Electron Spin Resonance Studies Research Articles

An effective way to control the radical reaction and its mechanism in EPDM under γ-ray irradiation

The effects of a compound that contains a xanthate group named DIP on the radical reactions and structural evolution of the ethylene propylene diene monomer (EPDM) were investigated. It was found that the structural evolution and long-term stability of the EPDM can be realized by controlling the radical reaction in the matrixes of EPDM during γ-ray irradiation. The results show that the DIP can prevent EPDM deterioration, when the γ-ray irradiation dose reaches 450 kGy, the retention rate of the elongation at break and tensile strength of the EPDM samples containing 1 wt% DIP could remain about 90% and 160%, while those of additive-free EPDM are only about 33% and 70%. On the other hand, the thermal stability of the EPDM samples decreases markedly with the dose increasing under γ-ray irradiation. However, the thermal decomposition temperature of the EPDM samples containing DIP remains basically unchanged after irradiation, and DIP can also improve the oxidation resistance of the EPDM. Electron spin resonance studies reveal that DIP can effectively control the radical reactions inside the EPDM during γ-ray irradiation. Rheology results show that the structural evolution of the EPDM can be well controlled under γ-ray irradiation owing to the presence of DIP in the EPDM matrixes. Density functional theory calculations indicate that the reversible radical reactions inside EPDM/DIP systems are crucial in realizing the long-term stability and controllable structural evolution of the EPDM under γ-ray irradiation.

Rhodamine B dye degradation using used face masks-derived carbon coupled with peroxymonosulfate

Catalytic carbon materials from used face masks (UFM) activated by peroxymonosulfate (PMS) were developed for the degradation of rhodamine B (RhB) dye in aqueous solution. The UFM-derived carbon (UFMC) catalyst had a relatively large surface area as well as active functional groups and promoted the generation of singlet 1O2 and radicals from PMS, giving a high RhB degradation performance (98.1% after 3 h) in the presence of 3 mM PMS. The UFMC could degrade only 13.7% at a minimal RhB dose of 10−5 M. The principal reactive oxygen species of sulphate (SO4•), hydroxyl radicals (•OH), and singlet 1O2 were discovered using electron paramagnetic resonance and radical scavenger studies. Finally, a toxicological plant and bacterial study was performed to demonstrate the potential non-toxicity of the degraded RhB water sample.

Synthesis of porous (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O high entropy oxide catalysts for peroxymonosulfate activation toward tetracycline degradation

The porous (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O high entropy oxide was synthesized by a facile solution combustion method. The X-ray diffraction (XRD) patterns showed that a rock-salt phase (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O nanocrystalline was successfully constructed after heat treatment above 800 °C. A porous microstructure with high specific surface area was determined by scanning electron microscope (SEM) and N2 adsorption analysis, respectively. The (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O high entropy oxide displayed excellent peroxymonosulfate (PMS) activation which could fully degrade the tetracycline (TC) within 24 min. Moreover, the effect of PMS concentration, the high entropy oxide dosage, pH value, temperature and coexisting anions on the degradation efficiency of TC was systematically studied. According to free radical quenching experiments and electron paramagnetic resonance studies, the possible mechanism of TC degradation over the (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O/PMS system was proposed. This work provided a research basis for the use of high entropy oxide for PMS activation in environmental treatment.

Electron Paramagnetic Resonance Studies of Irradiated Grape Snails (Helix pomatia) and Investigation of Biophysical Parameters.

A study of grape snails (Helix pomatia) using the electron paramagnetic resonance (EPR) spectroscopy method, where shells were exposed to ionizing gamma radiation, indicated that the effect of radiation up to certain doses results in the emergence of magnetic properties in the organism. The identification of the EPR spectra of the body and shell parts of the control and irradiated grape snails separately showed that more iron oxide magnetic nanoparticles are generated in the body part of the grape snail compared to the shells. A linear increase in free radical signals (g = 2.0023) in the body and shell parts of grape snails, and a non-monotonic change in the broad EPR signal (g = 2.32) characterizing iron oxide magnetic nanoparticles was determined depending on the dose of ionizing gamma radiation. Additionally, the obtained results showed that grape snails can be used as bioindicators for examining the ecological state of the environment. At the same time, the radionuclide composition of the body and shell parts of the grape snails and their specific activities were determined by CANBERRA gamma spectroscopy. The FTIR spectra of mucin, a liquid secreted by snails, were recorded.

Oxygen vacancy-rich BiOBr microflowers for enhancing photocatalytic reduction of nitrobenzene under visible light

BiOBr has successfully been used as a photocatalyst in the selective oxidations of alcohols and amines into carbonyl compounds, however its utilization in the photocatalytic reduction reactions, especially the transfer hydrogenation of nitrobenzene (NB) to valuable organic products such as aniline, azoxybenzene, and azobenzene has rarely been reported. For the first time, we reveal the feasibility of using oxygen vacancy-rich BiOBr flower-like microsphere (BBr_OV) as a photocatalyst and hydrazine monohydrate as a green hydrogen source for such reaction. The existence of OV is probed by high-resolution transmission electron, electron paramagnetic resonance and X-ray photoelectron studies. The NB reduction activity is boosted from ~29% for pristine BiOBr microplate to ~90% for the BiOBr enriched with oxygen vacancies. Detailed characterizations disclose that the enhanced photocatalytic performance is attributed to synergistic roles of oxygen defective and hierarchical flower-like structure, endowing the BBr_OV with efficient NB adsorption/activation, enlarge surface area, improved optical absorption, and increased charge carrier generation/separation efficiency. This work not only reveals a new application of OV-rich BiOBr in the photocatalytic transfer hydrogenation of nitroarene, but also highlights the promoting catalytic effect derived from rich OV surfaces.

Experimental evidence for spin–triplet states in Titanium implanted AlN film: An electron spin resonance study

Spin carrying defects in wide-bandgap semiconductors are promising candidates for the development of quantum information and quantum sensing technology. Here we report experimental evidence for the formation of paramagnetic defects in AlN films, subjected to high-energy hydrogen and titanium ion implantation. X-ray diffraction and Raman spectroscopy show that ion species and implantation process could alter the amount of local strain in AlN films. Electron spin resonance spectroscopy reveals resonance peaks with g-value higher than the one of a free electron (2.0023) for both H-implanted and Ti-implanted AlN films. The origin of these peaks is identified and attributed to different types of point defects. For the Ti-implanted film, in addition to the central peak, a half-field resonance peak has been detected and assigned to spin–triplet (S=1). These results provide new insight into the electronic spin state of point defects in AlN, which opens up interesting perspectives for applications to quantum devices.

Enhanced activation of peroxymonosulfate for ofloxacin rapid degradation and inhibition of metal leaching on LaNi0.6Co0.4O3 stably anchored at ZnO

The citrate sol-gel method was used to synthesize LaNi0.6Co0.4O3 anchored at ZnO (LaNi0.6Co0.4O3/ZnO) for activation of peroxymonosulfate to degrade ofloxacin in simulated wastewater. LaNi0.6Co0.4O3 nanoparticles were uniformly and firmly dispersed on ZnO support during the synthesis process. LaNi0.6Co0.4O3/ZnO had a rapid catalytic rate with an efficiency of 90% in 10 min, which was higher than that of LaNi0.6Co0.4O3 (87.7%). Meanwhile, LaNi0.6Co0.4O3/ZnO significantly inhibited metal ion leaching compared to LaNi0.6Co0.4O3 (Ni leaching: 0.128 mg/L to 0.022 mg/L, Co leaching: 0.083 mg/L to 0.012 mg/L). The composite material maintained great cyclic stability with efficiency of 93% after 5 cycles. Based on electron paramagnetic resonance studies and the quenching experiments, SO4·−、·OH、·O2− and 1O2 were the main reactive oxygen species involved in the reaction. The degradation intermediates of ofloxacin were detected by ICP-MS to propose the possible degradation pathways. This work provides an insight for perovskite catalyst for the activation of PMS to treat pharmaceutical wastewater.

Zero-Field Splitting in Cyclic Molecular Magnet {Cr8Y8}: A High-Frequency ESR Study

Cyclic 3d-4f molecular magnets have received considerable attention owing to their potential applications in high-density data storage and quantum information processing. As a rare example of ferromagnetic polynuclear Cr rings, {Cr8Y8} represents a valuable test bed to directly study the magnetic interaction between Cr3+ ions in large hexadecametallic {Cr8Ln8} (Ln = 4f metal) molecules. We have proposed a “single-J” model to approximate the low-temperature spin dynamics of {Cr8Y8} in our earlier study, while a zero-field splitting (ZFS) of the quantum levels was also suggested by the heat capacity data. In order to have a deeper understanding of the magnetism of {Cr8Y8}, it is necessary to verify the ZFS by means of high-resolution spectral methods and identify its origin. In this work, we present a high-frequency electron spin resonance (HF-ESR) study on the ZFS of {Cr8Y8}. The X-band ESR spectra consists of multi-peak structure, indicative of magnetic anisotropy that breaks the degeneracy between spin states in the absence of a magnetic field. HF-ESR spectra are collected to extract the ZFS parameters. We observed a sharp resonance peak due to the transitions between the S = 11 quantum levels and a broadband corresponding to a distribution of resonance peaks due to the ZFS of the S = 12 quantum levels. By analyzing HF-ESR spectra, we confirm the expected S = 12 ground state and determine its ZFS parameter D as −0.069 K, and, furthermore, we reproduce the spectra recorded at 154 GHz. The macrospin model proves to still be valid. The ZFS is attributed to the axial magnetic anisotropy, as found in some other Cr-based molecular wheels. The detailed HF-ESR investigation presented in this paper will benefit the studies on other {Cr8Ln8} wheels with magnetic Ln3+ ions and highlights the importance of the HF-ESR method as a high-resolution probe in determining the ZFS parameters with very small magnitude.

Effect of Gamma Irradiation on Fat Content, Fatty Acids, Antioxidants and Oxidative Stability of Almonds, and Electron Paramagnetic Resonance (EPR) Study of Treated Nuts.

Gamma irradiation has been applied as an efficient and inexpensive method for the sterilization of nuts for years. However, along with the benefits of such treatment, negative effects are possible because of the formation of reactive oxygen species with a toxic effect on important biologically active substances. Because of the scarce and contradictory information in the literature about gamma-irradiated almonds, the aim of our work was the examination of the lipid changes, antioxidant activity, and oxidative stability of almonds treated by 10 and 25 kGy gamma rays, as well as changes in intensity of the EPR spectra as an indicator for the stability of radiation-induced free radicals. The results revealed no significant differences in the EPR spectra of almonds treated at 10 and 25 kGy doses, neither in their intensity nor in kinetic behaviour. The EPR signals decayed exponentially over 250 days, with a decreasing of central line by 90%, with satellite lines by about 73%. No significant changes in the fat content, fatty acids composition, and acid value of irradiated almonds were observed. However, the amount of (alpha)tocopherols decreased from 292 to 175 mg/kg, whereas the conjugated dienes and trienes increased, K232 from 1.3 to 3 and K268 from 0.04 to 0.15, respectively, with the increasing of irradiation dose. The same was observed for total polyphenols in defatted almonds (1374 to 1520 mg/100 g), where in vitro antioxidant activity determined by ORAC and HORAC methods increased from 100 to 156 µmol TE/g and from 61 to 86 µmol GAE/g, respectively. The oxidative stability of oil decreased from 6 to 4 h at 120 °C and from 24.6 to 18.6 h at 100 °C (measured by Rancimat equipment). The kinetic parameters characterizing the oxidative stability of oil from 10 kGy irradiated almonds were studied before and after addition of different concentrations of ascorbyl palmitate as a synergist of tocopherols. Its effectiveness was concentration-dependent, and 0.75 mM ensured the same induction period as that of non-irradiated nut oil. Further enrichment with alpha-tocopherol in equimolar ratio with palmitate did not improve the oil stability. In conclusion, gamma irradiation is an appropriate method for the treatment of almonds without significant changes in fat content and fatty acids composition. The decreasing of oxidative stability after higher irradiation could be prevented by the addition of ascorbyl palmitate.

Transport and electron spin resonance studies in Mo-doped LaMnO3

We report the magnetic, electrical, thermoelectric, and magnetic resonance properties of the Mn-site doped manganite LaMn0.94Mo0.06O3. This sample undergoes an insulator-metal transition around 235 K, near the ferromagnetic Curie temperature (TC = 237 K) in zero external magnetic field. On the other hand, thermopower exhibits a maximum at TS = 258 K, which is 23 K higher than TC. This discrepancy is attributed to nucleation of ferromagnetic clusters (Griffiths phase) above TC, which is supported by the deviation of inverse susceptibility from Curie-Weiss from linear behavior below 270 K and non-linear field dependence of magnetization. The magnetic resonance spectra shows both paramagnetic and ferromagnetic resonance signals between 240 and 260 K. It is suggested that the ferromagnetic clusters enlarge in size with lowering temperature and percolate leading to long-range ferromagnetism and metallicity.

Regulation of diiron active site of sMMO through regulatory and reductase components from Methylosinus sporium 5.

Methanotrophs are key archaea for the regulation of methane gas (CH4), one of the major sources of greenhouse gas, through the expression of sMMO and pMMO. The structures and functions of sMMO, a bacterial multicomponent monooxygenase (BMM) superfamily, are being widely investigated to understand O2 and C-H activations in diiron active sites, although elucidation of its mechanism needs to overcome various factors. Recent advances through structural and spectroscopic support demonstrate conformational changes by component interactions of regulatory (MMOB) and inhibitory enzymes. In this presentation, the allosteric effects of sMMO will be described based on the structural and spectroscopic studies. The hydroxylation of CH4 is accelerated by the interaction of MMOB, and it induces conformational changes for controlling substrates and product pathways. The structures of whole sequences of MMOR have not yet been reported, although structures of FAD-/NADH-binding domain and ferredoxin domain from NMR studies have been reported. The electronic structure of MMOR is investigated through electron paramagnetic resonance (EPR) studies, since it cannot provide its electronic structure with structural information. The annealing method from MMOR shows that Cys50 is first oxidized when it transfers electrons in the [2Fe-2S]+ domain and a neural form of FAD is a major form of cofactor.

Experimental and computational studies of photoelectrochemical degradation of atrazine by modified nanoporous titanium dioxide

The presence of herbicides like Atrazine (ATZ) in groundwater from non-target runoff of the agriculture industry becomes a big concern due to its potential negative impacts on the environment and human health. The use of advanced oxidative processes (AOP) to remove harmful contaminants has been shown to be effective for wastewater treatment. Herein, we report on an advanced photoelectrochemical (PEC) approach based on electrochemically modified nanoporous TiO2 electrode for efficient degradation of ATZ. The electrochemical treated TiO2 electrodes were shown to have a six-fold increase in the photo-current density over the untreated ones. This increase in PEC activity was attributed to the increase in Ti3+ sites after the electrochemical modification, which was corroborated by low-temperature electron paramagnetic resonance (EPR) studies. The removal of ATZ by the PEC process resulted in a rate constant of 1.91 × 10−3 s−1, compared to 3.12 × 10−4 s−1 obtained by a strictly photocatalytic process. Liquid-Chromatography Mass-Spectrometric measurements showed the modified TiO2 electrodes highly effective at removing ATZ, with 96.1% removed after 10 h. Monitoring of the common degradation products desethyl atrazine (DEA), desisopropyl atrazine (DIA) and desethyl desisopropyl atrazine (DDA) revealed very low concentrations throughout the degradation process, indicating that further degradation was achieved. Quantum mechanical-based test for overall free radical scavenging activity (QM-ORSA) computational studies were performed and a mechanism for the N-dealkylation processes of ATZ has been proposed.

Dielectric resonator in rectangular ТЕ102 cavity for electron paramagnetic resonance study of thin films

The improved compared to a rectangular TE102 cavity geometry of a dielectric resonator (DR) suitable for studying thin films and coatings has been calculated and experimentally verified. It is shown that electron paramagnetic resonance (EPR) signal of SiOx films can be enhanced by using as the DR of two rectangular parallelepipeds fabricated from BaTi4O9 + 8.5% ZnO ceramics (ε=36) with dimension of 5.64×5.5 × 5.9 mm3 and a gap of up to 0.5 mm between them. Located inside a standard rectangular metal TE102 cavity of the X-band EPR spectrometer, the DR increases the filling factor by 5–12 times depending on the size of a sample studied. The experimental use of the DR allows to increase the EPR signal of the 950 nm SiOx thin film by a factor of approximately 4.

Iodoarene mediated efficient aerobic oxidation of aldehydes for carboxylic acids

Carboxylic acids are important chemical compounds with a wide range of applications in chemical science, pharmaceutics and material science. Despite tremendous progress in their synthesis with metal-catalysts over the past decade, sustainable, efficient metal-free strategies for aerobic oxidation of aldehydes in aqueous phase are highly desired. In particular, diverse carboxylic acids still remain difficult to be efficiently accessed with existing metal-free methods. Herein, a highly efficient iodoarene-mediated aerobic oxidation method for carboxylic acids in aqueous phase is reported. This approach unlocks access to a highly expanded number of carboxylic acids bearing functional groups on aromatic aldehydes and saturated/unsaturated aliphatic aldehydes. Detailed mechanistic studies using computation studies, isotope labelling, electron paramagnetic resonance studies and spectroscopic measurements provide strong support for the interception of hypervalent iodine intermediates through aldehyde hydrate.

Self-Organization Effects of Thin ZnO Layers on the Surface of Porous Silicon by Formation of Energetically Stable Nanostructures.

The formation of complex surface morphology of a multilayer structure, the processes of which are based on quantum phenomena, is a promising domain of the research. A hierarchy of pore of various sizes was determined in the initial sample of porous silicon by the atomic force microscopy. After film deposition by spray pyrolysis, ZnO nanoclusters regularly distributed over the sample surface were formed. Using the electron paramagnetic resonance (EPR) method it was determined that the localization of paramagnetic centers occurs more efficiently as a result of the ZnO deposition. An increase in the number of deposited layers, leads to a decrease in the paramagnetic center relaxation time, which is probably connected with the formation of ZnO nanocrystals with energetically stable properties. The nucleation and formation of nanocrystals is associated with the interaction of particles with an uncompensated charge. There is no single approach to determine the mechanism of this process. By the EPR method supplemented with the signal cyclic saturation, spectral manifestations from individual centers were effectively separated. Based on electron paramagnetic resonance and photoluminescence studies it was revealed that the main transitions between energy levels are due to oxygen vacancies and excitons.

Degradation of 1,3,6,8-tetrabromocarbazole by sulfidated zero-valent iron activated peroxydisulfate: Mechanistic insight and transformation pathways

Polyhalogenated carbazoles (PHCZs) are a kind of emerging contaminants which have widespread distribution, strong potential persistence, high bioaccumulation, and dioxin-like toxicity. In this study, we used sulfidated zero-valent iron (S-ZVI) synthesized by ball-milling to activate peroxydisulfate (PDS) for the degradation of 1,3,6,8-tetrabromocarbazole (1,3,6,8-BCZ). The initial 1 mg/L 1,3,6,8-BCZ was degraded by 92.9 % within 30 min in S-ZVI/PDS system. The pseudo-first-order rate constant was estimated as high as 0.182 min−1. Electron paramagnetic resonance (EPR) study and quenching experiments results revealed that •OH, 1O2, O2•−, and SO4•− played roles in the degradation of 1,3,6,8-BCZ, with their contribution percentages of 32.8 %, 32.5 %, 24.8 % and 9.9 %, respectively. By further density functional theory (DFT) calculations, radical addition by •OH and 1,4-cycloaddition by 1O2 were suggested as the dominant channels for 1,3,6,8-BCZ degradation, while O2•− exerted an indirect synergistic influence. Based on the identification of intermediates and analysis of Fukui indices, 1,3,6,8-BCZ degraded through three degradation pathways, namely hydroxylation, debromination, and C–N bond cleavage. The S/Fe molar ratio, S-ZVI dosage, PDS dosage, reaction temperature, initial pH, and water matrices had influences on the degradation in 1,3,6,8-BCZ, result in a great toxicity reduction. Overall, this research developed an effective and feasible approach for the treatment of PHCZs, and which gave deep insights into the vital roles and synergistic effects of various reactive species based on the combination of experimental study and theoretical calculation.

Efficient peroxymonosulfate activation by magnetic CoFe2O4 nanoparticle immobilized on biochar toward sulfamethoxazole degradation: Performance, mechanism and pathway

Utilizing biomass waste to create highly efficient biochar-based catalysts has drawn intensively interest since it adheres to the idea of waste recycling in environmental conservation. Herein, CoFe2O4 nanoparticles immobilized on biochar (BC) derived from rape straw were synthesized and applied in degrading sulfamethoxazole (SMX) by activating peroxymonosulfate (PMS). Experimental results indicated that the 30 wt% CoFe2O4/BC composite catalyst had the best catalytic activity with the SMX degradation efficiency of 93% within 20 min, which was probably the fact that BC as a carrier not only effectively inhibited the agglomeration of CoFe2O4 nanoparticles and increased the active sites, but also could simultaneously participate in the catalytic degradation reaction as an activator of PMS. In addition, cycle experiments illustrated that the as-prepared catalyst possessed the excellent stability, and the magnetic property measurements implied that they were convenient for separation and recovery. According to quenching experiments, electron paramagnetic resonance (EPR) and electrochemical studies, both radical and non-radical process participated into degrading SMX, where the generated SO4·-, ·OH and O2·- as the major radical active species while 1O2 and direct electron transfer were responsible for the non-radical route. Besides, using high-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis, a potential SMX degradation pathway was suggested. The present CoFe2O4/BC composite would be a promising PMS activation catalyst for environmental remediation.

Comparison study on ZnO and CuO gas sensing characteristics: Temperature modulated-dual selectivity towards benzene and xylene vapours

The selective detection of gaseous benzene, toluene, ethylbenzene, and xylene (BTEX) is challenging due to their similar molecular structures. In addition, BTEX vapours are extremely hazardous and carcinogenic. Thus, in the current study, n-type ZnO and p-type CuO nanostructures were synthesized utilizing various bases by a simple hydrothermal method. Among the tested sensors, the ZnO–NaOH-based sensor displayed a temperature dual-mode selectivity toward benzene with responses (Ra/Rg) of 2.5 and 24 at 5 and 100 ppm, respectively at 75 °C, and Ra/Rg ≈ 142 toward xylene vapour at 100 ppm at an operating temperature of 150 °C. While the CuO-based sensors showed poor response, sensitivity and selectivity towards tested analytes. Moreover, the ZnO–NaOH based sensor revealed enormous sensitivity of 1.21 ppm−1 and low limit of detection (LoD) of 0.018 ppm (i.e., 18 ppb) toward xylene. The ultra-sensitivity, selectivity, low LoD of ZnO–NaOH based sensor toward benzene and xylene are associated with the improved VO observed in the in-situ photoluminescence and electron paramagnetic resonance studies, and as well as the x-ray photoelectron spectroscopy analyses. The ZnO–NaOH-based sensor, which was stored for roughly 18 months (547 days), demonstrated a reliable repeatability and long-time operation stability for 22 h exposure to xylene. The superior sensitivity, stability, and selectivity indicate openly that the strategy of using various bases is a striking method for fabricating a temperature dual-mode selectivity for the detection of benzene and xylene vapours.

Modulation of the Work Function of TiO2 Nanotubes by Nitrogen Doping: Implications for the Photocatalytic Degradation of Dyes

The work function engineering in metal-oxide nanostructures by judicious doping of impurities is not straightforward as it introduces multiple defects in the system. In this regard, understanding the nitrogen (N) doping-induced modulation of Fermi levels in TiO2 nanotubes (TNTs) is challenging for visible-range photocatalytic applications. Here, 50 keV N ions are implanted in TNTs with a fluence range of 1014–1016 ions/cm2. X-ray diffraction and micro-Raman analyses demonstrate the formation of anatase-TiO2 in pristine TNTs, while the crystalline quality is significantly affected by increasing ion fluence. The evolution of Ti3+ is also established by X-ray photoelectron spectroscopy, whereas ultraviolet photoelectron spectroscopy reveals the reduction in work function due to the formation of oxygen vacancies, in good agreement with X-ray absorption spectroscopy and photoluminescence results. The electron paramagnetic resonance study further identifies the evolution of Ti3+/N-substitutional defect centers. Finally, an enhancement in visible-light-assisted methylene blue and Rhodamine B dye degradation is recorded up to a fluence of 1 × 1015 ions/cm2, and it is correlated with the N-ion implantation-induced formation of electrochemically active states near the conduction band minimum and the valence band maximum. The decrease in degradation efficiency beyond a critical fluence of 1015 ions/cm2 is discussed on the ground of ion-beam-mediated amorphization and the subsequent increase in electron–hole recombination in the defect states.

Cobalt(II) coordination to an N4-acenaphthene-based ligand and its sodium complex.

A new bifunctional N4-ligand was obtained via the condensation reaction of acenaphthenequinone and 2-picolylamine. A peculiarity of this synthesis is the formation of a new intramolecular C-C bond during the reaction. The structure and redox properties of the ligand were studied. The anion-radical form of the ligand was prepared via the chemical reduction of the latter with metallic sodium as well as in situ via its electrochemical reduction in a solution. The sodium salt prepared was structurally characterized using single-crystal X-ray diffraction (XRD). New cobalt complexes with the ligand in neutral and anion-radical forms were synthesized and further studied. As a result, three new homo- and heteroleptic cobalt(II) complexes were obtained, in which the cobalt atom demonstrates different modes of coordination with the ligand. Cobalt(II) complex CoL2 with two monoanionic ligands was prepared by the electrochemical reduction of a related L2CoBr2 complex or by treating cobalt(II) bromide with the sodium salt. XRD was used to study the structures of all cobalt complexes prepared. Magnetic and electron paramagnetic resonance studies were performed: CoII ion states with S = 3/2 and S = 1/2 were found for the complexes. A quantum-chemical study confirmed that the spin density is mainly located at the cobalt center.