Constructing π-Stacked Supramolecular Cage Based Hierarchical Self-Assemblies via π···π Stacking and Hydrogen Bonding

Abstract

Constructing supramolecular cages with multiple subunits via weak intermolecular interactions is a long-standing challenge in chemistry. So far, π-stacked supramolecular cages still remain unexplored. Here, we report a series of π-stacked cage based hierarchical self-assemblies. The π-stacked cage (π-MX-cage) is assembled from 16 [MXL]⁺ ions (M = Mn²⁺, Co²⁺; X = Br^-, SCN^-, Cl^-; and L = tris(2-benzimidazolylmethyl)amine) via 18 intermolecular π-stacking interactions. The tetrahedral cage, consisting of four [MXL]⁺ ions as the vertexes and six pairs of [MXL]⁺ ions as the edges, features 48 exterior N-H hydrogen bond donors for hydrogen bond formation with guest molecules. By variation of the M²⁺/X^- pair, the π-MX-cage demonstrates unique versatility for incorporating a wide variety of species via different hydrogen-bonding modes during the assembly of hierarchical superstructures. In specific, the π-MnBr-cages encapsulate acetonitrile (CH₃CN) or <i>cis</i>-1,3,5-cyclohexanetricarbonitrile (<i>cis</i>-HTN) molecules in the central voids, while a core-shell tetrahedral inorganic cluster [Mn(H₂O)₆]@([Mn(H₂O)₄]₄[Br₄^2-]₆) (Mn@Mn₄-cage) is captured within the interstitial regions between cages. The π-CoSCN-cages are capable of stabilizing reactive sulfur-containing species, such as S₂O₄^2-, S₂O₆^2-, and HSO₃^- ions, in the hierarchical superstructure. Finally, H₂PO₄^- ions are incorporated between π-CoCl-cages, resulting in an inorganic mesoporous framework. These results provide insights into further exploring the chemistry and hierarchical assembly of supramolecular cages based on π-π stacking intermolecular interactions.