A Preinstalled Protic Cation as a Switch for Superprotonic Conduction in a Metal–Organic Framework

Metal–organic frameworks (MOFs), made from various metal nodes and organic linkers, provide diverse research platforms for proton conduction. Here, we report on the superprotonic conduction of a Pt dimer based MOF, [Pt₂(MPC)₄Cl₂Co(DMA)(HDMA)·guest] (H₂MPC, 6-mercaptopyridine-3-carboxylic acid; DMA, dimethylamine). In this framework, a protic dimethylammonium cation (HDMA⁺) is trapped inside a pore through hydrogen bonding with an MPC ligand. Proton conductivity and X-ray measurements revealed that trapped HDMA⁺ works as a preinstalled switch, where HDMA⁺ changes its relative position and forms an effective proton-conducting pathway upon hydration, resulting in more than 105 times higher proton conductivity in comparison to that of the dehydrated form. Moreover, the anisotropy of single-crystal proton conductivity reveals the proton-conducting direction within the crystal. The present results offer insights into functional materials having a strong coupling of molecular dynamic motion and transport properties

Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site

Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been fabricated by the pulsed laser deposition of LixIr2O4 precursor and the subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a spinel (AB2O4) without A cations in the tetrahedral site, which is isostructural to lambda-MnO2. Ir ions form a pyrochlore sublattice, which is known to give rise to a strong geometrical frustration. This Ir spinel was found to be a narrow gap insulator, in remarkable contrast to the metallic ground state of rutile-type IrO2. We argue that an interplay of strong spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground state as in a layered perovskite Sr2IrO4.Comment: 9 pages, 3 figure

Guest‐selective gate‐opening by pore engineering of two‐dimensional Kagomè lattice porous coordination polymers

Porous coordination polymers (PCPs) with pore decoration have been used as materials for excellent storage and separation functions. The cooperative properties of flexible PCPs can be utilized to achieve the separation of mixtures of gaseous molecules having highly similar properties. The key to efficient molecular recognition and separation lies in increasing the degrees of freedom of the structure without sacrificing the stability of the system. However, the mechanism study of such behavior is still scarce in the literature. Here, we focused on PCPs with two-dimensional Kagomè lattice structures and functionalized the pores with various alkoxy pendant groups; this facilitated systematic tuning of the pore aperture size, the interlayer spacing, as well as the interactions between the host and adsorbed molecules. The combination of characterization techniques allowed us to observe a unique deformation of the lattice upon gas sorption, allowing the separation of gas molecules with similar physicochemical properties, such as propane and propylene

Real-Space Observation of Ligand Hole State in Cubic Perovskite SrFeO3_3

An anomalously high valence state sometimes shows up in transition-metal oxide compounds. In such systems, holes tend to occupy mainly the ligand $p$ orbitals, giving rise to interesting physical properties such as superconductivity in cuprates and rich magnetic phases in ferrates. However, no one has ever observed the distribution of ligand holes in real space. Here, we report a successful observation of the spatial distribution of valence electrons in cubic perovskite SrFeO$_3$ by high-energy X-ray diffraction experiments and precise electron density analysis using a core differential Fourier synthesis method. A real-space picture of ligand holes formed by the orbital hybridization of Fe 3$d$ and O 2$p$ is revealed. The anomalous valence state in Fe is attributed to the considerable contribution of the ligand hole, which is related to the metallic nature and the absence of Jahn-Teller distortions in this system.Comment: 14 pages, 4 figure

Structural‐Deformation‐Energy‐Modulation Strategy in a Soft Porous Coordination Polymer with an Interpenetrated Framework

German version: https://doi.org/10.1002/ange.202003186To achieve unique molecular‐recognition patterns, a rational control of the flexibility of porous coordination polymers (PCPs) is highly sought, but it remains elusive. From a thermodynamic perspective, the competitive relationship between the structural deformation energy (Edef) of soft PCPs and the guest interaction is key for selective a guest‐triggered structural‐transformation behavior. Therefore, it is vital to investigate and control Edef to regulate this competition for flexibility control. Driven by these theoretical insights, we demonstrate an Edef‐modulation strategy via encoding inter‐framework hydrogen bonds into a soft PCP with an interpenetrated structure. As a proof of this concept, the enhanced Edef of PCP enables a selective gate‐opening behavior toward CHCl₃ over CH₂Cl₂ by changing the adsorption‐energy landscape of the compounds. This study provides a new direction for the design of functional soft porous materials