Solid-Liquid Lithium Electrolyte Nanocomposites Derived from Porous Molecular Cages.

We demonstrate that solid-liquid nanocomposites derived from porous organic cages are effective lithium ion electrolytes at room temperature. A solid-liquid electrolyte nanocomposite (SLEN) fabricated from a LiTFSI/DME electrolyte system and a porous organic cage exhibits ionic conductivity on the order of 1 × 10-3 S cm-1. With an experimentally measured activation barrier of 0.16 eV, this composite is characterized as a superionic conductor. Furthermore, the SLEN displays excellent oxidative stability up to 4.7 V vs Li/Li+. This simple three-component system enables the rational design of electrolytes from tunable discrete molecular architectures.

Product Distribution from Precursor Bite Angle Variation in Multitopic Alkyne Metathesis: Evidence for a Putative Kinetic Bottleneck.

In the dynamic synthesis of covalent organic frameworks and molecular cages, the typical synthetic approach involves heuristic methods of discovery. While this approach has yielded many remarkable products, the ability to predict the structural outcome of subjecting a multitopic precursor to dynamic covalent chemistry (DCC) remains a challenge in the field. The synthesis of covalent organic cages is a prime example of this phenomenon, where precursors designed with the intention of affording a specific product may deviate dramatically when the DCC synthesis is attempted. As such, rational design principles are needed to accelerate discovery in cage synthesis using DCC. Herein, we test the hypothesis that precursor bite angle contributes significantly to the energy landscape and product distribution in multitopic alkyne metathesis (AM). By subjecting a series of precursors with varying bite angles to AM, we experimentally demonstrate that the product distribution, and convergence toward product formation, is strongly dependent on this geometric attribute. Surprisingly, we discovered that precursors with the ideal bite angle (60°) do not afford the most efficient pathway to the product. The systematic study reported here illustrates how seemingly minor adjustments in precursor geometry greatly affect the outcome of DCC systems. This research illustrates the importance of fine-tuning precursor geometric parameters in order to successfully realize desirable targets.

Impact of Shape Persistence on the Porosity of Molecular Cages.

Porous materials provide a plethora of technologically important applications that encompass molecular separations, catalysis, and adsorption. The majority of research in this field involves network solids constructed from multitopic constituents that, when assembled either covalently or ionically, afford macromolecular arrangements with micro- or meso-porous apertures. Recently, porous solids fabricated from discrete organic cages have garnered much interest due to their ease of handling and solution processability. Although this class of materials is a promising alternative to network solids, fundamental studies are still required to elucidate critical structure-function relationships that govern microporosity. Here, we report a systematic investigation of the effects of building block shape-persistence on the porosity of molecular cages. Alkyne metathesis and edge-specific postsynthetic modifications afforded three organic cages with alkynyl, alkenyl, and alkyl edges, respectively. Nitrogen adsorption experiments conducted on rapidly crystallized and slowly crystallized solids illustrated a general trend in porosity: alkynyl > alkenyl > alkyl. To understand the molecular-scale origin of this trend, we investigated the short and long time scale molecular motions of the molecular cages using ab initio molecular dynamics (AIMD) and classical molecular dynamics (MD) simulations. Our combined experimental and computational results demonstrate that the microporosity of molecular cages directly correlates with shape persistence. These findings discern fundamental molecular requirements for rationally designing porous molecular solids.

Kinetically Trapped Tetrahedral Cages via Alkyne Metathesis.

In dynamic covalent synthesis, kinetic traps are perceived as disadvantageous, hindering the system from reaching its thermodynamic equilibrium. Here we present the near-quantitative preparation of tetrahedral cages from simple tritopic precursors using alkyne metathesis. While the cages are the presumed thermodynamic sink, we experimentally demonstrate that the products no longer exchange their vertices once they have formed. The example reported here illustrates that kinetically trapped products may facilitate high yields of complex products from dynamic covalent synthesis.