Theoretical Insights into the Tuning of Metal Binding Sites of Paddlewheels in rht-Metal-Organic Frameworks.

Theoretical investigations of CO2 sorption are performed in four members of the highly tunable rht-metal-organic framework (MOF) platform. rht-MOFs contain two Cu(2+) ions that comprise the metal paddlewheels and both are in chemically distinct environments. Indeed, one type of Cu(2+) ion faces toward the center of the linker whereas the other type faces away from the center of the linker. Electronic structure calculations on the series of rht-MOFs demonstrate that one of the Cu(2+) ions has a consistently higher charge magnitude relative to the other. As a consequence, the Cu(2+) ion with the higher partial positive charge acts as the favored sorbate binding site at initial loading as revealed by grand canonical Monte Carlo (GCMC) simulations that include many-body polarization. It was found that the charge distribution about the copper paddlewheels is dependent on the type of functional groups present on the linker. This study demonstrates how the binding site about the metal paddlewheels in the rht-MOF platform can be controlled by changing the functionality on the organic ligand.