Synthesis and characterization of 1,3-alternate calix[4]arene-based metal-organic frameworks

Abstract

This research involves the syntheses of 1,3-alternate calix[4]arene derivatives to use as organic linkers in the construction of calix[4]arene-based metal-organic frameworks (MOFs). These organic linkers, 1,3-alternate calix[4]arene tetra-p-benzoic acid (3A) and 1,3-alternate calix[4]arene tetra-m-benzoic acid (3B) are structural isomers which the carboxylic acid groups are at para and meta positions of phenyl substituent units, respectively. Each of organic linkers was synthesized in 3 steps with total yields of 38 % for 3A and 34 % for 3B. The obtained organic linkers were employed in synthesis of metal-organic frameworks with various metal ions in dimethylformamide solvent by solvothermal syntheses methods in various containers; round-bottom flask, sealed tube, auto clave and the obtained 1,3-alternate calix[4]arene-based MOFs were investigated their morphologies and gas adsorption properties for the potential use in gas storage. Morphologies of obtained MOFs as micro-particles of MOFs were found in various forms, such as needle-like, cubic, rod and platelet shapes. The nitrogen adsorption-desorption isotherms featured as type III adsorption isotherm which was typical for nonporous materials. Fortunately, the single-crystals of both organic linkers and 1,3-alternate calix[4]arene-based MOFs were obtained which have been characterized by sc-XRD technique. The single-crystal structures of MOF prepared by using 3A and Zn(II) ion (named, CU-SCRU1) exhibited as three dimension structure via the arrangement of the polymeric coordinated linear chain. In the case of MOF that synthesized by using 3B and Zn(II) ion (named, CU-SCRU2), the coordinated bond between organic linker, 3B and Zn(II) ion formed to be a zig-zag polymeric chain and extended by intermolecular interaction to provide the three dimension frameworks. Moreover, in the reaction of 3B and Cd(II) ion yielded two different single-crystal structures. Their single-crystal X-ray diffraction study revealed that they were three dimensional framework, crystallizing in monoclinic (named, CU-SCRU3) and orthrorombic (named, CU-SCRU4). Apart from their gas adsorption property of 1,3-alternate calix[4]arene-based MOFs, their catalytic property were preliminary investigated but it was revealed that they were not suitable for using as catalyzing in Friedel-Craft alkylation reaction.