Enantioselective adsorption of limonenes and α-pinenes on germanium oxide metal-organic framework

Chiral metal-organic frameworks (CMOFs) are promising materials for catalysis, chromatography, and sensor applications. Typically, chirality in such frameworks is achieved by using chiral ligands. However, there are rare examples of CMOFs that form without any chiral source, usually via spontaneous symmetry breaking, resulting in supramolecular chirality. Germanium oxide framework SU-MB exhibits a unique mechanism of chirality emergence: during synthesis, only micropores of one handedness are selectively filled. This paper investigates the adsorption of limonene and α-pinene enantiomers on SU-MB. The framework demonstrated consistent enantioselectivity for both pairs of enantiomers, with a higher selectivity coefficient observed for α-pinenes than for limonenes. This difference arises from distinct trends in the isosteric heats of adsorption (Q _st ): for limonenes and (−)-α-pinene, Q _st approaches the heat of liquefaction with increasing adsorption, whereas for (+)-α-pinene, Q _st remains unchanged. These findings show that even a non-chiral crystal without chiral centers can exhibit enantioselectivity in adsorption processes, because of helical pores of one handedness.