Syntheses, structures, thermal stabilities and gas sorption properties of two rod-based microporous lead(II) polycarboxylate coordination frameworks

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Highlights

  • Two new lead(II)-polycarboxylic frameworks were synthesized through solvothermal methods and characterized.

  • Both compounds adopt rod-based 3D porous frameworks with 1D channels and exhibit high thermal stabilities.

  • Compound 1 has moderate nitrogen and hydrogen uptakes due to the presence of micropores in the structure.

Abstract

Two new lead(II)–organic frameworks Pb2(μ4-O)(bdc)·DMF (1) and Pb(ndc)(DMF) (2) (H2bdc = 1,4-benzenedicarboxylate, H2ndc = 2,6-naphthalenedicarboxylate, DMF = N,N′-dimethylformamide) were prepared through solvothermal methods. Single-crystal X-ray diffraction analysis indicated that compounds 1 and 2 exhibit rod-based three-dimensional (3D) porous frameworks with 1D channels. The carboxylate groups in both compounds adopt different types of coordination modes, and the coordination geometries of lead(II) centers in compound 1 and 2 are hemidirected and holodirected, respectively. Gas sorption results showed that compound 1 has moderate uptakes for nitrogen and hydrogen gases, owing to the existence of micropores in structures.

Graphical abstract

Two new lead(II)-polycarboxylic frameworks adopt rod-based 3D structures with 1D channels and exhibit high thermal stabilities. The existence of micropores in the structure of compound 1 is responsible practically for moderate nitrogen and hydrogen uptakes.

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Introduction

In recent years, metal-organic frameworks (MOFs) with high specific surface areas and permanent porosities have attracted extensive attention because of their potential applications in gas storage [1], separation [2], drug delivery [3], catalysis [4], and so on. The three-dimensional (3D) porous MOFs with intriguing structural topology have become excellent candidates for gas storage materials depending on the high specific surface areas, valid holes and firm bodies. Up to now, a large number of such MOFs were investigated for gas sorption properties with the center metal ions M2+ (M = Ni, Co, Mg, Mn, Zn, etc), while lead(II)-organic frameworks have rarely been studied on porosities and gas sorption properties.

Lead(II), the heavy toxic metal, is easy to extract, dense, highly malleable and stable to corrosion. The widespread use in industrial application mainly for battery making and recycling, oil refining, paint manufacturing has caused environmental contamination. To better know, the toxic mechanism, it is vital to understand its coordination properties: the lone pair of electrons, coordination number and coordination geometry. Different from transition metals, the main group metal lead(II) with large ionic radius and the stereochemically effective lone pair electrons offers variable possibilities of coordination numbers, and has been employed to build versatile geometries of holo- or hemi-directed, and therefore highly-linked lead(II)-organic frameworks [5]. It is interesting to investigate the perplexing architectures of 3D highly-linked lead(II) MOFs and especially of much significance to explore the gas storage of them. Unfortunately, to our knowledge, gas sorption properties of only three Pb-organic frameworks were investigated to date, [Pb(SDBA)] (H2SDBA = 4,4′-sulfonyldibenzoic acid) [6], [PbL2]·2DMF·6H2O and [PbL2]·DMF·2H2O (HL2 = N-(4-carboxyphenyl)isonicotinamide 1-oxide) [7]. Among them, the methane sorption of [Pb(SDBA)] accumulates to 2 wt% at 183 K, 2.2 atm but no uptake of nitrogen at low pressure (1 atm). In addition, the H2O vapor adsorption isotherms of desolvated [PbL2]·2DMF·6H2O and [PbL2]·DMF·2H2O display preferential behaviors over CO2 due to the hydrophilic nature of the channel.

The successful syntheses of these porous materials are mainly based on the concept of network design [8], in which the structures of organic ligands have played a key role [9]. Among them, mixed organic ligands composing of polycarboxylic acids (O-donor) and N-donor ligands have been used recently to construct porous MOFs [10], [11], [12], owing to their rich coordination modes with metal centers. Recently, both the O-donor carboxylate acids (1,4-benzenedicarboxylate (H2bdc) or 2,6-naphthalenedicarboxylate (H2ndc)) and the N-donor ligands (pyrazine, 4,4′-azopyridine (azpy)) were employed as mixing ligands by our group to react with lead(II) ions in N,N′-dimethylformamide (DMF) through the solvothermal method, in order to construct 3D porous lead(II) MOFs with intriguing topologies and permanent porosities. Unexpectedly, the N-donor ligands pyrazine and azpy did not coordinate with lead(II) centers, and then two new porous MOFs Pb2(μ4-O)(bdc)·DMF (1) and Pb(ndc)(DMF) (2) were isolated instead. In this contribution, we reported the syntheses, crystal structures and thermal stabilities of both materials, together with gas sorption properties of compound 1. To our knowledge, nitrogen and hydrogen gas sorption behaviors of lead(II)-polycarboxylate frameworks have not been documented previously.

Section snippets

Materials and physical measurements

1,4-Benzenedicarboxylate (H2bdc) and 2,6-naphthalenedicarboxylate (H2ndc), pyrazine, 4,4′-azopyridine (azpy), N,N′-dimethylamide (DMA), N,N′-dimethylformamide (DMF) and Pb(NO3)2 were purchased from J&K CHEMICA in a reagent grade and used without any purification. Infrared spectra as KBr pellets were recorded using Avatar Nicolet FT-1703x FT-IR spectrophotometer from 4000 to 400 cm1. Thermalgravimetric (TG) analyses were taken on a Pyris Diamond TGA analyzer at a heating rate of 10 °C min1.

Structural descriptions of compounds 1 and 2

Single-crystal X-ray diffraction analysis revealed that compound 1 belongs to the orthorhombic P212121 space group (Table 1). The asymmetric unit contains two crystallgraphically independent Pb centers, one bridged oxygen atom, one bdc ligand and one uncoordinated DMF molecule (Fig. 1). Each Pb center is four-coordinate and surrounded by two oxygen atoms from two different bdc ligands and two μ4-oxo atoms. The coordination geometry of Pb is hemidirected and can be described as a distorted ψ-PbO4

Conclusion

We have synthesized two new lead(II) MOFs constructed by aromatic polycarboxylate acids. Both compounds adopt rod-based 3D porous frameworks with 1D channels, and exhibit high thermal stabilities. The existence of micropores in the structure is responsible practically for moderate nitrogen and hydrogen uptakes. Our continuous studies are underway to seek porous lead MOFs with intriguing topologies and interesting sorption properties.

Acknowledgements

This research was supported by National Natural Science Foundation (51072072, 51102119) and Natural Science Foundation of Jiangsu Province (BK2010343, BK2011518).

References (26)

  • M.-L. Hu et al.

    Coord. Chem. Rev.

    (2011)
  • H. Zhou et al.

    J. Mol. Struct.

    (2009)
  • M. Liu et al.

    Inorg. Chim. Acta

    (2009)
  • S.-C. Chen et al.

    Inorg. Chem. Commun.

    (2009)
  • Y.-X. Tan et al.

    J. Mol. Struct.

    (2009)
  • C.-Y. Gao et al.

    J. Mol. Struct.

    (2008)
  • J. Wang et al.

    Microporous Mesoporous Mater.

    (2012)
  • S.-Q. Ma et al.

    Chem. Commun.

    (2010)
  • J.-R. Li et al.

    Chem. Soc. Rev.

    (2009)
  • P. Horcajada et al.

    Chem. Rev.

    (2012)
  • D. Farrusseng et al.

    Angew. Chem., Int. Ed.

    (2009)
  • J.-D. Lin et al.

    CrystEngComm

    (2010)
  • X.-M. Lin et al.

    Dalton Trans.

    (2012)
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