Reactions Of Transition Metal Ions Research Articles

Design, preparation, and combustion performance of energetic catalysts based on transition metal ions (Cu2+, Co2+, Fe2+) and 3-aminofurazan-4-carboxylic acid.

Development of energetic catalysts with high energy density and strong catalytic activity has become the focus and frontier of research, which is expected to improve the combustion performance and ballistic properties of solid propellants. In this work, three energetic catalysts, M(H2O)4(AFCA)2·H2O (AFCA = 3-aminofurazan-4-carboxylic acid, M = Cu, Co, Fe), are designed and synthesized based on the coordination reaction of transition metal ions and the energetic ligand. The target products are characterized by single crystal X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, optical microscopy, and scanning electron microscopy. The results reveal that Cu(H2O)4(AFCA)2·H2O crystallizes in the monoclinic space group, Dc = 1.918 g cm-3. Co(H2O)4(AFCA)2·H2O, and Fe(H2O)4(AFCA)2·H2O belong to orthorhombic space groups, their density is 1.886 g cm-3 and 1.856 g cm-3, respectively. In addition, the designed catalysts show higher catalytic activity than some reported catalysts such as Co(en)(H2BTI)2]2·en (H3BTI = 4,5-bis(1H-tetrazol-5-yl)-1H-imida-zole), Co-AzT (H2AzT = 5,5'-azotetrazole-1,1'-diol), and [Pb(BTF)(H2O)2]n (BTF = 4,4'-oxybis [3,3'-(1-hydroxy-tetrazolyl)]furazan) for the thermal decomposition of ammonium perchlorate (AP). The high-temperature decomposition peak temperatures of AP/Cu(H2O)4(AFCA)2·H2O, AP/Co(H2O)4(AFCA)2·H2O, and AP/Fe(H2O)4 (AFCA)2·H2O are decreased by 120.3 °C, 151.8 °C and 89.5 °C compared to the case of pure AP, while the heat release of them are increased by 768.8 J g-1, 780.5 J g-1, 750.9 J g-1, respectively. Moreover, the burning rates of solid propellants composed of AP/Cu(AFCA)2(H2O)4·H2O, AP/Co(AFCA)2(H2O)4·H2O and AP/Fe(AFCA)2(H2O)4·H2O are increased by 2.16 mm s-1, 2.53 mm s-1, and 1.57 mm s-1 compared with the case of pure AP. This research shows considerable application prospects in improving the combustion and energy performance of solid propellants, it is also a reference for the design and preparation of other novel energetic catalysts.

(Invited) Nanostructured Rocksalt-Based Positive Electrode Materials for Rechargeable Li/Na Batteries

In the past decade, lithium-enriched compounds, Li2MO3 (M = Mn4+, Ru4+ etc.), have been extensively studied for high-capacity positive electrode materials of lithium batteries. Although the origin of high reversible capacities was a debatable subject for a long time, recently it has been evidenced that charge compensation is partly achieved by solid-state redox of non-metal anions, i.e., oxide ions (anionic redox), coupled with redox reaction of transition metal ions (cationic redox), which is the basic theory used for classical lithium/sodium insertion materials. Recently, many cation-disordered rocksalt oxides have been proposed as a new series of electrode materials, which utilize reversible anionic redox. Nevertheless, insufficient electrode kinetics for the cation-disordered rocksalt system limits its use for practical applications. One simple strategy is to synthesize nanosized materials, which overcomes a problem of electrode kinetics (for electrons, holes and ions), and indeed electrode kinetics is significantly improved through nanosizing even for a non-lithium-excess and stoichiometric system.1) Moreover, Nanosized Li/Na-excess oxides also deliver large reversible capacities even at room temperature,2, 3) which shows much better electrode kinetics compared with as-prepared submicrometer-sized samples.From these findings, we discuss the advantages/disadvantages of “nanostructured” rocksalt-based electrode materialsto develop high energy Li/Na-ion batteries in the future.References Sato et al., and N. Yabuuchi., Journal of Materials Chemistry A, 6, 13943 (2018).Kobayashi et al., and N. Yabuuchi, Small, 15, 1902462 (6 pages) (2019).Kobayashi et al., and N. Yabuuchi, Materials Today, in-press, DOI: 10.1016/j.mattod.2020.03.002

The inhibition of the particulate matter-induced intrinsic apoptosis through metal-chelating in MLE-12 cells

Abstract Particulate matter containing transition metals has known to cause adverse health impacts. Reactive oxygen species (ROS) are overproduced by Fenton reaction of transition metal ions and occur to oxidative DNA damage with the induction of intrinsic apoptosis. Sargassum horneri, a brown alga, is one of rich sources for health functional compounds which can chelate transition metals. In this study, the inhibition of the PM-induced intrinsic apoptosis pathway by S. horneri ethanol extract (SHE) through metal-chelating in MLE-12 cells was investigated. When MLE-12 cells were exposed to PM, the titanium and iron contents were 1.05 and 4.55 Wt.%, respectively. However, after the SHE treatment at 125 μg/mL, they were significantly reduced to 0.35 and 0.02 Wt.%. Additionally, the reduction of iron concentration was observed at 62.5 μg/mL of SHE treatment which revealed the metal-chelating effect of SHE. The expressions of P53, Bax, Cytochrome-c, and cleaved caspase-3 involved in the intrinsic apoptosis were activated in MLE-12 after PM exposure and they were decreased by the SHE treatment at 62.5 and 125 μg/mL. On the other hand, the expression of caspase-8 related to the extrinsic apoptosis was not cleaved by PM exposure in MLE-12, which meant PM induced only intrinsic cell death. These results suggested that SHE can inhibit the PM-induced intrinsic apoptosis through metal-chelating in MLE-12. Funded by the Ministry of Oceans and Fisheries, Republic of Korea (Project NO. 20172085).

Modification of Electrochemical Behavior of Li-Rich Layered Oxide Cathode through Defect Consideration

Cathode materials formulated as xLi2MnO3-(1-x)LiMO2(M = Mn, Ni, Co, etc.) with layered structure received much attention due to their surprisingly high reversible capacity for Li-ion battery applications.[1,2] For better understanding of such high-capacity layered cathode, a systematic study on powder morphology, crystal structures and reaction mechanisms of Li1.2Mn0.54Ni0.13Co0.13O2 during electrochemical charge/discharge cycles were conducted. First, the capacity of Li-rich layered cathode powder was strongly affected by its particle size. To obtain various particle sizes of cathode powder, different powder synthesis routes have been adopted. By usng sol-gel process, particle size of Li1.2Mn0.54Ni0.13Co0.13O2 powder obtained is around 200 nm. On the other hand, Li1.2Mn0.54Ni0.13Co0.13O2 powder synthesized by solid-state reaction method gives particle size as coarse as 1.0μm. The initial discharge capacity of sol-gel processed Li-rich cathode was 250 mAh/g. After 40 cycles, the discharge capacity from the same cathode still shows a capacity as high as 205 mAh/g. However, for cathode powder from solid-state reaction, its initial capacity was 190 mAh/g that is 24% lower than that of sol-gel processed cathode. After 40 cycles, the capacity degraded to 137 mAh/g. The enhanced capacity of sol-gel processed Li-rich cathode is attributed to its enormous surface area and short Li diffusion distance provided for electrochemical reaction to take place. Although Li-rich layer-structured cathode material show a reversible capacity as high as 250 mAh/g at low rate, its electrochemical properties such as capacity loss at first cycle, rate capability and capacity fading still need to be examined and characterized. In this study, Li1.2Mn0.54Ni0.13Co0.13O2 were investigated. The TEM structural analysis shows that the evidence of spinel phase after cycling. It is believed that the transition from layered structure to spinel structure may also induce a large lattice distortion resulting in lattice breakdown and capacity fading. In additions, the phase transition may be caused by the redox reaction of transition metal ions through charging/discharging tests.

Investigation of Capacity Fading on Li-Rich Layered Composite Cathode Materials for Li Ion Batteries

the capacity of Li-rich layered cathode powder was strongly affected by its particle size. By using sol-gel process, particle size of Li1.2Mn0.54Ni0.13Co0.13O2 powder obtained is around 200 nm. On the other hand, Li1.2Mn0.54Ni0.13Co0.13O2 powder synthesized by solid-state reaction method gives particle size as coarse as 1.0μm. The initial discharge capacity of sol-gel processed Li-rich cathode was 250 mAh/g. After 40 cycles, the discharge capacity from the same cathode still shows a capacity as high as 205 mAh/g. However, for cathode powder from solid-state reaction, its initial capacity was 190 mAh/g that is 24% lower than that of sol-gel processed cathode. After 40 cycles, the capacity degraded to 137 mAh/g. The enhanced capacity of sol-gel processed Li-rich cathode is attributed to its enormous surface area and short Li diffusion distance provided for electrochemical reaction to take place. Furthermore, the TEM diffraction analysis of cycled Li[Li0.2Mn0.54Ni0.13Co0.13]O2 shows the evidence of spinel phase after cycling. It is believed that the transition from layered structure to spinel structure may also induce a large lattice distortion resulting in lattice breakdown and capacity fading. In additions, the phase transition may be caused by the redox reaction of transition metal ions through charging/discharging tests.

Influence of Na-substitution on the structure and electrochemical properties of layered oxides K0.67Ni0.17Co0.17Mn0.66O2 cathode materials

Layered K0.67-xNaxNi0.17Co0.17Mn0.66O2 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) cathodes for potassium-ion batteries were successfully prepared by a co-precipitation method. The influences of Na substitution were studied in detail and it was found that the Na content could change the crystalline structure (from single phase to biphase) and eventually affect the electrochemical properties. The moderate amount of Na could stabilize the layered structure, activate the redox reaction of transition metal ions and further improve the cycling and rate performance. The P3/P2-type K0.37Na0.3Ni0.17Co0.17Mn0.66O2 composite displayed enhanced cyclability with a reversible capacity of 86.1 mAh g−1 and 78.8 mAh g−1 kept after 100 cycles at 20 mA g−1, which was better than the pristine P3-K0.67Ni0.17Co0.17Mn0.66O2 (76.1 mAh g−1 and 65.3 mAh g−1 at the same condition, respectively). In addition, the K0.37Na0.3Ni0.17Co0.17Mn0.66O2 sample delivered a high capacity of 62 mAh g−1 even at 100 mA g−1, much higher than that of K0.67Ni0.17Co0.17Mn0.66O2 (47.8 mAh g−1). These results proved that appropriate metal doping could be a feasible solution to improve the performance of layered ternary cathode for potassium-ion batteries.

Electrolyte and SEI Decomposition Reactions of Transition Metal Ions Investigated by On-Line Electrochemical Mass Spectrometry

We use on-line electrochemical mass spectrometry (OEMS) to elucidate and quantify the electrolyte reduction on graphite caused by transition metal ions. To have a controlled system, we use ethylene carbonate (EC) with 1.5 M LiPF6 and representative amounts of Ni(TFSI)2 or Mn(TFSI)2 as model electrolytes, combined with a 2-compartment cell in which anolyte and catholyte are separated by an impermeable solid lithium ion conductor. Focusing on C2H4 evolution as a marker for EC reduction, we find that both Ni2+ and Mn2+ lead to enhanced gas evolution on pristine graphite electrodes once the potential is decreased to below the TM2+/TM0 redox potential, demonstrating that the reduced transition metals are active toward electrolyte reduction. If the electrodes are preformed in a TM-free electrolyte and subsequently cycled in an electrolyte containing either Mn2+ or Ni2+, the activity of nickel toward electrolyte decomposition is greatly reduced, whereas the electrolyte with manganese still shows a strong ongoing C2H4 generation. The use of vinylene carbonate during formation partially suppresses the gas evolution from manganese. Using OEMS and post-mortem ATR-FTIR, we finally show that reduced manganese can decompose organic SEI components into Li2CO3, thereby compromising the integrity of the SEI and enabling the additional reduction of electrolyte.

Substantiation for Oxywater Zwitterions and Singlet Oxygen Atoms Generation from Hydrogen Peroxide Molecules in Aqueous Solutions

Hydrogen peroxide is widely used as an oxidant. The results of thermodynamic calculations indicate the impossibility of spontaneous generation of hydroxyl and hydroperoxyl radicals from hydrogen peroxide in aqueous solutions. Hydrogen peroxide spontaneously decomposes in ferrous, ferric, and cupric Fenton reaction systems. Ferric xylenol orange and ferric pyridoxine complexes are oxidized rapidly and spontaneously by this oxidant. Hydrogen peroxide in aqueous solutions spontaneously oxidizes the sulfur atoms of hyposulfite anions and benzylpenicillin molecules. Thus, a hydrogen peroxide molecule generates another intermediate that differs from hydroxyl and hydroperoxyl radicals. Theoretical modeling shows that hydrogen peroxide can participate in the proton transfer reactions. Its isomerization to oxywater zwitterion with subsequent oxywater intramolecular disproportionation is a process that is very suitable for explaining all events of hydrogen peroxide decomposition and oxidative reactivity in aqueous systems. The oxywater zwitterion is a bipolar ion in which the opposite charges are localized on neighboring oxygen atoms. This determines the displacement of electron density from the negatively charged atom to the positively charged atom. As a result, the interoxygen bond heterolytically dissociates with liberation of a water molecule and formation of an oxygen atom (oxene) in a singlet quantum state. This atom has a vacant atomic orbital. The S-oxidation of benzylpenicillin and hyposulfite occurs via targeting of electron pairs of the sulfur atoms by the vacant atomic orbitals of the singlet oxygen atoms. We substantiate an oxene-mediated pathway of hydrogen peroxide disproportionation. A singlet oxygen atom interacts with a second hydrogen peroxide molecule through targeting the unshared electron pair of the oxygen atom by a vacant atomic orbital. The process may be called O-oxidation of hydrogen peroxide; it results in trioxidane (dihydrogen trioxide) formation. Hydrogen trioxide rapidly decomposes and produces water and singlet dioxygen. We have suggested a mechanism of the electron spin rotation during the singlet dioxygen quenching into the triplet quantum state. We have assumed the formation of a dimeric associate from singlet dioxygen antipodes by orbital parameter. Two simultaneous redox reactions (the electron exchange interaction) result in generation of two triplet dioxygen molecules. The first triplet molecule has +1 total electron spin, and the second one has –1 total electron spin. For Fenton reaction systems, the zwitterionization of hydrogen peroxide in Lewis acid-base complexes with metal ions is followed by intramolecular disproportionation of oxywater. The singlet oxene remains in complex with a metal ion. Ferrous iron ion changes its oxidation state to ferric due to rapid and inevitable one-electron transfer within the iron(II)-oxene complex. The ferric-oxyl complex is known as alpha-oxygen complex. In our opinion, the classic Fenton reaction occurs through alpha-complex formation. We maintain such view that is alternative to widespread conceptions of the hydroxyl radical generation or oxoferryl(IV) formation. We have reproduced electro-Fenton reactions of transition metal ions with electrogenerated hydrogen peroxide and presumably observed voltammetric signals for the singlet oxene atoms and oxyl radical anions (alpha-oxygen particles). The oxywater-oxene concept is successfully applicable to explain the catalytic activity of redox-inactive substances. We have used our oxywater-oxene concept for explanation of hydroperoxide monooxygen and dioxygen oxidative functionalization mechanisms in organic synthesis.

Mechanism of Capacity Fading of Li-Rich Layer-Structured Cathode Materials Based on TEM/Electrochemical Analyses

Recently, Li-rich layer-structured cathode formulated as xLi2MnO3 -(1-x)LiMO2(M = Mn, Ni, Co, etc.) exhibit high reversible capacity for Li-ion battery applications. Although Li-rich layer-structured cathode material show a reversible capacity as high as 250 mAh/g, its electrochemical properties such as capacity loss at first cycle, rate capability and capacity fading upon cycling still need to be investigated. A systematic study on crystal structures and electrochemical testing is employed. In this study, various compositions of xLi2MnO3 -(1-x)LiMO2 (M = Mn, Ni, Co, etc.) were investigated. The electron diffraction pattern of spinel structure was observed from a cycled layer-structured cathode particle. The transition from layered structure to spinel structure may induce a large lattice distortion resulting in lattice breakdown and capacity. Furthermore, the phase transition may be caused by the redox reaction of transition metal ions through repeated cycling tests. Discussion will be carried out based on the results of XRD, SEM, TEM analyses on cycled cathode materials

Understanding of Capacity Loss/Fading of Li-Rich Layer-Structured Cathode Materials Based on Structural/Electrochemical Analyses

Li-rich layer-structured cathode materials formulated as xLi2MnO3 -(1-x)LiMO2(M = Mn, Ni, Co, etc.) have received much attention due to their surprisingly high reversible capacity for Li-ion battery applications. For the understanding of these materials, a systematic study on complicated crystal structures and reaction mechanisms during electrochemical charge/discharge cycles is employed. Although Li-rich layer-structured cathode material show a reversible capacity as high as 250 mAh/g at low rate, its electrochemical properties such as capacity loss at first cycle, rate capability and capacity fading still need to be examined and characterized. In this study, several compositions of xLi2MnO3 -(1-x)LiMO2 (M = Mn, Ni, Co, etc.) were investigated. The TEM structural analysis shows that the evidence of spinel phase after cycling. It is believed that the transition from layered structure to spinel structure may induce a large lattice distortion resulting in lattice breakdown and capacity. In additions, the phase transition is caused by the redox reaction of transition metal ions through charging/discharging tests. Thus, the cycling behavior of Li-rich layer-structured oxides is studied by changing the oxidation state of transition metal ions in the layered structures. XRD, SEM, TEM will be used for characterization of cycled cathode materials.

Structural Variability and Gas Adsorption Properties of Coordination Polymers Constructed with Aromatic Multicarboxylic and Bidentate Ligands

AbstractThe self‐assembly reactions of transition metal ions and 1,3,5‐benzenetricarboxylic acid (H3btc) in the presence of auxiliary aromatic bidentate ligands 1,10‐phenanthroline (1,10‐phen) or 4,4′‐bipyridine‐N,N′‐dioxide (4,4′‐bpdo) have isolated four coordination polymers [Co18(btc)10(H2O)6(OH)6(1,10‐phen)6]·14H2O·3DMF (1) and [M3(btc)2(H2O)4(4,4′‐bpdo)]·2H2O·2DMF [M = Co (2), Mn (3), Ni (4)]. Single‐crystal X‐ray diffraction analysis revealed that the M3 clusters in the structure of 1–4 are connected by hydroxyl group oxygen atoms (or oxygen atoms from 4,4′‐bpdo ligands) and carboxyl groups to generate a three‐dimensional framework. The network of final assemblies can be adjusted by varying the type of auxiliary ligands (1,10‐phen, 4,4′‐bpdo). In addition, the gas adsorption properties of 2 are also investigated.

EQCM Analysis of Redox Behavior of CuFe Prussian Blue Analog in Mg Battery Electrolytes

A wide variety of ions and molecules can be accommodated in the framework structure of Prussian blue (PB) and its analogs (PBAs). Mono- and polyvalent ions accommodated in the PB framework structure and PBAs can be extracted or re-inserted by redox reactions of transition metal ions composing the framework for charge compensation. In the present work, we report the detailed mechanism of the electrochemical inseration/extraction of Mg2 + ions and the effect of anions on the redox chemistry of a PBA composed of Cu and Fe ions by electrochemical quartz crystal microbalance and X-ray absorption spectroscopy. Furthermore, we evaluated the PBA as an active material using aqueous and organic electrolytes for Mg battery systems, and clarified that the redox potential of CuFe-PBA is approximately 3 V vs. Mg/Mg2 + in both aqueous and organic electrolytes.

Coordination-Induced Assembly of Coordination Polymer Submicrospheres: Promising Antibacterial and in Vitro Anticancer Activities

Spheres-like coordination polymer architectures in submicro regimes have been synthesized from the hydrothermal reaction of transition metal ions and 3,5-bis(pyridin-3-ylmethylamino)benzoic acid (L1). The size of the final coordination polymer was dependent on the concentrations of reactants. Scanning electron microscopy studies monitored at numerous stages of growth reveal that coordination-induced morphology changes from uncoordinated flowerlike ligands to sphere-like coordination polymer particles. Moreover, variations of luminescent and antibacterial profiles are associated with coordination environments or the size of as-obtained coordination polymer samples. In addition, the newly synthesized Cu-based polymer particles may act as novel metal-based anticancer drugs in the future because of their potent in vitro anticancer activities against three chosen cancer lines MCF-7, HeLa, and NCI-H446.

Initial Stage of the Delithiation of Li1.2-xMn0.4Fe0.4O2 Positive Electrode Material for Lithium-Ion Batteries Studied by Electron Energy-Loss Spectroscopy

We have investigated initial stage of the delithiation of Li1.2-<I>x</I>Mn0.4Fe0.4O2 nanoparticles by means of transmission electron microscopy and electron energy-loss spectroscopy. It was found that depletion areas with diameters of less than 10 nm are preferentially formed at Fe-rich regions on the particle surfaces. Correlations between redox reactions of transition metal ions and formation of the depletion areas are discussed.

Metal complexes of a new ligand derived from 2,3-quinoxalinedithiol and 2,6-bis(bromomethyl)pyridine

The synthesis of a new ligand containing quinoxaline and pyridine subunits is described. The reaction of 2,3-quinoxalinedithiol with 2,6-bis(bromomethyl)pyridine leads to the isolation of bis(2-thio-3-mercaptoquinoxalino)-2,6-dimethylpyridine (L), which is a macrocyclic ligand precursor. The reaction of transition metal ions with L gives [M(L)X]X complexes (where M = Mn(II), Co(II), Cu(II), Ag(I), Zn(II), or Cd(II), and X = Cl or Br). The compounds were characterized by physical and spectroscopic measurements which indicated that the ligand is probably acting as a pentadentate NS4 chelating agent

Solvent displacement in transition metal complexes

Ligand exchange reactions of transition metal ions solvated by two acetone or two acetonitrile molecules with multidentate polyethers or pyridyl ligands are undertaken in a quadrupole ion trap mass spectrometer. The ability of the polyether or pyridyl ligand to displace one or both solvent molecules is correlated with the number of binding atoms in the multidentate ligand, the flexibility of the ligand along with its ability to fully coordinate or encapsulate the metal ion, and the strength of the solvent/metal bonds. The smaller polyethers displace one solvent molecule, thus generating stable (M + + polyether + solvent) complexes. The larger polyethers rapidly displace both solvent molecules, leading to formation of stable (M + + polyether) complexes, because of the ability of the large polyethers to encapsulate or fully coordinate the metal ion. The pyridyl ligands tend to favor formation of (M + + pyridyl ligand + solvent) mixed-ligand complexes, regardless of the number of nitrogen atoms or flexibility of the pyridyl ligand. The pyridyl ligands are unable to fully encapsulate the metal ion, so one solvent molecule may remain bound to the metal ion.

Bis(1,2-diselenooxalato)nickelate(II) and -cuprate(II) — the first diselenooxalate complexes

By the reaction of transition metal ions (Cu 2.Ni 2′) with 1,2-diselenooxalate the first selenooxalato complexes have been synthesized. The structure of the nickel complex, bis(1,2-diselenooxalato)nickelate(II).(BzlPh 8P) 2[Ni(dso) 2], has been determined by X-ray diffraction. The analogous Cu(II) complex. [Cu(dso) 2] 2, was identified by its ESR spectrum characterized by the following parameter set: g o = 2.042 and the 64Cu and 77Se hypertine coupling constants a o co = 79.1 × 10 4 cm 1 and a a Se = 48.6 × 10 4 cm 1 . respectively.

Mechanism of low-density lipoprotein oxidation

Peroxidation of LDL is thought to be important in the pathogenesis of atherosclerosis, but the mechanism by which peroxidation is initiated is uncertain. Hydroxyl radical is an initiating species formed by the reaction of transition metal ions with hydrogen peroxide and of superoxide radical with nitric oxide. However, the role of the nitric oxide radical in macrophage-mediated LDL oxidation is still uncertain. In most in vitro experiments, reactions involving preformed peroxides in the LDL are being examined rather than first-chain initiation. Superoxide and transition metal ions (which are present in advanced human arteriosclerotic lesions) can lead to peroxide decomposition and propagate LDL peroxidation. The 'seeding' peroxides in LDL could be generated by lipoxygenases (other than 5-lipoxygenase), originate from dietary fats, or be formed by endogenous peroxidation, but the possibility of artefactual formation of peroxides during prolonged LDL isolation procedures must not be disregarded.

Reactions of transition-metal ions with sulfur hexafluoride in the gas phase

The inertness of SF[sub 6] is well-known to be associated with the protective layer of F atoms which obstructs the access to the reactive S center by an attacking species. Previous gas-phase studies of SF[sub 6] involved reactants having high ionization energies, such as He[sup +], Ar[sup +], and N[sub 2][sup +], which are observed to yield predominantly SF[sub 5][sup +] either via F[sup [minus]] abstraction or dissociative charge transfer. This study shows that early transition metal ions, despite their low ionization potentials, can react with SF[sub 6] yielding product distributions much different from those of the reactions studied previously. In contrast, the reduced reactivity and mainly absence of reactivity observed for the late transition metal ions indicates that an empty d orbital is required for reaction. Rate constants for some selected early transition metal ion reactions are determined. Sc[sup +] was chosen to be studied in detail because a complete set of thermodynamic data on ScF[sub n][sup +/0] were available in the literature. The reaction pathways are derived and a reaction mechanism involving oxidative addition is proposed. 44 refs., 3 figs., 7 tabs.

Dynamic Solvent Effects on Electron‐Transfer Reactions

AbstractElectron‐transfer processes in solution are among the most important reactions in chemistry and biology. The huge number of redox reactions of transition metal ions and complexes, many preparatively important oxidations and reductions of organic compounds, photosynthesis, and metabolism are only a few examples where electron‐transfer reactions play a pivotal role. This ubiquity, as well as their relative simplicity, makes them excellent models for the study on a molecular level of chemical reactions in solution. A particularly important question in chemical reaction dynamics in solution is the influence of the solvent on the reaction rate. In this context one distinguishes between static and dynamic solvent effects. Static effects refer to the stabilization of reactants, transition state, and products, that is, how the solvent affects the free energies of these species and the energy of activation. This interpretation of solvent effects on all kinds of chemical reactions is well established. A more recent development is the investigation of the influence of solvent dynamics on the rate of a reaction. The transfer of an electron is usually thought to be triggered by a fluctuation of the dielectric polarization in the surrounding solvent. The dynamics of such fluctuations is determined by the finite response time of the orientational polarization of the solvent. Under certain conditions this dielectric response time can become the rate‐determining factor of the reaction. In this article I intend to give a review of these modern developments in the theory and experimental study of electron‐transfer processes. We shall see that solvent dynamics may lead to a whole plethora of phenomena in reaction dynamics. The concepts needed for their description are not limited to electron transfer but bear relevance to many other chemical reactions in solution.