Incorporating 4d and 5d metal ions into coordination frameworks offers a powerful route to quantum materials where orbital delocalization and spin-orbit coupling reshape magnetic and electronic ground states. However, such systems remain difficult to access synthetically. Here we report Mo(pyz)2I2, the first pyrazine-bridged square-lattice framework featuring a paramagnetic 4d metal center, obtained using a new organometallic precursor route that enables Mo incorporation. Structural and spectroscopic data establish a MoIII({pyz2}•-)I2 formulation and reveal pronounced ligand redox non-innocence accompanied by local symmetry breaking arising from a disordered distribution of neutral and reduced pyrazine linkers─the first experimental observation of local symmetry lowering in a pyrazine-based coordination solid. Magnetic measurements show strong antiferromagnetic interactions without clear evidence of long-range order, and electrical transport indicates narrow-gap semiconducting behavior. Extending pyrazine framework chemistry to the 4d block thus requires new synthetic strategies and reveals new local structural and magnetic degrees of freedom, positioning Mo(pyz)2I2 as a prototype for designing correlated and spin-orbit-entangled states in molecule-based quantum materials based on heavier transition metals.

Accessing high-spin configurations of transition metal phosphides defines a dividing line that prevents common properties of solid-state materials from being replicated within multiple-bonded molecular analogs. Here, we report the synthesis of a VIII phosphaethynolate complex, [(pyrNdipp)2V(PCO)] (2) in a halide metathesis with Na(OCP). Exposure of 2 to Lewis-basic ligands induces a one-electron reductive elimination of the PCO- moiety, generating VII complexes [(pyrNdipp)2V(L)2] (L = THF, DMAP; 3THF, 3DMAP). When 2 is instead photolyzed, a cascade of reduction, decarbonylation, and multiple-bond formation steps affords a high-spin and mixed-valent vanadium phosphide, [(pyrNdipp)2V═P═V(pyrNdipp)2] (4) comprising formal [V2III, IV] nodes. Structural characterization coupled with vibrational, UV-visible, and X-ray spectroscopic studies reveals an S4 symmetrical [V═P═V] centered architecture conforming to a fully delocalized, mixed-valency description. Theoretical studies demonstrate that 4 evades spin-pairing by leveraging the weak ligand-field splitting at the vanadium nodes, leading to a high-spin, ST = 3/2 ground state of this multiple-bonded, weakly Jahn-Teller distorted system.

Uranium dihydride UH2 is a metastable phase unknown in bulk form but accessible through thin-film synthesis. We prepared UH2 films by reactive dc sputtering on CaF2 (001) or Si(001) substrates, the latter equipped with a Mo buffer layer to suppress a U-Si interdiffusion. On CaF2, UH2 adopts the fluorite-type structure with a near[1 11] out-of-plane texture, four rotational domains, and a lattice parameter a = 539 +/- 3 pm without measurable strain, whereas the Mo-buffered film is polycrystalline. X-ray photoelectron spectroscopy confirmed complete hydrogenation and minimal oxidation. Magnetization and XMCD measurements show ferromagnetic ordering with Curie temperatures of 120-130 K and a uranium 5f moment of approximate to 0.9 mu B/U, dominated by the orbital contribution (mu L approximate to 1.4 mu B, mu S approximate to -0.5 mu B), in a good agreement with GGA + U computations, which otherwise overestimate absolute values of the spin and orbital components. The slightly reduced moment in thinner CaF2-supported films is attributed to surface U(IV) species. These results demonstrate that thin-film synthesis enables stabilization of UH2 and direct probing of 5f magnetism, opening pathways toward higher uranium hydrides and interface-engineered actinide systems.

Interfacial charge transfer (ICT) provides a powerful route to engineer electronic phases in correlated oxide heterostructures, yet predictive design principles remain elusive. Here, we systematically investigate superlattices composed of the 5d spin-orbit coupled semimetal SrIrO3 and a series of correlated 3d perovskites (LaMnO3, LaFeO3, LaCoO3, and NdNiO3), thereby establishing a quantitative framework for ICT across 3d/5d interfaces. Combining element-specific x-ray absorption spectroscopy with spatially resolved electron energy loss spectroscopy, a homogeneous electron transfer from the 5d to the 3d layers is directly quantified, reaching up to 0.35 e per unit cell in the cobaltate superlattice. We show that the magnitude of ICT scales linearly with the difference in electronegativity between the transition-metal oxide layers, identifying electronegativity-driven band alignment as the dominant mechanism for ICT. Beyond interfacial doping, we find that strong 3d-5d hybridization induces a complete low-spin to high-spin conversion in the cobaltate layers, demonstrating interface-controlled spin-state engineering without chemical substitution. These results establish electronegativity mismatch as a predictive design parameter for correlated oxide interfaces and provide a materials platform for tailoring band filling, orbital hierarchy, and spin configurations in quantum oxide heterostructures, paving the way towards advanced oxide electronics and next-generation information technologies.

Chromium thiophosphate (CrPS4) is a long-known material: a layered semiconducting antiferromagnet. Its recently discovered gate-tunable metamagnetic phase transitions, the remarkable positive and oscillating magnetoresistance as a tunnel barrier, and its Fano-resonance luminescence, elusive among the multitude of Cr3+ compounds, call for revisiting the understanding of its electronic structure, especially regarding how it relates to magnetic order. Here, we employ X-ray magnetic circular dichroism, implemented in both absorption and resonant inelastic X-ray spectroscopies, together with quantum many-body calculations, to unveil the role of metal-ligand covalency in mediating the metamagnetic transitions in CrPS4, using crystal-field and charge-transfer excitations as fingerprints of the evolving magnetic order. We reveal the role of extended superexchange paths involving P and S atoms, coupling interactions between the Cr spins across the different magnetic phases: antiferromagnetic, canted, and ferromagnetic. Our results elucidate the electronic states involved in these phases and provide prescriptions for engineering the metamagnetic phase diagram of CrPS4.

Molecular frameworks with ReO3- or perovskite-related topologies have been widely investigated for their structural versatility, yet examples displaying strong electronic and magnetic correlations have not been realized in such systems. Here we report the synthesis of Cr(pyrazine)3, a three-dimensional molecular framework adopting a cubic ReO3-type structure, in which Cr3+ ions are bridged exclusively by pyrazine radical anions. In Cr(pyrazine)3, antiferromagnetic coupling between the Cr3+ and radical sublattices, comparable in magnitude to that found in transition-metal oxides, leads to a nearly perfectly compensated ferrimagnetic ground state with an exceptionally small net magnetic moment. Owing to the symmetry and stoichiometry of the bipartite lattice, magnetic compensation persists over an extended temperature range rather than occurring only at a specific compensation temperature. Long-range magnetic order is observed well above room temperature, placing Cr(pyrazine)3 among the very few materials featuring robust compensated ferrimagnetism under ambient conditions.

Atomic layer epitaxy has been a powerful technique for several decades to grow epitaxial thin films of III-V and II-VI semiconducting compounds. However, the polycrystalline nature of thin films usually prevails for conducting and semiconducting binary oxides, which strongly limits their crystalline and structural quality. Here, we demonstrate the epitaxial growth of (002)-oriented kappa-Ga2O3 thin films with a subnm surface roughness on c-plane sapphire by atomic layer deposition at 350 degrees C and using the relatively unexplored combination of triethylgallium and O3 as chemical precursors. The 16 nm-thick kappa-Ga2O3 thin films exhibit an in-plane epitaxial relationship given by (060) kappa-Ga2O3||(300) alpha-Al2O3 and (200) kappa-Ga2O3||(110) alpha-Al2O3. The pure epitaxial kappa-Ga2O3 phase is further revealed using X-ray absorption near-edge structure and X-ray linear dichroism with synchrotron radiation along with transmission electron microscopy. In particular, the (004) X-ray diffraction peak for the kappa-Ga2O3 thin film grown at 350 degrees C is shown to have a remarkable full-width-at-half-maximum value of 0.1 degrees following rocking curve measurements, which is comparable to the typical lowest values reported for kappa-Ga2O3 thick films grown by more sophisticated epitaxial chemical and physical vapor deposition techniques. The optical bandgap energy is eventually evaluated at 4.8 eV from optical transmittance spectra. These findings show the high potential of atomic layer deposition for growing epitaxial Ga2O3 thin films at relatively low temperatures in the framework of atomic layer epitaxy, strongly challenging the well-known epitaxial physical and chemical deposition techniques.

We report the first structurally characterised coordination solids based on decamethylytterbocene, using bipyridine linkers to form YbCp*2(bipy) and YbCp*2(Me2bipy). Analogous to their mononuclear cousins known for intermediate valence, spectroscopic evidence suggests that YbCp*2(bipy) features a multiconfigurational ground state, composed of a superposition of an open-shell ligand non-innocent 4f13(π*)1 state and a closed- shell 4f14 state. Our findings mark a first step toward increasing electronic correlations in lanthanide-organic frameworks, with the aim of realising materials with coexisting electronic transport and emergent magnetic properties.

The solution self-assembly of trans-{EuI2} nodes and ditopic pyrazine or 4,4'-bipyridine leads to isoreticular 2D frameworks featuring the rare elongated triangular Archimedean tessellation pattern. The topology and the presence of intra-layer Eu(II)-Eu(II) antiferromagnetic interactions provide the prerequisites for geometrical spin frustration, which, due to the spin ground state degeneracy, is key for exotic magnetic phenomena such as enhanced magnetic refrigeration.

A single-step synthetic method to produce single crystals of the barlowite structural family is disclosed with iodobarlowite as a focus. The kagome lattice of iodobarlowite, Cu4(OH)6FI, is furnished by removal of 1/4 of the triangular lattice sites of iodobotallackite, Cu2(OH)3I. Single-crystal structures have been solved at 100 and 300 K, both of which show I- vacancies within the lattice with no attendant Cu vacancies. X-ray absorption spectroscopy and diffraction studies reveal only the presence of Cu(II), no F- substitution at the I- site, and no Cu vacancies, suggesting that the charge balance to accommodate the I- deficiency occurs through loss of protons from the bridging hydroxide ligands during hydrothermal synthesis. Unlike microcrystalline powders, single-crystalline Cu4(OH)6FI exhibits a single magnetic transition at 15 K, which contrasts with the large Weiss constant of theta = -163(5) K, highlighting the key role of geometric spin frustration in the kagome lattice to lower the critical temperature of the magnetically ordered state. Temperature-dependent susceptibility measurements indicate that the low temperature magnetic phase is associated with an uncompensated antiferromagnetic ordered state arising from the competing interactions between the four S = 1/2 Cu(II) spins of the iodobarlowite lattice.

Valence tautomerism in molecule-based f-block materials remains virtually elusive. As a result, the effects driving and controlling the valence conversion phenomenon are poorly understood. Herein, we unravel these fundamental factors by systematic chemical modification of a bona fide lanthanide coordination solid, SmI2(pyrazine)2(tetrahydrofuran), in which a complete, temperature-driven conversion between Sm(ii) and Sm(iii) occurs abruptly around 200 K. Solid solutions incorporating either divalent, diamagnetic metal ions or Sm(iii) ions feature disparate behavior. Substitution with redox-inactive, divalent metal ions invariably leads to lower conversion temperatures and reduced cooperativity. In contrast, incorporation of redox-inactive Sm(iii) ions leads to trapped pyrazine anion radicals in the ligand scaffold, shifting the valence tautomeric conversion phenomenon towards higher temperature with virtually no loss of cooperativity. These materials are rare examples of lanthanide-organic materials hosting mixed valency in both the lanthanide and organic scaffold, affording switchable conductivity associated with the valence tautomeric conversion.

While natural optical activity in crystals belonging to specific achiral point groups has been predicted by symmetry arguments, birefringence hampers its measurement in the UV-vis energy ranges. Here we use X-rays to reveal natural circular dichroism at the K-edges of copper and iron coordination salts crystallizing in the achiral point groups 4̅2m and 4̅ respectively. The experimental signals follow the angular dependence exactly as predicted by the symmetry of the point groups. In addition, an angular phase shift was observed for 4̅, which is explained by the crystalline a and b axes not being determined by the crystal point group but by the translation operations of the space group.

Bespoke van der Waals (vdW) crystals provide command over the confinement and transport of charge, spin, and heat within and between two-dimensional (2D) layers. We report a novel functionality in vdW crystals by actuating valence changes through molecular alloying. The net materials Cr(pyrazine)2Br2 and Cr(pyrazine)2I2 are aliovalent, hosting Cr(III) and Cr(II), respectively, due to disparate crystal field potentials. Pressurizing and thereby strengthening of the crystal field compresses the Cr(pyrazine)2I2 layers significantly, but no Cr valence change is induced. However, alloyed Cr(pyrazine)2I2_xBrx phases exhibit hysteretic and tunable Cr (II) -><- Cr(III) interconversions with concomitant charge injection into the net. The valence switch manifests drastic changes to the magnetization and the electrical conductivity, which varies by up to five orders of magnitude during the valence conversion. This use of coordination chemistry addresses a gap in vdW and 2D materials science, where electronic structure engineering via valence change events has remained elusive.

We measured x-ray linear dichroism (XLD) at the preedge of the x-ray absorption near-edge structure (XANES) of Ti and of one halogen (Cl) entering into the composition of some Ti-based MXene compounds. Density functional theory allowed us to retrieve the experimental spectra with a satisfying degree of accuracy and was used for deciphering the orbital and electronic anisotropies responsible for the XLD signal. XLD, measured at the K edge of the transition metal, depends on the nature of the MXene surface termination. XLD, measured at the K edge of the halogen termination, depends on the structure of the van der Waals (vdW) stacking between two adjacent MXene layers, so that it could be used as a signature of a given vdW stacking.

Magnetic cooling has the potential to replace conventional gas compression refrigeration. Materials such as La(Fe,Si)$_{13}$ exhibit a sizeable first-order magnetocaloric effect, and it is possible to tailor the phase transition towards room temperature by Mn-H-doping, resulting in a large temperature range for operation. Within this work, we discuss variations of the electronic and lattice structure in La(Fe,Si)$_{13}$ with increasing Mn content utilizing X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure spectroscopy (EXAFS). While XMCD shows a decrease of the magnetic polarization at the Fe K edge, low-temperature EXAFS measurements indicate increased positional disorder in the La environment that is otherwise absent for Fe and Mn. First-principles calculations link the positional disorder to an enlarged Mn-Si distance -- explaining the increased positional disorder in the La surrounding.

We present a novel instrument designed for advanced magnetic study, installed at the ID12 beamline of the European Synchrotron Radiation Facility in Grenoble, France. This instrument offers the unique capability to simultaneously measure element-specific microscopic and macroscopic properties related to the magnetic, electronic and structural characteristics of materials. In addition to X-ray absorption, X-ray magnetic circular dichroism alongside X-ray diffraction patterns, the macroscopic magnetization, volume changes, caloric properties and electrical resistivity of magnetic materials could be measured strictly under the same experimental conditions as a function of both magnetic field (up to ±7 T) and temperature (ranging from 2.05 K to 325 K). To demonstrate the capability of this new instrument, we present two case studies highlighting its performance in investigating first-order magneto-structural phase transitions, namely in DyCo2 and FeRh alloys.

Magnetic materials with complex spin textures present both fundamental and practical appeal. The complex patterns of magnetic moments emerging on underlying crystal lattices hold potential for robust information storage and processing, including the promise of topological quantum computing. The scope of materials that host such patterns, however, remains rather limited. Here we report a discovery of a complex spin texture in a noncentrosymmetric material that emerges from the structural frustration at the boundary between centrosymmetric parent structures MnCoGe (the hexagonal Ni2In or the orthorhombic TiNiSi structure type) and MnCoAs (the TiNiSi structure type). Our findings demonstrate that such structural frustration provides a powerful handle for identifying compositional spaces where complex magnetic behavior and associated nontrivial magnetic structures are likely to emerge. Thus, the new phase MnCoGe1/3As2/3 exhibits a modulated cycloidal antiferromagnetic arrangement of electron spins on a noncentrosymmetric lattice (of the hexagonal ZrNiAl type) that materializes in the space between centrosymmetric collinear ferromagnets. This work provides a pathway for discovering novel materials with exotic spin textures for next-generation spintronics and quantum technologies.

Molecule-based magnets hold promise for a variety of applications in information technologies owing to their chemical tunability. This feature can facilitate the integration of desired magnetic properties alongside additional functionalities within a single material. Although numerous cyanido-bridged assemblies are identified as multifunctional materials at cryogenic temperatures, achieving analogous behavior at room temperature remains a challenge. This study reports a cyanido-bridged compound, which shows ferrimagnetic ordering with a critical temperature exceeding 400 K. This breakthrough is achieved through the mechanochemical synthesis of vanadium(II)-hexacyanomolybdate(III) Prussian Blue Analog (PBA) under anhydrous conditions. The ferrimagnetic order is evidenced by SQUID (SQUID = superconducting quantum interference device) magnetometry and X-ray Magnetic Circular Dichroism (XMCD) spectroscopy. Both techniques unambiguously confirm the antiparallel alignment of vanadium and molybdenum magnetic moments. As a result, hexacyanomolybdate(III) is experimentally established as a viable precursor for the preparation of a new generation of high-temperature molecule-based magnets and multifunctional materials.

The interstellar diatomic molecule, phosphorus mononitride (P≡N), is highly unstable under conditions typical on Earth, and its utility for constructing elusive P-N π-bonded motifs has remained uncertain. Here, we show how Na(OCP) transfers a P atom to an electrophilic osmium nitride complex to form a metal-bound P≡N ligand. Quantum chemical calculations and X-ray absorption spectroscopy unveil a cumulenic [OsIV=N=P] electronic structure comprising orthogonal Os=N and N=P π-bonding. On reaction with elemental sulfur, the highly reduced P≡N ligand, formally [PN]2-, forms a trigonal planar [NPS2]2- motif. Chlorination instead transforms the P≡N ligand to a bent [NPCl]- group coordinated to OsIII (S = ½). [3 + 2] cycloaddition of this radical with azide forms an aromatic interpnictide, [PN4]-, that is inaccessible from the parent P≡N system. These findings provide a rare glimpse of the divergent reactivity of the alien P≡N molecule, paving the way to long-sought P-N multiple-bonded archetypes.

Manipulating the physical properties of solid matter using only photons is a major challenge in materials science. In this study, we present the photochemistry occurring in a single crystal of a simple cyanide complex, K4[MoIII(CN)7]·2H2O. Upon exposure to visible light at different wavelengths, a reversible breaking and reformation of dative bonds is triggered, resulting in a photoswitching of the MoIII coordination geometry between 6- and 7-coordinate. This transformation, in turn, induces a spin state change. The observed solid-state photochemical reactivity is robust, quantitative and occurs at a record-high temperature. It paves the way for the development of new photo-switchable high-temperature magnets and nanomagnets.