Carborane-Based Three-Dimensional Covalent Organic Frameworks

The predesignable porous structure and high structural flexibility of covalent organic frameworks (COFs) render this material desirable as a platform for addressing various cutting-edge issues. Precise control over their composition, topological structure, porosity, and stability to realize tailor-made functionality still remains a great challenge. In this work, we developed a new kind of three-dimensional (3D) carborane-based COF with a 7-fold interpenetrating dia topological diagram. The resulting COFs exhibited high crystallinity, exceptional porosity, and strong robustness. The slightly lower electronegativity of boron (2.04) than that of hydrogen (2.20) can lead to the polarization of the B–H bond into a Bδ+–Hδ− mode, which renders these COFs as high-performance materials for the adsorption and separation of hexane isomers through the B–Hδ−···Hδ+–C interaction. Significantly, the carborane content of obtained COFs reached up to 54.2 wt %, which gets the highest rank among all the reported porous materials. Combining high surface area, strong robustness, and high content of carborane, the obtained COFs can work as efficient adsorbents for the separation of the five hexane isomers with high separation factors. This work not only enhances the diversity of 3D functional COFs but also constitutes a further step toward the efficient separation of alkane isomers

Anisotropic Dzyaloshinskii–Moriya Interaction and Topological Magnetism in Two-Dimensional Magnets Protected by <i>P</i>4̅<i>m</i>2 Crystal Symmetry

As a fundamental magnetic parameter, Dzyaloshinskii–Moriya interaction (DMI), has gained a great deal of attention in the last two decades due to its critical role in formation of magnetic skyrmions. Recent discoveries of two-dimensional (2D) van der Waals (vdW) magnets has also gained a great deal of attention due to appealing physical properties, such as gate tunability, flexibility, and miniaturization. Intensive studies have shown that isotropic DMI stabilizes ferromagnetic (FM) topological spin textures in 2D magnets or their corresponding heterostructures. However, the investigation of anisotropic DMI and antiferromagnetic (AFM) topological spin configurations remains elusive. Here, we propose and demonstrate a family of 2D magnets with P4m2 symmetry-protected anisotropic DMI. More interestingly, various topological spin configurations, including FM/AFM antiskyrmion and AFM vortex–antivortex pair, emerge in this family. These results give a general method to design anisotropic DMI and pave the way toward topological magnetism in 2D materials using crystal symmetry

Ruderman–Kittel–Kasuya–Yosida-Type Interlayer Dzyaloshinskii–Moriya Interaction in Synthetic Magnets

Conduction electron spins interacting with magnetic impurity spins can mediate an interlayer exchange interaction, namely, the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction. This discovery opened the way to significant technological developments in the field of magnetic storage and spintronics. So far, the RKKY-type interlayer interaction has been found to construct symmetric coupling of magnetism; however, the asymmetric counterpart remains unexplored. Here we report unprecedented RKKY-type interlayer Dzyaloshinskii–Moriya interaction (DMI) in synthetic magnets, exhibiting a damped oscillatory feature. This asymmetric interlayer interaction is found to be dramatically dependent on the intermediate coupling layer. By introducing the Fert–Lévy model to the trilayer system, we reveal that the in-plane inversion symmetry breaking plays a pivotal role for generating interlayer DMI and the RKKY oscillation is an intrinsic behavior in metallic multilayers. Our finding fills up the empty block for RKKY-type asymmetric interlayer exchange coupling in comparison to the well-known (symmetric) RKKY-type interlayer exchange coupling