Supramolecular chirality, which is ubiquitous in natural substances, has now become one of the central issues of chemistry in both the academic and industrial sectors. [1, 2] Spontaneous resolution, such that the enantiomers are segregated upon crystallization, stands out in the separation and control of chirality, and is widespread in the materials science of chiral crystalline solids, liquid crystals, and monolayers. [3] Notably, the phenomenon of achiral components resolving to yield chiral crystals is relatively rare compared to the analogous process with chiral components or auxiliaries. [3c] Therefore, a series of scientific questions arise: are there enantiophobic and enantiophilic molecules? Or are packing forces responsible for conglomerate formation? [3b, 4] Contrary to static chirality, which is sustained by covalent linking, supramolecular chirality mediated by noncovalent intermolecular interactions may enable the formation of thermodynamically stable assemblies based on certain dynamic equilibria. [1b] In state-of-the-art research on chiral coordination polymers, [5] Aoyama et al. provided a wellestablished example of controllable homochiral crystallization, in which adjacent helices constructed from achiral components adopt the same handedness through intermolecular water-nitrate hydrogen bonding. [6] Later, Yan et al. described an unusual example of partial spontaneous resolution, which showed the progression from achiral species to chiral dimers, to chiral 2D layers, and finally to concomitant chiral and racemic crystals. [7] However, both of the above examples are not genuine polymorphs, [8] as they contain solvent molecules in their crystal structures that might preserve the homochiral discrimination but complicate the supramolecular interactions among chiral precursors. Herein, we report a unique example of concomitant and controllable chiral/racemic polymorphs for investigating how supramolecular chirality can be generated from achiral components.
The helix is one of the most attractive and evocative expressions of chirality, [9,10] especially one-dimensional (1D) metallohelical chains, which are proved to be more efficient