Discovery and introduction of a (3,18)-connected net as an ideal blueprint for the design of metal–organic frameworks

Journal name:
Nature Chemistry
Year published:
Published online


Metal–organic frameworks (MOFs) are a promising class of porous materials because it is possible to mutually control their porous structure, composition and functionality. However, it is still a challenge to predict the network topology of such framework materials prior to their synthesis. Here we use a new rare earth (RE) nonanuclear carboxylate-based cluster as an 18-connected molecular building block to form a gea-MOF (gea-MOF-1) based on a (3,18)-connected net. We then utilized this gea net as a blueprint to design and assemble another MOF (gea-MOF-2). In gea-MOF-2, the 18-connected RE clusters are replaced by metal–organic polyhedra, peripherally functionalized so as to have the same connectivity as the RE clusters. These metal–organic polyhedra act as supermolecular building blocks when they form gea-MOF-2. The discovery of a (3,18)-connected MOF followed by deliberate transposition of its topology to a predesigned second MOF with a different chemical system validates the prospective rational design of MOFs.

At a glance


  1. Topological exploration that led to the discovery of gea-MOF-1.
    Figure 1: Topological exploration that led to the discovery of gea-MOF-1.

    a, A combination of RE metal ions and ​2 fluorobenzoic acid enables the assembly of a hexanuclear RE cluster. The carbon atoms of the carboxylate ligands (that is, the points of extension) coincide with the 12 vertices of a cuo, which enables the hexanuclear cluster to act as a 12-connected molecular building block for MOF formation. b, Linking of 12-connected MBBs with either linear (two-connected) or square (four-connected) MBBs results in the formation of a fcu net or a ftw net, respectively. c, The 12-connected MBBs do not form structures when combined with triangular (3-connected) MBBs; however, the insertion of three extra RE ions into the hexanuclear cluster affords the evolution of a nonanuclear cluster coordinated by 18 carboxylate ligands. In this cluster, the points of extension coincide with the 18 vertices of an eto polyhedron. It therefore acts as an 18-connected MBB and, in combination with a triangular MBB, affords the assembly of a (3,18)-connected net, the gea net. In the skeletal molecular structures in a and c, RE, C, O and F are represented by purple, grey, red and light green, respectively, and H atoms are omitted for clarity. For clarity, fcu, ftw and gea topologies are represented as augmented nets.

  2. Cluster rearrangement and packing in gea-MOF-1.
    Figure 2: Cluster rearrangement and packing in gea-MOF-1.

    a, A proposed path that shows the evolution from the hexanuclear to the nonanuclear cluster. The upper part shows the hexanuclear cluster on its evolution into a nonanuclear cluster. The green triangles directly underneath represent the spatial arrangement of the RE atoms in the cluster and show the 30° rotation and the addition of three RE metal ions. The lower part demonstrates the effect of cluster evolution on the MBB points of extension, which increase from 12 (cuo) to 18 (eto). RE atoms from the hexanuclear cluster are in light green, and the additional RE atoms needed to form the nonanuclear cluster are in purple; C atoms from the carboxylates are in black for the top and bottom of the cluster (3-membered rings), and blue for the middle (6-membered rings). b, Views of the hexagonal close packing of the MBBs of gea-MOF-1. A and B layers from the hexagonal packing are represented in purple and yellow, respectively.

  3. SBB approach to design expanded gea-MOF-2.
    Figure 3: SBB approach to design expanded gea-MOF-2.

    a, Structural representations of gea-MOF-1. b, Topological analysis of gea-MOF-1 reveals the underlying (3,18)-connected gea net. c, The augmented 18-connected and 3-connected nodes that make up the underlying gea net have vertex figures of an eto and a triangle, respectively, and these vertex figures can be taken as general building blocks in the construction of other MOFs with gea topology. d, Using these vertex figures, the SBB approach allows the substitution of the 18-connected eto cluster with an 18-connected eto MOP. This MOP is itself constructed from nine square Cu dimers and 18 organic ligands: 12 bent dicarboxylic acids with a 120° angle between coordination sites and six dicarboxylic acids with a 90° angle. e, Substitution of the three-connected triangular ligand in gea-MOF-1 with a designed H6L ligand. H6L was designed to be compatible with the (3,18)-connected gea net by possessing the same triangular core and the appropriate ratio of dicarboxylic acid moieties. f, The 18-connected building blocks are linked by a triangular core in both gea-MOF-1 and gea-MOF-2, but the sizes of the building blocks are different in each MOF.

  4. Relationship between gea-MOF-1 and gea-MOF-2.
    Figure 4: Relationship between gea-MOF-1 and gea-MOF-2.

    a, Open spaces and general view of gea-MOF-1 reveal three types of cavity. b, Open spaces and general view of gea-MOF-2 showing that gea-MOF-1 and gea-MOF-2 are structurally related, but that gea-MOF-2 has an extra cavity relative to gea-MOF-1. c, The packing of the cavities in gea-MOF-1 and gea-MOF-2 are similar, but the nonanuclear RE clusters in gea-MOF-1 are replaced by cavity IV in gea-MOF-2. RE, Cu, C, N and O are represented in purple, green, grey, blue and red, respectively. For clarity, H atoms are omitted and the relative scales of gea-MOF-1 and gea-MOF-2 are not the same.

  5. gea-MOF-1 shows great potential for hydrocarbon separation.
    Figure 5: gea-MOF-1 shows great potential for hydrocarbon separation.

    a, ​CH4, ​CO2, ​C2H6, C3H8 and ​n-C4H10 single gas adsorption isotherms at 298 K. Based on the gradient of the isotherms at low pressure, the affinity of these molecules for gea-MOF-1 follows the sequence ​n-C4H10 > C3H8 ≫ ​C2H6 > ​CO2 > ​CH4. b, Predicted selectivities in the adsorption of gas mixtures with molar ratios of ​C2H6/​CH4 (5:95), C3H8/​CH4 (5:95) and ​n-C4H10/​CH4 (5:95) using IAST calculations. Selectivity is defined by the ratio of CnH2n+2 to ​CH4 in the phase adsorbed to gea-MOF-1, versus the initial gas-phase composition (5:95). These predict very high selectivity for ​n-C4H10 and C3H8 over ​CH4 and high selectivity for ​C2H6 over ​CH4 for gea-MOF-1. The different selectivity behaviour of gea-MOF-1 towards CnH2n+2 is mainly governed by the difference in the polarizabilities of the alkane species.


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Author information


  1. Functional Materials Design, Discovery and Development Research Group (FMD3), Advanced Membranes and Porous Materials Center (AMPM), Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia

    • Vincent Guillerm,
    • Łukasz J. Weseliński,
    • Youssef Belmabkhout,
    • Amy J. Cairns,
    • Karim Adil &
    • Mohamed Eddaoudi
  2. Kaust Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia

    • Valerio D'Elia
  3. Department of Chemistry, University of South Florida, 4202 East Fowler Ave., Tampa, Florida 33620, USA

    • Łukasz Wojtas


V.G. and M.E. contributed to the conceptual approach to designing the material synthetic experiments; V.G. carried out the synthetic experiments; V.G., Ł.W. and K.A. conducted and interpreted the crystallographic experiments; V.G. performed the topological analysis; Y.B. and A.J.C. conducted and interpreted low- and high-pressure sorption experiments and IAST models (Y.B.); V.D. designed, conducted and interpreted catalysis experiments; V.G., M.E. and Ł.J.W. envisioned, designed and synthesized (Ł.J.W.) the organic hexacarboxylic ligand; V.G., Y.B. and M.E. wrote the manuscript.

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Crystallographic information files

  1. Supplementary information (23 KB)

    Crystallographic data for compound gea-MOF-1

  2. Supplementary information (40 KB)

    Crystallographic data for compound gea-MOF-2

  3. Supplementary information (23 KB)

    Crystallographic data for compound Tb(III) hexanuclear cluster

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