Breaking the linear correlations for enhanced electrochemical nitrogen reduction by carbon-encapsulated mixed-valence Fe_(7)(PO_(4))_(6)

Electrochemical nitrogen reduction(NRR)is deemed as a consummate answer for the traditional Haber–Bosch technology.Breaking the linear correlations between adsorption and transition-state energies of intermediates is vital to improve the kinetics of ammonia synthesis and obtain a less energy-intensive process.Herein,carbon-encapsulated mixed-valence Fe_(7)(PO_(4))_(6) was prepared and applied as an electrocatalyst for high-efficiency NRR.A dramatic faradaic efficiency(FE)of 36.93%and an NH_(3) production rate of 13.1μg h^(-1) mg_(cat)^(-1) were obtained at-0.3 V versus RHE,superior to nearly all Fe-based catalysts.Experiments and DFT calculations revealed that the superior performance was ascribed to the synergistic effect of mixed-valence iron pair,which braked the linear correlations to improve the kinetics of ammonia from collaborative hydrogenation and*NH_(3) separation.This work proves the feasibility of mixedvalence catalysts for nitrogen reduction and thus opening a new avenue towards artificial nitrogenfixation catalysts.

A Novel Mixed-valence and Capped-keggin Structural Polyoxometal Complex:{[Co(dien)]_4-[(PO_4)Mo_8~Ⅴ(W_(0.56)^(Ⅵ)Mo_(0.44)^(Ⅵ))_4O_(33)(OH)_3 ]}·nH_2O(n≈1)

A novel inorganic-organic hybrid compound, {[Co（dien）]4[0aO4）MoV8（wV10.56MoV10.44）4- O33（OH）3]}＇nH20 （1, n = 1, dien = diethylenetriamine）, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system with a = 11.927（2）, b = 13.328（3）, c = 19.306（4）A, a = 93.76（3）, β = 94.14（3）, γ = 109.99（3）°, V= 2863.2（12） A3, space group P1 and Z = 2 at 173 K. The final full-matrix least-squares refinement converged to R = 0.049 for 9621 observed reflections with 1 〉 2σ（I） and wR = 0.139 for all data （9871） and S = 1.073. Crystal structure analysis shows that 1 contains a kind of the first reported mixed-valence and molybdenum-tungsten mixed-distributed e-Keggin structural polyanion capped by four Co（dien） fragments with the main group element P occupying the center site. These results were further confirmed by energy-dispersive X-ray spectroscopy （EDS）, X-ray powder diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR）, Raman spectroscopy, Thermogravimetry （TG） and X-ray photoelectron spectroscopy （XPS） analyses.

Synthesis and Crystul Structure of A New Mixed-Valence Complex of Copper (Ⅰ, Ⅱ) α-Methacrylate with Triphenylphosphine and Methanol

Copper (Ⅱ) α-methacrylate reacts with triphenylphosphine to form whxed-valence copper (Ⅰ,Ⅱ) complex Cu4(CH2=C(CH3)COO)6(PPh3)4(CH3OH）2 in methanol solution. The crystal and molecular structure of the complex has been detendned by single crystal X-ray structural analysis. This material forms pale green crystals with triclinic symmetry, space group Pi, a=1 .3567(2) nm, b=1.3946 (3) nm, c=1.4569 (3) nm, α=66.069 (14)0, β=84.234 (14)0 γ=69.975 (13)0,R=0.0536.

Self-assembly of a Mixed-valence Cu(Ⅰ)/Cu(Ⅱ)Coordination Polymer Derived from a Conformationally Flexible Tripodal Phosphoric Trimide Ligand

Reaction of a tripodal ligand, N,N＇,N＇＇-tris（3-pyridinyl） phosphoric trimide（TPPA） and CuBr_2·2H_2O result in the assembly of a new polymeric copper coordination polymer, which was characterized by single-crystal diffraction, infrared spectroscopy and elemental analysis. The polymer crystallizes in the triclinic system, space group P1 with a = 9.0964（5）, b = 10.2592, c = 10.5822（8） A, V = 933.01（9） A3, Z = 2, C_（30）H_（24）Br_4Cu_3N_（12）O_2P_2, M_r = 985.02, D_c = 1.753 g/cm3, F（000） = 4072 and μ（MoKα） = 0.746 mm^（-1）. The final R and w R are 0.0588 and 0.1329 for 4260 observed reflections with I 〉 2σ（I）. Cu（Ⅰ） is tetrahedrally coordinated and Cu（Ⅱ） center adopts square planar coordination geometry. Because of the flexibility of the TPPA ligands, the pyridyl rings rotate though a certain angle and three pyridyl rings on the same TPPA rotate by about 45° with respect to the central P=O groups. TPPA ligand acts as a tridentate ligand and is coordinated with three metal centers with its pyridyl donors to form a 2D-sheet like structure, and it is further connected by N-H···O and N-H···Br, resulting in a 3D network packing. Oxidation states of the metal center have been determined by bond valence sum calculation.

Electrochemical and Spectroelectrochemical studies of Mixed-Valence Heteropolyanion VMo_(12)O_(40)^(n-)(n=4,5,6) in Aprotic Media

The mixed-valence heteropolyanion VMo12O40 n-(where n=4,5,6) in aprotic media wasinvestigated by cyclic voltammatry and in-situ FTIR and UV-visible-near-lRspectroelectrochemical methods. The results indicate that the heteropolyanion VMo12O403-undergoes three reversible one electron transfer reductions and the mixed-valenceheteropolyanion VMo12O40n-(where n=4,5,6) was formed after electroreduction. The spectraof the aforementioned mixed-valence compounds were characterized by in-situspectroelectrochemical mathods

Synthesis,Crystal Structure and MMCT Property of a New Mixed-valence Cyanide-bridged Binuclear Complex

A new mixed-valence cyanide-bridged complex, Br3Fe（p-NC）RuBr（dppm）2 （dppm = bis（diphenylphosphino）methane）, was obtained through the reaction between trans-（dppm）2C1- RuCN and FeBr3. Its crystal structure was characterized. Electronic absorption spectra indicate the existence of metal-to-metal charge transfer （MMCT） and this complex is Class II mixed valence complexes according to the classification of Robin and Day. Magnetic analysis shows it is paramagnetic.

Studies of Mixed-valence Compounds(Ⅰ)──In-Situ FTIR and UV-Visible-Near-IR Spectroelectrochemical Studies of Mixed-valence Isopolyanion Mo_6O_(19)^(3-) in Aprotic Media

The mixed-valence isopolyanion Mo6O193- was investigated by means of cyclic voltammographic, in-situ FTIR and UV-Visible-Near-IR spectro-electrochemicalmethods in aprotic media. The experimental results indicate that the Mo6O193-was formed whereafter Mo6O193- was reduced, (E0' = - 0. 690 V, n = 1 ). The characteristic absorptions of Mo6O193- are 500 nm, 900 nm and 1100 nm in UV-VisibleNear-IR spectrum and 940 cm-1 in IR spectrum.

SYNTHESIS AND STRUCTURE OF A MIXED-VALENCE HEXAMOLYBDENUM COMPLEX [Et_4N]_2[Mo_6O_(19)H_4]

A hexamolybdenum complex, [Et_4N]_2[Mo_6O_(19)H_4] crystal, with pentavalent and hexavalent molybdenum has been obtained in the solution of DMF and CH_3OH as organic solvents using MoCl_5 as a starting material. The crystallographic parameters obtained by X-ray diffraction analysis are: crthorhombic, a=10. 757(3), b=10. 763(2), c=14. 238(4)A, =1648. 9A^3; Z=2; space group Pnnm; final R=0. 047; final Rw=0. 051^(**)

SYNTHESIS AND CHARACTERIZATION OF MONOVALENT AND MIXED-VALENCE COMPLEXES OF COPPER WITH 2-THIOURACIL

Five polynuclear monovalent and mixed-valence complexes of copper with 2-thiouracil were synthesized. They were characterized by the molar conductivity, electromc spectra, infrared spectroscopy, thermogravimetric and magnetic susceptibility measurements. Their coordination properties and tentative structures were discussed.

Studies on A Novel Mixed-Valence Complex of Copper(Ⅰ,Ⅱ)α-Methacrylate with Imidazole and Aqua

A novel mixed-valence copper (Ⅰ,Ⅱ) complex Cu3 [CH2=C(CH3) COO]5 (imH)3 (H2O)has been synthesized and characterized by XPS spectra and single crystal X-ray structural analysis.The title complex crystallized in monoclinic space group P21/c, with α=11 .225 (3), b=13.9023 (12),c=24.559 (2), β=92.372 (10)°and Z=4. Final R=0.0495 for 5546 reflections [I＞2σ (Ⅰ)].

Mo8^ⅤW2^ⅥO26（C5H5N）8·2H2O： A Novel Mixed-valence Heterometal Polyoxometalate

A new mixed-valence heterometal cluster Mo8VW2VIO26（C5H5N）8·2H2O has been synthesized under solvothermal conditions and characterized by X-ray single-crystal diffraction, IR, UV-vis and XPS spectroscopy. The title compound crystallizes in the triclinic system, space group P1 with a = 11.708（3）, b = 12.018（4）, c = 13.316（4） A, α = 112.184（4）, β = 97.844（4）, γ = 110.043（3）°, V = 1551.9（8） A3 and Z = 1 at 293（2） K. The final full-matrix least-squares refinement converged to R = 0.0414 for 4460 observed unique reflections with I 〉 2σ（I） and w R = 0.1290 for all data（5352） and S = 1.015. In addition, its thermal stability and fluorescent property have also been investigated.

Carbon nanotube-supported mixed-valence Mn_(3)O_(4) electrodes for high-performance lithium-oxygen batteries

Lithium-oxygen batteries(LOBs)have extensive applications because of their ultra-high energy densities.However,the practical application of LOBs is limited by several factors,such as a high overpotential,poor cycle stability,and limited rate capacity.In this paper,we describe the successful uniform loading of Mn_(3)O_(4) nanoparticles onto multi-walled carbon nanotubes(Mn_(3)O_(4)@CNT).CNTs form a conductive network and expose numerous catalytically active sites,and the one-dimensional porous structure provides a convenient channel for the transmission of Li+and O2 in LOBs.The electronic conductivity and electrocatalytic activity of Mn_(3)O_(4)@CNT are significantly better than those of MnO@CNT because of the inherent driving force facilitating charge transfer between different valence metal ions.Therefore,the Mn_(3)O_(4)@CNT cathode obtains a low overpotential(0.76 V at a limited capacity of 1000 mAh g^(-1)),high initial discharge capacity(16895 mAh g^(-1) at 200 mA g^(-1)),and long cycle life(97 cycles at 200 mA g^(-1)).This study provides evidence that transition metal oxides with mixed-valence states are suitable for application as efficient cathodes for LOBs.

Ultrahigh electrochemical performance in mixed-valence Cu_(1.85)Sebased anode for supercapacitors

Mixed-valence is an effective way to achieve high electrochemical performance of anodes for supercapacitor.However,inordinate mixed valence with more structural defects leads to structural instability.The development of mixed valence electrodes that can maintain a stable structure during the defect formation process is the key to resolving this problem.Cu_(2-x)Se with mixed-valence is a potential candidate,the stable monoclinic structure of Cu2Se can be transformed into another stable cubic structure(x>0.15).Herein,Cu_(1.85)Se anode with mixed valence reveals the ultrahigh specific capacity of 247.8 mA·h/g at 2 A/g.Furthermore,the introduction of multi-walled carbon nanotubes(MWCNTs)into Cu1.85Se further improves the specific capacity(435 mA·h/g at 2 A/g).XRD shows that the introduction of MWCNTs can improve the reversibility via chemical interactions and accelerate the electron transfer in the Cu1.85Se/MWCNTs.Notably,the assembled symmetric supercapacitor(SC)device expresses a high energy density of 41.4 W·h/kg,and the capacity remains 83%even after 8000 charge/discharge cycles.This research demonstrates the great potential of developing high specific capacity anode materials for superior performance supercapacitor.

Some exact results for mixed-valence lattice model

The exact eigenstates of the Hamiltonian of the mixed-valence lattice model are constructed by using the Bethe ansatz. The Bethe ansatz equations are obtained from the periodic boundary conditions. The results show that this system is also completely integrable.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence{Fe^(Ⅲ)_(4)Fe^(Ⅱ)_(4)}Cubes

The engineering of switchable moleculeswith dramatic magnetic change is currently among themost active areas in chemical research.Here,two cyanide-bridged mixed-valence{Fe^(Ⅲ)_(4)Fe^(Ⅱ)_(4)}cubes were prepared,both of which,interestingly,exhibited reversible thermally inducedmetal-to-metal charge transfer(MMCT)behavior between{Fe^(Ⅲ,LS)_(4)Fe^(Ⅱ,HS)_(4)}and{Fe^(Ⅱ,LS)_(4)Fe^(Ⅲ,HS)_(4)}configurations with the transition temperature(T_(1/2))of 274 and 230 K,respectively.These cubes provided a rare example of discrete homometallic complexes exhibiting the reversible MMCT rather than spin crossover behavior.In stark contrast to the heterometallic Fe/Co system,in which the charge transfer(CT)and spin transition(ST)processes occur simultaneously,the detailed structural and Mössbauer spectroscopy analyses confirmed the CT property without involving ST.In addition,both of these cubes showed excellent redox flexibility in solutionwith seven quasi accessible electronic states.

Structural limiting factors of mixed-valent tin oxides in photoelectrochemical application:A comparative exploration

Photoelectrocatalytic(PEC)materials for harvesting solar energy can be discovered from existing photocatalytic semiconductors.Nonetheless,mixed valence tin oxides,a group of widely reported visible light active photocatalysts,can hardly be developed into efficient PEC photoelectrodes.To overcome this difficulty by clarifying its origin,two typical mixed valence tin oxides,Sn^(2+):SnO_(2) microrods and porous Sn_(3)O_(4) particles were deliberately prepared as the models.Sn^(2+):SnO_(2) microrods of less porosity exhibited a photocurrent over ten times higher than Sn_(3)O_(4) particles.Photo-electrochemical impedance spectroscopy revealed this was due to their charge kinetics difference,specifically the internal transport/-transfer responding to the morphology.Moreover,hydroxyl residuals from synthesis were found to be very inhibitive for the PEC efficiency as well,which was in coherence with our TGA and Raman spectroscopic study.These finding experimentally proved the necessity of reconsidering the surface area,crystallinity,and defects when developing photocatalysts into efficient PEC structures.

A Mixed-valent Hexanuclear Cu~Ⅱ-Cu~ⅠComplex with Unusual Tridentate pbi Ligand (pbi = 2-(2-Pyridyl)-benzimidazole)

A mixed-valent hexanuclear complex [Cu^ⅡCu^Ⅰ2（pbi）2Br2]2 （pbi = （2-（2-pyridyl）-benzimidazole） exhibiting a dimeric unit bridged by two Br atoms was synthesized by hydrothermal reaction Interestingly, there exist intramolecular and intermolecular n^zstacking interactions as well as metalaromatic ring interactions in the title complex. The crystal belongs to the monoclinic system, space group P1, with a = 7.1061（9）, b = 12.1008（13）, c = 14.0711（17） A, α=91.742（8）,β=100.155（9）, γ=90.486（7）°, V = 1190.3（2） A^3, Z = 2, C48H32Br4CucoNt2, Mr = 1477.74, Dc= 2.061 g/cm^3, F（000） = 718, μ（MoKα） = 6.039 mm^-1, the final R = 0.0481 and wR = 0.0974 for 3426 observed reflections （I 〉 2σ（I））.

Pressure-Induced Charge-Order Melting and Reentrant Charge Carrier Localization in the Mixed-Valent Pb3Rh7O15

The mixed-valent Pb3Rh7O15 undergoes a Verwey-type transition at Tv≈180K, below which the development of Rh3＋3＋/Rh4＋4＋ charge order induces an abrupt conductor-to-insulator transition in resistivity. Here we investigate the effect of pressure on the Verwey-type transition of Pb3Rh7O15 by measuring its electrical resistivity under hydrostatic pressures up to 8GPa with a cubic anvil cell apparatus. We find that the application of high pressure can suppress the Verwey-type transition around 3GPa, above which a metallic state is realized at temperatures below ～70K, suggesting the melting of charge order by pressure. Interestingly, the low-temperature metallic region shrinks gradually upon further increasing pressure and disappears completely at P〉7GPa, which indicates that the charge carriers in Pb3Rh7O15 undergo a reentrant localization under higher pressures. We have constructed a temperature-pressure phase diagram for Pb3Rh7O15 and compared to that of Fe3O4, showing an archetype Verwey transition.

Crystal Structure of La4V5SiO4O22—A Mixed—Valence Lanthanum Vanadium（

The title compound was prepared by solid state reaction of LaCl_3/V inan evacuated silica tube where the silicon came from the reaction tube. The compoundcrystallizes in monoclinic space group C2/m with cell dimensions of a=13. 482 (7), b=5. 604(3), c=11. 091(3) A, β=100. 44(3)°, V=824(1) A3, Mr= 1274. 66 , Dc=5. 14 g/cm3, F(000) = 1150, μ- 13. 20 mm-1 and Z=2; final R=0. 061, Rw=0. 054for 1037 observed reflections (Ⅰ>3σ(Ⅰ) ) . It is isostructural with quasi-ZD Pr_4V_5Si_4O_(22)compound with the Ⅴ-Ⅴ distances across the shared VO6 octahedral edges of 2. 802 Aand vanadium ions show mixed-valence(Ⅲ/Ⅳ) with an average value of+ 3. 2.

Synthesis and characterization of a new Mo-Fe-S cluster compound containing MoO_3S_3 unit and mixed-valent Mo atoms [Et_4N]_2[Mo_2Fe(CO)_4(S,O-C_6H_4-1,2)_3Cl_2]

Reaction of [Mo3(CO)7(S,O-C6H4-1,2)3]2- with FeCl2 in MeCN at 60℃ affords a new Mo-Fe-S cluster complex containing MoO3S3 unit and mixed-valeut Mo atoms, [Et4N]2[Mo2Fe-(CO)4(O,S-C6H4-1,2)aCl2] (1). 1 is characterized by elemental analysis, IR, Mossbauer spectra, X-ray photoelectron spectra and mass spectra. And the structure of 1 is suggested as the structure which contains a [Mo(S,O-C6H4-1,2)3] unit of which the two of three sulfur atoms link to a Mo(CO)4-moiety and the three oxygen atoms are coordinated to a FeCl2 ligand.