Geometry: Polyhedra and Networks

MOFs with Carboxylate Ligands

• Oxalate ligands can form 2D and 3D homo and bimetallic networks depending on the choice of counter ions
• When the counterion is NR4+, 2D layers of hexagonal honeycomb are formed

MOFs with Benzene 1,4-Dicarboxylate

• Dimensionality: 1-3
• Form 1D to 3D porous networks

MOFs with Benzene Tricarboxylic Acids

• BTC, Benzene tricarboxylic acid, trimesic acid, e.g., HKUST-1
• Form porous multidimensional networks
• Flexible tripodal benzene-1,3,5-triacetic acid

MOFs with Polynuclear Building Nodes

• Introduction of metal clusters into MOFs leads to new functional solid-state materials
• Carboxylic acid ligands provide a wide range of rigid network due to their ability to aggregate metal ions into clusters termed as secondary building units (SBU)
• Common SBUs: square paddle wheel [M2(COO)4], octahedral basic zinc acetate cluster, trigonal prismatic oxo-centered trimers, trigonal planar

Dinuclear Building Nodes

• Square paddle wheel [Cu2(COO)4] SBUs are connected by ditopic BDC linkers to form layers of square topology

MOF-5

• Composed of octahedral Zn4O(—COO)6 SBUs, consisting of four tetrahedral ZnO4 units sharing a common vertex, joined by ditopic BDC linkers to give a 3D framework structure of primitive cubic (pcu) topology
• Open porous structure, with large cavities making up 61% of the unit cell volume and are filled with solvent molecules

Isoreticular MOFs

• Pore size can be expanded with the use of long linkers, such as biphenyl, tetrahydropyrene, pyrene, and terphenyl

MOF with Two Different Connectors

• Example: MOF with two different connectors, such as BTC and BDC

M3O and M4O Nodes (SBU)

• M3O nodes: trigonal prism joint, example: [Fe3O(COO)6]
• M4O nodes: octahedral joint, example: MOF-5, alpha-Po, stable up to 400°C and highly porous

High Nuclearity Building Nodes

• High nuclearity clusters can form MOF SBUs, example: [Ni6(OH)6(1,4-cdc)3(H2O)6], 2D structure, hexanuclear prismatic nickel cluster SBU

Function of Porous MOFs

• Gas sorption or storage, such as H2, CH4, and CO2
• Criteria for improvement: interaction with the gas, interpenetration, doping, unsaturated metal sites, and functionalization of ligands

Zeolitic Imidazolate Framework (ZIF)

• Sod: truncated octahedron, zinc(II) nitrate, and imidazolate-2-carboxyaldehyde (ICA)
• Aperture of 3.5 Å and a pore size of 11.2 Å

MOFs in Catalysis

• Catalysis, such as cyanosilylation of aldehydes, oxidation of hydrocarbons, oxidation of sulfides, and cycloaddition of CO2 and epoxides

MOF-5 and MIL-100

• MOF-5: alpha-Po, stable up to 400°C and highly porous
• MIL-100: Fe-based, catalytically active, and porous

MOF-101 (Cr)

• Cyanosilylation of aldehydes, oxidation of hydrocarbons, oxidation of sulfides, and cycloaddition of CO2 and epoxides

Activation of CO2

• MOFs can be used for the activation of CO2

Wells Notation

• Honeycomb: (6,3) topology
• Uniform net: (n,p) notation, where n is the size of the smallest circuit and p is the connectivity of nodes

Topology of Interpenetration

• Interpenetrating: two or more networks penetrate without connecting each other

3D MOFs

• Topologies: diamond, primitive cubic (alpha-Po), PtS, CdSO4, CaB6, NbO, and rutile
• Examples: MOF-2, MOF-5, and HKUST-1