Positional Effect of a Neutral Linker on the Three-Component MOFs: Room Temperature Synthesis, Structural...

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• Metal-organic frameworks (MOFs) are crystalline porous materials with diverse applications.
• Developing new MOFs with specific functionalities, such as catalytic activity, is an active research area.

Purpose of the Study:

• To synthesize and characterize novel 2D metal-organic frameworks (MOFs) using a mixed-ligand approach.
• To investigate the structural, thermal, and chemical properties of the synthesized MOFs.
• To explore the catalytic potential of these MOFs in organic synthesis.

Main Methods:

• Room temperature synthesis of MOFs using tetrakis(3-pyridyloxymethylene)methane (3-tpom) and 4,4'-(1,3,4-oxadiazole-2,5-diyl)-dibenzoate (oxdz²⁻) ligands.
• Single-crystal X-ray diffraction for structural determination of MOF 2.
• FTIR spectroscopy and powder X-ray diffraction for structural comparison of MOFs 1 and 2.
• FESEM, TEM, and XPS for comprehensive material characterization.
• Heterogeneous catalysis for coumarin-3-carboxylic acid synthesis.

Main Results:

• Successful synthesis of two isostructural 2D MOFs, {[Zn₂(3-tpom)₂(oxdz)²]·4H₂O}n (1) and {[Cd₂(3-tpom)₂(oxdz)²(H₂O)₂]·6H₂O}n (2), in good yields.
• Both MOFs exhibit high thermal stability (up to 305 °C) and resistance to polar solvents.
• The crystal structure of MOF 2 reveals heptacoordinated Cd centers in a pentagonal bipyramidal geometry.
• The MOFs possess rectangular pores lined with uncoordinated pyridyl groups, offering Lewis acidic metal sites and Brønsted basic sites.
• MOFs 1 and 2 effectively catalyze the synthesis of coumarin-3-carboxylic acid and derivatives under mild, sustainable conditions (25 °C, methanol).

Conclusions:

• The mixed-ligand approach enables the room temperature synthesis of robust 2D MOFs.
• The unique pore environment and synergistic catalytic sites make these MOFs promising heterogeneous catalysts.
• These MOFs offer a sustainable pathway for the synthesis of valuable coumarin derivatives.