JIAO Jing-Jing LI Zi-Jin ZHENG F-Kun LIU Bi-Zhn CUI Yong

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Synthesis, Structure and Characterization of a 3Chiral Carboxylateand Phosphonate Metal-organic Framework Based on 1,1?-Biphenol Ligand①

JIAO Jing-JingaLI Zi-JianaZHENG Fa-Kunb②LIU Bai-Zhanc②CUI Yonga②

a(200240)b(350002)c(200240)

A novel phosphonate-based chiral metal-organic framework 1 was synthesized from2-symmetric 1,1?-biphenol-based ligandand structurally characterized by single-crystal and powder X-ray diffraction, Fourier-transform infrared spectra (FTIR), circular dichroism (CD) and thermogravimetric analyses (TGA).Two neighboring Mn ions are linked by two carboxylate groups and one phosphate group to form a di-manganese unit [Mn2] and each [Mn2] cluster in 1 is linked by five ligands, generating a 3network with fns topology.In addition, the photolu- minescence properties of 1 and H4L were investigated.

biphenol, phosphonate,manganese, chiral metal-organic framework, photoluminescence;

1 INTRODUCTION

Metal-organic frameworks (MOFs) made from metal ions linked by organic ligands have emerged as one ofthe most fascinating porous crystalline materials with high thermal and chemical stability[1-8].They have attracted increasing interest in recent years as functional materials with potential applica- tions in gas adsorption, sensing, catalysis, separation, and others[9-13].

Organic ligands bearing different steric or elec- tronic groups are known to make a big difference in metal-ligand bonding as well as structures of transition metal complexes.We have reported dif- ferent structures built by 1,1?-biphenol carbonate derivatives[14-16], while 1,1?-biphenol-derived phos- phoric acid ligands and ligands decorated with fluoride substituents at the 3,3?-position were studied rarely.The ligands of chiral phosphoric acids derived from axiallybiaryl were considered as powerful Br?nsted acid or Leiws acid/Br?nsted base catalysts in homogeneous asymmetric reactions[17, 18], promoting to assemble them in solid porous materials and to be applied as heterogeneous catalyst.The bond strength of C–F has been the strongest in organic chemistry so far, and intro- ducing fluorine element to the ligand may enhance MOFs’ chemical resistance, thermal resistance and hydrophobicity which may significantly make them great appealing in the industrial production and life science as well[19, 20].In this work, we report the synthesis, structure, thermal stability and photo- luminescence of the 3framework based the 1,1?- biphenol carbonate phosphoric acid ligand bearing fluoride substituents with manganese.

2 EXPERIMENTAL

2.1 Materials and apparatuses

All of the chemicals were commercially available, and utilized without further purification.The IR (KBr pellet) spectra were recorded (400～4000 cm-1region) on a Nicolet Magna 750 FT-IR spectrometer.TGA were carried out in N2atmosphere at a heating rate of 20oC/min on a STA449C integration thermal analyzer.UV-vis absorption spectra were recorded on a Lambda 20 UV-vis Spectrometer (Perkin Elmer, Inc., USA).The fluorescence spectra were imple- mented on a LS 50B Luminescence Spectrometer (Perkin Elmer, Inc., USA).The CD spectra were recorded on a J-800 spectropolarimeter (Jasco, Japan).Elemental analyses were performed with an EA1110 CHNS-0 CE elemental analyzer.

2.2 Synthesis of 1

Tetracarboxylate ligand derived from chiral 1,1-biphenol-derived phosphoric acids that is func- tionalized with 3,5-bisfluorophenyl substituents at the 3,3?-position (H4L) was prepared according to literature.A mixture of MnCl2(31.5 mg, 0.25 mmol), H4L (9.0 mg, 0.01 mmol), DMA (3 mL), and NaOH aqueous solution (0.02 mmol) in a capped vial was heated at 100oC for 24 h.Colorless crystals of 1({[Me2NH2]2[Mn6(L3)(H2O)4(DMA)]·2DMA·5H2O}n) were filtered, washed with N,N?-dimethylacetamide (DMA) and methanol (MeOH) respectively, and dried at room temperature.Yield: 4.15 mg (74%).Anal.Calcd.for MOF 1, C142H109F12Mn6N5O48P3: C, 51.59; H, 3.30; N, 2.12%.Found: C, 50.07; H, 3.10; N, 2.51%.FTIR (KBr pellet,/cm-1): 510 (w), 549 (w), 621 (w), 666 (w), 721 (m), 783 (m), 839 (w), 858 (m), 787.68 (m), 987 (m), 1041 (m), 1111 (s), 1249 (m), 1368 (vs), 1435 (s), 1622 (vs), 1657 (vs), 2931 (s), 3387 (s).

2.3 Crystallographic measurements and structure determination

Single-crystal XRD data for 1 were collected on a Bruker D8 VENTURE CMOS photon 100 diffrac- tometer with Helios MX multilayer monochromatic Curadiation (= 1.54178 ?) at 173(2) K.The structure was solved by direct methods with SHELXS-2014 and refined with SHELXL-2014[21]using OLEX 2.0[22].All the non-hydrogen atoms were refined by full-matrix least-squares techniques with anisotropic displacement parameters, and the hydrogen atoms were geometrically fixed at the calculated positions attached to their parent atoms, and treated as riding atoms.Contributions to scattering due to these highly disordered solvent molecules were removed using the SQUEEZE routine of PLATON[23]; Structures were then refined again using the data generated.The crystal data and selected bond lengths and bond angles are given in Tables 1 and 2, respectively.

Table 1. Crystallographic Data of Compound 1

Table 2. Selected Bond Lengths (?) and Bond Angles (°)

Symmetry transformations used to generate the equivalent atoms for 1: #1:–1/2, –+1/2, –+1; #2: –+1/2, –+1,–1/2; #3: –+1,+1/2, –+1/2; #4:+1/2, –+1/2, –+1; #5: –+1,+1/2, –+3/2; #6: –+1/2, –+1,+1/2; #7: –+3/2, –+1,–1/2; #8: –+1,–1/2, –+3/2; #9: –+1,–1/2, –+1/2; #10: –+3/2, –+1,+1/2

3 RESULTS AND DISCUSSION

3.1 Synthesis and characterization of 1

As shown in Scheme 1, MOF 1 was synthesized through solvent thermal reactions between MnCl2and tetracarboxyl-functionalized Biphenol ligand H4L.The phase purity was established by the general agreementbetween the experimental and simulatedX-ray powder diffraction patterns (Fig.1).Circular dichroism (CD) studies of ()-1 showed bands at 216 nmwith positive Cotton effect,whileother two bands occurred at 238 and 271nm with negative Cotton effect (Fig.2).The CD spectra of 1made fromandenantiomers of H4L are mirror imaged of each other, indicative of their enan- tiomeric nature.As shown in Fig.3, the TGA of 1 was investigated under a N2atmosphere from 40 to 800oC, and the result indicates that two free DMA and five free water guest molecules accommodated during the handling of the sample are released below 200oC with 8.7% weight loss (calcd.8.8%), while one coordinated DMA molecule and four coordinated water molecules wereremoved from 200 to 445oCwith 5.3% weight loss (calcd.5.2%).With further heating, the framework will decompose.The ultraviolet visible light absorption of MOF 1 was mostly due to the transition of n-*and-*of the ligand[24](Fig.4).

3.2 Structural description

Single-crystal X-ray diffraction study reveals that 1 crystallizesin chiral space group212121.The Mn ion adopts a distorted octahedral geometry by binding to one oxygen atom from a water or DMA molecule and five oxygen atoms from two bidentate and one chelated carboxylate groups and one bidentate/bridging phosphonate group.Two neighboring Mn ions linked by two carboxylate groups and one phosphate group form a di-man- ganese unit [Mn2].The ligand exhibits an- heptadentate coordination fashion, binding to eight Mn ions of five [Mn2] unitsfour carboxylate groups and one phosphonate group (Fig.5).Adjacent dimetal cores are linked by L to generate a left-handed 31helix, leading to a tube with an opening of 6.8′6.8 ?2along the-axis.As shown in Fig.6a, 6b, such helical metal-carboxylate chains are linked by phosphonate groups of L from other chains, which run around a 61axis to give a 3network with 1deformed hexagonal channels.The channels have an opening size of 2.6?′1.7? (measured from van der Waals surfaces).With respect to the topology, 1 has one vertex, represented by the [Mn2(CO2)4(PO4)(H2O)2] or [Mn2(CO2)4(PO4)(DMA)] unit and one bent edge (linker) leading to a 5-c net with the fns topology (Fig 6c).Calculations using PLATON indicated that 1 has about 62.0% void volume available for the guest inclusion[23].

Scheme 1. Synthesis of 1

Fig.1. Simulated and experimental PXRD patterns of 1

Fig.2. CD spectra of ()/()-1

Fig.3. TGA curve of 1

Fig.4. UV-vis spectra of H4L and 1

3.3 Photoluminescence

Upon excitation at 300 nm, as shown in Fig.7, the free ligand H4L displays a fluorescent emission at 390 nm, while the emission of 1 excited at 352 nm exhibits 38 nm blue-shift.The observed shift in the emissions for 1 originated from the coordination actions of the carboxylate groups and the phos- phoric acid groups to the Mn(II) ions, which effec- tively increases the rigidity of the ligand and reduces the loss of energy[25].

Fig.5. Two kinds of coordination modes for [Mn2] in 1. Hydrogen atoms and guest molecules are omitted for clarity

Fig.6. (a) Open channels in diameters of ~2.6 × 1.7 ?2and ~6.8 ×6.8 ?2, (b) 3framework along theaxis and (c) Simplified topology in 1

Fig.7. Fluorescent emission spectra of H4L and 1

4 CONCLUSION

In conclusion, 1,1?-biphenol-derived phosphoric acidsthat are functionalized with 3,5-bisfluoro- phenylsubstituents at the 3,3?-position were there- fore designed for 1 construction with manganese.It was characterized by single-crystal and powder X-ray diffraction, CD, TGA and UV-vis.In addition, the photoluminescence of 1 and the free ligand was also explored.

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25 January 2018;

3 Jun 2018 (CCDC 1818359)

NSFC (No.21431004, 21522104 and 21620102001), “973” Program (No.2014CB932102 and 2016YFA0203400), the Shanghai “Eastern Scholar” Program SSTC-14YF1401300, and the Key Project of Basic Research of Shanghai (17JC1403100)

Zheng Fa-Kun.Male, professor.E-mail: zfk@fjirsm.ac.cn; Liu Bai-Zhan.Male, E-mail: liubzh@sh-tobacco.com.cn; Cui Yong.Male, professor.E-mail: yongcui@sjtu.edu.cn

10.14102/j.cnki.0254-5861.2011-1962