Chemistry of Materials最新文献

Stabilizingdesirable polymorphs of solid-state materials has beenat the forefront of materials research for decades. While severaltheories exist for targeting specific polymorphs of conventional solids,few strategies are available for metal–organic frameworks (MOFs),despite the superior performance of certain structures in gas sorption,luminescence, and other applications. Here, we report that particlesize dictates the phase selectivity of the MOF Cu(1,2,3-triazolate)₂ (Cu(TA)₂). Whereas micron-sized crystals stabilizein a tetragonal space group at room temperature, preparing particlessmaller than 200 nm furnishes a previously unreported structure withorthorhombic symmetry. A suite of variable-temperature and variable-pressurespectroscopy and X-ray diffraction analysis indicates that metal-linkerbonding becomes more flexible in smaller particles, even within agiven crystallographic phase. These results suggest smaller particlesadopt phases impossible in bulk crystals because their softer latticesaccommodate distorted geometries─an explanation that complementsongoing debates about the mechanism of phase stabilization in conventionalsolids. These results therefore provide potential design strategiesfor phase selectivity of MOFs and broader classes of materials ingeneral.

We study the ultrafast light-induced excited spin statetrapping(LIESST) process in a cyanide-bridged Fe–Cr spin-crossovermaterial CsFe^II[Cr^III(CN)₆]·1.3H₂O. This material consists of an original Fe^II–NC–Cr^III units, responsible for the thermal spin transition (ST)of the low ligand field Fe ST site from a low-spin (LS) Fe^II_LS to a high-spin (HS) Fe^II_HS states.Although electronic structures suggest that a metastable HS statecan be reached by photoexcitation, no LIESST to this HS state hasyet been observed using conventional techniques. In addition, partof the units exhibits a thermally driven cyanide flip toward the Fe^II_LS–CN–Cr^III sites, whereFe is always LS by the high ligand field. By combining optical andIR spectroscopic studies, we investigated whether light excitationis ineffective in inducing the LIESST or whether it causes the cyanideflip. Our results reveal that photoexcitation indeed generates theHS state, but its lifetime is limited to a few picoseconds by ultrafaststructural relaxation. Excitation at 800 nm predominantly triggersa Fe-centered d–d transition at the ST site, whereas excitationat 530 nm induces metal-to-metal charge transfer (MM’CT) atboth ST and flipped sites. For the ST site, both excitation pathwaysgenerate the HS state within less than 200 fs, which launches coherenttorsional motion of the cyanide-bridged network, and this HS statedecays to a LS state within 3.5 ps. In contrast, at the flipped site,530 nm excitation selectively populates a transient MM’CT Fe^III_LS–Cr^II*, which decays withoutinducing spin state switching nor cyanide flipping. Overall, the photoinducedHS state rapidly decays, due to the counteracting pressure of therigid cyanide-bridged lattice, preventing long-lived LIESST and cooperativeswitching.

The Nowotny chimney–ladder (NCL) phase in theFe–Gesystem near Fe₂Ge₃ composition is a promisingthermoelectric material owing to its characteristic coexistence ofdegenerate electronic transport and strongly suppressed lattice thermalconductivity, yet the structural and compositional origins of thisbehavior remain incompletely understood. Synchrotron diffraction showsthat samples prepared with nominal Fe₂Ge₃ compositioncrystallize as an incommensurately modulated NCL phase close to FeGe_1.52. From the superspace description, we derive and refinefor the first time a three-dimensional commensurate approximant, Fe₂₇Ge₄₁ (tP272). Chemical-bondinganalysis based on the model of Fe₂Ge₃ revealsa three-dimensional framework of heteroatomic multiatomic Fe–Geinteractions without homoatomic Fe–Fe or Ge–Ge bonds.DFT calculations for the Fe₂₇Ge₄₁ approximantshow that slight Ge excess in comparison with Fe₂Ge₃ shifts the Fermi level into the conduction band, yieldinga nominal carrier concentration of ∼10²¹ cm^–3, consistent with Hall measurements, and explainingthe degenerate n-type behavior without extrinsicdonors. The electronic structure is characterized by a high density-of-stateseffective mass (∼11 m_e), arisingfrom convergence of flat conduction bands near the Fermi level. Despitehigh elastic moduli and a moderate Grüneisen parameter, thelattice thermal conductivity is low (∼1.8 W m^–1 K^–1 at 300 K), corresponding to an estimated phononmean free path of approximately 8 Å. The failure of the Debye–Callawaymodel to reproduce this value indicates additional phonon scattering,which may be related to the incommensurate structure and bonding inhomogeneity.Overall, the incommensurate Fe–Ge NCL phase combines degenerateelectronic transport with phonon-glass-like thermal behavior.

Chemists rationalize and design magnetic materials throughstructure-propertyrelationships built on pairwise exchange couplings J, which energy-mapping methods now extract routinely from first principles.Yet whenever four magnetic centers close a loop, as in the CuO₂ planes of the cuprates or the square nets of infinite-layeroxides, a four-spin ring (cyclic) exchange J_ring can arise, reshaping magnetic ground states and corruptingthe very J values used for design. What has beenmissing is a practical way to obtain it: a direct, local extractionof the kind the four-state method provides for J.We supply it by generalizing that method to a 16-state (2⁴) scheme, and we automate the complete workflow in the openly available Mag4 package, a fully automatic implementation of the four-statefamily of methods: from a single cif file, Mag4 proposesthe supercell that isolates the couplings, generates the density functionaltheory (DFT) inputs in the exchange-correlation flavour of the user’schoice, extracts J and J_ring with the band-gap and local-moment diagnostics that certify them,and predicts the magnetic order, its propagation vector, and the criticaltemperature. Symmetry reduces the 16 configurations to six or eightinequivalent energies, so the cost is modest. The derivation alsoshows that the conventional four-state magnetic coupling, J, is itself ring-renormalized, by ∓2J_ringS² with the sign set bythe reference state. T-La₂CuO₄ confirms thisquantitatively: three concordant routes agree on J_ring to 0.2%, giving J_ring/J₁ = 0.25, and a four-state J₁ quoted without naming its reference is wrongby 12% in this material. The direct 16-state extraction itself provesreference-dependent, the Néel and ferromagnetic baths bracketingthe mapping value: a fourth-order fingerprint of interactions beyondthe pair-plus-ring model, which additional reference baths resolveinto a bare J_ring and a converging towerof six- and eight-spin loop couplings. SrFeO₂ (S = 2), with the same plaquette yet J_ring/J = 0.006, provides the negative control:a plaquette is necessary for ring exchange, far from sufficient: astructure-property criterion that chemists can screen against whensearching for materials hosting strong multi-spin magnetism.

Energetic molecular perovskites (EMPs) are a high-energysubclassof molecular perovskites that integrate oxidizers and fuels withina single framework. However, the structures of reported EMPs remainrather limited, and the structural contribution and governing roleof their component ions remain elusive. Herein, we develop an A-sitecation-templated strategy to direct the spatial orientation of N–H···Ohydrogen bonds, enabling the rational engineering of two Cs-basedEMPs with distinct 3D frameworks: trigonal DCP-1 and tetragonal TCP-1.The inductive effect of the A-site cation in framework constructionis elucidated. Unlike H₂hmta²⁺, H₂dabco²⁺ features a unique parallel N–H vector field,which drives the connection of [Cs(ClO₄)₆] octahedrathrough a rare alternating face-sharing and corner-sharing mode. Thisassembly results in the first EMP crystallizing in the R3̅c space group. Such structural divergence,governed by the spatial orientation of hydrogen bonds, leads to asignificant differentiation in physicochemical properties. This worknot only introduces cesium into EMPs for the first time but also expandsthe structural diversity of EMPs by introducing an unusual trigonalframework. The universal principle of tailoring crystal structuresand energetic properties by A-site hydrogen-bond vectors is revealed,providing insights into next-generation high-performance energeticmaterials.

Chalcogenide perovskiteshave emerged as promising lead-free materialsfor photovoltaic and thermoelectric applications. Among them, BaZrS₃ has attracted particular attention due to its thermal andchemical stability, favorable optoelectronic properties, and low thermalconductivity. Here, we combine molecular dynamics and Monte Carlosimulations based on a machine-learned interatomic potential withscanning transmission electron microscopy to investigate mixing thermodynamicsand phase stability in the BaZrS_3xSe_3–3x system. We identify an unusualordered structure, with signatures of anion ordering persisting atroom temperature, most prominently at 33% S, where S and Se atomsform alternating layers within the crystal. Free-energy calculationsyield the temperature–composition phase diagram, includinga nonperovskite δ phase in the Se-rich limit and a perovskitephase in the S-rich limit, separated by a broad two-phase region.Analysis of the dielectric function and the absorption coefficientdemonstrates that composition, crystal structure, and anion orderingjointly control the optical band gap. Selenium alloying enables tuningbetween approximately 1.5 and 1.9 eV, while anion ordering withina given composition reduces the gap by about 0.2 eV. Lastly, variationsbetween structural polymorphs give rise to band gap differences ofup to 0.5 eV.

An isovalent anion substitution approach allowed forthe discoveryof two noncentrosymmetric ternary selenides, Sr₂SiSe₄ and Sr₂SnSe₄. Sr₂SiSe₄ crystallizes in the α-Eu₂GeS₄ type, monoclinic space group P2₁, withlattice parameters a = 6.8866(19) Å, b = 7.0062(19) Å, c = 8.520(2) Å,β = 108.200(6)°, and Z = 2, while Sr₂SnSe₄ adopts the γ-Sr₂GeSe₄ type, orthorhombic space group Ama2, withlattice parameters a = 10.4802(10) Å, b = 10.6965(10) Å, c = 7.5411(7) Å,and Z = 4. Calculated PBE band gaps show that Sr₂SiSe₄ (E_g = 2.31 eV)and Sr₂SnSe₄ (E_g = 2.05 eV) both exhibit a broad transparency window in the infraredregion along with moderate band gaps, avoiding two-photon absorptionfrom 2090 nm lasers. The nonlinear optical response of Sr₂SiSe₄ was experimentally determined using AgGaS₂ as a reference, indicating that the material is phase-matchable,producing an intensity approximately 0.5 times that of AgGaS₂ using a 2090 nm laser. In addition to its promising nonlinear opticalproperties, Sr₂SiSe₄ exhibits ultralow thermalconductivity (0.46 W m^–1 K^–1 at523 K) despite being composed of rather light elements compared toBi₂Te₃ and PbTe, making it an interesting─andless toxic─potential candidate for thermoelectric energy conversionapplications.

Layered palladium diselenide (PdSe₂) is anemergingfunctional dichalcogenide whose structural flexibility enables tunableelectronic, magnetic, and transport properties. However, controlledaccess to compositionally substituted and metastable polymorphs remainschallenging using conventional synthetic approaches. Here, we reporta benchtop solution-phase route for the rapid and scalable synthesisof highly crystalline orthorhombic PdSe₂ (o-PdSe₂) and its polymorphs induced by aliovalent substitutions.This sustainable approach enables controlled phase evolution and yieldsmaterials suited for detailed structural, spectroscopic, magnetic,and transport studies. Using this platform, we achieve substitutionat the Pd site with both 3d and 5d transition metals, Mn and Pt, respectively. Approximately 10 at.% Mn substitution preserves the orthorhombic framework while inducinga complex magnetic ground state. In contrast, Pt substitution stronglymodifies Se–Se dimer stability and drives sequential structuraltransformations. Unlike Pd, Pt prefers a 4+ oxidation state, resultingin a partial destabilization of the Se–Se dumbbells and formationof monoclinic I2/a polymorph withmixed Pt²⁺/Pt⁴⁺ centers at low Pt content (∼12at. %). This structural reorganization induced by minute amounts ofPt drastically alter charge and heat transport properties, includinga carrier-type switch from p-type to n-type conduction, a narrowing of the bandgap, and ultralow thermalconductivity of 0.27 Wm^1–K^–1 at300 K. At higher Pt content (≥30 at. %), Pd is progressivelyforced to +4 oxidation state resulting in the complete destabilizationof the Se–Se dimers and structural transformation into a trigonalmetallic phase with [MSe₆] octahedra. These results establisha versatile soft chemical route to compositionally and structurallytunable PdSe₂-based materials with emergent magnetic andtransport properties, alluding to their promise for energy conversionand storage applications.

Zeolitic imidazolateframework (ZIF) biocomposites are widely studiedfor their potential in biocatalysis and biomedicine. However, theirpreparation is highly sensitive to precursor composition, concentration,washing conditions, and operator-dependent handling procedures. Here,we combine a semiautomated syringe-pump system, high-throughput samplepreparation, and digital data visualization to map synthesis–structure–propertyrelationships in ZIF biocomposites. A programmable four-syringe pumpplatform was used to systematically prepare 360 distinct samples intriplicate, yielding 1080 samples. The investigated synthetic parameterswere relative amounts of metal, ligand, protein, the total precursorconcentration, and the washing protocol. Structural, chemical, andfunctional characterization yielded a data set of ∼2250 entriescomprising crystalline-to-amorphous ratios, IR-based protein-to-frameworkratios, encapsulation efficiency, and loading capacity. We note thatexploring such a large data set manually can be challenging and thatcurrent static visualizations can hide meaningful trends. With theaim of enabling a customized and interactive exploration of the data,we designed the ZIF Biocomposite Explorer App (ZIF-BEA), which supportsuser-defined navigation in the space of the variables, providing directaccess to experimental data and material properties. We anticipatethat integrating large experimental data sets with interactive digitalplatforms may expedite the design of MOF-based biocomposites, whileproviding a transferable tool for the exploration of other classesof functional materials.

Electrolyte solvation chemistry is central to the advancementofnext-generation lithium metal batteries. The Li⁺ solvationstructure is closely related to ion transport, interphase chemistry,and cell performance. However, most efforts still examine solvationstructures at microscopic length scales without accounting for theinterfacial electric field that develops during cell operation. Here,we reorganize the reported solvation strategies into a framework integratingtwo perspectives: the length scale of the solvation structure andthe presence of the interfacial electric field, spanning from static(field-free) microscopic solvation to dynamic (field-driven) solvationnetworks. Within this framework, we benchmark the electrochemicalperformance of representative strategies, connect the characterizationmethods and governing physics that operate at each length scale, andidentify the failure modes that limit each electrolyte component.We discuss design directions for dynamic solvation networks and provideinsights into aligning laboratory advances with industrial requirements.