Tetramine Aspect Ratio and Flexibility Determine Framework Symmetry for Zn₈L₆Self‐Assembled Structures

Abstract

We derive design principles for the assembly of rectangular tetramines into Zn 8 L 6 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 2formylpyridine in acetonitrile into a single Zn 8 L 6 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 tetraaniline 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.

A Diverse Array of Large Capsules Transform in Response to Stimuli

“…Two distinct Zn II ···Zn II distances between Zn II centers with opposite handedness around the equatorial plane, 13.63 and 17.41 Å, were observed (Figure a), where a pentatopic ligand bridges pairs of zinc ions, and the Zn II ···Zn II distance where two tridentate ligand coordination vectors point away from each other is longer than the case where the vectors point toward each other (Figure S45). This opposing conformation of one out of the five ligand arms results in opposite handedness of the bound Zn II center, which we inferred to result in a reduction of strain within this irregular structure. Aromatic stacking and electrostatic interactions between G and Zn-4 (Figure b) were inferred to induce the structural transformation of Zn-2 into Zn-4 .…”

A Water‐ and Base‐Stable Iminopyridine‐Based Cage That Can Bind Larger Organic Anions

“…While the exact reason for the failure of obtaining a tetrahedron are difficult to elucidate, there are several factors that might be at play: (1) ligand 3 features a reduced aspect ratio (length-to-width ratio) compared to the ligand used for the construction of Fe 4 L 6 tetrahedron I, a factor that is known to influence the geometry and the composition of coordination cages. [74,75] (2) The absence of bulky substituents on the NDI moiety might also facilitate the π-π-stacking between the ligands (Figure 3c). π-π-stacking was observed to influence the outcome of related self-assembly processes.…”

Systematic exploration of accessible topologies of cage molecules via minimalistic models

“…[17][18][19][20][21] Structure generation and evaluation of the relative stability of different topologies can help drive or rationalise experimental efforts. 16,[22][23][24][25][26] However, these calculations are costly or too approximate (oen neglecting solvent/ion effects and exibility), and the thermodynamics of each step is not always enough of the picture (e.g., when kinetic traps are present). When introducing asymmetry, for example, combinatorial explosion quickly leads to an intractable number of isomers, topologies or congurations that must be studied to consider self-sorting outcomes.…”