(687b) The Role of Solvent in the Room Temperature Synthesis of Two Isomeric Metal-Organic Frameworks

Two isomeric Metal-Organic Frameworks (MOFs) with the chemical formula Zn₂(X)₂(TED) (X = terephthalic acid, 2,3,5,6-tetramethyl terepthalic acid, dimethyl terephthalic acid, and anthracene dicarboxylic acid) have been synthesized via a fast, room temperature synthesis procedure to produce DMOF-1 or ZnBD which differ by topology. It was found that functionalization of the BDC ligand results in the formation of the DMOF-1 structure. This is a result of the imposed steric effects that prevent the formation of the Kagome lattice. Solvent choice was found to play a vital role in the synthesis of ZnBD when using BDC as a ligand and is the determining factor in the MOF topology that is formed. When dimethylformamide (DMF) was used as the solvent, the synthesis resulted in the formation of ZnBD, whereas methanol produced DMOF-1. The synthesized MOFs were found to have similar water stability, both degraded upon exposure to 50% relative humidity at 25 °C, and both are hydrophobic. Additionally CO₂ adsorption isotherms of ZnBD were collected and compared to those previously reported for DMOF-1. ZnBD adsorbs less CO₂ at low pressures, but reaches similar capacity at 20 bar. This can be explained by the nature of the large hexagonal pore in ZnBD (15 Å) compared to the smaller pore opening (7.5 Å) in DMOF-1. The heat of adsorption for CO₂ on ZnBD was calculated to be ~20 kJ/mol at zero coverage, which is slightly lower than what has been reported for DMOF-1.