Coordinative Alignment in the Pores of MOFs for the Structural Determination of N-, S-, and P-Containing Organic Compounds Including Complex Chiral Molecules

Abstract

Coordinative alignment of target small molecules onto a chiral metal-organic framework (MOF-520)provides a powerful method to determine the structures of small molecules through single-crystal X-ray diffraction (SXRD). In this work, the structures of 17 molecules with eight new coordinating functionalities and varying size have been determined by this method, four of which are complex molecules being crystallized for the first time. The chirality of the MOF backbone not only enables enantioselective crystallization of chiral small molecules from a racemic mixture but also imposes diastereoselective incorporation upon achiral molecules. Crystallographic studies assisted by density functional theory (DFT) calculations indicate that the stereoselectivity of MOF-520 not exclusively comes from the steric confinement of the chiral pore environment but also from asymmetric chemical bonding of the target molecules with the framework that is able to provide sufficient energy difference between possible coordination configurations.