and hence the novel [Mo8O26]4− polyoxoanion is chiral. According to the reported literature, the novel [Mo8O26]4− in D-1 is the first chiral octamolybdate anion. The O−Mo−O bond angles in {MoO6} octahedra range from 71.6(2)−173.9(2)°, and the Mo−O bond lengths range are between 1.693(6) and 2.386(5) Å, while the Mo−O bond lengths in the {MoO4} tetrahedron in the range of 1.695(5)−1.864(5) Å, and the O−Mo−O bond angles in the range of 104.2(3)−115.2(2)°, these data in accordance with the literature that have been reported.15 The BVS calculated that the Mo atom is +6 in the compounds D-1 and L-1 (Table S3). Each [Mo8O26]4− cluster can be viewed as a hexadentate ligand and connect to six Cu cations through its terminal oxygen atoms (Figure S6). As illustrated in Figure 3a, the Cu1 and Cu3 cations are linked by 4,4′-bipy to give a onedimensional (1D) right handed (D) helical infinite chain [-Cu34,4′-bipy-Cu1-4,4′-bipy-Cu3-]n. Another type of 1D righthanded infinite helical chain [-Cu4-4,4′-bipy-Cu2-4,4′-bipyCu5-]n is built from 4,4′-bipy, Cu2, Cu4, and Cu5 cations. Observed chirality of chiral helical chains can be understood in the aspect of the twist of 4,4′-bipy ligands, as well as the asymmetrical coordination mode without mirror symmetry around the [Mo8O26]4− polyoxoanions (Figure 2).20 On the

Therefore, we only discuss the structure of compound D-1 in detail. Compound D-1 crystallizes in the orthorhombic crystal system, chiral space group C2221, and consists of a crystallographically unique [Mo8O26]4− polyoxoanion, four copper cations, and six 4,4′-bipy ligands (Figure 1). Copper cations

Figure 1. Asymmetric unit of compounds D-1 and L-1 (all H atoms omitted for clarity).

exhibit two kinds of coordination environments. (i) Cu1 and Cu2 ions are four-coordinated by one oxygen atom from the [Mo8O26]4− polyoxoanion and three nitrogen atoms from three individual 4,4′-bipy ligands, forming a distorted tetrahedron (Figure S4). (ii) The Cu3, Cu4, and Cu5 ions are fivecoordinated by two O atoms of two separate [Mo8O26]4− polyoxoanions and three nitrogen atoms from three 4,4′-bipy; the coordination geometry around the Cu3, Cu4, and Cu5 ions can be described as a distorted trigonal bipyramid (Figure S5). The lengths of Cu−N bonds range from 1.947(16) to 2.102(20) Å, while Cu−O bonds lengths are in the range of 2.310(35)−2.775(95) Å. The bond valence sum (BVS) calculated that the valence of the copper cations is +1, in accordance with the crystal color and literature that have been reported (Table S3).17 In the presence of Cu(II), 4,4′-bipy quintessentially not only serves as an organic ligand but also as reducing agent under hydrothermal conditions. This typically

Figure 2. Coordination environment around [Mo8O26]4− polyoxoanion in D-1 (a) and L-1 (b). 9038

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Figure 3. (a) Space-filling representation of 1D single helical chain formed by Cu1 and Cu3 centers and 4,4′-bipy ligands; (b) topological lefthanded and right-handed helical chains.

Figure 4. (a) Ball−stick representation of single 3D MOF of D-1 composed of [-Cu1-4,4′-bipy-Cu3-4,4′-bipy-Cu1-]n viewed down the a axis; (b) topological single 3D MOF of D-1.

Figure 5. (a) 3D structure of D-1 consist of MOFs and [Mo8O26]4− anions; (b) scheme showing the (10,3) topology of D-1, the [Mo8O26]4− anions is simplified as a red sphere.

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topology. Wells described seven uniform (10,3)-connected networks, and as we all known, the inherent characteristic of (10,3) topological MOFs is having chirality; their chirality commonly derives from the spatial combination of achiral fragments rather than chiral additives.23,24 Compared with D-1, the L-1 are constructed of left-handed helices, such L-helices are linked by 4,4′-bipy into 3D chiral frameworks. Left-handed [Mo8O26]4− clusters are imbedded within the 3D interpenetrating MOFs (Figure S9). Powder X-ray Diffraction. The PXRD measurements for the compounds D-1 and L-1 were determined at room temperature (Figure S10). The result shows that there is almost no difference in diffraction peak positions between the calculated XRD pattern and experimental XRD pattern. It indicates that the compounds are phase purity. This conclusion corresponds with the results of the X-ray crystallographic analysis. CD Spectrum. As we can see from Figure 7, single crystals display dark and light in the presence of polarized light due to

other hand, the chirality transfers from the homochiral [Mo8O26]4− polyoxoanions to the helical chains through Cu1−O13, Cu2−O12, Cu3−O18, Cu3−O19, Cu4−O21, Cu5−O7, with bond lengths varying from 2.31 to 2.78 Å (Figure S6).21 D-Helical chains are further bridged to four adjacent helical chains through the 4,4′-bipy ligands into 3D homochiral MOFs, respectively (Figure 4, Figure S8). The small and lager channels are 13.17 × 13.62 Å2 and 24.68 × 24.37 Å, respectively. Therefore, chiral polyoxoanion transmit the chirality to the helical chains, then to the whole framework through bonding metal−organic segment or simple metal cations.21a The Flack parameter of 0.007(9) for D-1 also demonstrates that the absolute configurations are correct. It is worth mentioning that the whole homochiral MOFs is a 8-fold interpenetrated framework with a (10, 3)-connected topological net in compound D-1. In other words, on removing the [Mo8O26]4− polyoxoanion, the remainder is a 3D threeconnected 8-fold interpenetrated net (Figure 5). In order to have a better understanding of this complicated network, multidimensional structures can be reduced to simple nodes and connecting nets through TOPOS analysis software. The copper cation links three 4,4′-bipy, and each 4,4′-bipy links two copper cations, so copper cations can be counted as 3connected nodes (Figure 4b). As shown in Figure 6, two such

Figure 7. Photographs of crystals D-1 (light) and L-1 (dark) viewed in the presence of polarized light by using a polarized light microscope.

chirality, while there is almost no difference between them in morphology, color, and size in nature light. Therefore, the enantiomer D-1 and L-1 can be separated manually.25 To further study the chiroptical activity of this compound, their circular dichroism (CD) spectra were measured. The solid state CD spectra of two compounds are the mirror image inversion, revealing that compounds D-1 and L-1 are a pair of enantiomers (Figure 8). Enantiomer D-1 and L-1 clearly showed four Cotton effects at about 221, 228, 237, and 251 nm in the wavelength

Figure 6. 8-fold interpenetrated (10,3) network in D-1 (yellow, black, light blue, and violet 3D MOFs constructed of [-Cu1-4,4′-bipy-Cu34,4′-bipy-Cu1-]n,, red, pink, green, and blue 3D MOFs constructed of [-Cu4-4,4′-bipy-Cu2-4,4′-bipy-Cu5-]n).

individual networks are intertwined to form 1D tubiform. For sake of satability, three pairs of other identical but independent networks take up the much larger tubular channels, consequently giving eight interpenetrating networks. Differing from this interpenetration mode, the normal mode exhibits eight identical but independent networks interpenetrated in a parallel fashion in the same directions, and presents continuous rows of nodes along the channels.22 The Schläfli symbol for this (10,3)-connected network determined by TOPOS is {10(5).10(5).10(5)}, which is assigned to the (10, 3)-a, srs

Figure 8. CD spectra for complex D-1 and complex L-1. 9040

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Claridge, J. B.; Cussen, E. J.; Prior, T. J.; Rosseinsky, M. J. Design, chirality, and flexibility in nanoporous molecule-based materials. Acc. Chem. Res. 2005, 38, 273−282. (c) Wang, X. L.; Qin, C.; Wang, E. B.; Su, Z. M.; Li, Y. G.; Xu, L. Self-assembly of nanometer-scale [Cu24I10L12]14+ cages and ball-shaped Keggin clusters into a (4,12)connected 3D framework with photoluminescent and electrochemical properties. Angew. Chem., Int. Ed. 2006, 45, 7411−7514. (d) Pope, M. T.; Müller, A. Chemistry of the polyoxometalates: current variations of an old subject with interdisciplinary relations. Angew. Chem. 1991, 103, 56−70. (e) Long, D. L.; Burkholder, E.; Cronin, L. Polyoxometalate clusters, nanostructures and materials: From self-assembly to designer materials and devices. Chem. Soc. Rev. 2007, 36, 105−121. (2) (a) Chen, Z. l.; Su, Y.; Xiong, W.; Wang, L. X.; Liang, F. P.; Shao, M. Controlling the dimensionalities and structures of homochiral Zn(II) and Cd(II) compounds of N-(p-tosyl)-S-carboxymethyl-Lcysteine via tuning the connecting modes of metal ions and chiral linkers by different kinds of ancillary ligands. CrystEngComm 2009, 11, 318−328. (b) Custelcean, R.; Ward, M. D. Chiral discrimination in low-density hydrogen-bonded frameworks. Cryst. Growth Des. 2005, 5, 2277−2287. (c) Xiong, R. G.; You, X. Z.; Abrahams, B. F.; Xue, Z. L.; Che, C. M. Enantioseparation of racemic organic molecules by a zeolite analogue. Angew. Chem., Int. Ed. 2001, 40, 4422−4425. (d) Evans, O. R.; Ngo, H. L.; Lin, W. Chiral porous solids based on lamellar lanthanide phosphonates. J. Am. Chem. Soc. 2001, 123, 10395−10396. (3) Miller, J. S. Interpenetrating lattices-materials of the future. Adv. Mater. 2001, 13, 525−527. (4) (a) Burkholder, E.; Zubieta, J. Solid state coordination chemistry: construction of 2D networks and 3D frameworks from phosphomolybdate clusters and binuclear Cu(II) complexes. The syntheses and structures of [{Cu2(tpypyz)(H2O)2}(Mo5O15)(HOPO3)2]·nH2O [n = 2, 3; tpypyz = tetra(2-pyridyl)pyrazine]. Chem. Commun. 2001, 2056− 2057. (b) Long, D. L.; Tsunashima, R.; Cronin, L. Polyoxometalates: Building blocks for functional nanoscale systems. Angew. Chem., Int. Ed. 2010, 49, 1736−1738. (5) (a) Mizuno, N.; Misono, M. Heterogeneous catalysis. Chem. Rev. 1998, 98, 199−217. (b) Zou, C.; Zhang, Z. J.; Xu, X.; Gong, Q. H.; Li, J.; Wu, C. D. A Multifunctional organic−inorganic hybrid structure based on MnIII−porphyrin and polyoxometalate as a highly effective dye scavenger and heterogenous catalyst. J. Am. Chem. Soc. 2012, 134, 87−90. (6) Ibrahim, M.; Lan, Y. H.; Bassil, B. S.; Xiang, Y. X.; Suchopar, A.; Powell, A. K.; Kortz, U. Hexadecacobalt(II)-containing polyoxometalate-based single-molecule magnet. Angew. Chem., Int. Ed. 2011, 50, 4708−4711. (7) Yin, Q. S.; Tan, J. M.; Besson, C.; Geletii, Y. V.; Musaev, D. G.; Kuznetsov, A. E.; Luo, Z.; Hardcastle, K. I.; Hill, C. L. A fast soluble carbon-free molecular water oxidation catalyst based on abundant metals. Science 2010, 328, 342−345. (8) (a) Ju, W. W.; Zhang, H. T.; Xu, X.; Zhang, Y.; Xu, Y. Enantiomerically pure lanthanide−organic polytungstates exhibiting two-photon absorption properties. Inorg. Chem. 2014, 53, 3269−3271. (b) Miao, H.; Wan, H. X.; Liu, M.; Zhang, Y.; Xu, X.; Ju, W. W.; Zhu, D. R.; Xu, Y. Two novel organic−inorganic hybrid molybdenum(V) cobalt/nickel phosphate compounds based on isolated nanosized Mo/ Co(Ni)/P cluster wheels. J. Mater. Chem. C 2014, 2, 6554−6560. (9) (a) Han, Q. X.; He, C.; Zhao, M.; Qi, B.; Niu, J. Y.; Duan, C. Engineering chiral polyoxometalate hybrid metal−organic frameworks for asymmetric dihydroxylation of olefins. J. Am. Chem. Soc. 2013, 135, 10186−10189. (b) Ma, F. J.; Liu, S. X.; Sun, C. Y.; Liang, D. D.; Ren, G. J.; Wei, F.; Chen, Y. G.; Su, Z. M. A sodalite-type porous metalorganic framework with polyoxometalate templates: adsorption and decomposition of dimethyl methylphosphonate. J. Am. Chem. Soc. 2011, 133, 4178−4181. (c) Song, J.; Luo, Z.; Britt, D. K.; Furukawa, H.; Yaghi, O. M.; Hardcastle, K. I.; Hill, C. L. A multiunit catalyst with synergistic stability and reactivity: a polyoxometalate-metal organic framework for aerobic decontamination. J. Am. Chem. Soc. 2011, 133, 16839−16846. (d) Zou, C.; Zhang, Z. J.; Xu, X.; Gong, Q. H.; Li, J.; Wu, C. D. A Multifunctional organic−inorganic hybrid structure based

range of 200−400 nm. The four absorption bands can be ascribed to the O → Mo LMCT transition for the [Mo8O26]4− anion. IR Spectra. The IR spectra is presented in Figure S11. As we can see from the spectra, it can be described from the following two regions: (1) the characteristic peak at 903 cm−1 corresponds to the vibrations of MoO units, those at 798 and 630 cm−1 were assigned to the vibrations of the Mo−O−Mo groups; (2) the peaks at 1597 and 1385 cm−1 correspond to the stretching vibrations of CC and CN, respectively.

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CONCLUSIONS In summary, we have synthesized a pair of enantiomeric compounds by a self-assembled method without any chiral auxiliaries. These compounds consist of chiral polyanions and 3D chiral organic skeletons, which are assembled from chiral double helical chains and achiral 4,4′-bipy ligands. The successful preparation of the title compounds D-1 and L-1 not only demonstrates that it is practicable to synthesize chiral compounds by a self-assembled method, but also it has direct significance to prepare chiral compounds in the future. For a follow-up study, we will design and synthesize new chiral POMs-based MOFs with an entangled system, and the other properties of these compounds need ongoing research.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01057. Selected bond distances and angles of D-1 and L-1, conventional physical measurement results consisting of TG curves, IR spectra, PXRD patterns for D-1 and L-1 (PDF) Accession Codes

CCDC 1527363−1527364 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: 86-25-83587857. Fax: 8625-83211563. ORCID

Yan Xu: 0000-0001-6059-075X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Natural Science Foundation of China (Grant 21571103), the Major Natural Science Projects of the Jiangsu Higher Education Institution (Grant 16KJA150005), and the Qing Lan Project.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b01057 Inorg. Chem. 2017, 56, 9036−9043

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DOI: 10.1021/acs.inorgchem.7b01057 Inorg. Chem. 2017, 56, 9036−9043

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DOI: 10.1021/acs.inorgchem.7b01057 Inorg. Chem. 2017, 56, 9036−9043