Face-directed self-assembly of an electronically active Archimedean polyoxometalate architecture

Journal name:
Nature Chemistry
Volume:
2,
Pages:
308–312
Year published:
DOI:
doi:10.1038/nchem.581
Received
Accepted
Published online

Abstract

The convergent assembly of metal–organic frameworks has enabled the design of porous materials using a structural building unit approach, but functional systems incorporating pre-assembled structural building unit ‘pore’ openings are rare. Here, we show that the face-directed assembly of a ring-shaped macrocyclic polyoxometalate structural building unit, {P8W48O184}40− with an integrated 1-nm pore as an ‘aperture synthon’, with manganese linkers yields a vast three-dimensional extended framework architecture based on a truncated cuboctahedron. The 1-nm-diameter entrance pores of the {P8W48O184}40− structural building unit lead to approximately spherical 7.24-nm3 cavities containing exchangeable alkali-metal cations that can be replaced by transition-metal ions through a cation exchange process. Control over this process can be exerted by either electrochemically switching the overall framework charge by manipulating the oxidation state of the manganese linker ions, or by physically gating the pores with large organic cations, thus demonstrating how metal–organic framework-like structures with integrated pores and new physical properties can be assembled.

At a glance

Figures

  1. Open framework material 1 is built from the face-directed assembly of a highly anionic {P8W48O184}40− molecular building unit, which incorporates a 1-nm pore, combined with electrophilic manganese linkers, which are redox-switchable.
    Figure 1: Open framework material 1 is built from the face-directed assembly of a highly anionic {P8W48O184}40− molecular building unit, which incorporates a 1-nm pore, combined with electrophilic manganese linkers, which are redox-switchable.

    ac, The highly accessible three-dimensional network 1 crystallizes in cubic space group Pm-3m: packing of manganese-linked {P8W48O184}40− clusters forming a truncated cuboctahedron (a), crystal packing of [Mn8(H2O)48P8W48O184]24− (1a) along the crystallographic a axis (b), packing of manganese-linked {P8W48O184}40− clusters around a truncated cuboctahedron (c). Red polyhedral, WO6; red spheres, oxygen; yellow spheres, manganese; pink spheres, phosphorus. All alkali metal cations and solvent water molecules have been omitted for clarity.

  2. Face-directed assembly of six {P8W48O184}40− heteropolyanions through multiple {Mn–O–W} bonds along all axes, giving rise to a geometrically well-defined Archimedean solid: the truncated cuboctahedron.
    Figure 2: Face-directed assembly of six {P8W48O184}40− heteropolyanions through multiple {Mn–O–W} bonds along all axes, giving rise to a geometrically well-defined Archimedean solid: the truncated cuboctahedron.

    The geometrical arrangement of these fragments into the three-dimensional scaffold is shown, where yellow spheres represent the approximately spherical void space (∼7.24 nm3) within the cavity of each cuboctahedral building unit. Red wires, WOx; yellow wires, MnOx. All alkali-metal cations and solvent water molecules have been omitted for clarity.

  3. UV spectrophotometric exchange experiments were used to establish the cation exchange capabilities of the solvent-accessible voids of 1 over a 24-h period.
    Figure 3: UV spectrophotometric exchange experiments were used to establish the cation exchange capabilities of the solvent-accessible voids of 1 over a 24-h period.

    This figure summarizes the exchange study of CuII(NO3)2·3H2O plus [Mn8(H2O)48P8W48O184]24− (1a) and oxidized (1aox). Elemental analysis and UV spectroscopic studies show that Cu2+ replaces K+ and Li+ in the channels and cavities of 1. a, General experimental scheme for the cation exchange experiments and the principal results. b, General experimental procedure, complete with a photograph showing the visual observation of Cu(ii) uptake into single crystals of 1. c, Plot of uptake of Cu(ii) into the cavities of 1 and 1ox over a 24-h period. For 1 this corresponds to an uptake of 0.73 mmol Cu2+ per gram of 1; for oxidized 1ox this corresponds to 0.37 mmol Cu2+ per gram of 1ox (∼50% difference between the two redox phases: 1 to 1ox).

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Affiliations

  1. WestCHEM, Department of Chemistry, The University of Glasgow, University Avenue, Glasgow G12 8QQ, UK

    • Scott G. Mitchell,
    • Carsten Streb,
    • Haralampos N. Miras,
    • Thomas Boyd,
    • De-Liang Long &
    • Leroy Cronin

Contributions

S.M. and L.C. designed experiments, analysed data, prepared the figures and wrote the manuscript. C.S. provided invaluable advice and assisted with the PXRD. H.M. performed electrochemistry measurements. D.L. checked the crystallography. T.B. verified the synthesis.

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