Phase Transfer of Rhodium(II)-Based Metal-Organic Polyhedra Bearing Coordinatively-Bound Cargo Enables Molecular Separation.

The transfer of nanoparticles between immiscible phases can be driven by externally-triggered changes in their surface composition. Interestingly, phase transfers can enhance the processing of nanoparticles and enable their use as vehicles for transporting molecular cargo. Herein we report extension of such phase transfers to encompass porous Metal-Organic Polyhedra (MOPs). We report that a hydroxyl-functionalized, 2.5 nm in size cuboctahedral Rh(II)-based MOP can be transferred between immiscible phases by pH changes or by cation-exchange reactions. We demonstrate use of this MOP to transport coordinatively-bound cargo between immiscible layers, including into solvents in which the cargo is insoluble. As proof-of-concept that our phase-transfer approach could be used in chemical separation, we employed Rh(II)-based MOPs to separate a challenging mixture of structurally similar cyclic aliphatic (tetrahydrothiophene) and aromatic (thiophene) compounds. We anticipate that transport of coordinatively-bound molecules will open new avenues for molecular separation based on the relative coordination affinity that the molecules have for the Rh(II) sites of MOP.