Transducing thermal energy into mechanical movements via molecular reconfigurations offers a cutting-edge approach to thermal actuating materials,which could be applied to sensors,energy harvesting and storage devices...Transducing thermal energy into mechanical movements via molecular reconfigurations offers a cutting-edge approach to thermal actuating materials,which could be applied to sensors,energy harvesting and storage devices[1].Thermal expansion is a pivotal aspect in solid state chemistry,intricately intertwined with various factors such as crystal structure,chemical composition,electronic configuration,microstructure,and defects.Most materials undergo isotropic and positive thermal expansion(PTE)because of the disharmonic vibrational amplitudes of their chemical bonds.Moreover,anisotropic thermal expansion(ATE)and negative thermal expansion(NTE)are fascinating physical attributes of solids,which can originate from electronic or magnetic mechanisms,as well as through a transverse phonon mechanism in insulating lattice solids.展开更多
The spin crossover（SCO） compound [Fe（bapbpy）（NCS）2],where bapbpy contains two fused N,N-bis（2-pyridyl）amines,has been studied by DFT/TD-DFT/BS-DFT methods.Several density functionals and basis sets were used i...The spin crossover（SCO） compound [Fe（bapbpy）（NCS）2],where bapbpy contains two fused N,N-bis（2-pyridyl）amines,has been studied by DFT/TD-DFT/BS-DFT methods.Several density functionals and basis sets were used in the calculation to obtain optimized geometries of the compound in the low-（LS） and high-spin（HS） states.The vibrational modes and IR spectra,spin splitting energies,excited states and UV/Vis absorption spectra were obtained.The structural parameters of the calculated isolated complex are in good agreement with the X-ray data.We investigate three dimers of [Fe（bapbpy）（NCS）2] complex for their magnetic properties.It has been found that the complex（1,3） has ferromagnetic character while the others are antiferromagnetic in nature by using a broken symmetry approach in the DFT framework（BS-DFT） with support from the coupling constant values（J） and spin density plots.展开更多
Luminescent spin crossover(SCO) materials have attracted significant interest owing to their potential applications in magneto-optical switches. However, the majority of previously reported FeII-based SCO complexes ar...Luminescent spin crossover(SCO) materials have attracted significant interest owing to their potential applications in magneto-optical switches. However, the majority of previously reported FeII-based SCO complexes are adversely affected by fluorescence quenching in the solid-state. Here, we have constructed the first mononuclear FeIIcomplex decorated with an aggregation-induced emission(AIE) luminophore(i.e., tetraphenylethylene) that exhibits synergistic SCO and fluorescence behavior. Intriguingly, we obtained two types of crystals in different solvent systems, both displaying distinct magnetic bistability and fluorescence properties. The fluorescence intensity was observed to track the magnetic susceptibility, which confirmed that SCO and solid-state fluorescence operate synergistically. We introduce a novel approach for the construction of luminescent SCO compounds using an AIEgen as a luminophore, which leads to fluorescence emission in the solid-state, thus allowing us to study the synergy between SCO and fluorescence.展开更多
Three iron （III） complexes with the formula of [Feat（X）L2]BPh4 were studied, in which a pentadentate Schiff-base ligand （H2L2 = bis （3-methoxysalicylideneiminopropyl） methylamine） and a counter anion BPh4 were...Three iron （III） complexes with the formula of [Feat（X）L2]BPh4 were studied, in which a pentadentate Schiff-base ligand （H2L2 = bis （3-methoxysalicylideneiminopropyl） methylamine） and a counter anion BPh4 were fixed, and three monodentate ligands, 3-Mepy （3-methylpyridine）, 4-NH2py （4-aminopyridine）, and 2-Meim （2-methylimidazole） were used as the axial ligand X. The temperature dependence of magnetic susceptibility measurements demonstrated that [Fem（3-Mepy）L2]BPh4 showed a gradual spin equilibrium between HS （high-spin） （S = 5/2） and LS （low-spin） （S = 1/2） states, [Fem（4-NH2py）L2]BPh4 showed a steep SCO （spin crossover） and [FeIH（2-Melm）L2]BPh4 was in the HS state even at 100 K. The single crystal X-ray analyses demonstrated that [FelH（4-NH2py）L2]BPh4 has an one-dimensional chain structure constructed by intermolecular hydrogen bonding between 4-amino group of 4-NH2py and methoxy oxygen of adjacent molecular-cation. The crystal structure of [FenI（3-Mepy）L2]BPh4 has no such intermolecular interaction and its SCO site behaves independently, and the crystal structure of [FeIII（2-Meim）L2]BPh4 has a NH...n interaction between imidazole group of 2-Meim of cation and a phenyl group of anion BPh4. The result demonstrates that the intermolecular hydrogen bonding affects SCO profile significantly.展开更多
Spin crossover(SCO),characterized by distinct high-spin(HS)and low-spin(LS)states,has potential applications in memory,electronic,and electroluminescent devices.The OFF/ON switching of SCO is crucial for obtaining bis...Spin crossover(SCO),characterized by distinct high-spin(HS)and low-spin(LS)states,has potential applications in memory,electronic,and electroluminescent devices.The OFF/ON switching of SCO is crucial for obtaining bistable magnetic properties.However,there are few strategies for achieving this switching.Herein,based on a ligand chemical doping strategy,we report an Fe(Ⅲ)solid solution that can be prepared using a ligand chemical doping strategy,enabling not only the OFF/ON switching of SCO but also the fine-tuning of the spin transition temperature(T_(c))within a 45 K range near room temperature.The experimental results show that when the polar ligand doping ratio reaches 20%,SCO behavior is triggered,and the crystal phase transforms significantly,becoming loose and flexible.Furthermore,T_(c) can be continuously regulated as the ligand-doping ratio increases.Density functional theory(DFT)calculations reveal that solid packing-induced molecular distortion blocks SCO,whereas loosely flexible packing triggers SCO via fluorinated ligand chemical doping.展开更多
Thermoelectric materials,capable of converting temperature gradients into electrical power,have been traditionally limited by a trade-off between thermopower and electrical conductivity.This study introduces a novel,b...Thermoelectric materials,capable of converting temperature gradients into electrical power,have been traditionally limited by a trade-off between thermopower and electrical conductivity.This study introduces a novel,broadly applicable approach that enhances both the spin-driven thermopower and the thermoelectric figure-of-merit(zT)without compromising electrical conductivity,using temperature-driven spin crossover.Our approach,supported by both theoretical and experimental evidence,is demonstrated through a case study of chromium doped-manganese telluride,but is not confined to this material and can be extended to other magnetic materials.By introducing dopants to create a high crystal field and exploiting the entropy changes associated with temperature-driven spin crossover,we achieved a significant increase in thermopower,by approximately 136μV K^(-1),representing more than a 200%enhancement at elevated temperatures within the paramagnetic domain.Our exploration of the bipolar semiconducting nature of these materials reveals that suppressing bipolar magnon/paramagnon-drag thermopower is key to understanding and utilizing spin crossover-driven thermopower.These findings,validated by inelastic neutron scattering,X-ray photoemission spectroscopy,thermal transport,and energy conversion measurements,shed light on crucial material design parameters.We provide a comprehensive framework that analyzes the interplay between spin entropy,hopping transport,and magnon/paramagnon lifetimes,paving the way for the development of high-performance spin-driven thermoelectric materials.展开更多
Comprehensive Summary.Three three-dimensional Hofmann-type metal-organic frameworks(MOFs)[Fe(bpn){Ag(CN)_(2)}_(2)]·Ph_(2)S(1·Ph_(2)S,bpn=1,4-di(pyridin-4-yl)naphthalene,Ph_(2)S=diphenylsulfide),[Fe(bpn){Ag(C...Comprehensive Summary.Three three-dimensional Hofmann-type metal-organic frameworks(MOFs)[Fe(bpn){Ag(CN)_(2)}_(2)]·Ph_(2)S(1·Ph_(2)S,bpn=1,4-di(pyridin-4-yl)naphthalene,Ph_(2)S=diphenylsulfide),[Fe(bpn){Ag(CN)_(2)}_(2)]·Ph_(2)SO(1·Ph_(2)SO,Ph_(2)SO=diphenylsulfoxide)and[Fe(bpn){Ag(CN)_(2)}_(2)]·Ph_(2)SO_(2)(1·Ph_(2)SO_(2),Ph_(2)SO_(2)=diphenylsulfone)were synthesized by employing sulfur-containing aromatic vips varying in oxidation states.1·Ph_(2)S performed a complete four-step spin crossover(SCO)behavior with the sequence of HS↔~LS_(1/3)HS_(2/3)↔~LS_(1/2)HS_(1/2)↔~LS_(2/3)HS_(1/3)↔LS,while an incomplete two-step SCO profile with the sequence of HS↔~LS_(1/3)HS_(2/3)↔~LS_(2/3)HS_(1/3) and a faint SCO behavior at low temperature for 1·Ph_(2)SO and 1·Ph_(2)SO_(2).Photomagnetic experiments indicate the light-induced excited spin-state trapping(LIESST)effect in 1·Ph_(2)S and the bi-directional LIESST effect for 1·Ph_(2)SO and 1·Ph_(2)SO_(2).Variable-temperature structural analyses reveal the evolution of host-vip synergy and highlight the mechanism of adaptive deformation of vips mediated by phenyl rotation amid spin transition.As the oxidation state of sulfur-containing vips increases,the host-vip cooperation within the lattice is limited by the steric effect,which stabilizes the high-spin state and consequently diminishes the SCO capability in this system.These results demonstrated herein open a new perspective on host-vip chemistry within SCO frameworks.展开更多
Macroscopic polarization switching achieved through directional electron transfer or spin crossover(SCO)has attracted considerable attention because of its potential applications in data storage devices,sensors,and en...Macroscopic polarization switching achieved through directional electron transfer or spin crossover(SCO)has attracted considerable attention because of its potential applications in data storage devices,sensors,and energy converters.Here,by substituting the central metal and anion of a reported compound,[Fe(RR-cth)Co(SS-cth)(μ-dhbq)](AsF_(6))_(3),we obtained two dinuclear compounds that crystallize in the polar space group,P2_(1),[Fe(RR-cth)Ga(SS-cth)(μ-dhbq)](X)_(3)(X=AsF_(6)and ClO_(4)).Among them,complex 1(AsF_(6))_(3)exhibited a two-step magnetic transition,including SCO behavior near 50 K and a gradual valence tautomerism(VT)behavior that occurred over a wide temperature range up to at least 250 K.The SCO behavior of complex 1(AsF_(6))_(3)can be triggered by changes in temperature or the application of magnetic fields,leading to a polarization change of approximately 0.5μC cm^(−2).The transition entropy of 55.9 J K^(−1)mol^(−1)during the SCO process was obtained using the Clausius-Clapeyron equation.Contrarily,complex 1(ClO_(4))_(3)only exhibited gradual VT behavior from a low temperature to room temperature.Single-crystal X-ray diffraction,variable-temperature infrared spectroscopy,and pyroelectric measurements confirmed the gradual VT process that occurs over a wide temperature range in both complexes.This study broadens the range of polarization switching molecular systems by replacing the central metal and anion,thereby facilitating the development of multifunctional molecular materials.展开更多
Comprehensive Summary,Regulating spin crossover(SCO)behavior,especially controlling the spin transition steps,is an important scientific issue,mainly because people aim to control spin bistability and multistability.P...Comprehensive Summary,Regulating spin crossover(SCO)behavior,especially controlling the spin transition steps,is an important scientific issue,mainly because people aim to control spin bistability and multistability.Presently,SCO bistability can be regulated by changing the ligand-modifying species,non-coordinated anions,vip molecules,and metal-ion dopant.However,the control of multistability is extremely challenging,especially in Fe(III)SCO compounds.Here,we report that[FeIII(H-5-Br-thsa)(5-Br-thsa)]·H2O(5-Br-thsa=(5-bromo-2-hydroxybenzylidene)hydrazinecarbothioamide),a compound we have reported before,exists in two polymorphic forms:polymorph 1 exhibits three-step SCO,and polymorph 2 shows five-step SCO,with multi-step SCO behavior effectively regulated by polymorphism.According to single-crystal and powder X-ray diffractometry,polymorphs 1 and 2 crystallize in different space groups during their spin transitions,with two-step symmetry breaking observed(Pbcn→Pnc2→Pbcn for polymorph 1;P21/n→Pn→P21/n for polymorph 2).We realized that the behavior of these two polymorphs depends significantly on the structure,including(i)the average Fe—N bond distance,(ii)deformation of octahedral FeIII atoms,and(iii)distinct crystal packing,which account for the large differences observed in magnetic properties.展开更多
Comprehensive Summary To better understand the impact of different anions on the structures and SCO properties of the CoII SCO complexes,six new complexes[Co(terpy-CH_(2)OH)_(2)]A_(2)·sol(terpy-CH_(2)OH=4′-(hydr...Comprehensive Summary To better understand the impact of different anions on the structures and SCO properties of the CoII SCO complexes,six new complexes[Co(terpy-CH_(2)OH)_(2)]A_(2)·sol(terpy-CH_(2)OH=4′-(hydroxymethyl)-2,2′;6′,2″-terpyridine,A=Br^(–)(1,sol=1.5H_(2)O),I^(–)(2),N_(3)^(–)(3,sol=2H_(2)O),H_(3)BCN^(–)(4),OTf^(–)(5),and TsO^(–)(6,sol=4H_(2)O·CH_(3)CN),have been synthesized and characterized.All six compounds consist of mononuclear[Co(terpy-CH_(2)OH)_(2)]^(2+)cations and charge-balancing anions that differ in size,shape,and hydrogen bonding capacity.Complexes 1,2,3,and 6 displayed incomplete gradual SCO transitions,whereas 4 and 5 exhibited abrupt hysteretic spin transitions with loops of 12 and 16 K(250.0—262.0 K for 4,and 370.0—386.0 K for 5,respectively),closely resembling our previously reported complexes with SCN^(–)and SeCN^(–)anions.The occurrence of the order-disorder transition of the CH2OH groups and their transition temperatures are determined by the size and hydrogen bonding capability of the anions.Remarkably,the transition temperatures of complexes with H_(3)BCN^(–),SCN^(–),OTf^(–),and SeCN^(–)anions exhibit an upward trend as the size and mass of the anions increase,as confirmed through detailed single crystal structure analyses conducted in both high-spin and low-spin states for all four complexes.展开更多
Precise manipulation of the catalytic spin configuration and delineation of the relationship between spin related properties and oxidation pathways remain significant challenges in Fenton-like processes.Herein,encapsu...Precise manipulation of the catalytic spin configuration and delineation of the relationship between spin related properties and oxidation pathways remain significant challenges in Fenton-like processes.Herein,encapsulated cobalt nanoparticles and cobalt-nitrogen-doped carbon moieties,endowed with confinement effects and variations in shell curvature were constructed via straightforward pyrolysis strategies,inducing alterations in magnetic anisotropy,electronic energy levels and spin polarization.The enhanced spin polarization at cobalt sites leads to a reduction in crystal field splitting energy and an increase in electronic spin density.This phenomenon facilitated electron transfer from cobalt orbitals to pz orbitals of oxygen species within peroxymonosulfate molecules,thereby promoting the formation of high-valent cobalt species.The encapsulation effectively stabilized cobalt nanoparticles,mitigating their dissolution or deactivation during reactions,which in turn enhances stability and durability in continuous flow processes.The high-valent cobalt species within the shell exhibit increased exposure and generate localized high concentrations,thereby intensifying interactions with migrating pollutants and enabling efficient and selective oxidation of emerging compounds with elevated redox potentials.This work underscores the profound impact of confined encapsulation curvature and spin polarization characteristics of metal sites on catalytic oxidation pathways and performance,opening novel avenues for spin engineering in practical environmental catalysis.展开更多
Spin-crossover(SCO)complexes with multiple spin states are promising candidates for high-order magnetic storage and multiple switches.Here,by employing the N,N'-4-dipyridyloxalamide(dpo)ligand,we synthesize two Ho...Spin-crossover(SCO)complexes with multiple spin states are promising candidates for high-order magnetic storage and multiple switches.Here,by employing the N,N'-4-dipyridyloxalamide(dpo)ligand,we synthesize two Hofmann-type metal-organic frameworks(MOFs)[Fe(dpo){Ag(CN)_(2)}_(2)]·3DMF(1)and[Fe(dpo){Ag(CN)_(2)}_(2)]·0.5MeCN·2DEF(2),which exhibit vip dependent four-step SCO behaviors with the sequences of LS→~LS_(2/3)HS_(1/3)→LS_(1/2)HS_(1/2)→~LS_(3/10)HS_(7/10)→HS and LS→~LS_(2/3)HS_(1/3)→LS_(1/2)HS_(1/2)→~LS_(1/4)HS_(3/4)→HS,respectively.Therefore,the incorporation of hydrogen-donating/hydrogen-accepting groups into the Hofmann-type MOFs may effectively explore the multi-step SCO materials by tuning hydrogen-bonding interactions.展开更多
The engineering of switchable materials with controllable stimuli-responsive multistability remains challenging in materials science.Herein,we present syntheses and structural and magnetic studies of a one-dimensional...The engineering of switchable materials with controllable stimuli-responsive multistability remains challenging in materials science.Herein,we present syntheses and structural and magnetic studies of a one-dimensional cobalt(Ⅱ)coordination polymer[(enbzp)Co(bpy)](ClO_(4))_(2)·-MeOH·H2O(1;enbzp=N,N′-(ethane-1,2-diyl)bis(1-phenyl-1-(pyridin-2-yl)methanimine,bpy=4,4′-bipyridine)and its desolvated analogue[(enbzp)Co(bpy)](ClO_(4))_(2)(2),obtained by reversible single-crystal-to-single-crystal(SCSC)transformation.展开更多
The synthesis of new Schiff base-like ligands with asymmetric substituents pattern and their iron complexes with pyridine as axial ligand is described. Two of the ligands and one of the iron（II） complexes were chara...The synthesis of new Schiff base-like ligands with asymmetric substituents pattern and their iron complexes with pyridine as axial ligand is described. Two of the ligands and one of the iron（II） complexes were characterized by single crystal X-ray structure analysis. One of the the iron（II） complexes shows spin crossover behavior while the others remain in the high spin state. The influence of the reduced symmetry of the ligand on the properties of the complexes is discussed.展开更多
Synergistic fluorescent spin crossover(SCO)bifunctional molecular materials have novel applications in the molecule-based magneto-optical switches.Herein,we report two novel three-dimensional(3D)Hofmann-type fluoresce...Synergistic fluorescent spin crossover(SCO)bifunctional molecular materials have novel applications in the molecule-based magneto-optical switches.Herein,we report two novel three-dimensional(3D)Hofmann-type fluorescent SCO complexes[Fe^(II)-(tppe)MI(CN)_(2)]ClO_(4)·nSolv(tppe=tetra-(4-pyridylphenyl)ethene,M=Ag(tppe-Ag),Au(tppe-Au)).Both complexes show one-step abrupt SCO with the transition temperature of 230 K for tppe-Ag,and 245 K for tppe-Au accompanied by a color change from red to light yellow.The SCO process is confirmed by the variable-temperature single-crystal X-ray diffraction analysis on tppe-Ag.For the first time,the abnormal increase in emission intensity and concomitant large bathochromic shifts in the fluorescence spectra during the SCO process are realized in the 3D Hofmann-type coordination polymers expanded by the tetradentate tppe ligand.Moreover,tppe-Ag exhibits the unprecedented fluorescence emission from green to the edge of yellow.展开更多
The utilization of spin crossover(SCO)to modulate the luminescence properties in smart multifunctional materials and multichannel sensors is promising.However,it is challenging to build a strong coupling between SCO a...The utilization of spin crossover(SCO)to modulate the luminescence properties in smart multifunctional materials and multichannel sensors is promising.However,it is challenging to build a strong coupling between SCO and luminescence in one system.Herein,we present a mononuclear compound[Fe(tpe-abpt)_(2)(SeCN)_(2)]·4DMF(1·4DMF,tpe-abpt:(4-(1,1,2,2-tetraphenylethene))-N-(3,5-bis(pyridin-2-yl)-4H-1,2,4-triazol-4yl)methanimine)showing aggregation-induced emission(AIE)and thermally induced SCO properties.Variable-temperature single-crystal structural analysis reveals that SCO changes the number of pathways and strength of intermolecular interactions,resulting in deactivation of nonradiative decay and significant enhancement of luminescence.The photoluminescence(PL)intensity of 1·4DMF exhibited a fivefold increase upon the spin transition from the low-spin to the high-spin states.In contrast with the current strategy of controlling the Förster resonance energy transfer(FRET)process by utilizing SCO to tune the overlap degree between the emission band of the luminophore and UV–vis absorption band of high-spin and low-spin states,we developed a new approach to tune the intermolecular interactions between AIE luminogens(AIEgens)by utilizing a subtle SCO-induced structural transformation,therefore leading to effective coupling between SCO and luminescence and a significant change in luminescence upon SCO.Our results provide a rational strategy to build smartmultifunctionalizedmaterials with remarkably synergetic SCO and luminescence.展开更多
Spin crossover(SCO)is commonly accompanied by a synchronous phase transition.A few phase transitioncoupled SCO compounds have been reported,yet the synergy between SCO and phase transition on different time scales has...Spin crossover(SCO)is commonly accompanied by a synchronous phase transition.A few phase transitioncoupled SCO compounds have been reported,yet the synergy between SCO and phase transition on different time scales has not been explored.Herein,we report an[Fe(H-5-Cl-thsa-Et)(5-Cl-thsa-Et)]·H2O(1·H2O;H2-5-Cl-thsa-Et=5-chloro-salicylaldehyde ethylthiosemicarbazone)Fe(III)complex that displays a two-dimensional supramolecular structure and SCO behavior above room temperature.Its dehydrated form1 exhibits a two-step spin transition with aplateau in the temperature-dependent magnetization(M−T)curve at room temperature and a 51 K thermal hysteresis loop(Tc↑↓=299/248 K)at a rate of 5 K/min.The improved SCOperformance in 1 could be attributed to the stronger intralayer but weaker interlayer interactions,which is supported by single-crystal structural analysis and density functional theory calculations.Remarkably,complex 1 displays an unusual scan rate-dependent SCO behavior at rates of 0.5−30 K/min,in whichM−T curveplateaus appear at lower scan rates(<10 K/min)but vanish at faster scan rates(≥10 K/min).Scan rate-dependent differential scanning calorimetry,powder X-ray diffractometry,timedependent magnetic moment decays,and infrared spectroscopy consistently reveal that the slow structural relaxation is coupled with a slowcrystallographic phase transition,which is the mechanism for the unusual scan rate-dependent SCO.展开更多
Light alkanes non-oxidative dehydrogenation is an attractive non-oil route for olefins production.The alkane dehydrogenation reaction is limited by thermodynamic equilibrium,and the C-H bond cleavage is commonly consi...Light alkanes non-oxidative dehydrogenation is an attractive non-oil route for olefins production.The alkane dehydrogenation reaction is limited by thermodynamic equilibrium,and the C-H bond cleavage is commonly considered as the rate-determined step.The valence state of metal sites in catalysts will influence the stabilization of the vital intermediate(i.e.,C_(x)H_(y)...M^(δ+)...H)during the C-H bond cleavage process,which in turn affects the catalytic reactivity.Herein,we explicitly investigated the effect of different valence states of framework-Fe in silicate-1 zeolite on ethane dehydrogenation reaction through the combination of experimental and theoretical study.Fe(Ⅱ)-S-1 and Fe(Ⅲ)-S-1 catalysts are successfully synthesized by ligand-assisted in situ crystallization method,In-situ C_(2)H_6-FTIR shows the higher coverage of hydrocarbon intermediates on Fe(Ⅱ)-S-1,Under the same evaluation co nditio n,Fe(Ⅱ)-S-1 exhibits a higher space time yield of ethylene.Density functional theory(DFT)results reveal that the more coordinate-unsaturated and electron-enriched Fe(Ⅱ)sites boost the first C-H bond activation by slight deformation and efficient electron donation with C_(2)H_(5)^(*)species.Remarkably,the second C-H bond cleavage on Fe(Ⅱ)-S-1 undergoes a spin-crossing process from quintet state to triplet state,which involves a two-electro n-two-orbital interaction,further promoting the formation of ethylene.Microkinetic analysis is consistent with the experimental and DFT results.This work could provide methodology for elucidating the effect of metal valence states on catalytic performance as well as offer guidance for designing more efficient Fe-zeolite catalysts.展开更多
Molecular materials showing synergetic coupling of near-infrared(NIR)fluorescence and spin-crossover(SCO)are promisingly applicable in in-vivo bioimaging,temperature sensing,and spintronic devices.Whilst the related s...Molecular materials showing synergetic coupling of near-infrared(NIR)fluorescence and spin-crossover(SCO)are promisingly applicable in in-vivo bioimaging,temperature sensing,and spintronic devices.Whilst the related study faces formidable challenges.In this work we graft the NIR fluorophore xanthene onto the dipyridyl substituted triazole ligand and construct a new Febased SCO material,{Fe^(Ⅱ)(ddxc-abpt)_(2)[N(CN)_(2)]_(2)}(1,ddxc-abpt:(E)-4-(((3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)imino)methyl)-N,N-diethyl-2,3-dihydro-1H-xanthen-6-amine).Magnetic studies indicate that compound 1 exhibits thermally induced SCO property in both the solid and solution state.Variable-temperature fluorescence emission spectra reveal a remarkable 7-fold increase in photoluminescence intensity upon the transition from the low-spin state at 110 K to the high-spin state at 280 K,which is the record of all reported coupled fluorescence-SCO materials.Variable-temperature ultraviolet-visible(UV-Vis)absorption spectra show a significant change in absorption intensity within the fluorescence emission window,consistent with the Förster resonance energy transfer(FRET)mechanism.Time-dependent density functional theory(TD-DFT)calculations demonstrate that the strong coupling is attributed to disrupted energy transfer between the xanthene fluorophore and high-spin Fe^(Ⅱ)center.Our work provides a feasible approach for expanding the synergetic SCO-fluorescence materials to the NIR-I wavelength region,and hopefully contributes to the applications of tunable NIR-SCO molecule-based sensors and devices.展开更多
Spin-crossover(SCO)materials that reversibly switch between high-and low-spin states have potential for the storage of spin state-relative information,and have gained much attention incorporating secondary physical pr...Spin-crossover(SCO)materials that reversibly switch between high-and low-spin states have potential for the storage of spin state-relative information,and have gained much attention incorporating secondary physical properties,such as fluorescence and magneto-optical switching.In this study,we synthesized three octanuclear metal-organic cages(MOCs)using tetraphenylethylene-based luminophores,aldehydes,and Fe^(Ⅱ)salts,by subcomponent self-assembly approach,namely[Fe1]-[Fe3].By controlling the ligand-field strength and vip encapsulation,we finely tuned their SCO properties.Among them,MOC[Fe2]displayed nearly complete SCO behavior in the solid state,which is rare for high-nuclearity complexes.We also demonstrated the coupling of SCO with fluorescence emission in these MOCs by using isostructural Zn^(Ⅱ)complexes([Zn1]-[Zn3])as control experiments,for the first time.Theoretical calculations revealed the energy-transfer mechanism between fluorophores and SCOactive centers,which emphasizes the significant contribution of d-d transitions in the interplay between the occurrence of SCO and fluorescence emission.展开更多
基金supported by the National Natural Science Foundation of China(22171155)Natural Science Foundation of Shandong Province(ZR2022YQ07)Taishan Scholar Program(tsqn202306166).
文摘Transducing thermal energy into mechanical movements via molecular reconfigurations offers a cutting-edge approach to thermal actuating materials,which could be applied to sensors,energy harvesting and storage devices[1].Thermal expansion is a pivotal aspect in solid state chemistry,intricately intertwined with various factors such as crystal structure,chemical composition,electronic configuration,microstructure,and defects.Most materials undergo isotropic and positive thermal expansion(PTE)because of the disharmonic vibrational amplitudes of their chemical bonds.Moreover,anisotropic thermal expansion(ATE)and negative thermal expansion(NTE)are fascinating physical attributes of solids,which can originate from electronic or magnetic mechanisms,as well as through a transverse phonon mechanism in insulating lattice solids.
基金Supported by the Natural Science Foundation of Shandong Province(No.Y2006B43)
文摘The spin crossover（SCO） compound [Fe（bapbpy）（NCS）2],where bapbpy contains two fused N,N-bis（2-pyridyl）amines,has been studied by DFT/TD-DFT/BS-DFT methods.Several density functionals and basis sets were used in the calculation to obtain optimized geometries of the compound in the low-（LS） and high-spin（HS） states.The vibrational modes and IR spectra,spin splitting energies,excited states and UV/Vis absorption spectra were obtained.The structural parameters of the calculated isolated complex are in good agreement with the X-ray data.We investigate three dimers of [Fe（bapbpy）（NCS）2] complex for their magnetic properties.It has been found that the complex（1,3） has ferromagnetic character while the others are antiferromagnetic in nature by using a broken symmetry approach in the DFT framework（BS-DFT） with support from the coupling constant values（J） and spin density plots.
基金Nankai University for the startup funds in support of young talented researcherssupported by the National Natural Science Foundation of China(NSFC, Nos. 21971124, 22035003)。
文摘Luminescent spin crossover(SCO) materials have attracted significant interest owing to their potential applications in magneto-optical switches. However, the majority of previously reported FeII-based SCO complexes are adversely affected by fluorescence quenching in the solid-state. Here, we have constructed the first mononuclear FeIIcomplex decorated with an aggregation-induced emission(AIE) luminophore(i.e., tetraphenylethylene) that exhibits synergistic SCO and fluorescence behavior. Intriguingly, we obtained two types of crystals in different solvent systems, both displaying distinct magnetic bistability and fluorescence properties. The fluorescence intensity was observed to track the magnetic susceptibility, which confirmed that SCO and solid-state fluorescence operate synergistically. We introduce a novel approach for the construction of luminescent SCO compounds using an AIEgen as a luminophore, which leads to fluorescence emission in the solid-state, thus allowing us to study the synergy between SCO and fluorescence.
文摘Three iron （III） complexes with the formula of [Feat（X）L2]BPh4 were studied, in which a pentadentate Schiff-base ligand （H2L2 = bis （3-methoxysalicylideneiminopropyl） methylamine） and a counter anion BPh4 were fixed, and three monodentate ligands, 3-Mepy （3-methylpyridine）, 4-NH2py （4-aminopyridine）, and 2-Meim （2-methylimidazole） were used as the axial ligand X. The temperature dependence of magnetic susceptibility measurements demonstrated that [Fem（3-Mepy）L2]BPh4 showed a gradual spin equilibrium between HS （high-spin） （S = 5/2） and LS （low-spin） （S = 1/2） states, [Fem（4-NH2py）L2]BPh4 showed a steep SCO （spin crossover） and [FeIH（2-Melm）L2]BPh4 was in the HS state even at 100 K. The single crystal X-ray analyses demonstrated that [FelH（4-NH2py）L2]BPh4 has an one-dimensional chain structure constructed by intermolecular hydrogen bonding between 4-amino group of 4-NH2py and methoxy oxygen of adjacent molecular-cation. The crystal structure of [FenI（3-Mepy）L2]BPh4 has no such intermolecular interaction and its SCO site behaves independently, and the crystal structure of [FeIII（2-Meim）L2]BPh4 has a NH...n interaction between imidazole group of 2-Meim of cation and a phenyl group of anion BPh4. The result demonstrates that the intermolecular hydrogen bonding affects SCO profile significantly.
基金supported by the National Natural Science Foundation of China(NSFC 22275100 and 22301142).
文摘Spin crossover(SCO),characterized by distinct high-spin(HS)and low-spin(LS)states,has potential applications in memory,electronic,and electroluminescent devices.The OFF/ON switching of SCO is crucial for obtaining bistable magnetic properties.However,there are few strategies for achieving this switching.Herein,based on a ligand chemical doping strategy,we report an Fe(Ⅲ)solid solution that can be prepared using a ligand chemical doping strategy,enabling not only the OFF/ON switching of SCO but also the fine-tuning of the spin transition temperature(T_(c))within a 45 K range near room temperature.The experimental results show that when the polar ligand doping ratio reaches 20%,SCO behavior is triggered,and the crystal phase transforms significantly,becoming loose and flexible.Furthermore,T_(c) can be continuously regulated as the ligand-doping ratio increases.Density functional theory(DFT)calculations reveal that solid packing-induced molecular distortion blocks SCO,whereas loosely flexible packing triggers SCO via fluorinated ligand chemical doping.
基金funding support by the National Science Foundation(NSF)under grant numbers CBET-2110603the Air Force Office of Scientific Research(AFOSR)under contract number FA9550-12-1-0225supported by the State of North Carolina and the National Science Foundation(award number ECCS-2025064).
文摘Thermoelectric materials,capable of converting temperature gradients into electrical power,have been traditionally limited by a trade-off between thermopower and electrical conductivity.This study introduces a novel,broadly applicable approach that enhances both the spin-driven thermopower and the thermoelectric figure-of-merit(zT)without compromising electrical conductivity,using temperature-driven spin crossover.Our approach,supported by both theoretical and experimental evidence,is demonstrated through a case study of chromium doped-manganese telluride,but is not confined to this material and can be extended to other magnetic materials.By introducing dopants to create a high crystal field and exploiting the entropy changes associated with temperature-driven spin crossover,we achieved a significant increase in thermopower,by approximately 136μV K^(-1),representing more than a 200%enhancement at elevated temperatures within the paramagnetic domain.Our exploration of the bipolar semiconducting nature of these materials reveals that suppressing bipolar magnon/paramagnon-drag thermopower is key to understanding and utilizing spin crossover-driven thermopower.These findings,validated by inelastic neutron scattering,X-ray photoemission spectroscopy,thermal transport,and energy conversion measurements,shed light on crucial material design parameters.We provide a comprehensive framework that analyzes the interplay between spin entropy,hopping transport,and magnon/paramagnon lifetimes,paving the way for the development of high-performance spin-driven thermoelectric materials.
基金supported by the NSFC(22488101)Guangdong Provincial Foundation for Basic and Applied Basic Research(2023A1515110402)+3 种基金Huizhou University Doctoral Research Initiation Project(No.2022JB052)Special Fields of Focus for General Colleges and Universities in Guangdong Province(High-end Equipment Manufacturing)(2023ZDZX3035)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(23ptpy73)Science and Technology Program of Guangzhou,China(2024A04J4433).
文摘Comprehensive Summary.Three three-dimensional Hofmann-type metal-organic frameworks(MOFs)[Fe(bpn){Ag(CN)_(2)}_(2)]·Ph_(2)S(1·Ph_(2)S,bpn=1,4-di(pyridin-4-yl)naphthalene,Ph_(2)S=diphenylsulfide),[Fe(bpn){Ag(CN)_(2)}_(2)]·Ph_(2)SO(1·Ph_(2)SO,Ph_(2)SO=diphenylsulfoxide)and[Fe(bpn){Ag(CN)_(2)}_(2)]·Ph_(2)SO_(2)(1·Ph_(2)SO_(2),Ph_(2)SO_(2)=diphenylsulfone)were synthesized by employing sulfur-containing aromatic vips varying in oxidation states.1·Ph_(2)S performed a complete four-step spin crossover(SCO)behavior with the sequence of HS↔~LS_(1/3)HS_(2/3)↔~LS_(1/2)HS_(1/2)↔~LS_(2/3)HS_(1/3)↔LS,while an incomplete two-step SCO profile with the sequence of HS↔~LS_(1/3)HS_(2/3)↔~LS_(2/3)HS_(1/3) and a faint SCO behavior at low temperature for 1·Ph_(2)SO and 1·Ph_(2)SO_(2).Photomagnetic experiments indicate the light-induced excited spin-state trapping(LIESST)effect in 1·Ph_(2)S and the bi-directional LIESST effect for 1·Ph_(2)SO and 1·Ph_(2)SO_(2).Variable-temperature structural analyses reveal the evolution of host-vip synergy and highlight the mechanism of adaptive deformation of vips mediated by phenyl rotation amid spin transition.As the oxidation state of sulfur-containing vips increases,the host-vip cooperation within the lattice is limited by the steric effect,which stabilizes the high-spin state and consequently diminishes the SCO capability in this system.These results demonstrated herein open a new perspective on host-vip chemistry within SCO frameworks.
基金supported by JSPS KAKENHI(grant nos.23H04862,24K21783,24K17698 and 23K04681)support from the Murata Science and Education Foundation(grant no.M24AN117)The synchrotron radiation experiments were performed at the BL01B1 of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute(proposal no.2021B1342)。
文摘Macroscopic polarization switching achieved through directional electron transfer or spin crossover(SCO)has attracted considerable attention because of its potential applications in data storage devices,sensors,and energy converters.Here,by substituting the central metal and anion of a reported compound,[Fe(RR-cth)Co(SS-cth)(μ-dhbq)](AsF_(6))_(3),we obtained two dinuclear compounds that crystallize in the polar space group,P2_(1),[Fe(RR-cth)Ga(SS-cth)(μ-dhbq)](X)_(3)(X=AsF_(6)and ClO_(4)).Among them,complex 1(AsF_(6))_(3)exhibited a two-step magnetic transition,including SCO behavior near 50 K and a gradual valence tautomerism(VT)behavior that occurred over a wide temperature range up to at least 250 K.The SCO behavior of complex 1(AsF_(6))_(3)can be triggered by changes in temperature or the application of magnetic fields,leading to a polarization change of approximately 0.5μC cm^(−2).The transition entropy of 55.9 J K^(−1)mol^(−1)during the SCO process was obtained using the Clausius-Clapeyron equation.Contrarily,complex 1(ClO_(4))_(3)only exhibited gradual VT behavior from a low temperature to room temperature.Single-crystal X-ray diffraction,variable-temperature infrared spectroscopy,and pyroelectric measurements confirmed the gradual VT process that occurs over a wide temperature range in both complexes.This study broadens the range of polarization switching molecular systems by replacing the central metal and anion,thereby facilitating the development of multifunctional molecular materials.
基金supported by the National Natural Science Foundation of China(NSFC,21971124,22275100,22150710513)the Ph.D.Candidate Research Innovation Fund of the NkU School of Materials Science and Engineering.
文摘Comprehensive Summary,Regulating spin crossover(SCO)behavior,especially controlling the spin transition steps,is an important scientific issue,mainly because people aim to control spin bistability and multistability.Presently,SCO bistability can be regulated by changing the ligand-modifying species,non-coordinated anions,vip molecules,and metal-ion dopant.However,the control of multistability is extremely challenging,especially in Fe(III)SCO compounds.Here,we report that[FeIII(H-5-Br-thsa)(5-Br-thsa)]·H2O(5-Br-thsa=(5-bromo-2-hydroxybenzylidene)hydrazinecarbothioamide),a compound we have reported before,exists in two polymorphic forms:polymorph 1 exhibits three-step SCO,and polymorph 2 shows five-step SCO,with multi-step SCO behavior effectively regulated by polymorphism.According to single-crystal and powder X-ray diffractometry,polymorphs 1 and 2 crystallize in different space groups during their spin transitions,with two-step symmetry breaking observed(Pbcn→Pnc2→Pbcn for polymorph 1;P21/n→Pn→P21/n for polymorph 2).We realized that the behavior of these two polymorphs depends significantly on the structure,including(i)the average Fe—N bond distance,(ii)deformation of octahedral FeIII atoms,and(iii)distinct crystal packing,which account for the large differences observed in magnetic properties.
基金supported by the National Natural Science Foundation of China(22273036,21973039)Y.-C S.acknowledges the support from the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX23_0108).
文摘Comprehensive Summary To better understand the impact of different anions on the structures and SCO properties of the CoII SCO complexes,six new complexes[Co(terpy-CH_(2)OH)_(2)]A_(2)·sol(terpy-CH_(2)OH=4′-(hydroxymethyl)-2,2′;6′,2″-terpyridine,A=Br^(–)(1,sol=1.5H_(2)O),I^(–)(2),N_(3)^(–)(3,sol=2H_(2)O),H_(3)BCN^(–)(4),OTf^(–)(5),and TsO^(–)(6,sol=4H_(2)O·CH_(3)CN),have been synthesized and characterized.All six compounds consist of mononuclear[Co(terpy-CH_(2)OH)_(2)]^(2+)cations and charge-balancing anions that differ in size,shape,and hydrogen bonding capacity.Complexes 1,2,3,and 6 displayed incomplete gradual SCO transitions,whereas 4 and 5 exhibited abrupt hysteretic spin transitions with loops of 12 and 16 K(250.0—262.0 K for 4,and 370.0—386.0 K for 5,respectively),closely resembling our previously reported complexes with SCN^(–)and SeCN^(–)anions.The occurrence of the order-disorder transition of the CH2OH groups and their transition temperatures are determined by the size and hydrogen bonding capability of the anions.Remarkably,the transition temperatures of complexes with H_(3)BCN^(–),SCN^(–),OTf^(–),and SeCN^(–)anions exhibit an upward trend as the size and mass of the anions increase,as confirmed through detailed single crystal structure analyses conducted in both high-spin and low-spin states for all four complexes.
文摘Precise manipulation of the catalytic spin configuration and delineation of the relationship between spin related properties and oxidation pathways remain significant challenges in Fenton-like processes.Herein,encapsulated cobalt nanoparticles and cobalt-nitrogen-doped carbon moieties,endowed with confinement effects and variations in shell curvature were constructed via straightforward pyrolysis strategies,inducing alterations in magnetic anisotropy,electronic energy levels and spin polarization.The enhanced spin polarization at cobalt sites leads to a reduction in crystal field splitting energy and an increase in electronic spin density.This phenomenon facilitated electron transfer from cobalt orbitals to pz orbitals of oxygen species within peroxymonosulfate molecules,thereby promoting the formation of high-valent cobalt species.The encapsulation effectively stabilized cobalt nanoparticles,mitigating their dissolution or deactivation during reactions,which in turn enhances stability and durability in continuous flow processes.The high-valent cobalt species within the shell exhibit increased exposure and generate localized high concentrations,thereby intensifying interactions with migrating pollutants and enabling efficient and selective oxidation of emerging compounds with elevated redox potentials.This work underscores the profound impact of confined encapsulation curvature and spin polarization characteristics of metal sites on catalytic oxidation pathways and performance,opening novel avenues for spin engineering in practical environmental catalysis.
基金supported by the National Key Research and Development Program of China(No.2018YFA0306001)the National Natural Science Foundation of China(Nos.21950410521,21771200and 21773316)the Pearl River Talent Plan of Guangdong(No.2017BT01C161)。
文摘Spin-crossover(SCO)complexes with multiple spin states are promising candidates for high-order magnetic storage and multiple switches.Here,by employing the N,N'-4-dipyridyloxalamide(dpo)ligand,we synthesize two Hofmann-type metal-organic frameworks(MOFs)[Fe(dpo){Ag(CN)_(2)}_(2)]·3DMF(1)and[Fe(dpo){Ag(CN)_(2)}_(2)]·0.5MeCN·2DEF(2),which exhibit vip dependent four-step SCO behaviors with the sequences of LS→~LS_(2/3)HS_(1/3)→LS_(1/2)HS_(1/2)→~LS_(3/10)HS_(7/10)→HS and LS→~LS_(2/3)HS_(1/3)→LS_(1/2)HS_(1/2)→~LS_(1/4)HS_(3/4)→HS,respectively.Therefore,the incorporation of hydrogen-donating/hydrogen-accepting groups into the Hofmann-type MOFs may effectively explore the multi-step SCO materials by tuning hydrogen-bonding interactions.
基金supported by the Stable Support Plan Program of Shenzhen Natural Science Fund(no.20200925151834005)the National Natural Science Foundation of China(nos.21671095,21901108,and 22173043)。
文摘The engineering of switchable materials with controllable stimuli-responsive multistability remains challenging in materials science.Herein,we present syntheses and structural and magnetic studies of a one-dimensional cobalt(Ⅱ)coordination polymer[(enbzp)Co(bpy)](ClO_(4))_(2)·-MeOH·H2O(1;enbzp=N,N′-(ethane-1,2-diyl)bis(1-phenyl-1-(pyridin-2-yl)methanimine,bpy=4,4′-bipyridine)and its desolvated analogue[(enbzp)Co(bpy)](ClO_(4))_(2)(2),obtained by reversible single-crystal-to-single-crystal(SCSC)transformation.
文摘The synthesis of new Schiff base-like ligands with asymmetric substituents pattern and their iron complexes with pyridine as axial ligand is described. Two of the ligands and one of the iron（II） complexes were characterized by single crystal X-ray structure analysis. One of the the iron（II） complexes shows spin crossover behavior while the others remain in the high spin state. The influence of the reduced symmetry of the ligand on the properties of the complexes is discussed.
基金supported by the National Natural Science Foundation of China(21771115,21971142)。
文摘Synergistic fluorescent spin crossover(SCO)bifunctional molecular materials have novel applications in the molecule-based magneto-optical switches.Herein,we report two novel three-dimensional(3D)Hofmann-type fluorescent SCO complexes[Fe^(II)-(tppe)MI(CN)_(2)]ClO_(4)·nSolv(tppe=tetra-(4-pyridylphenyl)ethene,M=Ag(tppe-Ag),Au(tppe-Au)).Both complexes show one-step abrupt SCO with the transition temperature of 230 K for tppe-Ag,and 245 K for tppe-Au accompanied by a color change from red to light yellow.The SCO process is confirmed by the variable-temperature single-crystal X-ray diffraction analysis on tppe-Ag.For the first time,the abnormal increase in emission intensity and concomitant large bathochromic shifts in the fluorescence spectra during the SCO process are realized in the 3D Hofmann-type coordination polymers expanded by the tetradentate tppe ligand.Moreover,tppe-Ag exhibits the unprecedented fluorescence emission from green to the edge of yellow.
基金supported by the National Natural Science Foundation of China(grant nos.22025101,91961114,21871039,22173015,22071017,and 21771049)the Fundamental Research Funds for the Central Universities,China.
文摘The utilization of spin crossover(SCO)to modulate the luminescence properties in smart multifunctional materials and multichannel sensors is promising.However,it is challenging to build a strong coupling between SCO and luminescence in one system.Herein,we present a mononuclear compound[Fe(tpe-abpt)_(2)(SeCN)_(2)]·4DMF(1·4DMF,tpe-abpt:(4-(1,1,2,2-tetraphenylethene))-N-(3,5-bis(pyridin-2-yl)-4H-1,2,4-triazol-4yl)methanimine)showing aggregation-induced emission(AIE)and thermally induced SCO properties.Variable-temperature single-crystal structural analysis reveals that SCO changes the number of pathways and strength of intermolecular interactions,resulting in deactivation of nonradiative decay and significant enhancement of luminescence.The photoluminescence(PL)intensity of 1·4DMF exhibited a fivefold increase upon the spin transition from the low-spin to the high-spin states.In contrast with the current strategy of controlling the Förster resonance energy transfer(FRET)process by utilizing SCO to tune the overlap degree between the emission band of the luminophore and UV–vis absorption band of high-spin and low-spin states,we developed a new approach to tune the intermolecular interactions between AIE luminogens(AIEgens)by utilizing a subtle SCO-induced structural transformation,therefore leading to effective coupling between SCO and luminescence and a significant change in luminescence upon SCO.Our results provide a rational strategy to build smartmultifunctionalizedmaterials with remarkably synergetic SCO and luminescence.
基金supported by the National Natural Science Foundation of China(NSFCnos.21971124 and 22035003).
文摘Spin crossover(SCO)is commonly accompanied by a synchronous phase transition.A few phase transitioncoupled SCO compounds have been reported,yet the synergy between SCO and phase transition on different time scales has not been explored.Herein,we report an[Fe(H-5-Cl-thsa-Et)(5-Cl-thsa-Et)]·H2O(1·H2O;H2-5-Cl-thsa-Et=5-chloro-salicylaldehyde ethylthiosemicarbazone)Fe(III)complex that displays a two-dimensional supramolecular structure and SCO behavior above room temperature.Its dehydrated form1 exhibits a two-step spin transition with aplateau in the temperature-dependent magnetization(M−T)curve at room temperature and a 51 K thermal hysteresis loop(Tc↑↓=299/248 K)at a rate of 5 K/min.The improved SCOperformance in 1 could be attributed to the stronger intralayer but weaker interlayer interactions,which is supported by single-crystal structural analysis and density functional theory calculations.Remarkably,complex 1 displays an unusual scan rate-dependent SCO behavior at rates of 0.5−30 K/min,in whichM−T curveplateaus appear at lower scan rates(<10 K/min)but vanish at faster scan rates(≥10 K/min).Scan rate-dependent differential scanning calorimetry,powder X-ray diffractometry,timedependent magnetic moment decays,and infrared spectroscopy consistently reveal that the slow structural relaxation is coupled with a slowcrystallographic phase transition,which is the mechanism for the unusual scan rate-dependent SCO.
基金the financial support from the National Natural Science Foundation of China (22035009,22178381)the National Key R&D Program of China (2021YFA1501301,2021YFC2901100)。
文摘Light alkanes non-oxidative dehydrogenation is an attractive non-oil route for olefins production.The alkane dehydrogenation reaction is limited by thermodynamic equilibrium,and the C-H bond cleavage is commonly considered as the rate-determined step.The valence state of metal sites in catalysts will influence the stabilization of the vital intermediate(i.e.,C_(x)H_(y)...M^(δ+)...H)during the C-H bond cleavage process,which in turn affects the catalytic reactivity.Herein,we explicitly investigated the effect of different valence states of framework-Fe in silicate-1 zeolite on ethane dehydrogenation reaction through the combination of experimental and theoretical study.Fe(Ⅱ)-S-1 and Fe(Ⅲ)-S-1 catalysts are successfully synthesized by ligand-assisted in situ crystallization method,In-situ C_(2)H_6-FTIR shows the higher coverage of hydrocarbon intermediates on Fe(Ⅱ)-S-1,Under the same evaluation co nditio n,Fe(Ⅱ)-S-1 exhibits a higher space time yield of ethylene.Density functional theory(DFT)results reveal that the more coordinate-unsaturated and electron-enriched Fe(Ⅱ)sites boost the first C-H bond activation by slight deformation and efficient electron donation with C_(2)H_(5)^(*)species.Remarkably,the second C-H bond cleavage on Fe(Ⅱ)-S-1 undergoes a spin-crossing process from quintet state to triplet state,which involves a two-electro n-two-orbital interaction,further promoting the formation of ethylene.Microkinetic analysis is consistent with the experimental and DFT results.This work could provide methodology for elucidating the effect of metal valence states on catalytic performance as well as offer guidance for designing more efficient Fe-zeolite catalysts.
基金supported by the National Natural Science Foundation of China(22025101,22222103,22173015)the Fundamental Research Funds for the Central Universities(DUT22LAB606)Liaoning Binhai Laboratory(LBLE-2023-02),China。
文摘Molecular materials showing synergetic coupling of near-infrared(NIR)fluorescence and spin-crossover(SCO)are promisingly applicable in in-vivo bioimaging,temperature sensing,and spintronic devices.Whilst the related study faces formidable challenges.In this work we graft the NIR fluorophore xanthene onto the dipyridyl substituted triazole ligand and construct a new Febased SCO material,{Fe^(Ⅱ)(ddxc-abpt)_(2)[N(CN)_(2)]_(2)}(1,ddxc-abpt:(E)-4-(((3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)imino)methyl)-N,N-diethyl-2,3-dihydro-1H-xanthen-6-amine).Magnetic studies indicate that compound 1 exhibits thermally induced SCO property in both the solid and solution state.Variable-temperature fluorescence emission spectra reveal a remarkable 7-fold increase in photoluminescence intensity upon the transition from the low-spin state at 110 K to the high-spin state at 280 K,which is the record of all reported coupled fluorescence-SCO materials.Variable-temperature ultraviolet-visible(UV-Vis)absorption spectra show a significant change in absorption intensity within the fluorescence emission window,consistent with the Förster resonance energy transfer(FRET)mechanism.Time-dependent density functional theory(TD-DFT)calculations demonstrate that the strong coupling is attributed to disrupted energy transfer between the xanthene fluorophore and high-spin Fe^(Ⅱ)center.Our work provides a feasible approach for expanding the synergetic SCO-fluorescence materials to the NIR-I wavelength region,and hopefully contributes to the applications of tunable NIR-SCO molecule-based sensors and devices.
基金supported by the National Natural Science Foundation of China(92061106,22101021,22071009)the Ministry of Science and Higher Education of the Russian Federation(State assignment in the field of scientific activity,project No.FENW-2023-0017)。
文摘Spin-crossover(SCO)materials that reversibly switch between high-and low-spin states have potential for the storage of spin state-relative information,and have gained much attention incorporating secondary physical properties,such as fluorescence and magneto-optical switching.In this study,we synthesized three octanuclear metal-organic cages(MOCs)using tetraphenylethylene-based luminophores,aldehydes,and Fe^(Ⅱ)salts,by subcomponent self-assembly approach,namely[Fe1]-[Fe3].By controlling the ligand-field strength and vip encapsulation,we finely tuned their SCO properties.Among them,MOC[Fe2]displayed nearly complete SCO behavior in the solid state,which is rare for high-nuclearity complexes.We also demonstrated the coupling of SCO with fluorescence emission in these MOCs by using isostructural Zn^(Ⅱ)complexes([Zn1]-[Zn3])as control experiments,for the first time.Theoretical calculations revealed the energy-transfer mechanism between fluorophores and SCOactive centers,which emphasizes the significant contribution of d-d transitions in the interplay between the occurrence of SCO and fluorescence emission.
