Tetramine Aspect Ratio and Flexibility Determine Framework Symmetry for Zn8L6 Self-Assembled Structures

We derive design principles for the assembly of rectangular tetramines into Zn8L6 pseudo-cubic coordination cages. Because of the rectangular, as opposed to square, geometry of the ligand panels, and the possibility of either Delta or ? handedness of each metal center at the eight corners of the pseudo-cube, many different cage diastereomers are possible. Each of the six tetra-aniline subcomponents investigated in this work assembled with zinc(II) and 2-formylpyridine in acetonitrile into a single Zn8L6 pseudo-cube diastereomer, however. Each product corresponded to one of four diastereomeric configurations, with T, T-h, S-6 or D-3 symmetry. The preferred diastereomer for a given tetra-aniline subcomponent was shown to be dependent on its aspect ratio and conformational flexibility. Analysis of computationally modeled individual faces or whole pseudo-cubes provided insight as to why the observed diastereomers were favored.

Automated summary

We have derived design principles for assembling rectangular tetramines into Zn8L6 pseudo-cubic coordination cages. The ligand panels' rectangular geometry and the handedness of each metal center at the corners of the pseudo-cube result in multiple possible cage diastereomers. However, our experiments showed that each tetra-aniline subcomponent assembled with zinc(II) and 2-formylpyridine into a single Zn8L6 pseudo-cube diastereomer. The preferred diastereomer depended on the subcomponent's aspect ratio and conformational flexibility.