Recent Advances in Mechanistic Understanding of Metal-Free Carbon Thermocatalysis and Electrocatalysis with Model Molecules

Metal-free carbon,as the most representative heterogeneous metal-free catalysts,have received considerable interests in electro-and thermo-catalytic reac-tions due to their impressive performance and sustainability.Over the past decade,well-designed carbon catalysts with tunable structures and heteroatom groups coupled with various characterization techniques have proposed numerous reaction mechanisms.However,active sites,key intermediate species,precise structure-activity relationships and dynamic evolution processes of carbon catalysts are still rife with controversies due to the monotony and limitation of used experimental methods.In this Review,we sum-marize the extensive efforts on model catalysts since the 2000s,particularly in the past decade,to overcome the influences of material and structure limitations in metal-free carbon catalysis.Using both nanomolecule model and bulk model,the real contribution of each alien species,defect and edge configuration to a series of fundamentally important reactions,such as thermocatalytic reactions,electrocatalytic reactions,were systematically studied.Combined with in situ techniques,isotope labeling and size control,the detailed reaction mechanisms,the precise 2D structure-activity relationships and the rate-determining steps were revealed at a molecular level.Furthermore,the outlook of model carbon catalysis has also been proposed in this work.

Engineering hierarchical quaternary superstructure of an integrated MOF-derived electrode for boosting urea electrooxidation assisted water electrolysis

Controllable design of the catalytic electrodes with hierarchical superstructures is expected to improve their electrochemical performance.Herein,a self-supported integrated electrode(NiCo-ZLDH/NF)with a unique hierarchical quaternary superstructure was fabricated through a self-sacrificing template strategy from the metal–organic framework(Co-ZIF-67)nanoplate arrays,which features an intriguing well-defined hierarchy when taking the unit cells of the NiCo-based layered double hydroxide(NiCo-LDH)as the primary structure,the ultrathin LDH nanoneedles as the secondary structure,the mesoscale hollow plates of the LDH nanoneedle arrays as the tertiary structure,and the macroscale three-dimensional frames of the plate arrays as the quaternary structure.Notably,the distinctive structure of NiCo-ZLDH/NF can not only accelerate both mass and charge transfer,but also expose plentiful accessible active sites with high intrinsic activity,endowing it with an excellent electrochemical performance for urea oxidation reaction(UOR).Specially,it only required the low potentials of 1.335,1.368 and 1.388 V to deliver the current densities of 10,100 and 200 mA cm^(-2),respectively,much superior to those for typical NiCo-LDH.Employing NiCo-ZLDH/NF as the bifunctional electrode for both anodic UOR and cathodic HER,an energy-saving electrolysis system was further explored which can greatly reduce the needed voltage of 213 mV to deliver the current density of 100 mA cm^(-2),as compared to the conventional water electrolysis system composed of OER.This work manifests that it is prospective to explore the hierarchically nanostructured electrodes and the innovative electrolytic technologies for high-efficiency electrocatalysis.

Introducing hydroxyl groups to tailor the d-band center of Ir atom through side anchoring for boosted ORR and HER

Tuning the coordination atoms of central metal is an effective means to improve the electrocatalytic activity of atomic catalysts.Herein,iridium(Ir) is proposed to be asymmetrically anchored by sp-N and pyridinic N of hydrogen-substituted graphdiyne(HsGDY),and coordinated with OH as an Ir atomic catalyst(Ir_(1)-N-HsGDY).The electron structures,especially the d-band center of Ir atom,are optimized by these specific coordination atoms.Thus,the as-synthesized Ir_(1)-N-HsGDY exhibits excellent electrocatalytic performances for oxygen reduction and hydrogen evolution reactions in both acidic and alkaline media.Benefiting from the unique structure of HsGDY,IrN_(2)(OH)_(3) has been developed and demonstrated to act as the active site in these electrochemical reactions.All those indicate the fresh role of the sp-N in graphdiyne in producing a new anchor way and contributing to promote the electrocatalytic activity,showing a new strategy to design novel electrochemical catalysts.

Deciphering the potassium storage phase conversion mechanism of phosphorus by combined solid-state NMR spectroscopy and density functional theory calculations

Phosphorus is the potential anode material for emerging potassium-ion batteries(PIBs)owing to the highest specific capacity and relatively low operation plateau.However,the reversible delivered capacities of phosphorus-based anodes,in reality,are far from the theoretical capacity corresponding to the formation of K3P alloy.And,their underlying potassium storage mechanisms remain poorly understood.To address this issue,for the first time,we perform high-resolution solid-state31P NMR combined with XRD measurements,and density functional theory calculations to yield a systemic quantitative understanding of(de)potassiation reaction mechanism of phosphorus anode.We explicitly reveal a previously unknown asymmetrical nanocrystalline-to-amorphous transition process via rP←→(K_(3)P_(11),K_(3)P_(7),beta-K_(4)P_(6))←→(alpha-K4P6)←→(K_(1-x)P,KP,K_(4-x)P3,K_(1+x)P)←→(amorphous K4P3,amorphous K3P)that are proceed along with the electrochemical potassiation/depotassiation processes.Additionally,the corresponding KP alloys intermediates,such as the amorphous phases of K_(4)P_(3),K_(3)P,and the nonstoichiometric phases of“K_(1-x)P”,“K_(1+x)P”,“K_(4-x)P_(3)”are experimentally detected,which indicating various complicated K-P alloy species are coexisted and evolved with the sluggish electrochemical reaction kinetics,resulting in lower capacity of phosphorus-based anodes.Our findings offer some insights into the specific multi-phase evolution mechanism of alloying anodes that may be generally involved in conversion-type electrode materials for PIBs.

Hydrothermal Synthesis and Crystal Structure of a Square Grid Coordination Copper(II) Polymer from 1,4-Bis(imidazole-1-ylmethyl)benzene

The title compound [Cu（bix）2（NO3）z·H2P]n 1 （bix = 1,4-bis（imidazole-1-ylme-thyl） benzene） has been synthesized by hydrothermal method. Its crystal structure is of monoclinic, space group P1^- with a = 8.3075（13）, b = 9.4725（13）, c = 10.0192（13） A, α = 91.088（4）, β = 104.063（6）, γ = 101.88（1）, V = 746.5（3） A^3, Z = 1, C28H30N10O7Cu1, Mr = 682.16, Dc = 1.518 g/cm^3, μ = 0.796 mm^-1, F（000） = 353, the final R = 0.0535 and wR = 0.0996 for 2921 observed reflections with I 〉 2σ（I）. Each bix ligand binds two Cu（Ⅱ） ions to form a 2-D（4,4） square grid layer, which is connected by hydrogen bonds showing large channels occupied by solvated water molecules and nitrate anions.

Synthesis, Structure and Magnetic Properties of a Linear Trinuclear Mn(II) Complex with a Multifunctional Group Ligand

By use of a new ligand containing both salicylic acid moiety and salicylaldehyde Schiff base moiety, 5-（2-hydroxybenzylideneamino）-2-hydroxybenzoic acid （H3L）, a linear trinuclear Mn（II） complex was prepared. This complex crystallizes in triclinic, space group P1 with a = 12.0196（7）, b = 13.7440（13）, c = 15.7554（14） , α = 111.529（3）, β = 96.691（2）, γ = 94.802（2）o, C96H100Mn3N6O32, Mr = 2014.64, V = 2382.0（3） 3, Z = 1, μ = 0.478, Dc = 1.404 g/cm3, F（000） = 1049, R = 0.0554 and wR = 0.1610 for 8973 observed reflections （I 〉 2σ（I））. The complex consists of a trinuclear cluster and two solvate ethanol molecules. Three linearly disposed Mn atoms, with an inversion center on the central one, are bridged by six carboxylate groups from six bulky mono-anionic ligands （H2L-）, and the octahedral coordination spheres for each of the metal centers are thus formed, with the aid of additional ligation of two small molecules （ethanol and water） to both ends. The magnetic properties of the title complex are also included in this paper.

A Series of Mononuclear Complexes Constructed from Transition Metals and Amino Acid Derived Ligands: Syntheses, Structures and Photoluminescence

Eight neutral mononuclear complexes constructed from transition metals （M = Co（Ⅱ）, Ni（Ⅱ）, Cu（Ⅱ）, Zn（Ⅱ）, Cd（Ⅱ）） and ligands N-（2-pyridylmethyl）-L-phenylalanine （L-Hpmpa） and N-（2-pyridylmethyl）-L-tyrosine （L-Hpmtyr） have been synthesized by both hydrothermal and conventional room temperature reactions. Four of them have been structurally characterized by single-crystal X-ray diffractions. They are： [Co（L-pmpa）2·2H2O] 1, [Ni（L-pmpa）2·2H2O] 2, [Cu（L-pmpa）2·2H2O] 3 and [Cu（L-pmtyr）2·2H2O] 4. Single-crystal X-ray analysis, IR and elemental analysis revealed that complexes 1, 2 and 3 are isostructural. Powder X-ray diffraction, IR and elemental analysis revealed that complexes 4, 5 （Zn[L-pmtyr]2·2H2O）, 6 （Cd[L-pmtyr]2·2H2O）, 7 （Co[L-pmtyr]2·2H2O） and 8 （Ni[L-pmtyr]2·2H2O） are isostructural. The photoluminescence properties of L-Hpmtyr ligand, compounds 5 and 6 were also investigated.

Synthesis,Crystal Structure and Properties of a Nanotubular Metal-organic Framework(MOFs) Based on Cu(Ⅱ) Oxide Chains and Benzenedicarboxylates

A new cooper benzenedicarboxylate metal-organic coordination polymer,[Cu（μH2O）（BDC）]n·nDMF（1,H2BDC = 1,4-benzenedicarboxylate acid,DMF = N,N＇-dimethylfor-mamide）,has been successfully synthesized under hydrothermal conditions and characterized by IR spectroscopy,elemental analysis,thermogravimetric analysis and single-crystal X-ray diffraction.This complex crystallizes in triclinic,space group P1 with a = 6.605,b = 10.44780（10）,c = 11.0881（6） ,α = 62.064（11）,β = 73.410（15）,γ = 78.404（16）°,C11H13CuNO6,Mr = 318.76,V = 645.79（8） 3,Z = 2,Dc = 1.639 g/cm3,F（000） = 326,μ = 1.712 mm-1,the final R = 0.0362 and wR = 0.1330 for 2055 observed reflections with I 〉 2σ（I）.The title compound contains infinite inorganic chains constructed by Cu oxygen octahedra by sharing corners and edges.Each chain is connected by BDC linkers to four other chains to form a three-dimensional framework with irregular rhombic channels where the DMF molecules are encapsulated.

Synthesis, Crystal Structure and Band Structure of Eu_3Sn_5 with Arachno-type Zintl Anions

A new polar intermetallic compound, Eu3Sn5, has been synthesized by solid-state reaction of the corresponding pure elements in a stoicbiometric ratio in a welded tantalum tube at high temperature. Its crystal structure was established by single-crystal X-ray diffraction. EuaSn5 crystallizes in orthorhombic, space group Cmcm with a = 10.466（11）, b = 8,445（8）, c = 10.662（12）/k, V = 942.4（17）A^3, Z = 4, Mr = 1049.33, De= 7.396 g/cm^3, ,μ = 32.578 mm^-1, F（000） = 1756, the final R = 0.0236 and wR = 0.0472 for 535 observed reflections with I 〉 2σ（I）. Its structure belongs to the modified Pu3Pd5 type. It is isostructural with SraSn5 and Ba3Sn5, featuring [Sn5] square pyramidal clusters described as “arachno” according to the Wade-Mingos electron counting rules. The europium cations are located at the voids between the square pyramidal clusters. Results of the extended Htickel band structure calculations indicate that Eu3Sn5 is metallic.

Synthesis and Structure of a Mn(Ⅱ)-triazolyl Coordination Polymer Consisting of Dinuclear Units

The reaction of bis（1,2,4-triazolyl-4-yl） （btr） and MnClO4-6H20 gave rise to a Mn（II） complex comprised of unprecedented dinuclear Mn（II） units, {[Mn2（btr）s（H20）5]- （ClO4）4（H20）2]n （1）. Single-crystal X-ray diffraction analysis revealed that 1 crystallizes in the monoclinic space group C2/c. btr adopts two types of bridging modes. One serves as μ-N1 ：N2 bridge through one triazolyl ring of btr forming a dinuclear Mn（II） unit, and the other adopts an exo-bidentate mode using two nitrogen atoms from each triazolyl ring and links the dinuclear units into a 2D cationic layer. ClO4 acts as a counter anion and does not take part in coordination. Interestingly, 2D layers are packed in an ABCABC mode. ClO4- and uncoordinated water molecules locate between the adjacent layers, and extensive hydrogen bonds further stabilize the whole framework.

Synthesis, Crystal Structure and Photoluminescent Property of a 3D Hydrogen-bonded Supramolecular Compound with Large Channels

The title compound, [Pd（2,2′-bipy）2]（Haadip）2·4H2O, was synthesized via the hydrothermal reaction of PdCl2 with 5-aminodiacetic isophthalic acid （H4adip） in an acetic acid water solution. It was characterized by elemental analysis and infrared spectrum. Crystal data for C44H44N6O20Pd： monoclinic, space group P21/n, a = 11.0674（2）, b = 9.9716（2）, c= 20.5770（3）A, β = 92.7300（3）°, V = 2268.29（7）A^3, Z = 2, Mr = 1083.25, Dc = 1.586 g/cm^3, F（000） = 1112,μ = 0.499 mm^-1, 2（MoKa） = 0.71073 A, T = 293（2） K, 2θmax = 51.38°, GOOF = 1.067, R = 0.0268 and wR = 0.0710 for 3770 reflections with 1 〉 2σ（I）. X-ray diffraction studies reveal that the title compound has an interesting 3D microporous architecture via hydrogen bonds with the cations located inside the channel.

Synthesis, Crystal Structure and Characterization of a New Zinc Citrate Complex

A new Zn-citrate coordination complex {K[Zn（C6H5O7）（H2O）]}n（1） was synthesi- zed via hydrothermal reaction. In the crystal structure of complex 1, each citrate serves as thequadricdentate ligand coordinating to three Zn（II） ions, forming a zigzag chain, and such chains are further connected into a 3D network by the K＋ linkers. Crystal data for complex 1： triclinic, space group Pī, α = 7.3487（9）, b = 7.5397（6）, c = 9.6772（8） A, α = 76.894（8）, β = 68.260（10）, γ = 65.155（10）°, V = 450.34（7） ？3 and Z = 2. Other characterizations by elemental analysis, IR, TG and fluorescence were also described.

Synthesis and Crystal Structure of a New Zn(Ⅱ) Coordination Polymer Constructed by 1,2,4,5-Benzenetetracarboxylate

A new Zn（Ⅱ） coordination polymer [Zn3（btec）（OH）2（H2O）2]n （1, btec = 1,2,4,5- benzenetetracarboxylate） has been synthesized by hydrothermal reaction and its structure was determined by single-crystal X-ray diffraction analysis. The title compound crystallizes in mono- clinic, space group C2/c, with a = 19.580（3）, b = 5.0137（8）, c = 15.975（3）, β = 121.629（2）°, V = 1335.3（4）3, C10H8O12Zn3, Mr = 516.27, Z = 4, Dc = 2.568g/cm3, μ = 5.419 mm-1, F（000） = 1016, R = 0.0590 and Rw = 0.1279 for 1110 observed reflections （I 2σ（I））. X-ray analysis shows that the asymmetric unit of the title compound contains two crystallographically unique Zn（Ⅱ） atoms which are connected through the bridging carboxylate oxygen atoms of the btec ligands and μ2-bridging oxygen atoms of water molecules to generate an infinite one-dimensional chain. The adjacent chains are linked together through the benzene rings of the btec ligands to form a two-dimensional polymeric network. The adjacent two-dimensional layers are further connected together by the benzene rings of btec ligands to give the final three-dimensional structure. The benzene rings act as pillars between two layers.

Synthesis,Structure,and Property of a Three-dimensional Channel Quaternary Compound:Cs_(0.75(6))Er_(4.43(5))In_(3.32(6))S_(12)

A new quaternary rare-earth sulfide, Cs0.75（6）Er443（5）In3.32（6）S12 （1）, is discovered by high temperature solid state reactions with a slight excess of CsCI flux. The structure is characterized by single-crystal X-ray diffraction data, while crystallizes in hexagonal space group P63/m （No. 176） with a = 12.0329（6）, c = 3.8693（5）A, V= 485.18（7） A3, Z = 1, Mr = 1606.57, Dc = 5.499 g/cm3,μ = 25.457 mm-1, F（000） = 752, the final R = 0.0337 and wR = 0.0904 for 328 observed reflections with I 〉 2σ（I）. Its structure features a three-dimensional framework with hexagonal channels that are centered by Cs cations. Such channels are formed by double chains of edge-sharing M（1）S6 （M（1） = Er（1）/In（1）） octahedra and single chains of Er（2）S6 triprism interconnected by corner-sharing. The syntheses, single-crystal analyses, optical band gap and magnetic property are reported.

Synthesis, Crystal Structure and Gas Adsorption of a Trimeric Nickel-based Coordination Polymer

A trimeric porous coordination framework [Ni_3(TPTC)(IN)_2(μ_2-H_2O)_2(CH_3OH)_2)]n· x(solvents)(1, TPTC = terphenyl-3,3?,5,5??-tetracarboxylic acid, IN = isonicotinic acid) was synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, single-crystal and powder X-ray diffraction. It crystallizes in monoclinic space group C2/c with a = 33739(12), b = 14.820(5), c = 13.568(5) ?, β = 97.388(6)o, V = 6728(4) ?3, Z = 4, Mr = 965.35, Dc = 0.953 g·cm^(-3), F(000) = 1955.5, μ = 0.881 mm^(–1), GOOF = 1.072, the final R = 0.0859 and w R = 0.2424 for 5284 observed reflections with I > 2σ(I). The structure of 1 is constructed from the linkage of trinuclear {Ni_3} second building units through TPTC and IN spacers, forming a 4,8-connected network of Schl?fli symbol {32.42.52}{34.46.58.68.72}. The CO2 uptake values for 1 are 97.9 m^2·g^(-1) at 273 K and 66.2 m^2·g^(-1) at 298 K, while its N_2 adsorption values are 8.5 m^2·g^(-1) at 273 K and 4.9 m^2·g^(-1) at 298 K, respectively. These results show that 1 has high CO_2/N_2 adsorption selectivity at ambient conditions.

Modulating the Electronic Structures of Single-walled Carbon Nanotubes by Filling with Electron Acceptors and the Effect on Their Reactivity with Aryl Diazonium Salts

The electronic structures of single-walled carbon nanotubes （SWCNTs） were modulated by filling with tetracyanoquinodimethane （TCNQ）, a strong electron acceptor. The structures of TCNQ-filled SWCNTs were checked by X-ray diffraction analysis, high-resolution transmission electron microscopy and Raman spectroscopy. Optical absorption spectroscopy demonstrated an enhanced reactivity between aryl diazonium and semiconducting SWCNTs.

Syntheses and Crystal Structures of Two 3D Zinc(II) Compounds Involving Coordination and Hydrogen Bonds

Two zinc（Ⅱ） compounds, [Zn（L）（H2O）2]n 1 and [Zn（4,4＇-bpy）（H2O）4]（L） 2 （H2L = trans,trans-1,3 butadiene 1,4-dicarboxylic acid）, were synthesized by hydrothermal methods and characterized by single-crystal X-ray diffraction analyses. Compound 1 crystallizes in monoclinic, space group C2/c with a=15.4970（16）, b = 5.4976（6）, c = 10.7113（12） A, β=96.298（6）°, C6H8O6Zn, Mr = 241.50, V = 907.06（17） A^3, Z = 4, D, = 1.768 g/cm^3, F（000） = 488,μ = 2.703 mm^-1, S = 1.060, the final R = 0.0256 and wR = 0.0660 for 968 observed reflections with Ⅰ 〉 2σ（Ⅰ）. Compound 2 crystallizes in triclinic, space group P1^- with a = 6.915（2）, b = 7.166（2）, c = 10.363（3） A, α = 73.250（4）, β = 84.429（4）, γ = 61.605（3）°, C16H2ON2O8Zn, Mr = 433.70, V = 432.1 （2） A^3, Z = 1, D, = 1.667 g/cm^3, F（000） = 224 and μ= 1.471 mm^-1, S = 1.118, the final R = 0.0486 and wR = 0.1077 for 1352 observed reflections with Ⅰ〉 2σ（Ⅰ）. Upon using the assembly strategy of combination of coordination polymer chains with intermolecular hydrogen bonds, three-dimensional frameworks of complexes 1 and 2 were formed.

Hydrothermal Synthesis and Crystal Structure of One Novel 1-D Copper(Ⅱ)-organic Framework:{[Cu_2(PP)_2(CBPC)]_2·7H_2O}_n

One novel 1-D copper（Ⅱ）-organic compound,namely {[Cu2（PP）2（CBPC）]2·7H2O}n（1,H2CBPC=1-[（2＇-carboxybiphenyl-4-yl）methyl]-2-propylimidazole-4-carboxylic acid,HPP=3-（2-pyridyl）pyrazole）,was synthesized under hydrothermal conditions.X-ray diffraction analyses reveal that the two Cu（Ⅱ） ions in the distorted dimer [Cu2（PP）2] of 1 are linked by the carboxylate oxygen atoms on the phenyl and imidazole rings,respectively,forming one interesting snake-like chain.Single-crystal X-ray analyses reveal that it crystallizes in monoclinic,space group C2/c with a=30.656（8）,b=12.715（3）,c=22.405（5）,β=122.758（3）°,V=7344（3）3,Z=4,Mr=1681.65,Dc=1.521 g/cm3,F（000）=3464,μ=1.221 mm-1,the final R=0.0453 and wR=0.1023 for 4617 observed reflections with Ⅰ 〉2σ（Ⅰ）.

Synthesis,Structure and Characterization of a 3D Chiral Carboxylate and Phosphonate Metalorganic Framework Based on 1,1?-Biphenol Ligand

A novel phosphonate-based chiral metal-organic framework 1 was synthesized from C2-symmetric 1,1？-biphenol-based ligand and structurally characterized by single-crystal and powder X-ray diffraction, Fourier-transform infrared spectra（FTIR）, circular dichroism（CD） and thermogravimetric analyses（TGA）. Two neighboring Mn ions are linked by two carboxylate groups and one phosphate group to form a di-manganese unit [Mn2] and each [Mn2] cluster in 1 is linked by five ligands, generating a 3D network with fns topology. In addition, the photoluminescence properties of 1 and H4 L were investigated.

A Novel 3D Extended Network Cobalt Paradodecatungstate:Synthesis,Characterization and Crystal Structure of [Co(H_2O)_5]_2[Co(H_2O)_4]_3[H_2W_(12)O_(42)]·11H_2O

A cobalt paradodecatungstate [Co（H2O）5]2[Co（H2O）4]3[H2W12O42]·11H2O has been successfully synthesized and structurally characterized by X-ray crystallography. Structure analysis indicates that the title compound is of monoclinic, space group P21/n, with a = 13.449（3）, b = 19.585（4）, c = 13.990（3） °A, = 113.79（3）°, V = 3371.8（12） °A^3, Z = 2, R = 0.0519 and wR = 0.1242. The title compound exhibits a novel 3D extended network structure constructed by interconnecting the paradodecatungstate polyanion [H2W12O42]^10- clusters and cobalt^11 coordination ions.