Variation of desolvation behavior in two isostructural metal–organic frameworks based on a flexible, racemic bifunctional organic linker

Abstract

A racemic mixture of the chiral ligand 4,4′-(1,2-dihydroxyethane-1,2-diyl)dibenzoic acid was used to prepare two isostructural metal–organic frameworks, CPO-49-Zn and CPO-49-Mn, which contain coordinated solvent molecules at the metal site. The compounds showed different behavior upon desolvation. The dissociation of the solvent molecule from the metal site leads to a single-crystal-to-single-crystal transformation. In CPO-49-Zn, a change of coordination geometry from trigonal bipyramidal to tetrahedral occurs at the zinc atom. In CPO-49-Mn, a rearrangement of coordination mode of a carboxylate group occurs instead, leading to a 4+1 coordination of the manganese cation in the form of a capped distorted tetrahedron. N2 gas adsorption confirms that both desolvated structures are permanently porous. The behavior of the compounds upon heating has also been studied using variable temperature powder X-ray diffraction. The presence of a coordinated solvent molecule in the as-synthesized structures indicates the possibility to access the metal cation with reactive substrates. Both materials were evaluated in the catalytic oxidation of styrene. CPO-49-Mn showed significantly higher conversion than the CPO-49-Zn material.