Decrease In Coordination Number Research Articles

Theoretical study of the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH

The coordination environment of Cu (the coordination number and arrangement of surface atoms) plays an important role in CO2 hydrogenation to CH3OH. Compared with the extensive studies of the effects of coordination number, the comprehensive effects of coordination number and arrangement of surface atoms were seldom explored in literature. To unravel the effects of surface Cu coordination environment on CO2 hydrogenation to CH3OH, the adsorption and reaction behaviors of H2 and CO2 on Cu(111), (100), (110) and (211) with different coordination numbers and arrangement of surface Cu were systematically calculated by density functional theory (DFT) and kinetic Monte Carlo (kMC) simulation. It was found that the adsorption energies of intermediates in CO2 hydrogenation on Cu surfaces increase with the decrease of coordination number. When the Cu coordination numbers are similar, the charge density on the open surface derived from the different atom arrangement becomes larger and leads to stronger interaction with intermediates than that on the compact one. DFT calculation and kMC simulation indicate that methanol formation pathway follows CO2*→HCOO*→HCOOH*→H2COOH*→H2CO*→CH3O*→CH3OH* on four Cu facets; CO formation is via CO2 direct dissociation on Cu(111), (100) and (110) but COOH* dissociation on (211). The low-coordinated surface Cu with more openness on Cu(211) is the highly active site for CO2 hydrogenation to CH3OH with high turnover of frequency (3.71 × 10−4 s−1) and high selectivity (87.17 %) at 600 K, PCO2 = 7.5 atm and PH2 = 22.5 atm, which is much higher than those on Cu(111), (100) and (110). This work unravels the effects of coordination environment on CO2 hydrogenation at the molecular level and provides an important insight into the design and development of catalysts with high performance in CO2 hydrogenation to CH3OH.

DEM investigation on flow instability of particulate assemblies under coupling between volumetric and axial strains

AbstractThe discrete element method (DEM) is employed to investigate the impact of coupling between volumetric and axial strains on the flow liquefaction vulnerability of 3D cubic particulate specimens. The virtual testing program conducted here encompasses a wide range of initial states and varying degrees of coupling between volumetric and axial strains. Utilizing data obtained from DEM simulations, the evolution of micro- and macroscale variables, including coordination number, contact fabric anisotropy, redundancy index, strong force networks, invariants of the effective stress tensor, and excess pore-water pressure, is examined. Results from DEM tests indicate that coupling expansive volumetric strain with axial strain leads to a gradual loosening of the load bearing microstructure, a decrease in coordination number, and a faster change in contact anisotropy. DEM simulations demonstrate that the triggering of flow liquefaction instability is followed by a sudden increase in contact fabric anisotropy and abrupt drops in coordination number and redundancy index. Moreover, a detailed analysis of the findings suggests that the stress ratio at the onset of post-peak softening decreases with increasing expansive volumetric strains.

Molecular dynamics simulations of the local structure and physicochemical properties of CaCl2 molten salt

Abstract CaCl2 molten salt, as a common electrolyte in the process of molten salt electrolysis, has a high decomposition potential and a strong ability to bind O2−. So the study of the structure and properties of CaCl2 is significant for the molten salt electrolysis. In this paper, molecular dynamics simulations (MD) method was used to investigate the variation rule of the local structure and physicochemical properties of CaCl2 molten salt with temperature. The results show that the temperature has less effect on the heterozygous ion pairs and more effect on the homozygous ion pair. With the increase of temperature, the interaction between ion pairs is weakened, the coordination number decreases, the local structure changes a little, and the structural configuration tends to be an irregular octahedral structure with vacancies. The calculated self-diffusion coefficients, viscosities, and ionic conductivities are consistent well with the reality, but there is a significant error in densities due to the strong polarization effect of Ca2+ compared to the reality. The local structure directly determines the thermodynamic properties of the molten salts. This study promotes the basic theoretical research on alkaline earth metal-containing molten salts and is an important reference for the study of molten salt electrolysis process.

Impact of organic phosphates on the structure and composition of short-range ordered iron nanophases.

Organic phosphates (OP) are important nutrient components for living cells in natural environments, where they readily interact with ubiquitous iron phases such as hydrous ferric oxide, ferrihydrite (FHY). FHY partakes in many key bio(geo)chemical reactions including iron-mediated carbon storage in soils, or iron-storage in living organisms. However, it is still unknown how OP affects the formation, structure and properties of FHY. Here, we document how β-glycerophosphate (GP), a model OP ligand, affects the structure and properties of GP-FHY nanoparticles synthesized by coprecipitation at variable nominal molar P/Fe ratios (0.01 to 0.5). All GP-FHY precipitates were characterized by a maximum solid P/Fe ratio of 0.22, irrespective of the nominal P/Fe ratio. With increasing nominal P/Fe ratio, the specific surface area of the GP-FHY precipitates decreased sharply from 290 to 3 m2 g-1, accompanied by the collapse of their pore structure. The Fe-P local bonding environment gradually transitioned from a bidentate binuclear geometry at low P/Fe ratios to monodentate mononuclear geometry at high P/Fe ratios. This transition was accompanied by a decrease in coordination number of edge-sharing Fe polyhedra, and the loss of the corner-sharing Fe polyhedra. We show that Fe(iii) polymerization is impeded by GP, and that the GP-FHY structure is highly dependent on the P/Fe ratio. We discuss the role that natural OP-bearing Fe(iii) nanophases have in biogeochemical reactions between Fe-P and C species in aquatic systems.

High-throughput computational materials screening of transition metal peroxides.

Semiconductor materials of abnormal stoichiometric ratio often exhibit unique properties, yet it is still a challenge to determine the structures of such materials in an efficient way. Herein, we propose a method for structurally biased screening according to the coordination numbers and the numbers of Wyckoff positions, balancing the atom local environment and the global symmetry of structures. Based on first-principles calculations, we have predicted two metastable peroxides P21/c-ScO2 and Pmmn-TiO3 with more than six coordination points. For these two structures, the most stable intrinsic defect is the oxygen vacancy (VO) at the peroxide anion (O2-2), which induces the absence of antibonding orbital formed by O2-2 near the valence band maximum. With the introduction of VO, the decrease of coordination numbers leads to charge recombination, and results in the appearance of an ordered phase TiO2.5 with stronger Ti-O orbital hybridization. The proposed method presents a promising and feasible approach for the screening of novel compounds.

Two-dimensional lithium-intercalated Ti3C2Tx MXene for highly selective neodymium (Ⅲ) adsorption

Recovering rare earth elements (REEs) from low-concentration REE-bearing waste streams has been deemed as a sustainable approach to diversity REE supply and reduce environmental burden. However, highly selective separation of trivalent Fe3+ and Al3+ impurities during low-concentration REE processing still remains a critical challenge. In this study, two-dimensional multilayered MXene adsorbents TCFs were successfully prepared and utilized for Nd3+ adsorption via selective etching of Al element in Ti3AlC2. It was found that LiF/HCl-etched TCF-2 can simultaneously realize effective Al etching, interlayer spacing expansion and in-situ Li+ intercalation. The intercalated Li+ amount was up to 4.44 wt% (6.40 mmol/g). Compared with HF-etched TCF-1, TCF-2 demonstrated boosted adsorption kinetics (2 h), large adsorption capacity (517.79 mg/g), impressively high selectivity (Nd3+/Fe3+ SF = 221, Nd3+/Ca2+ SF = 858, Nd3+/Mg2+ SF = 3545), and broad working pH range (2–7). Various experimental characterizations reveal that selective Nd3+ recovery is owing to the ion-exchange and surface complexation induced by interlayer Ti-O/Ti-OH of TCF-2. Specifically, the extended X-ray sorption fine structure (EXAFS) results, in combination with density functional theory (DFT) calculations, further confirm the Nd3+ is selectively adsorbed by forming surfaced complexes structure in the interlayer. And this is also evidenced by the decrease of Nd-O distances and high coordination number. The present results illustrate that alkaline metal ion-intercalated MXene could serve as a promising candidate to efficiently remove trivalent Fe3+ impurities for REEs recovery.

Molecular dynamics simulation on thermophysical properties and local structure of ternary chloride salt for thermal energy storage and transfer system

Ternary chloride salt (NaCl–KCl–MgCl2) is considered as a potential high temperature thermal storage material owing to its low melting point, excellent thermal properties and low cost. However, the thermophysical properties of ternary chloride salts are difficult to measure under high-temperature conditions. In this study, the microscopic model of ternary chloride salt is constructed by Materials Studio software. The ratio of Na ions, K ions, Mg ions and Cl ions in the simulation system is determined according to the molar ratio of NaCl–KCl–MgCl2 eutectic ternary chloride salt. The total number of ions is identified based on computational resources and the accuracy of simulation results, and the number of the four ions in the system is finally determined. LAMMPS software is used to simulate the microstructure and calculate the thermal properties. Simulation results indicate that as the temperature increases, the distance between cluster ions increases, while the coordination number decreases, resulting in the ion association weakens. Simulation results of thermophysical properties are in good agreement with the experimental measurements. The decrease in density and viscosity is attributed to the weakening of ion association with increasing temperature. All the results are expected to provide reliable guidance for the design and preparation of next-generation concentrating solar thermal energy storage materials.

A study of particle flow in a ribbon reactor: Effect of ribbon configuration on mixing and heat transfer performance

The mixing and heat transfer of particles are two important operating units in the lithium-ion battery industry due to the cycling performance of the cathode is mainly dependent on the mixing and heat transfer performance of granular matter, such as needle coke and asphalt particles. In this work, simulations of the particle mixing and heat transfer process in a ribbon reactor were conducted based on the three-dimensional discrete element method (DEM). The stacking angle test, rotary drum, and thermal conductivity test were designed to obtain the DEM parameters. The trajectory of tracer particles, total velocity fluctuation, coordinate number, and relative standard deviation (RSD) were used to analyze the mixing and heat transfer process. It was found that particles in the ribbon reactor experience two types of movement. The first one is high-speed tangential movement, and the second one is low-speed recirculation movement in the vertical plane. Particles near the vessel wall and impeller shaft are first heated and a cold core is generated in the initial stage of heat transfer. Results obtained indicate that the mixing performance increases slightly with the increase of ribbon number. The mixing performance increases with the increase of velocity fluctuation and the decrease of coordination number, and the heat transfer can be improved by enhancing the mixing performance of granular matter. Increasing the ribbon width and ribbon pitch can improve the heat transfer performance, while the ribbon pitch has little influence on the mixing performance.

Niobium incorporation into rare-earth doped aluminophosphate glasses: Structural characterization, optical properties, and luminescence

Luminescent Rare Earth (RE3+) doped phosphate glasses with molar composition (1-x)(60P2O5 – 15ZnO – 5Al2O3 – 10BaO – 10PbO)-xNb2O5 (x = 0, 10, 20 and 30 wt%) doped with 1.0, 1.2 and 0.3 wt% of Eu2O3, Yb2O3 and Er2O3, respectively, were prepared by conventional melt cooling. The glasses were characterized by optical reflectance, Raman scattering, and multinuclear (31P, 27Al, and 93Nb) solid-state NMR spectroscopy. Monotonic 31P chemical shift changes as a function of Nb2O5 content are consistent with the successive formation of Nb-O-P linkages. Aluminum is found in four-, five-, and six-coordination, with a successive decrease in average coordination number with increasing niobium content, while 93Nb NMR indicates three distinct niobium environments in these glasses. Incorporation of Nb2O5 has the expected effects on refractive index values, optical basicity, optical electronegativity, Urbach Energy, and the indirect bandgap, while RE3+ emission properties are only slightly modified. Under UV excitation, narrow emission bands are observed arising from 5D0→7FJ (J = 0, 1, 2, 3, and 4) transitions of Eu3+. At least two distinct Eu3+ lifetime values are observed, suggesting a spread of different ionic environments within the glass structure. Co-doping with Er3+/Yb3+ promotes emission in the infrared region, with a emission band maximum near 1535 nm and a width of 30.65 nm under excitation at 980 nm. Based on the results, these glasses may be potential candidates for energy conversion from infrared or UV region to the visible region and also infrared solid-state emitters.

An investigation of Al2O3 induced variations in the structural parameters in strontium borosilicate glasses using solid state NMR.

The physical properties of oxide glasses are crucially dependent on the atomistic structural speciation. In this study, we investigate the variation in the local ordering in the glass network of strontium borosilicate glasses (34.82 SrO, 51.84 B2O3, 13.34 SiO2 in mol%) with a progressive substitution of B2O3 by Al2O3 and estimate the structural parameters: the oxygen packing fraction, and the average network coordination number. The coordination of the network forming cations at various glass compositions is determined using 11B, 27Al, and 29Si solid-state nuclear magnetic resonance (SSNMR). The SSNMR reveals that at the higher substitution of B2O3 by Al2O3 in the glass composition, the coordination network of Al3+ exists predominantly in the 4 coordinated state, the network forming B3+ cations transform from a tetrahedral BO4 to a trigonal BO3 structure, and the Q4 form of silicates is dominant. The average coordination number and the oxygen packing fraction were calculated using the parameters obtained from the SSNMR results, and it is observed that the average coordination number decreases, and the oxygen packing fraction increases on incorporating Al. It is interesting to note that some of the thermophysical properties of these compositions closely follow the pattern shown by the average coordination number and the oxygen packing fraction.

Phase Relations of Ni2In-Type and CaC2-Type Structures Relative to Fe2P-Type Structure of Titania at High Pressure: A Comparative Study

Density functional theory (DFT) based on first-principles calculations was used to study the high-pressure phase stability of various phases of titanium dioxide (TiO2) at extreme pressures. We explored the phase relations among the following phases: the experimentally identified nine-fold hexagonal Fe2P-type phase, the previously predicted ten-fold tetragonal CaC2-type phase of TiO2, and the recently proposed eleven-fold hexagonal Ni2In-type phase of the similar dioxides zirconia (ZrO2) and hafnia (HfO2). Our calculations, using the generalized gradient approximation (GGA), predicted the Fe2P → Ni2In transition to occur at 564 GPa and Fe2P → CaC2 at 664 GPa. These transitions were deeply investigated with reference to the volume reduction, coordination number decrease, and band gap narrowing to better determine the favorable post-Fe2P phase. Furthermore, it was found that both transitions are mostly driven by the volume reduction across transitions in comparison with the small contribution of the electronic energy gain. Additionally, our computed Birch–Murnaghan equation of state for the three phases reveals that CaC2 is the densest phase, while Ni2In is the most compressible phase.

Operando X-ray Absorption Spectroscopy Study of SnO2 Nanoparticles for Electrochemical Reduction of CO2 to Formate

Tin-based electrocatalysts exhibit a remarkable ability to catalyze CO2 to formate selectively. Understanding the size-property relationships and exploring the evolution of the active size still lack complete understanding. Herein, we prepared SnO2 nanoparticles (NPs) with a controllable size supported on commercial carbon spheres (SnO2/C-n, n = 1, 2, and 3) by a simple low-temperature annealing method. The transmission electron microscopy/scanning transmission electron microscopy images and fitting results of the small-angle X-ray scattering profile confirm the increased size of SnO2 NPs due to the increase of SnO2 loading. The catalytic performance of SnO2 has proved the size-dependent effect during the CO2 reduction reaction process. The as-prepared SnO2/C-1 displayed the maximum Faradic efficiency of formate (FEHCOO-) of 82.7% at -1.0 V versus reversible hydrogen electrode (RHE). In contrast, SnO2/C-2 and SnO2/C-3 with larger particle sizes achieved lower maximum FEHCOO- and larger overpotential. Moreover, we employed operando X-ray absorption spectroscopy to study the evolution of the oxidation state and local coordination environment of SnO2 under working conditions. In addition to the observed shifts of the rising edge of Sn K-edge X-ray absorption near-edge structure spectra to a lower energy side as the applied voltage decreases, the decreased coordination number of Sn in the Sn-O scattering path and the presence of Sn metal contribution in the extended X-ray absorption fine structure spectra verify the reduction of SnO2 to SnOx and metallic Sn.

C(spn)−X (n=1–3) Bond Activation by Iron

AbstractThe iron‐catalyzed oxidative addition of C(spn)−X bonds (n=1–3 and X=H, CH3, Cl) in archetypal model substrates H3C−CH2−X, H2C=CH−X and HC≡C−X to Fe(CO)4was investigated using relativistic density functional theory at ZORA‐OPBE/TZ2P. The C(spn)−X bonds become substantially stronger going from C(sp3)−X to C(sp2)−X to C(sp)−X, whereas the oxidative addition reaction barrier decreases along this series. Our activation strain and energy decomposition analyses expose that the decreased reaction barrier for the oxidative addition going fromsp3tosp2tospstems from a relief of the destabilizing (steric) Pauli repulsion between the catalyst and substrate. This originates from the decreasing coordination number of the carbon atom that goes from four in C(sp3)−X to three in C(sp2)−X to two in C(sp)−X. In analogy with our previous results on palladium‐catalyzed oxidative additions, this enhances the stabilizing catalyst–substrate interaction, which is able to overcome the more destabilizing strain associated with the stronger C(spn)−X bonds. This work again demonstrates that iron‐based catalysts can resemble the behavior of their well‐known palladium analogs in the oxidative addition step of cross‐coupling reactions.

Molecular Dynamics Simulation of Thermophysical Properties and the Microstructure of Na2CO3 Heat Storage Materials

In recent years, heat storage technology has attracted wide attention in the fields of renewable energy storage for its relatively high melting point, high heat storage capacity and economy, Na2CO3 and eutectic salt mixtures containing Na2CO3 are promising candidates in the field of solar energy storage. In this paper, a molecular dynamics (MD) simulation of Na2CO3 was conducted with the Born–Mayer potential function. The simulated solid–liquid phase change temperature is 1200 K, and the error is 5.4%. The heat capacity at constant pressure (Cp) is higher in liquid than in solid, the average Cp of solid is 1.45 J/g and that of liquid is 1.79 J/g, and the minimum error is 2.8%. The simulation results revealed the change rules of density and thermal expansion coefficient of Na2CO3 in the process of heating up, and these changes were analyzed by radial distribution functions (RDF) and angular distribution functions (ADF). Moreover, the RDF and ADF results show that the atomic spacing of Na2CO3 increases, the coordination number decreases, and the angle distribution between atoms becomes wider as the temperature rises. Finally, this paper examined the microscopic changes of ions during the phase transition of Na2CO3 from solid to liquid. It is concluded that the angle change of CO32− in the liquid state is more sharply. This study improves the understanding of the thermodynamic properties and local structure of Na2CO3 and provides theoretical support for Na2CO3 heat storage materials.

In-situ induced sulfur vacancy from phosphorus doping in FeS2 microflowers for high-efficiency lithium storage

In this work, via in-situ induction of phosphorus doping, FeS2 microflowers with sulfur vacancies were rationally designed and fabricated for lithium-ion batteries (LIBs). Phosphorus doping enlarged interlayer spacings, effectively enhanced the conductivity and facilitated the diffusion and intercalation/deintercalation of Li+. Moreover, the in-situ induced sulfur vacancies also partly rearranged electronic structures and increased more active adsorption sites for Li+. The P1.0-FeS2-x electrode delivered the excellent rate performance (642.6 mAh/g at 5.0 A/g) and long-cyclic performance (544.7 mAh g-1 at 2.0 A/g after 1000 cycles). X-ray absorption fine structure spectroscopy was employed to reveal the decrease of Fe oxidation state and coordination number, confirming sulfur vacancies were in-situ induced through phosphorus doping process. Density function theory calculation declared the doping of phosphorus atoms and in-situ induced sulfur vacancies in FeS2 could effectively adjust the charge distribution at the active sites for Li adsorption, which enhanced the conductivities and facilitated the electrochemical reaction kinetics. The anionic doping strategy may provide new ideas and routes of constructing transition metal sulfides for high-performance LIBs.

C(spn )-X (n=1-3) Bond Activation by Palladium.

We have studied the palladium‐mediated activation of C(sp n)−X bonds (n = 1–3 and X = H, CH3, Cl) in archetypal model substrates H3C−CH2−X, H2C=CH−X and HC≡C−X by catalysts PdLn with Ln = no ligand, Cl−, and (PH3)2, using relativistic density functional theory at ZORA‐BLYP/TZ2P. The oxidative addition barrier decreases along this series, even though the strength of the bonds increases going from C(sp 3)−X, to C(sp 2)−X, to C(sp)−X. Activation strain and matching energy decomposition analyses reveal that the decreased oxidative addition barrier going from sp 3, to sp 2, to sp, originates from a reduction in the destabilizing steric (Pauli) repulsion between catalyst and substrate. This is the direct consequence of the decreasing coordination number of the carbon atom in C(sp n)−X, which goes from four, to three, to two along this series. The associated net stabilization of the catalyst–substrate interaction dominates the trend in strain energy which indeed becomes more destabilizing along this same series as the bond becomes stronger from C(sp 3)−X to C(sp)−X.

To the question of oxidation on the surface of oxides: temperature- programmed oxidation of cyclohexanol

Temperature-programmed reaction (TPR) method with mass spectrometric control of the products was used to study of cyclohexanol oxidation into cyclohexanone on individual and mixed oxides supported by γ-Al2O3 and silica gel. In the TPR profiles the temperature of a maximum rate of cyclohexanone formation varies from 125°C for MoO3/Al2O3 to 235°C for less active CuO/Al2O3. The catalytic activity of individual oxides decreases in the order MoO3/Al2O3> V2O5/SiO2 > Fe2O3/Al2O3 > Bi2O5/Al2O3 > TiO2/SiO2 ≈ СeO2/Al2O3 > TiO2/Al2O3 > SnO2/Al2O3. As "reactive" oxygen in our TPR experiment was supplied only from oxide lattice, oxide activity is determined by different energy of the surface Me – O bonds. The approach to search for mixed active oxides based on decreasing coordination number of O2- ions is proposed, that confirmed by the example of CuO-WO3/Al2O3 catalyst. The mixed supported oxides, especially CuOCrO3/Al2O3, CuO-MoO3/Al2O3, MoO3-SnO2/Al2O3 and Bi2O3–SnO2/Al2O3, are more active in С6Н12О + 1/2О2 → С6Н10О + Н2О oxidation. The synthesized CuO-CrO3/Al2O3 catalyst provides cyclohexanone formation without side cyclohexanol dehydration and can be used for the oxidation of ethylene glycol – methanol mixture into methyl glycolate. CuO-Cr2O3/Al2O3 with a spinel structure of CuCr2O4 ([CuO4] 6− tetrahedra, Cu2+ sp3-hybridization) is more active in cyclohexanol oxidation than CuO/Al2O3 with flat [CuO4] 6−squares, Cu2+ dsp2-hybridization. This is explained by the lower energy of Cu-O bonds at sp3-hybridization of Cu2+ ions.

Response to the Variation of Clay Minerals During ASP Flooding in the Saertu Oilfield in the Songliao Basin

In this paper, the variation of clay minerals and their influence on reservoir physical properties and residual oil before and after ASP flooding are analyzed. The results show that the total amount of clay minerals in reservoirs decreases after ASP flooding in the ultra-high-water-cut-stage reservoirs of the Naner Zone in the Saertu Oilfield, Songliao Basin. Therein, the illite content reduces, while the content of illite smectite mixed-layer and chlorite increases. The content of kaolinite varies greatly. The content of kaolinite decreases in some samples, while it increases in other samples. The clay minerals block the pore throat after ASP flooding. As a result, the pore structure coefficient and the seepage tortuosity increase, the primary intergranular pore throat shrinks, and the pore–throat coordination number decreases. Nevertheless, the dissolution of clay minerals reduces the pore–throat ratio and increases porosity and permeability. The variation of clay minerals after ASP flooding not only intensifies the reservoir heterogeneity but also affects the formation and distribution of residual oil. The residual oil of the oil–clay mixed adsorption state is a newly formed residual oil type related to clay, which accounts for 44.2% of the total residual oil reserves, so it is the main occurrence form of the oil in reservoirs after ASP flooding. Therefore, the exploitation of this type of residual oil has great significance to enhance the oil recovery in ultra-high-water-cut-stage reservoirs.

Percolation on Lieb lattices

We study site- and bond-percolation on a class of lattices referred to as Lieb lattices. In two dimensions the Lieb lattice (LL) is also known as the decorated square lattice, or as the CuO_{2} lattice; in three dimensions it can be generalized to a layered Lieb lattice or to a perovskite lattice. Emergent electronic phenomena, such as topological states and ferrimagnetism, have been predicted to occur in these systems, which may be realized in optical lattices as well as in solid state. Since the study of the interplay between quantum fluctuations and disorder in these systems requires the availability of accurate estimates of geometrical critical parameters, such as percolation thresholds and correlation length exponents, here we use Monte Carlo simulations to obtain these data for LLs when a site (or bond) is present with probability p. We have found that the thresholds satisfy a mean-field (Bethe lattice) trend, namely that the critical concentration, p_{c}, increases as the average coordination number decreases; our estimates for the correlation length exponent are in line with the expectation that there is no change in the universality class.

Relation Between Coordination and Lewis‐Acid Property of MOF‐Derived Mononuclear Zn(II) Catalyst Toward Epoxide Hydroxylation

AbstractLewis‐acid properties of the coordinatively unsaturated metal ions are highly relevant to the coordination environment; however, it remains a challenge to establish the coordination structure‐activity relationship, especially in heterogeneous catalysis. Here, a typical metal‐organic framework, ZIF‐8, is selected as the precursor to prepare Lewis‐acid based Zn−N/P−C mononuclear catalysts, with well‐designed external structures but difference in the local coordination. The obtained mononuclear Zn(II) catalysts can not only inherit the advantages of MOF in coordination, but also simulate the homogeneous environment during the catalysis owing to the monodispersed metal sites in ZIF‐8. Eventually, relation between coordination and Lewis‐acid property toward epoxide hydroxylation has been illustrated. Results show the substituted coordination atom of P and the decrease of coordination number strongly enhance the Lewis‐acidity of Zn2+, causing the TOF values changes from 8.7 to 80.1 h−1 based on Zn content. The work affords an understanding and inspiration of coordination environment matters toward Lewis‐acid catalysis in organic transformations.