Rapid preparation of flexible porous coordination polymer nanocrystals with accelerated guest adsorption kinetics

Journal name:
Nature Chemistry
Year published:
Published online


Porous coordination polymers, in particular flexible porous coordination polymer networks that change their network structure on guest adsorption, have enormous potential in applications involving selective storage, separation and sensing. Despite the expected significant differences in their adsorption properties, porous coordination polymer nanocrystals remain largely unexplored, and there have been no reports about studies on flexible porous coordination polymer nanocrystals, mainly due to a lack of preparation methods. Here, we present a new technique for the rapid preparation of porous coordination polymer nanocrystals that combines non-aqueous inverse microemulsion with ultrasonication. Uniform nanocrystals of {[Zn(ip)(bpy)]}n (ip = isophthalate, bpy = 4,4′-bipyridyl; CID-1), a flexible porous coordination polymer, have been prepared by this method and analysed using field-emission scanning electron microscopy, energy-dispersive X-ray analysis, infrared spectroscopy, Raman spectroscopy and X-ray powder diffraction. A model for particle formation and growth is presented and discussed. Adsorption experiments with methanol show that the overall adsorption capacities of nanoparticles and bulk are almost identical, but the shapes of the sorption isotherms differ significantly and the adsorption kinetics increase dramatically.

At a glance


  1. Schematic of CID-1 and FE-SEM images of coordination compounds obtained by various reaction processes.
    Figure 1: Schematic of CID-1 and FE-SEM images of coordination compounds obtained by various reaction processes.

    a, Schematic of guest-induced structure transformation of CID-1. Reproduced with permission from ref. 49. be, FE-SEM images of bulk synthesized CID-1 (bulk-CID-1) (b), gel-like coordination polymer synthesized without sonication (c), nanocrystals of NCID-1a at low magnification (d), and nanocrystals of NCID-1a at high magnification (e). The thickness of the particles in e is between 10 and 20 nm.

  2. FE-SEM images of NCID-1b–g.
    Figure 2: FE-SEM images of NCID-1b–g.

    a,b, Increasing W leads to larger nanorods of NCID-1b (∼500 nm (length) × 100 nm (width) × 30 nm (thickness), a), but at W > 3, heterogeneous particles result due to instability of the microemulsion (W = 5; b). c,d, Although an increase in the ligand/ion concentration (M(CID)) to 200 mM does not affect the size and morphology of the nanocrystals (c), decreasing it to 20 mM results in a plate-like crystal morphology (d). e,f, At a higher concentration of AOT in heptane (M(AOT) = 1 M), particle size did not change remarkably (e), but reducing the AOT concentration (M(AOT) = 100 mM) resulted in heterogeneous particles (f).

  3. XRPD patterns of bulk-CID-1 and NCID-1a in different states.
    Figure 3: XRPD patterns of bulk-CID-1 and NCID-1a in different states.

    ad, As-synthesized bulk-CID-1 ⊃ DMF (a), as-synthesized nanocrystals of NCID-1a ⊃ DMF (b), dried bulk-CID-1 (c) and dried nanocrystals of NCID-1a (d). e,f, In situ XRPD pattern of bulk-CID-1 (e) and NCID-1a (f) at 300 K under 14 kPa methanol vapour (P/P0 = 0.75).

  4. Model for PCP nanoparticle formation and growth.
    Figure 4: Model for PCP nanoparticle formation and growth.

    After careful addition of 5 ml AOT/heptane solution to a 196 µl mother solution in DMF, the two-phase system is sonicated for 10 min. Formation of the inverse microemulsion rapidly leads to multiple nucleation events. As a result of sonication, the reversible formation of metal–ion bonds in combination with constant merging of droplets leads to particle growth. Particle size rapidly extends the droplet size of the initial microemulsion, leading to aggregation of the growing nanocrystals and surface coordination of AOT. This surface coordination of AOT also limits diffusion of metal ions and ligand to the crystal surface, which eventually limits particle growth and reaction yield.

  5. Gas adsorption properties of bulk-CID-1 and NCID-1a.
    Figure 5: Gas adsorption properties of bulk-CID-1 and NCID-1a.

    a,b, Adsorption and desorption isotherms for methanol at 293 K on bulk-CID-1 (black circles) and NCID-1a (grey squares) (a), and expansion in the low relative pressure region (b). The open and filled symbols represent adsorption and desorption, respectively. c, Kinetics of adsorption of methanol on bulk-CID-1 (black circles) and NCID-1a (grey squares) at 293 K.


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Author information


  1. DWI e.V. and Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Pauwelsstrasse 8, 52056 Aachen, Germany

    • Daisuke Tanaka,
    • Artur Henke,
    • Krystyna Albrecht,
    • Martin Moeller &
    • Juergen Groll
  2. Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan

    • Keiji Nakagawa &
    • Susumu Kitagawa
  3. Institute for Integrated Cell-Material Sciences, Kyoto University Katsura, Nishikyo-ku, Kyoto 615-8510, Japan

    • Susumu Kitagawa
  4. Kitagawa Integrated Pore Project, Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST) Kyoto Research Park, 134, Chudoji Minami-machi, Shimogyo-ku, Kyoto 600-8813, Japan

    • Susumu Kitagawa


D.T., S.K. and J.G. conceived and designed the experiments. D.T., A.H. and K.N. performed the experiments. D.T., A.H., K.N., K.A. and J.G. analysed the data. D.T., A.H., K.A., M.M., S.K. and J.G. contributed to writing the paper. All authors contributed to the optimization of the experiments.

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