Cation-based Structural Tuning of Pyridine Dipyrrolate Cages and Morphological Control over Their Self-assembly

Abstract

Different pyridine dipyrrolate cages including cage-based dimers and polymers may be fabricated in a controlled manner from the same two starting materials, namely, an angular ligand 1 and Zn­(acac)2, by changing the counter cation source. With tetrabutylammonium (TBA+) and dimethyl viologen (DMV2+), Cage-3 and Cage-5 are produced. In these cages, two ligands act as bridges and serve to connect together two cage subunits to produce higher order ensembles. In Cage-3 and Cage-5, the TBA+ and DMV2+ counter cations lie outside the cavities of the respective cages. This stands in contrast to what is seen with a previously reported system, Cage-1, wherein dimethylammonium (DMA+) counter cations reside within the cage cavity. When the counter cations are tetraethylammonium (TEA+) and bis­(cyclopentadienyl) cobalt­(III) (Cp2Co+), polymeric cage materials, PC-1 and PC-2, are formed, respectively. The counter cations thus serve not only to balance charge but also to tune the structural features as a whole. The organic cations used in the present study also act to modulate the further assembly of individual cages. The present cation-based tuning emerges as a new method for a fine-tuning of the multidimensional morphology of self-assembled inorganic materials.

Pillararenes Trimer for Self-Assembly

“…"Click" reaction is a very efficient synthesis strategy for obtaining the "star-shaped" pillararenes trimer. For example, the first pillararenes trimer PT1 (Scheme 1) was synthesized by using the general condition of click reactions, i.e., copper (I) catalyzed Huisgen-type azide-alkyne cycloaddition reaction between azido-pillar [5]arene (X1, Scheme 3) and tripropargylamine with a high yield of 91% [15]. By using the same synthesis strategy, PT5 (Scheme 1) [22] is also produced by coupling the pillar [5]arenes precursors X6 (Scheme 3) together.…”

“…For example, PT3 (Scheme 1) was synthesized by rationally connecting three units of pillararenes (X4, Scheme 3) together via the reaction between 1,3,5-benzenetricarbonyl trichloride and dihydrazide moieties in dichloromethane for 12 h [21]. By using very similar synthesis procedure but different pillar [5]arenes precursors such as X9 (Scheme 3), 1,3,5-benzenetricarbonyl trichloride can also act as the core structure in another trimer-PT7 (Scheme 1) [24]. In addition, the 1,3,5-benzenetricarbonyl trichloride could perform an esterification in chloroform with three equivalent of pillararenes precursor X5 (Scheme 3) to obtain another star-shaped trimer, PT4 (Scheme 1) [19].…”

“…Different from the above star-shaped pillararenes trimers, there is a particular linear pillararenes trimer, PT6 (Scheme 1), which is synthesized by a quinoline monofunctionalized pillar [5] arene X7 and bis-bromhexine functionalized X8 (Scheme 3) in n-butanol [23]. Due to the possession of quinoline and pillararenes subunits, this "N-type" tri-pillararenes-based foldamer could contribute π-π stacking interaction sites for further self-assembly.…”

“…A particular pillararenes trimer X13⊃G6 ( Figure 1) was designed by only employing noncovalent bonds between the cavity of naphthalimide monofunctionalized pillar [5] arene X13 (Scheme 1) and pyridine moieties on the star-shaped guest G6 (Scheme 2) [28]. In the noncovalent pillararenes trimer, the pillararenes subunit only acts as a linker to interact with the tripodal core, providing an occupied cavity for further control over the advanced self-assemblies.…”

“…Self-assembly has attracted much more attention in fundamental researches of material science and interesting applications to practical engineering areas [1,2], e.g., providing not only inspiring methodological strategy in processing, but also solid functional materials to balance morphologies and properties [3]. Building ideal self-assembly begins from the molecular level [2,4,5], i.e., designing the structural geometry of molecules, modifying them with proper functional moieties, introducing and choosing proper inter/intramolecular interactions, as well as controlling the behavior of assembled molecules. Thus, designing appropriate building blocks from the molecular level is very significant in the construction of multi-dimensional self-assembly [2].…”