Important Elements of Spin-Exciton and Magnon-Exciton Coupling.

The recent discovery of spin-exciton and magnon-exciton coupling in a layered antiferromagnetic semiconductor, CrSBr, is both fundamentally intriguing and technologically significant. This discovery unveils a unique capability to optically access and manipulate spin information using excitons, opening doors to applications in quantum interconnects, quantum photonics, and opto-spintronics. Despite their remarkable potential, materials exhibiting spin-exciton and magnon-exciton coupling remain limited.

Imaging nanomagnetism and magnetic phase transitions in atomically thin CrSBr.

Since their first observation in 2017, atomically thin van der Waals (vdW) magnets have attracted significant fundamental, and application-driven attention. However, their low ordering temperatures, T, sensitivity to atmospheric conditions and difficulties in preparing clean large-area samples still present major limitations to further progress, especially amongst van der Waals magnetic semiconductors. The remarkably stable, high-T vdW magnet CrSBr has the potential to overcome these key shortcomings, but its nanoscale properties and rich magnetic phase diagram remain poorly understood.

CrSBr: An Air-Stable, Two-Dimensional Magnetic Semiconductor.

The discovery of magnetic order at the 2D limit has sparked new exploration of van der Waals magnets for potential use in spintronics, magnonics, and quantum information applications. However, many of these materials feature low magnetic ordering temperatures and poor air stability, limiting their fabrication into practical devices. In this Mini-Review, we present a promising material for fundamental studies and functional use: CrSBr, an air-stable, two-dimensional magnetic semiconductor.

Two-dimensional heavy fermions in the van der Waals metal CeSiI.

Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases, which remains a significant challenge because traditional intermetallic heavy-fermion compounds have three-dimensional atomic and electronic structures. Here we report comprehensive thermodynamic and spectroscopic evidence of an antiferromagnetically ordered heavy-fermion ground state in CeSiI, an intermetallic comprising two-dimensional (2D) metallic sheets held together by weak interlayer van der Waals (vdW) interactions.

Exciton-coupled coherent magnons in a 2D semiconductor.

The recent discoveries of two-dimensional (2D) magnets and their stacking into van der Waals structures have expanded the horizon of 2D phenomena. One exciting application is to exploit coherent magnons as energy-efficient information carriers in spintronics and magnonics or as interconnects in hybrid quantum systems. A particular opportunity arises when a 2D magnet is also a semiconductor, as reported recently for CrSBr (refs.

Spin Waves and Magnetic Exchange Hamiltonian in CrSBr.

CrSBr is an air-stable two-dimensional (2D) van der Waals semiconducting magnet with great technological promise, but its atomic-scale magnetic interactions-crucial information for high-frequency switching-are poorly understood. An experimental study is presented to determine the CrSBr magnetic exchange Hamiltonian and bulk magnon spectrum. The A-type antiferromagnetic order using single crystal neutron diffraction is confirmed here.

Coupling between magnetic order and charge transport in a two-dimensional magnetic semiconductor.

Semiconductors, featuring tunable electrical transport, and magnets, featuring tunable spin configurations, form the basis of many information technologies. A long-standing challenge has been to realize materials that integrate and connect these two distinct properties. Two-dimensional (2D) materials offer a platform to realize this concept, but known 2D magnetic semiconductors are electrically insulating in their magnetic phase.

Exchange Bias in a Layered Metal-Organic Topological Spin Glass.

The discovery of conductive and magnetic two-dimensional (2D) materials is critical for the development of next generation spintronics devices. Coordination chemistry in particular represents a highly versatile, though underutilized, route toward the synthesis of such materials with designer lattices. Here, we report the synthesis of a conductive, layered 2D metal-organic kagome lattice, Mn(CS), using mild solution-phase chemistry.

Cu[Ni(2,3-pyrazinedithiolate)] Metal-Organic Framework for Electrocatalytic Hydrogen Evolution.

The application of metal-organic frameworks (MOFs) as electrocatalysts for small molecule activation has been an emerging topic of research. Previous studies have suggested that two-dimensional (2D) dithiolene-based MOFs are among the most active for the hydrogen evolution reaction (HER). Here, a three-dimensional (3D) dithiolene-based MOF, Cu[Ni(2,3-pyrazinedithiolate)] (), is evaluated as an electrocatalyst for the HER.

Crystallographic characterization of the metal-organic framework Fe(bdp) upon reductive cation insertion.

Precisely locating extra-framework cations in anionic metal-organic framework compounds remains a long-standing, yet crucial, challenge for elucidating structure-performance relationships in functional materials. Single-crystal X-ray diffraction is one of the most powerful approaches for this task, but single crystals of frameworks often degrade when subjected to post-synthetic metalation or reduction. Here, we demonstrate the growth of sizable single crystals of the robust metal-organic framework Fe(bdp) (bdp = benzene-1,4-dipyrazolate) and employ single-crystal-to-single-crystal chemical reductions to access the solvated framework materials AFe(bdp)·THF (A = Li, Na, K).

Magnetic ordering through itinerant ferromagnetism in a metal-organic framework.

Materials that combine magnetic order with other desirable physical attributes could find transformative applications in spintronics, quantum sensing, low-density magnets and gas separations. Among potential multifunctional magnetic materials, metal-organic frameworks, in particular, bear structures that offer intrinsic porosity, vast chemical and structural programmability, and the tunability of electronic properties. Nevertheless, magnetic order within metal-organic frameworks has generally been limited to low temperatures, owing largely to challenges in creating a strong magnetic exchange.

Two-dimensional, conductive niobium and molybdenum metal-organic frameworks.

The incorporation of second-row transition metals into metal-organic frameworks could greatly improve the performance of these materials across a wide variety of applications due to the enhanced covalency, redox activity, and spin-orbit coupling of late-row metals relative to their first-row analogues. Thus far, however, the synthesis of such materials has been limited to a small number of metals and structural motifs. Here, we report the syntheses of the two-dimensional metal-organic framework materials (HNMe)Nb(Cldhbq) and Mo(Cldhbq) (HCldhbq = 3,6-dichloro-2,5-dihydroxybenzoquinone), which feature mononuclear niobium or molybdenum metal nodes and are formed through reactions driven by metal-to-ligand electron transfer.

Selective, High-Temperature O Adsorption in Chemically Reduced, Redox-Active Iron-Pyrazolate Metal-Organic Frameworks.

Developing O-selective adsorbents that can produce high-purity oxygen from air remains a significant challenge. Here, we show that chemically reduced metal-organic framework materials of the type AFe(bdp) (A = Na, K; bdp = 1,4-benzenedipyrazolate; 0 < ≤ 2), which feature coordinatively saturated iron centers, are capable of strong and selective adsorption of O over N at ambient (25 °C) or even elevated (200 °C) temperature. A combination of gas adsorption analysis, single-crystal X-ray diffraction, magnetic susceptibility measurements, and a range of spectroscopic methods, including Na solid-state NMR, Mössbauer, and X-ray photoelectron spectroscopies, are employed as probes of O uptake.

Metal-Diamidobenzoquinone Frameworks via Post-Synthetic Linker Exchange.

Metal-organic frameworks with amidic linkers often exhibit exceptional physical properties, but, owing to their strong metal-nitrogen bonds, are exceedingly challenging to isolate through direct synthesis. Here, we report a route to access metal-diamidobenzoquinone frameworks from their dihydroxobenzoquinone counterparts via postsynthetic linker exchange. The parent compounds (MeNH)[ML] (M = Zn, Mn; HL = 2,5-dichloro-3,6-dihydroxo-1,4-benzoquinone) undergo linker exchange upon exposure to a solution of monodeprotonated 2,5-diamino-3,6-dibromo-1,4-benzoquinone or 2,5-diamino-3,6-dichloro-1,4-benzoquinone, proceeding through single-crystal-to-single-crystal reactions.

A Single-Ion Conducting Borate Network Polymer as a Viable Quasi-Solid Electrolyte for Lithium Metal Batteries.

Lithium-ion batteries have remained a state-of-the-art electrochemical energy storage technology for decades now, but their energy densities are limited by electrode materials and conventional liquid electrolytes can pose significant safety concerns. Lithium metal batteries featuring Li metal anodes, solid polymer electrolytes, and high-voltage cathodes represent promising candidates for next-generation devices exhibiting improved power and safety, but such solid polymer electrolytes generally do not exhibit the required excellent electrochemical properties and thermal stability in tandem. Here, an interpenetrating network polymer with weakly coordinating anion nodes that functions as a high-performing single-ion conducting electrolyte in the presence of minimal plasticizer, with a wide electrochemical stability window, a high room-temperature conductivity of 1.

Effects of Covalency on Anionic Redox Chemistry in Semiquinoid-Based Metal-Organic Frameworks.

Two iron-semiquinoid framework materials, (HNMe)Fe(Cl dhbq) () and (HNMe)Fe(Cl dhbq)(SO) (Cl dhbq = deprotonated 2,5-dichloro-3,6-dihydroxybenzoquinone) (), are shown to possess electrochemical capacities of up to 195 mAh/g. Employing a variety of spectroscopic methods, we demonstrate that these exceptional capacities arise from a combination of metal- and ligand-centered redox processes, a result supported by electronic structure calculations. Importantly, similar capacities are not observed in isostructural frameworks containing redox-inactive metal ions, highlighting the importance of energy alignment between metal and ligand orbitals to achieve high capacities at high potentials in these materials.

Control of Electronic Structure and Conductivity in Two-Dimensional Metal-Semiquinoid Frameworks of Titanium, Vanadium, and Chromium.

The isostructural, two-dimensional metal-organic frameworks (HNMe)M(Cldhbq) (M = Ti, V; Cldhbq = deprotonated 2,5-dichloro-3,6-dihydroxybenzoquinone) and (HNMe)Cr(dhbq) (dhbq = deprotonated 2,5-dihydroxybenzoquinone) are synthesized and investigated by spectroscopic, magnetic, and electrochemical methods. The three frameworks exhibit substantial differences in their electronic structures, and the bulk electronic conductivities of these phases correlate with the extent of delocalization observed via UV-vis-NIR and IR spectroscopies. Notably, substantial metal-ligand covalency in the vanadium phase results in the quenching of ligand-based spins, the observation of simultaneous metal- and ligand-based redox processes, and a high electronic conductivity of 0.