Metal-Organic Nanotubes With Molecular Valves

Novel metal-organic frameworks with one-dimensional channels – metal-organic nanotubes (MONTs) – show potential for extremely selective separations based on their nanoscale structure.  A class of MONTs has been synthesized in which phenyl groups provide flexible rotors that act as molecular-scale valves, either allowing transport down the axial dimension of the nanotube when in the "open" position, or preventing transport in the "closed" position.  The ability to control the position of the valve remains a subject of investigation.  In this work, we present a comparison between experimentally determined crystal structures and simulated molecular models of a suite of MONTs.  The experimental work indicates that the choice of solvent (DMA, DMF, NMP, water) can be used to control the orientation of the valve.  This choice, and the relative influences of steric hindrance and electronic effects are assessed.  The simulation work provides an understanding of the molecular-level mechanism.  Structural and energetic properties are reported, which yield insight into a broader application of molecular valve control in MONTs.