Exploring the Limits of Transition‐Metal Fluorination at High Pressures

Fluorination is a proven method for challenging the limits of chemistry, both structurally and electronically. Here we explore computationally how pressures below 300 GPa affect the fluorination of several transition metals. A plethora of new structural phases are predicted along with the possibility for synthesizing four unobserved compounds: TcF₇, CdF₃, OsF₈, and IrF₈. The Ir and Os octaflourides are both predicted to be stable as quasi‐molecular phases with an unusual cubic ligand coordination, and both compounds formally correspond to a high oxidation state of +8. Electronic‐structure analysis reveals that otherwise unoccupied 6p levels are brought down in energy by the combined effects of pressure and a strong ligand field. The valence expansion of Os and Ir enables ligand‐to‐metal F 2p→M 6p charge transfer that strengthens M?F bonds and decreases the overall bond polarity. The lower stability of IrF₈, and the instability of PtF₈ and several other compounds below 300 GPa, is explained by the occupation of M?F antibonding orbitals in octafluorides with a metal‐valence‐electron count exceeding 8.     

On the Upper Limits of Oxidation States in Chemistry

The concept of oxidation state ( OS ) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum‐chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS =+9 was observed for the isolated [IrO₄]⁺ cation in vacuum. The prediction of OS =+10 for isolated [PtO₄]²⁺ cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. For high OS species, oxidation of the ligands, for example, of O^?2 with formation of ^.O^?1 and O?O bonds, and partial reduction of the metal center may be favorable, possibly leading to non‐Lewis type structures.     

Electron pairing and chemical bonds: Bonding in hypervalent molecules from analysis of Fermi holes

Bonding in the hypervalent molecules SF₄, BrF₅, PF₅, and SF₆ was studied using multicenter bond order indices and examination of the eigenvalues and the eigenvectors of the Fermi holes of the constituent atoms. Diagonalization of the Fermi holes provided quantitative validation of Musher's categorization of hypervalency with SF₄ and BrF₅ representative of type I, and PF₅ and SF₆ belonging to type II. The eigenvalues and eigenvectors of type I molecules distinguished between classic two-center two-electron bonds and three-center four-electron bonds, whereas the results of diagonalization for type II molecules demonstrated the presence of substantial reorganization of the valence state of the central atom leading to equivalent bonds and the highest expected symmetry of the molecule. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 760–771, 1999     

高压下MgO的热弹性研究

The thermoelastic properties of MgO over a wide range of pressure and temperature are studied using the first-principles plane wave pseudopotential method within the generalized gradient approximation. It is shown that MgO remains in the B1 (NaCl) structure at all pressures existing within the Earth, and transforms into the CsCl-type structure at 397 GPa. The athermal elastic moduli of MgO are calculated, as a function of pressure up to 150 GPa. The calculated results are in excellent agreement with experimental data at zero pressure and compare favorably with other pseudopotential predictions over the pressure regime studied. MgO is found to be highly anisotropic in its elastic properties, with the magnitude of the anisotropy first decreasing between 0 and 20 GPa and then increasing from 20 GPa to 150 GPa. The Cauchy condition is found to be strongly violated in MgO, reflecting the importance of noncentral many-body forces. The thermodynamic properties of MgO are consistent with the experimental data at ambient condition.     

碱性水溶液中甲醛在硅电极表面的电化学行为及其对硅化学刻蚀的影响

研究了KOH水溶液中氧化剂甲醛在p-Si和n-Si(100)单晶半导体电极表面的电化学行为及其对硅化学刻蚀表面形貌的影响．实验结果表明,甲醛不仅影响p-和n-型半导体电极在碱性溶液中的阳极氧化峰电流,而且在负电位区能在Si(100)电极上发生还原．在光照条件下,p-Si(100)电极上也观测到了HCHO的电化学还原及光电流倍增效应．甲醛在硅电极表面的电化学还原反应分两步进行,反应终产物为甲醇．此外,HCHO能有效抑制碱性溶液中Si表面“金字塔”型表面粗糙颗粒的形成。     

Clathrate Hydrates of Sulfur Hexafluoride at High Pressures

The pressure dependence (0.4 Mpa–1.3 GPa) of the hydrate decomposition temperatures in the sulfur hexafluoride-water system has been studied. In addition to the known low-pressure hydrate SF₆17H₂O of Cubic Structure II, two new high-pressure hydrates have been found. X-ray analysis in situ showed the gas hydrate forming in the sulfur hexafluoride-water system above 50 MPa at room temperature to be of Cubic Structure I. The ability of water to form hydrates whose structures depend on the guest molecule size under normal conditions and at high pressures is discussed.     

SiO2粉末在非水高浓度聚合物溶液中的分散

ＳｉＯ_２粉末在非水高浓度聚合物溶液中的分散陈立富（厦门大学化学系,厦门,３６１００５）关键词ＳｉＯ_２,氢键,分散剂无机粉末（如碳,ＳｉＯ２等）与高分子聚合物组成的复合材料可优化高聚物的导电性能、机械性能及化学稳定性等。一般来说,只有当非常细小的粉末...     

Beyond Oxides: Nitride as a Ligand in a Neutral IrIXNO3 Molecule Bearing a Transition Metal at High Oxidation State

Theoretical calculations utilizing relativistic ZORA Hamiltonian point to the conceivable existence of an IrNO₃ molecule in C_3v geometry. This minimum is shown to correspond to genuine nonavalent iridium nitride trioxide, which is a neutral analogue of cationic [IrO₄]⁺ species detected recently. Despite the presence of nitride anion, the molecule is protected by substantial barriers exceeding 200 kJ mol⁻¹ against transformations leading, for example, to global minimum (O=)₂Ir−NO, which contains metal at a lower formal oxidation state.     

In-Situ Electronegativity and the Bridging of Chemical Bonding Concepts

One challenge in chemistry is the plethora of often disparate models for rationalizing the electronic structure of molecules. Chemical concepts abound, but their connections are often frail. This work describes a quantum-mechanical framework that enables a combination of ideas from three approaches common for the analysis of chemical bonds: energy decomposition analysis (EDA), quantum chemical topology, and molecular orbital (MO) theory. The glue to our theory is the electron energy density, interpretable as one part electrons and one part electronegativity. We present a three-dimensional analysis of the electron energy density and use it to redefine what constitutes an atom in a molecule. Definitions of atomic partial charge and electronegativity follow in a way that connects these concepts to the total energy of a molecule. The formation of polar bonds is predicted to cause inversion of electronegativity, and a new perspective of bonding in diborane and guanine−cytosine base-pairing is presented. The electronegativity of atoms inside molecules is shown to be predictive of pK_a.     

Possible Mechanisms of String Formation in Complex Plasmas at Elevated Pressures

Possible mechanisms of particle attraction providing formation of the field aligned microparticle strings in complex plasmas at elevated gas pressures are theoretically investigated in the light of the Plasmakristall-4 (PK-4) experiment on board the International Space Station. The particle interaction energy is addressed by two different approaches: (i) using the dynamically screened wake potential for small Mach numbers derived by Kompaneets et al., in 2016, and (ii) introducing effect of polarization of the trapped ion cloud by discharge electric fields. Is is found that both approaches yield the particle interaction energy which is independent of the operational discharge mode. In the parameter space of the performed experiments, the first approach can provide onset of the particle attraction and string formation only at gas pressures higher than 40–45 Pa, whilst the mechanism based on the trapped ion effect yields attraction in the experimentally important pressure range 20–40 Pa and may reconcile theory and observations.     

Toward Extreme Biophysics: Deciphering the Infrared Response of Biomolecular Solutions at High Pressures

Biophysics under extreme conditions is the fundamental platform for scrutinizing life in unusual habitats, such as those in the deep sea or continental subsurfaces, but also for putative extraterrestrial organisms. Therefore, an important thermodynamic variable to explore is pressure. It is shown that the combination of infrared spectroscopy with simulation is an exquisite approach for unraveling the intricate pressure response of the solvation pattern of TMAO in water, which is expected to be transferable to biomolecules in their native solvent. Pressure‐enhanced hydrogen bonding was found for TMAO in water. TMAO is a molecule known to stabilize proteins against pressure‐induced denaturation in deep‐sea organisms.     

变温核磁共振对壳聚糖/磷酸甘油盐温敏性水凝胶的初步研究

采用变温核磁共振技术对壳聚糖/磷酸甘油盐温敏性水凝胶体系的凝胶化过程进行跟踪研究. 实验结果表明, 壳聚糖中氢和磷酸甘油盐中磷的化学位移均随着温度的升高而变化, 其中壳聚糖中氢的化学位移向高场移动而磷酸甘油盐中磷的化学位移向低场移动. 在凝胶温度附近, 壳聚糖中H-2(D)的化学位移变化出现转折点, 表明其所处的化学环境发生了突变. 随着体系中磷酸甘油盐含量的增加或者pH值的增大, 壳聚糖中H-2(D)的化学位移愈加偏向高场, 体系的凝胶温度则越低. 由此, 我们提出如下壳聚糖/磷酸甘油盐温敏性水凝胶的凝胶机理: 随着温度的升高, 壳聚糖通过氨基正离子与磷酸甘油盐形成的静电吸引被破坏, 随之由于壳聚糖分子链间形成大量氢键而发生凝胶化.     

Conductivity of Dilute Aqueous Electrolyte Solutions at High Temperatures and Pressures Using a Flow Cell

A flow-through electrical conductance cell was assembled in order to measuremolar conductances of dilute aqueous electrolytes with a high degree of accuracyat high temperatures and pressures. The design of the cell is based on the conceptdeveloped at the University of Delaware and built in 1995, with modificationsthat will allow the cell to operate at much higher temperatures (to 600°C) andpressures (to 300 MPa). At present, the cell has been tested successfully bymeasuring aqueous (10^–4-10^–3 mol-kg^–1) solutions of LiCl, NaCl, and KCl attemperatures 25–410°C and pressures 9.8–33 MPa. The results are in goodagreement with reported values, including those measured with the Delawareflow-through cell. These new results are also complementary to our previousresults, which were measured with a static high-pressure cell. Measurements attemperatures near the critical point of water (374°C, 22.1 MPa) require the useof lower solution concentrations that were unachievable in the past with thestatic cell.     

Exploring Supramolecular Assembly Space of Cationic 1,2,4-Selenodiazoles: Effect of the Substituent at the Carbon Atom and Anions

Chalcogenodiazoles have been intensively studied in recent years in the context of their supramolecular chemistry. In contrast, the newly discovered cationic 1,2,4-selenodiazole supramolecular building blocks, which can be obtained via coupling between 2-pyridylselenyl halides and nitriles, are virtually unexplored. A significant advantage of the latter is their facile structural tunability via the variation of nitriles, which could allow a fine tuning of their self-assembly in the solid state. Here, we explore the influence of the substituent (which derives from the nitrile) and counterions on the supramolecular assembly of cationic 1,2,4-selenodiazoles via chalcogen bonding.     

Exploring the Limits of Bivalency by DNA‐Based Spatial Screening

Multivalency can facilitate complex formation when monovalent receptor–ligand interactions are weak. However, enhanced binding of two multivalent binding partners should be avoidable, for example when bivalent receptors ought to utilize multimolecular interactions to cross‐link binding partners. We herein report the first systematic study to assess the criteria deciding whether a bivalent system engages in bivalency‐enhanced interactions or cross‐linking. We used DNA‐instructed self‐assembly to arrange the cucurbit[7]uril–adamantane host–guest system in 70–360 Å distance. Measurements and statistical mechanics analyses revealed that the affinity gain is controlled by 1) the distance between recognition modules, 2) the scaffold flexibility, and, importantly, 3) the strength of the monovalent interaction. We show that the bivalency effect can extend beyond 150 Å and discuss how, on the contrary, weak monovalent interactions reduce the concentration threshold for cross‐linking. The findings are of interest for inhibitor design.     

Exploring the Limits of Emulsion Polymerization of Styrene for the Synthesis of Polymer Nanoparticles

Summary. Suspensions of polymer nanoparticles in water (latices) with average particle diameters between 20 and 80 nm were synthesized by batch emulsion polymerization of styrene using sodium dodecyl sulphate (SDS) as surfactant and potassium persulphate (KPS) as initiator. The influence of surfactant concentration, initiator concentration, monomer concentration, and reaction temperature on the final average particle diameters and size distributions of the latices were studied. The number of particles generated was proportional to the 0.56 power of the emulsifier concentration and to the 0.37 power of the initiator concentration in the whole concentration range which was observed. Furthermore, the final number of particles was dependant on the reaction temperature to the 2.06 power. With these correlations the average particle number as well as the average particle size could be estimated, and the results were in good agreement (±6%) with the experimental values. A reduction of the monomer/water ratio from 1:5 to 1:20 yielded smaller particle diameters, while leaving the particle number unaffected. The lower particle size limits for monomer ratios of 1:10 and 1:15 were estimated with diameters of about 18 and 16 nm.     

In situ chemical oxidation of aniline by persulfate with iron(Ⅱ) activation at ambient temperature

<正>The kinetics of aniline degradation by persulfate processes with iron(Ⅱ) activation at ambient temperature was investigated in this study.With iron(Ⅱ) as initiator,the oxidation reactions were found to follow a biphasic rate phenomenon:a rapid transformation followed by a slow but sustained oxidation process.In the first 30 s,the reaction mainly relies on the persulfate-Fe~(2+) reaction in which aniline is oxidized rapidly.After 30 s,the aniline was still oxidized but the rate of reaction tended to be slower and the rates were clearly linear-proportional.After the initial fast oxidation,the reactions appeared to follow a pseudo-first-order model.     

Natural Abundance 15N and 13C Solid‐State NMR Chemical Shifts: High Sensitivity Probes of the Halogen Bond Geometry

Solid‐state nuclear magnetic resonance (SSNMR) spectroscopy is a versatile characterization technique that can provide a plethora of information complementary to single crystal X‐ray diffraction (SCXRD) analysis. Herein, we present an experimental and computational investigation of the relationship between the geometry of a halogen bond (XB) and the SSNMR chemical shifts of the non‐quadrupolar nuclei either directly involved in the interaction (¹⁵N) or covalently bonded to the halogen atom (¹³C). We have prepared two series of X‐bonded co‐crystals based upon two different dipyridyl modules, and several halobenzenes and diiodoalkanes, as XB‐donors. SCXRD structures of three novel co‐crystals between 1,2‐bis(4‐pyridyl)ethane, and 1,4‐diiodobenzene, 1,6‐diiodododecafluorohexane, and 1,8‐diiodohexadecafluorooctane were obtained. For the first time, the change in the ¹⁵N SSNMR chemical shifts upon XB formation is shown to experimentally correlate with the normalized distance parameter of the XB. The same overall trend is confirmed by density functional theory (DFT) calculations of the chemical shifts. ¹³C NQS experiments show a positive, linear correlation between the chemical shifts and the C?I elongation, which is an indirect probe of the strength of the XB. These correlations can be of general utility to estimate the strength of the XB occurring in diverse adducts by using affordable SSNMR analysis.