Observation of Ferroelastic and Ferroelectric Domains in AgNbO_(3) Single Crystal

Compared to AgNbO_(3) based ceramics, the experimental investigations on the single crystalline AgNbO_(3), especially the ground state and ferroic domain structures, are not on the same level. Here, based on successfully synthesized AgNbO_(3) single crystal using a flux method, we observed the coexistence of ferroelastic and ferroelectric domain structures by a combination study of polarized light microscopy and piezoresponse force microscopy.This finding may provide a new aspect for studying AgNbO_(3). The result also suggests a weak electromechanical response from the ferroelectric phase of AgNbO_(3), which is also supported by the transmission electron microscope characterization. Our results reveal that the AgNbO_(3) single crystal is in a polar ferroelectric phase at room temperature, clarifying its ground state which is controversial from the AgNbO_(3) ceramic materials.

Activity promotion of Rh_(1)Ca_(x)/Al_(2)O_(3) single-atom catalyst in 1-octene hydroformylation:a volcano curve exists between Ca adding ratio and catalytic activity

Single-atom catalysts(SACs)are considered the best candidates for olefin hydroformylation due to their combined advantages of homogeneous and heterogeneous catalysts.Unlike conventional organo-phosphine modification,Rh SAC is modified by introducing Ca,resulting in a significant increase in activity(maximum~5.7-fold)and stability.Furthermore,a volcano curve between Ca addition ratio and catalytic activity is found.Introducing Ca significantly increases activity by decreasing the energy barrier,but excessive Ca decreases activity due to hindering substrate adsorption and reaction.

Upgrading waste NO_(x)into amino acids via electrocatalysis on Co nanoparticles encapsulated in hollow carbon nanofibers

Electrocatalytic conversion of waste nitrogen oxide(NO_(x))into value-added nitrogenous chemicals,especially amino acid,is an emerging strategy to alleviate NO_(x)pollution.However,this process suffers from the coexistence of multiple competitive reactions leading to complex product distribution and low efficiency,and thus the rational design and modulation of efficient catalysts remains a formidable challenge.Herein,well-designed Co nanoparticles encapsulated in hollow carbon nanofiber(CoHCNF)were constructed to promote the amino acid electrosynthesis via dealing waste NO_(x)coupling with biomass-derived keto acids.Ascribed to the rapid reactant diffusion,electron transport and efficient contact with abundant accessible Co catalytic sites stemmed from the unique hollow nanotubular structure,Co-HCNF manifested impressive glycine synthesis performance in one-pot adopting NO as the nitrogen source with Faradaic efficiency(FE)of 41.7%and a corresponding yield rate of 222.3μmol h^(-1)as well as 120 h robust stability.Interestingly,it also demonstrates an excellent performance with the FE of 42.8%for NO_(3)~-solution as the nitrogen source.Specially,this strategy displays a broad universality for the synthesis of other amino acids.This work not only highlights the importance of hollow-structuring electrocatalyst towards upgrading wasted NO_(x)species into amino acids,but also promotes the further development of electrosynthetic systems for high-valued N-containing organic chemicals.

Light-induced stepped thermal relaxation in a Hofmann-type metal-organic framework

Spin-crossover(SCO)materials with light-induced multistability have potential applications in multi-addressable opto-magnetic memory devices and multiple switches.Here,we reported a three-dimensional Hofmann-type metal-organic framework(MOF)[Fe(bpy){Pt(CN)_(4)}]·coumarin(1·coumarin,bpy=4,4′-bipyridine),which exhibits an incomplete and hysteretic SCO behavior.Most importantly,the light-induced stepped thermal relaxation(LISTR)with obvious magnetic plateau for a hidden intermediate spin state is firstly realized.This hidden spin state is also observed for the first time in the thermal relaxation after light-assisted spin state annealing(LASSA).Meanwhile,an extremely rare bi-directional light-induced excited spin-state trapping(LIESST)with the highest reverse-LIESST temperature is observed.Therefore,five spin states can be captured in 1·coumarin and the tristability can be modulated below 102 K through the excitation-relaxation mechanism.Hence,the light-and temperatureinduced multistability provides a new strategy for developing multistable materials.

An Isolable Phosphinogermylyne as a Synthon of One-Coordinate GeⅠRadical

Reduction of chlorogermylene MsFluindtBu-GeCl 1 with potassium graphite(KC8)afforded putative germylyne radical MsFluindtBu-Ge 2 as confirmed by electron paramagnetic resonance(EPR)spectroscopy.However,it slowly decayed via C—H bond activation at the fluorenyl moiety to yield a bis(germylene)3 at room temperature.By using a Lewis base to stabilize the unoccupied p orbital at the GeⅠradical center,acyclic two-coordinate GeⅠradicals MsFluindtBu-Ge(IMe4)4(IMe4=1,3,4,5-tetramethyl-imidazolin-2-ylidene),MsFluindtBu-Ge(IiPr)5(IiPr=1,3-diisopropyl-4,5-dimethyl-imidazolin-2-ylidene),MsFluindtBu-Ge(PMe3)6 were isolated in crystalline forms.The unpaired electron in 4-6 mainly resides at the Ge 4p orbital as revealed by EPR spectroscopic studies and theoretical calculations.Interestingly,facile ligand exchange of PMe3 in 6 with IMe4 and IiPr was observed to afford 4 and 5,respectively.Moreover,phosphinogermylyne 6 reacted with PhEEPh(E=S,Se),4-tetrabutylphenylacetylene(Ar'CCH),[CpMo(CO)3]2 and nBu3SnH to furnish germylenes MsFluindtBu-GeEPh(E=S 7,Se 8),MsFluindtBu-GeCH=CHAr'9,a germylyne complex MsFluindtBu-Ge≡Mo(CO)2Cp 10 and a Ge(Ⅳ)compound MsFluindtBu-GeH2SnnBu311,respectively.The reactivity studies demonstrate that 6 can act as a synthon of one-coordinate germylyne radical attributing to labile coordination of trimethylphosphine.

Inclusion of methylviologen dication in a cadmium tetracyanoplatinate host clathrate showing photochromism and photoluminescence modulation

A cadmium tetracyanoplatinate host clathrate,(MV)[Cd_(2){Pt(CN)_(4)}_(3)]·2(H_(2)O)(1),including a methylviologen dication (MV^(2+)) was synthesized,and the crystal structures,photochromic and photoluminescence properties were investigated.In 1,the alternatively parallel stacking between the MV^(2+)dications as electron acceptors in the channels and the electron donors[Pt1(CN)_(4)]^(2-) units in the host frameworks give a unique donor-acceptor (DA) system.Under UV irradiation,the electron transfer between MV^(2+) and[Pt(CN)_(4)]^(2-) ions generates MV^(·+)radicals with a photochromic behavior from pale-yellow to blue.This process occurs through single-crystal-to-single-crystal (SCSC) transformation and obvious structure variation of viologen cations is successfully observed.Moreover,the spectral overlap between the emission bands of 1 and the absorption around 623 nm for the MV^(·+) radicals leads to a modulation of the photoluminescence.

From geometric to charge-distribution symmetry:deeper insights into lifting the performance of dysprosium single-ion magnets

Crystal-field symmetry of lanthanide ions plays a critical role in suppressing quantum tunneling of magnetization(QTM)in single-molecule magnets(SMMs),but high-performance SMM design and modulation remain challenging only in view of the geometric symmetry of the first coordination sphere.Herein,two bis(semicarbazone)/bis(thiosemicarbazone)dysprosium singleion magnets with pentagonal bipyramid geometry were reported,and bis(thiosemicarbazone)lanthanide complexes have never been reported to the best of our knowledge.They served as good archetypes to study the magneto-structural relationships based on the charge distribution.The complex with more ideal geometric symmetry displays fast zero-field QTM with negligible“effective barrier”,owing to the defective charge distribution.By modulating the transverse crystal field via the replacement of the O sites with the less charged and larger radius S atoms,it results in lower geometric but higher charge-distribution symmetry,giving rise to the significant suppression of QTM and the enhancement of reversal barrier up to ca.1,000 K.These results demonstrate that the charge-distribution symmetry can be chemically tailored by modification of the crystal field,which is essential for designing high-performance SMMs.

Modulation of ionic arrangement in polar magnet by chemical pressure

The similarity of local structure-connection pattern and volumetrically compressive strain between host and guest phases can be used to stabilize heteroid metastable matter and tune the local structure and properties.Here a series of metastable ABO_(3)(A=Mn;B=Mn_(0.5)Mo_(0.5),Mn_(1/3)Ta_(2/3),and Mn_(0.5)Ta_(0.5)) were trapped in LiTaO_(3) to form solid-solutions,where the difference of solid solubility limit reveals the barrier of size effect on chemical pressure.All samples show antiferromagnetic characters,in which the(LiTaO_(3))_(1-x)-[Mn(Mn_(0.5)Mo_(0.5))O_(3)]_(x) series exhibit more complex magnetic and dielectric behaviors with the increasing of metastable guest phase,stemming from the complex interactive mechanism between Mn^(2+)and Mo^(6+).The cell parameter variation of (LiTaO_(3))_(1-z)-[Mn(Mn_(0.5)Ta_(0.5))O_(3)]_zshows a more regularly changing tendency,on account of the smallest size barrier.These findings show that chemical pressure can effectively stimulate the physical pressure to intercept and modulate a metastable phase at atomic-scale by compressibility effect between like structures at ambient pressure.

Structural diversity and reactivity of d^(10) metal-(4-pyridylthio)acetate system

The hydrothermal synthesis and crystal structures of four coordination polymers, namely, 2D [Zn(μ3-ta)(pytaH)]n (1), 2D [Zn(μ3-pyta)Cl]n (2), 1D [Cd(μ-pyta)2(H2O)]n (3), and 3D [Cd(μ3-pyta)(μ-Cl)]n (4) (pyta = (4-pyridylthio)acetate, ta = thioglycolate), are reported. They are based on (4-pyridylthio)acetate and its derived ligand. The ta2ligand present in 1 was generated from an in situ C(sp2)-S bond cleavage of the pyta ligand. In these compounds, versatile intermolecular interactions, such as close S…S interactions and strong (O―H…O/N/S) or weak (C―H…O/S, C―H…Cl) hydrogen bonding interactions, play an important role in the formation of three-dimensional supramolecular networks in the solid state.

Direct observation of the ultrafast energy transfer in a porphyrin and ruthenium dyad

The luminescence dynamics of a polypyridyl ruthenium II [Ru（phen）2（ip）]2＋ and 5,10,15,20- tetraphenylporphyrin （H2TPP） dyad have been measured by using time-resolved fluorescence spectroscopy. The transient luminescent spectra of the dyad show an ultrafast energy transfer within 300 ps after pho- toexcitation of the [Ru（phen）2（ip）]2＋ at 453 am. However, no energy transfer has been observed as the excitation wavelength is 400 nm, corresponding to the absorption peak of H2TPP. The origin of the energy transfer from [Ru（phen）2（ip）]2＋ to H2TPP has been analyzed according to the FSrster energy-transfer theory.

Enhancing single-molecule magnet behavior of linear Co~Ⅱ-Dy~Ⅲ-Co~Ⅱ complex by introducing bulky diamagnetic moiety

Single-molecule magnets(SMMs)are regarded as promising candidates for ultrahigh-density storage,quantum information processing and molecular spintronics.It is a crucial challenge for chemists to modulate magnetic dynamics of SMMs.Here,we successfully synthesized two 3d-4f polynuclear compounds[Co_2Dy(TTTT^(Cl))_2(MeOH)]NO_3·3MeOH(1)and[Co_2Dy(TTTT^(Cl))_2(MeOH)][Co(HTTTT^(Cl))](NO_3)_2·2.5MeOH·2H_2O(2),where H_3TTTT^(Cl)=2,2′,2′′-(((nitrilotris(ethane-2,1-diyl))tris(azanediyl))tris(methylene))tris-(4-chlorophenol).On applying the approach by co-crystallization of bulky diamagnetic moiety,the effective energy barrier enhances from 401 K(1)to 536 K(2),which are both among the highest d-f heterometallic SMMs.

Reversible on-off switching of spin-crossover behavior via photochemical [2+2] cycloaddition reaction

Herein,we report the first example showing the reversible on-off switching of spin-crossover(SCO)property by solid state photochemical[2+2]reaction.The ultraviolet(UV)light-induced[2+2]cycloaddition reaction of 3-spy ligands in a twodimensional(2D)Hofmann-type framework[Fe(3-spy)_(2){Pd(CN)_(4)}](1,3-spy=3-styrylpyridine),which shows a hysteretic twostep SCO behavior,gives a 3D Hofmann-type framework[Fe(rctt-3-ppcb){Pd(CN)_(4)}](2,rctt-3-ppcb=rctt-1,3-bis(3-pyridyl)-2,4-bis(phenyl)cyclobutane,r=reference group,c=cis and t=trans)accompanied with the disappearing of SCO properties.Moreover,upon heating at 250℃ for 12 h,the rctt-3-ppcb ligand in 2 could be partially dedimerized to 3-spy with 68%completion through single-crystal-to-single-crystal(SCSC)transformation,giving the annealing complexes[Fe(3-spy)1.36(rctt-3-ppcb)0.32{Pd(CN)_(4)}](3)which display an incomplete SCO behavior.The 2■3 interconversion is successfully achieved via continuous UV irradiation and thermal annealing,demonstrating the effectiveness of photochemical[2+2]reaction on switching on-off SCO properties.

Defect-manipulated magnetoresistance and above-room-temperature ferromagnetism in two-dimensional BaNi_(2)V_(2)O_(8)

The intricate correlation between multiple degrees of freedom and physical properties is a fascinating area in solid state chemistry and condensed matter physics.Here,we report a quantum-magnetic system BaNi_(2)V_(2)O_(8)(BNVO),in which the spin correlation was modulated by unusual oxidation state,leading to different magnetic behavior.The BNVO was modified with topochemical reduction(TR)to yield TR-BNVO with partially reduced valance state of Ni^(+)in the two-dimensional NiO_(6)-honeycomb lattice.Accordingly,the antiferromagnetic order is suppressed by the introduction of locally interposed Ni^(+)and oxygen vacancies,resulting in a ferromagnetic ground state with the transition temperature up to 710 K.A positive magnetoresistance(7.5%)was observed in the TR-BNVO at 40 K under 7 T.These findings show that topological reduction is a powerful approach to engineer low-dimensional materials and accelerate the discovery of new quantum magnetism.

Multiresponsive Spin Crossover Driven by Rotation of Tetraphenylborate Anion in an Iron(Ⅲ)Complex

Dynamic molecular materials,which involvemechanical motions in crystals,usually exhibit tunable properties related to conformational polymorphs.Herein,we describe a solvent-free molecular crystal[{FeⅢ(salten)}2(TPB)](BPh_(4))_(2)(Ⅰ)developed by associating the rotatable tetraphenylborate anion with the spin crossover(SCO)binuclear iron(Ⅲ)cation.The solvent-free phaseⅠcan undergo a temperature-induced phase transformation to phaseⅡ,during which rotation of the BPh4−anion interplays with the SCO component,giving rise to fascinating variations in SCO(from gradual to abrupt)and dielectric properties.Most importantly,an unexpected polymorphic transformation fromⅡtoⅢorⅣ,with increasing magnetic hysteresis,is realized by exposingⅡto water or ethanol vapor;the transition is reversible by heating.This rare successive transformation is further rationalized by theoretical calculations.Hence,this multiresponse system provides a new way for modulating synergistic effects and designing dynamic SCO materials by integrating intramolecular motions in the crtystal lattice.

A dual-switching spin-crossover framework with redox regulation and guest response

A dual-switching spin crossover metal-organic framework(SCO-MOF)[Fe(TPB){Pt^(Ⅱ)(CN)_(4)}]·3iPrOH·4H_(2)O(TPB=1,2,4,5-tetra(pyridin-4-yl)benzene)is developed via the combination of redox-active framework and tunable guests.The reversible structural transformation between[Pt^(Ⅱ)(CN)_(4)]^(2-) and[Pt^(Ⅳ)Br_(2)(CN)_(4)]^(2-)moieties can be manipulated by redox post-synthetic modification(PSM),which results in the change of SCO behaviors from step-wise to one-step.The influences of the oxidative addition of bromides on the ligand field splitting of Fe side are further explored by density functional theory calculations.Besides,the modulation of hysteretic four-/three-step,one-step and four-step SCO behaviors can be achieved by tuning the composition of guest molecules.Therefore,the combination of electronic bistability,redox reaction and guest recognition in a homogeneous lattice provides a utility platform for designing multi-responsive molecule-based materials.

Spherical lanthanide nanoclusters toward white-light emission and cell membrane imaging

Lanthanide doping is an effective strategy for modulating the emission of emitters.Herein,by changing the cluster composition to control the energy transfer pathway,the application potential of high-nuclearity lanthanide cluster(HLC)as white-light emitter has been confirmed for the first time.Specifically,by precisely controlling the proportion of GdIII,TbIII,and EuIII ions in reactants,we obtained a spherical heterotrimetallic nanocluster Gd_(10)Tb_(12)Eu_(10),a white-light emitter with quantum yield(QY)of 12.58%and lifetime of 327.14μs.High-resolution electrospray ionization mass spectrometry(HRESI-MS)demonstrates that homometallic nanoclusters Ln_(32)(Ln=Gd,Tb,and Eu)are tetracationic clusters and are highly stable in solution.The peripheral dense organic ligands provide a protective layer for the cluster core,which improves the stability of Ln_(32) in aqueous solution,avoids the contact between metal centers and bioactive molecules,and greatly reduces the biological toxicity.In cell imaging experiments,cationic clusters Ln_(32) are mainly localized on the cell membrane with negative charge distribution.As far as we know,this is the first time that spherical lanthanide nanoclusters have been used for membrane imaging of living cell,opening the door for the application of HLCs in biological imaging.

Pressure-Induced Intermetallic Charge Transfer and Semiconductor- Metal Transition in Two-Dimensional AgRuO_(3)

The intricate correlation between charge degrees of freedom and physical properties is a fascinating area of research in solid state chemistry and condensed matter physics.Herein,we report on the pressureinduced successive charge transfer and accompanied resistive evolution in honeycomb layered ruthenate AgRuO_(3).Structural revisiting and spectroscopic analyses affirm the ilmenite type R-3 structure with mixed valence cations as Ag^(+1/+2)Ru^(+4/+5)O_(3) at ambient pressure.In-situ pressure-and temperature-dependent resistance variation reveals a successive insulatormetal-insulator transition upon pressing,accompanied by unprecedented charge transfer between Ag and Ru under applied pressure,and a further structural phase transition in the insulator region at higher pressure.These phenomena are also corroborated by in-situ pressure-dependent Raman spectra,synchrotron X-ray diffraction,bond valence sums,and electronic structure calculations,emphasizing the dominated rare Ag2+,and near zero thermal expansion in the ab-plane in the metallic zone mostly due to the Jahn-Teller effect of d9-Ag2+.The multiple electronic instabilities in AgRuO_(3) may offer new possibilities toward novel and unconventionally physical and chemical behaviors in strongly correlated honeycomb lattices.

V_(8)C_(7)/C稳定的超细Ru纳米颗粒用于全pH下的析氢反应

The development of cost-effective electrocatalysts with high efficiency and long durability for hydrogen evolution reaction(HER)remains a great challenge in the field of water splitting.Herein,we design an ultrafine and highly dispersed Ru nanoparticles stabilized on porous V_(8)C_(7)/C matrix via pyrolysis of the metal-organic frameworks V-BDC(BDC:1,4-benzenedicarboxylate).The obtained Ru-V_(8)C_(7)/C composite exhibits excellent HER performance in all p H ranges.At the overpotential of 40 mV,its mass activity is about 1.9,4.1 and 9.4 times higher than that of commercial Pt/C in acidic,neutral and alkaline media,respectively.Meanwhile,Ru-V_(8)C_(7)/C shows the remarkably high stability in all p H ranges which,in particular,can maintain the current density of 10 m A cm^(-2)for over 150 h in 1.0 mol L^(-1)phosphate buffer saline(PBS).This outstanding HER performance can be attributed to the high intrinsic activity of Ru species and their strong interface interactions to the V_(8)C_(7)/C substrate.The synergistic effect of abundant active sites on the surface and the formed Ru-C-V units at the interface promotes the adsorption of reaction intermediates and the release of active sites,contributing the fast HER kinetics.This work provides a reference for developing versatile and robust HER catalysts by surface and interface regulation for pH tolerance.

Di- and tetranuclear heterometallic CuⅡ-LnⅢ complexes (Ln = Gd and Dy): Synthesis, structure and magnetic properties

Four 3d-4f heterometallic complexes, [CuⅡ LnⅢ (bpt) 2 (NO 3 ) 3 (MeOH)] (Ln = Gd, 1; Dy, 2; bptH = 3,5-bis(pyrid-2-yl)-1,2,4- triazole), [CuⅡ 2 LnⅢ 2 (μ-OH) 2 (bpt) 4 Cl 4 (H 2 O) 2 ]·6H 2 O (Ln = Gd, 3; Dy, 4), have been synthesized under solvothermal conditions. X-ray structural analyses reveal that 1 and 2 are isostructural while 3 and 4 are isostructural. In each complex, the copper and gadolinium or dysprosium ions are linked by two triazolate bridges and form a CuⅡ -LnⅢ dinuclear unit. The intramolecular Cu-Ln distances are 4.542, 4.525, 4.545 and 4.538 for 1, 2, 3 and 4, respectively. Two dinuclear CuLn units are bridged by two OH- groups into the zig-zag tetranuclear {CuⅡ 2 LnⅢ 2 } structures with the Ln(Ⅲ) Ln(Ⅲ) distances of 3.742 and 3.684 for 3 and 4, respectively. Magnetic studies show that the antiferromagnetic CuⅡ-LnⅢ interactions occur in 1 (J CuGd = 0.21 cm-1 ) and 2. The antiferromagnetic interaction occurs in complex 3 with J CuGd = 0.82 cm-1 and J GdGd = 0.065 cm-1 , while dominant ferromagnetic interaction occurs in complex 4.