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 Δ or Λ 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, S₆ or D₃ 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.