A set of environmentally responsive metal-organic [3]rotaxanes is described. These mechanically interlocked macromolecules may be prepared in quantitative yield via a one-pot procedure involving treatment of a flexible tetracationic macrocycle, known as the Texas-sized molecular box, with tri-1,3,5-benzenetricarboxylate anion and silver cations (Ag(+)). The use of this three-component mixture gives rise to a metal-organic [3]rotaxane via a self-assembly process that occurs under ambient conditions in DMSO-d6 solution. The complex is stable in the presence of excess TFA. However, disassembly of the [3]rotaxane to produce anion-box associated entities may be triggered by adding a competitive counteranionic species (e.g., I(-)). Adding excess Ag(+) serves to reverse this decomplexation process. The nature of the [3]rotaxane complex could be fine-tuned via application of an external stimulus. Increasing the temperature or adding small molecules (e.g., D2O, methanol-d4, acetonitrile-d3, DMF-d7, acetone-d6, or THF-d8) to the initial DMSO-d6 solution induces conformational flipping of the macrocycle within the overall complex (e.g., from limiting chair to chairlike forms). Support for the molecular stimuli responsive nature of the various structures came from solution-phase one- and two-dimensional ((1)H, 1D and 2D NOESY) NMR spectroscopic studies carried out in DMSO-d6. The core metal-linked rotaxane unit was characterized via single-crystal X-ray diffraction analysis. Initial evidence that the present self-assembly process is not limited to the use of the Ag(+) cation came from studies involving Cd(2+); this replacement results in formation of 2D metal-organic rotaxane-containing frameworks (MORFs).

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Li-rich layered materials that have Co-free and Mnrich 3d-transition metals have the potential to increase the achievable energy density of batteries because they are inexpensive and yield high capacity by exploiting an additional oxygen redox reaction. However, these have low electrochemical activity and sustainability, with severe voltage fade, rapid capacity decay, and poor rate capability. Here, we report sustainable cycling stability and fast rate capability of Co-free Li2MnO3-based Li-rich layered materials that are governed by the electrochemical activation process during the 1st cycle and that this process can be controlled by the degree of the cation disordering in the pristine material. From the comparative study of two samples that have different degrees of cation disordering in the same composition, an increase in cation disordering in the pristine material strongly improves its tolerance to structural changes in the bulk and on the surface during the activation process at the 1st cycle, leading to less structural changes for subsequent cycles. As a result, high electrochemical activity and superior rate capability in subsequent cycles can be achieved even with the cation disordering in the pristine. Furthermore, we verified the findings by developing an additional material that had higher cation disordering in the pristine structure than the samples tested and showing that the additional sample has improved rate capability and cycle retention. This understanding that sustainable electrochemical characteristics are governed by an activation process in the 1st cycle, which can be controlled by a structural feature of the pristine material, will be useful in the design of low-cost, Li-rich layered materials that can achieve sustainable high energy density and fast rate capability for Li-ion batteries.

We use both molecular dynamics (MD) and continuum models to analyze the electric double layer structure and pressure acting on the wall of a symmetrically valenced ionic liquid in a nanoconfinement. The nanoslit width varies from 20 times ion size to an ion size, in which the Bazant, Storey, and Kornyshev model may not be compatible. However, the comparison with the MD model shows that the continuum model can successfully predict the averaged charge density and decay of the pressure. The continuum model also shows the exact location of the first and second layer of ions from the confinement wall when considering both steric and correlation effects. However, the continuum model does not account for the oscillatory behaviors of the ion density and the pressure due to the typical characteristics of ionic discreteness, and it slightly overestimates the counterion concentrations compared with the MD analysis. In conclusion, the continuum model can be used to estimate the overall tendency of the pressure acting on the wall when ionic liquid is confined in nanometer thickness, though the oscillatory behavior of the pressure, which originates from the discreteness of ions, cannot be predicted exactly. It can provide useful information in designing nanoporous structures for various electrochemical applications.

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