MOFs (metal-organic frameworks) based on fluorinated and perfluorinated aromatic carboxylate ligands: directed synthesis, structures, and properties

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MOFs (metal-organic frameworks) and coordination polymers (CPs) are an intensely studied research area of modern solid state and materials chemistry. Recently, attempts have been made to optimize the gas storage and separation properties of these compounds by incorporating partial and perfluorinated linker ligands. Also in terms of thermal and chemical stability, these modified materials are expected to have improved properties. However, the references in the literature, whether this is actually successful, are contradictory, since there are only few isostructural MOFs with different degrees of fluorination at which comparative investigations can be carried out.We present a concept based on a simple structural parameter, namely the torsion angle between the carboxylate group and the phenyl ring, which makes it possible to selectively prepare isostructural MOFs with aromatic carboxylate ligands with different degrees of fluorination. Comparative investigations on the chemical and thermal stability as well as the gas adsorption properties for different polar and non-polar gases shall be carried out on these MOFs thus synthesized. In particular, the changed polarity within the MOF pore is important due to the fluorination of the ligand. A simple experiment was developed, which allows the polarity changes to be determined by the incorporation of a solvatochromic dye into the MOF pores. These results shall be correlated with measurements of the contact angle to determine the hydrophobicity of the respective MOFs and theoretical calculations (in cooperation).