Cations Anions Research Articles

Ion-Exchange Strategy Enabling Direct Reformation of Unreliable Perfluorinated Cationic Polymer for Robust Proton Exchange Membrane towards Hydrogen Fuel Cells

Perfluorosulfonated anionic ionomers are known for their robust ion conductivity and chemical and mechanical stability. However, the structure and transport property degradation of perfluorinated cationic polymers (PfCPs) are not well understood. Herein, we propose an ion-exchange strategy to identify the structural degradation, ion transport mechanisms, and architectural reformation of PfCPs. Particularly, we demonstrate that the utility of a –SO2–N+ strategy employing the Menshutkin reaction cannot yield reliable PfCPs and anion-exchange membranes, but can yield an unreliable zwitterionic intermediate (cations–anions molar ratio is approximately 7.6%). Moreover, the degradation products were efficiently reformed as proton exchange membranes (PEMs), and the as-reformed PEMs achieved an ion-exchange capacity (IEC) value (0.89 mmol g−1), meanwhile retaining more than 94.7% of their initial capacity. Furthermore, the fuel cell assembled with reformed PEMs displayed a power density of 0.91 Wcm−2 at 2.32 A cm−2, which was 90.1% of that of the robust perfluorosulfonic acid PEMs. Our combined findings shed some fresh light on the state of understanding of the structure–property relationship in PfCPs.

Nano-Plasticity of an Electrified Ionic Liquid/Electrode Interface: Uncovering Hard-Soft Structuring via Controlled Metal Fill Factor.

Ionic liquids (ILs) nanostructuring at electrified interfaces is of both fundamental and practical interest as these materials are increasingly gaining prominence in energy storage and conversion processes. However, much remains unresolved about IL potential-controlled (re)organization under highly polarized interfaces, mostly due to the difficulty of selectively probing both the distal and proximal surface layers of adsorbed ions. In this work, the structural dynamics of the innermost layer (<10 nm from the surface) were independently interrogated from that of the ionic layers in the sub-surface region (>100 nm from the surface), using an infrared (IR) spectroscopy approach. By tuning the metal fill factor of gold films deposited on conductive metal oxide-modified IR internal reflection elements, the charge-driven (re)structuring of the inner and distal layers of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate is unveiled. Within a relatively wide potential region (∼±1 V) bounding the potential of zero charges, the ionic liquid is shown to undergo a reversible (i.e., soft) reorganization whereby the innermost layer of anions (cations) is exchanged by a layer of cations (anions). Kinetically unhindered changes in the number density of constituent cations and anions largely follow electrostatic expectations in the subsurface region, whereas the innermost layer exhibits a pronounced hysteresis and very slow relaxation. Under larger negative potential bias, IL restructuring is characterized by a highly irreversible (i.e., hard) and intense interfacial densification of the BMPy+ cations, consistent with the formation of nanoscale segregated liquids. The outcomes of this work reveal a plastic IL nanostructuring under a strong electric field.

Latent Solvent Induced Reliable Interfacial Chemistry Toward Highly Reversible Zn Anodes

AbstractAqueous zinc‐ion batteries have garnered renewed interest owing to their inherent safety and cost‐effectiveness. However, Zn anode suffers from notorious side reactions and dendrite growth, compromising the battery performance. Designing anion‐containing solvation structures to facilitate the in situ formation of a solid electrolyte interphase (SEI) layer proves effective in protecting Zn anode, yet balancing the inherent interactions between the cations‐solvents and cations–anions remains a significant challenge. Herein, latent solvent (hexafluoroisopropanol) with specific anion‐philic and cation‐phobic properties is introduced, which can remarkably increase Zn(TFSI)2 solubility in water and induce anion‐containing solvation structures. The introduction of latent solvent enables anions to preferentially decompose, giving rise to an anion‐derived SEI layer. More interestingly, the direct anion‐cation interaction endows Zn2+ species with stepwise dehydration, minimizing the adsorption of water on Zn anode. The anion‐derived SEI layer and optimized de‐solvation process work in synergy to enable homogeneous Zn deposition and ensure high reversibility. When coupled with a NaV3O8·1.5H2O (NVO) cathode, the resultant full cell delivers a high‐capacity retention of 87.8% after 2000 cycles at 1 A g−1. This work provides valuable insights into the advanced latent solvent electrolyte design and beyond.

Determination of Physicochemical Water Quality of the Ghis-Nekor Aquifer (Al Hoceima, Morocco) Using Hydrochemistry, Multiple Isotopic Tracers, and the Geographical Information System (GIS)

The chemical characterization of the Ghis-Nekor groundwater has become a concern of many researchers in Morocco. It is a crucial indicator for the environment situation and the socioeconomic development of this Moroccan region. Indeed, it helps decisionmakers carry out conscious and sustainable management. For this reason, 20 samples of the Ghis-Nekor aquifer were examined in terms of physicochemical parameters such as pH, temperature, electrical conductivity (EC), and total alkalinity (Alk), major cations–anions (Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, NO3−, and TDS), isotopic elements (δ18O, δ2H, and δ13C), and concentrations of Br and Sr anions in 2020. Furthermore, spatial data analysis with a geographic information system (GIS) using the ArcGis software (Redlands, California, USA). Indeed, static maps show significant water quality information that helps characterize the groundwater of the study area. The spatial analysis by the GIS indicates that except the EC (from 2630 to 6950 mS/cm), all the physical parameters showed standard concentration values in most of the samples. A significant concentration above the Moroccan norm of groundwater quality for sodium (Na+) from 264.3 to 1500 mg/L, chlorides (Cl−) concentrations from 408.3 to 1510 mg/L, SO42− from 313.1 to 999.2 mg/L, and bicarbonate (HCO3−) from 283.7 to 679.8 mg/L was observed, while all the points exceeded the recommended standards norm for SO42−. Most of the points met the potability standards for potassium (K+). In terms of the isotopic elements, the concentration values of δ18O were from −3.92‰ to –5.60‰, while the δ2H concentration values varied between −28.67‰ and −39.99‰. The analysis revealed values of carbon isotope δ13C ranging between −3.15‰ and −8.61‰, thus suggesting that the origin of the carbon is mineral, mainly deriving from calcite dissolution. The analysis of the bromide and strontium contents made it possible to discriminate the origin of the salinity anomalies. The Cl/Br, Br/Cl, and Sr/Ca molar ratios distinguished the areas of influence of geological setting (saliferous facies outcrops) or anthropogenic effect (wastewater). The results of the analysis shed light on factors of contamination, which are as follows: urban zones (Imzourene, Ait Youssef, and Souani) and agricultural activities. Therefore, the use of these waters could pose a risk to the health of humans and animals. Similarly, the GIS is a practical and effective tool for the Ghis-Nekor groundwater quality diagnostics and could help decisionmakers establish solutions.

Regulating lithium-ion flux in the solid electrolyte interphase layer to prevent lithium dendrite growth on lithium metal anode

High theoretical capacity and lowest electrochemical potential make lithium metal anode the most suitable anode material for lithium-ion batteries (LIBs). However, Lithium dendrite growth on lithium metal anode hinders proper discharge capacity and practical cycle life of LIBs. It dues to high lithium-ion flux in the solid electrolyte interphase (SEI) layer versus low diffusion in anode structure. Herein, we employ argon and oxygen plasma to modify commercial polypropylene separator surface to negatively functionalize the separator surface and discuss the influence of increasing surface negative charge on lithium dendrite growth and formation of SEI layer. Comparing electrochemical and battery performance of unmodified and plasma modified separators demonstrates, increased negative surface charge prevents lithium dendrite growth and makes a uniform and thin SEI layer due to lowering lithium-ion flux in the SEI layer. More precisely, we conduct that coulombic interaction between plasma modified separator's surface and electrolyte's cations (anions) can regulate lithium-ion flux in the SEI layer, preventing lithium dendrite growth and making thin homogeneous SEI layer on lithium metal anode structure.

Density, Speeds of Sound, and Refractive Index of Pure and Binary Mixtures of Ionic Liquids Based on Imidazolium Cations and Tetrafluoroborate Anions with Cyclohexylamine

Density, Speeds of Sound, and Refractive Index of Pure and Binary Mixtures of Ionic Liquids Based on Imidazolium Cations and Tetrafluoroborate Anions with Cyclohexylamine

Electronic-ionic coupling in perovskite based solar cells: Implications for device stability

Ion migration into blocking layers toward the metallic electrodes is studied within a semiconductor device model framework. We find that ion leakage into the blocking layers and their accumulation at the electrode interface are significantly affected by the electronic injection barrier at the contact. Specifically, we find that if the device structure promotes, under light, hole (electron) accumulation within the perovskite layer, these excess holes (electrons) would release an almost equivalent number of cations (anions) into the transport layers toward the contacts. Our analysis suggests that it would be beneficial to include intentional doping of the blocking layers and that it should follow the “just enough” strategy.

Complex Epitaxy of Tetragonal Tungsten Bronze K–Ta–Nb–O Nanorods

Tetragonal tungsten bronze (TTB) phases possess numerous important properties (ferroelectricity, multiferroicity, piezoelectricity, optical nonlinearity, electro-optics) that can be achieved by modifying their composition, in addition to their ability to grow as very anisotropic crystals. In this study, K-5.06(Ta0.57Nb0.43)(10.99)O-30 tetragonal tungsten bronze phase thin films were grown by a pulsed laser deposition technique on (001)SrTiO3 and R-plane sapphire substrates. The films grew according to two modes with respect to the substrate surface, that is, as vertical nanorods with the [001] direction perpendicular to the substrate surface and as horizontal nanorods with the [001] orientation parallel to the substrate surface and out-of-plane direction. Both vertical and horizontal nanorods present epitaxial relationships with the substrates. Careful study of epitaxial relationships showed a complex growth on both substrates that can be described in the framework of domain matching epitaxy resulting in several antiphase domain formations for both kinds of nanorods. These particular configurations are due to a high degree of coincidence between cations (anions) of the film with those of the substrate. This study shows the ability of ferroelectric TTB phases to grow as one-dimensional objects with the possibility to tailor their polarization direction either normal to or parallel to the substrate surface.

Chemical Characterization of Fine Atmospheric Particles of Water-Soluble Ions and Carbonaceous Species in a Tropical Urban Atmosphere over the Eastern Indo-Gangetic Plain

ABSTRACT Ambient fine aerosols and their sources were evaluated in an eastern Indian megacity, Kolkata (KOL), from September 2010 to August 2011. A submicron aerosol sampler (SAS) with two stage stacked filter units (SFU) was devised for simultaneous but discrete collection of water-soluble inorganic ions (WSII) and carbonaceous aerosols (CA; elemental carbon (EC) and organic carbon (OC)). Characteristics of the WSII and CA were identified using ion chromatography and an OC-EC analyzer, respectively, adopting the Interagency Monitoring of PROtected Visual Environments (IMPROVE-A) protocol. The mean annual concentrations of the WSII showed a predominance of cations (anions), consisting of Ca2+, Mg2+, and Na+ (Cl–, NO3–, and SO42–), with secondary aerosols (NH4+, NO3–, and SO42–) and Ca2+ each constituting 25% and 30%, respectively, of the total WSII (TWSII). The highest mean monthly concentration of SO42– and NO3– was observed during the winter month of February and the summer months of March and May, respectively. A pronounced peak in the monthly mean for the non-sea salt-K+ (nss-K+) concentration was noticed during October and April, implying the strong influence of biomass burning emissions during these months. Among the sea salt (SS), anthropogenic (AN), and dust (DT) sources of the TWSII, a predominant contribution from DT in August and from AN in November, April, and May was inferred. The mean annual concentration of OC was three times higher than that of EC, with 43% of it being secondary OC. Whereas the major sources of OC were inferred to be paved dust, coal combustion, and biomass burning, those of EC were industrial and motor-vehicle non-exhaust emissions, coal combustion, and motor vehicle exhaust.

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12 Cl11 ].

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B12 Cl11 ]- spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of "superelectrophilic" dications. [B12 Cl11 Ng]- adducts, with Ng binding energies of 80 to 100 kJ mol-1 , contain B-Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B12 Cl11 ]- anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B12 Cl11 CO]- and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B12 Cl11 ]- results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C6 H5 ]+ . This introduces the new chemical concept of "dipole-discriminating electrophilic anions."

Physical and Electrochemical Properties of Ionic Liquids Based on Quaternary Phosphonium Cations and Carboxylate Anions as Electrolytes

A new group of ionic liquids based on tetraethylphosphonium and tetrabutylphosphonium cations together with several carboxylate anions is proposed and presented in this report. In obtained ionic liquids, tetrabutylphosphonium formate and tetrabutyl-phosphonium lactate became room temperature ionic liquids. It was found that the phosphonium ionic liquids showed the typical VTF-type convex curve behaviors. The phosphonium ionic liquids also had a high cathodic stability similar to those of the TFSA- and FSA-anion based phosphonium ionic liquids. On the other hand, relatively low anodic potential window was observed. The thermal stability of the phosphonium ionic liquids showed higher thermal stabilities than those of the corresponding ammonium ionic liquids.

Effects of Alkali Cations and Halide Anions on the Self-Assembly of Phosphatidylcholine in Oils.

The interactions between ions and phospholipids are closely associated with the structures and functions of cell membrane. Instead of conventional aqueous systems, we systematically investigated the effects of inorganic ions on the self-assembly of lecithin, a zwitterionic phosphatidylcholine, in cyclohexane. Previous studies have shown that addition of inorganic salts with specific divalent and trivalent cations can transform lecithin organosols into organogels. In this study, we focused on the effect of monovalent alkali halides. Fourier transform infrared spectroscopy was used to demonstrate that the binding strength of the alkali cations with the phosphate of lecithin is in the order Li+ > Na+ > K+. More importantly, the cation-phosphate interaction is affected by the paired halide anions, and the effect follows the series I- > Br- > Cl-. The salts of stronger interactions with lecithin, including LiCl, LiBr, LiI, and NaI, were found to induce cylindrical micelles sufficiently long to form organogels, while others remain organosols. A mechanism based on the charge density of ions and the enthalpy change of the ion exchange between alkali halides and lecithin headgroup is provided to explain the contrasting interactions and the effectiveness of the salts to induce organogelation.

Physical and Electrochemical Properties of Ionic Liquids Based on Quaternary Phosphonium Cations and Carboxylate Anions As Electrolytes

Ionic liquids (ILs) have been developed for a wide variety of electrochemical applications due to their unique physicochemical properties such as favorable solubility of organic and inorganic compounds, relatively high ionic conductivity, no measurable vapor pressure, high thermal stability, low flammability, etc. Another advantage of ILs is a designability of the ion structures. Although many kinds of ILs have been already investigated, phosphonium-based ILs have rarely been proposed. We have previously designed and synthesized the phosphonium ILs together with typical anion species such as bis(trifluoromethylsulfonyl)amide (TFSA) and bis(fluorosulfornyl)amide (FSA) anions.1,2 On the other hand, interests in ILs consisting of carboxylic acid based anions have been increasing in recent years. In this work, we synthesize the ILs based on quaternary phosphonium cations (tetraethylphosphonium, P2222 +, and tetrabutylphosphonium, P4444 +) in combination with carboxylate anions such as formate (HCO2 -), acetate (MeCO2 -) and propionate (EtCO2 -), characterizing the physicochemical and electrochemical properties of the ILs as a new family of IL-based electrolyte.The preparation of the phosphonium ILs was carried out by neutralization reactions of the precursor phosphonium hydroxides with the carboxylic acids. The obtained ILs were dried under high vacuum for at least 10 h at 60◦C. We also prepared the corresponding ammonium salts by the same procedure for comparison. The physicochemical and electrochemical properties such as conductivity (ac impedance method), viscosity (a cone-plate type viscometer), density, melting point (DSC), thermal decomposition temperature (TGA) and electrochemical window (linear sweep voltammetry using a conventional three-electrode cell) were measured under dry argon atmosphere. Table 1 summarizes the physicochemical properties of the ILs obtained in this work. The almost compounds were low-melting white solids; however only P4444-HCO2 became a liquid at ambient temperature. The conductivity and viscosity of P4444-HCO2 depended on temperature, showing the Arrhenius-type convex curve behaviors. This means a typical electrolyte behavior generally observed in IL media. P4444-HCO2 showed the lowest viscosity and highest conductivity in the three P4444-based phosphonium salts, which might be attributed to the anion sizes of the three phosphonium salts. It should be noted that the thermal decomposition temperatures of the phosphonium salts were much higher than those of the corresponding ammonium salts, revealing the high thermal stability of the carboxylic anion based phosphonium ILs (Fig. 1). In the electrochemical measurements, it was found that P4444-HCO2 had a high cathodic stability similar to those of the TFSA- and FSA-anion based phosphonium ILs. On the other hand, relatively low anodic potential window up to 0.7 V vs. Ag/Ag+ was observed, which seems likely to be due to the anodic oxidation of formate anion.

Half-metallicity and electronic structures for carbon-doped group III-nitrides: Calculated with a modified Becke-Johnson potential

The electronic structures and magnetism for carbon-doped group III-nitrides are investigated by utilizing the first principle method with the modified Becke-Johnson potential. Calculations show that carbon substituting cations (anions) would induce the group III-nitrides to be paramagnetic metals (half-metallic ferromagnets). Single carbon substituting nitrogen could produce 1.00μB magnetic moment. Electronic structures indicate that the carriers-mediated double-exchange interaction plays a crucial role in forming the ferromagnetism. Based on the mean-field theory, the Curie temperature for carbon-doped group III-nitrides would be above the room temperature. Negative chemical pair interactions imply that carbon dopants tend to form clustering distribution in group III-nitrides. The nitrogen vacancy would make the carbon-doped group III-nitrides lose the half-metallic ferromagnetism.

The detailed crystal and electronic structures of the cotunnite-type ZrO2

Abstract The detailed crystal and orbital-decomposed electronic structures of cotunnite-type ZrO2 have been investigated by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation as well as taking into account on-site Coulomb repulsive interaction (GGA+U). The optimized structure shows that the O I and O II anions are surrounded by an arbitrary tetrahedron of four Zr cations and an arbitrary pentahedron of five Zr cations, respectively, in turn, the Zr cation is surrounded by an arbitrary tetrakaidecahedron formed by nine oxygen ligands. Although one more Zr cation is coordinated to O II , the larger bond lengths between O II and its adjacent five Zr cations ( d O II − Zr ) than those between O I and its adjacent four Zr cations ( d O I − Zr ) makes density of states (DOS) of s and three p ( p x , p y and p z ) states of the O II anion driving down in lower energy region and driving up in higher energy region. No crystal-field splitting is observed between three p ( p x , p y and p z ) states of anions O I and O II (between three p ( p x , p y and p z ) states and five d ( d xy , d yz , d xz , d z 2 and d x 2 - y 2 ) states of cation Zr) is resulted from the arrangements of the surrounding cations (anions) do not have any symmetry. The additional covalent character upon Zr–O ionic bonds is attributed to the hybridization of itinerant Zr(5s) and less filled Zr(4d) states to the separated O(2s) and O(2p) states.

Photo Catalytic Applications of Zinc Oxide Nanorods for the Analysis of Chlorimuron Herbicide Residues in Water by LC-MS/MS

Photo Catalytic Applications of Zinc Oxide Nanorods for the Analysis of Chlorimuron Herbicide Residues in Water by LC-MS/MS Zinc oxide (ZnO) nanorods having the size 100 to 250 nm diameters and 1 to 2 μm length were used as photo-catalyst for the decontamination of sulfonylurea urea herbicide chlorimuron in water. The study was conducted in milli Q water, at three different buffer solutions of pH 4.0, 7.0 and 9.0 under direct sunlight at two different concentrations. The optimum concentration of catalyst required for the complete degradation was established as 0.1 g l-1. The degradation of herbicide in neutral pH water was faster when compared with acidic and basic pH solutions in presence of ZnO catalyst. The influence of cations (Fe2+, Cu2+ and Ni2+) anions (ClO4-, Cl-, CO32-) had shown no significant degradation, but Fe2+ contributed positively to the degradation. Influence of surfactant was studied with cetyltrimethylammonium bromide (CTAB), sodium decyl sulfate (SDS) and Brij-35. The presence of surfactant SDS showed slight increase in the degradation rate. Residues, breakdown products were quantified and confirmed by liquid chromatography electro spray tandem mass spectrometry (LC-ESI-MS/MS). The method has the limit of quantification 0.1 μg/L in water. The dissipation of residues showed first order kinetics, DT 50 and DT 90 were calculated from the dissipation data.

Quantum chemical studies on nanostructures of the hydrated methylimidazolium–based ionic liquids

The B3LYP and M06-2X suits of density functional theory in conjunction with the 6-311++G(2d,2p) basis set were employed to investigate the nanostructures formed from the interaction between water molecules and ionic liquids based on methylimidazolium cation (MIM(+)) with the anions (X1-5 = CH3COO(-), CF3COO(-), NO3(-), BF4(-), and N(CN)2(-)) on a molecular level. Based on the calculated Gibbs free binding energies, the predicted stability order of nanostructures in the gas phase is [MIM]X1 > [MIM]X2 > [MIM]X3 > [MIM]X4 > [MIM]X5. The estimated solvation enthalpy of ions implied that the stability of anions NO3 (-) and CH3COO(-) in water is greater than those of MIM(+) and other anions. Tendency of hydrated anions to react with hydrated cations to form the solvated ion pairs is slightly smaller than the tendency of hydrated anions (cations) to react with unsolvated cations (anions). The strengths of the interactions in studied categories follow the trend X-W > MIM-W > [MIM]X -W.

The detailed geometrical and electronic structures of monoclinic zirconia

The detailed geometrical and orbital-decomposed electronic structures of monoclinic ZrO2 have been investigated by using the first-principle projector augmented wave (PAW) potential within the generalized gradient approximation as well as taking into account on-site Coulomb repulsive interaction (GGA+U). The optimized structure shows the OI atom locates slightly outside the plane of an arbitrary triangle formed by three coordinated Zr atoms and the OII atom is inside an arbitrary tetrahedron formed by four coordinated Zr atoms; in turn, the Zr atom is surrounded by an arbitrary decahedron formed by seven oxygen ligands. Compared to OI atom coordinated to three Zr atoms in an almost planar environment, one more coordinated Zr atom and thus an arbitrary tetrahedron environment of total four coordinated Zr atoms makes density of states (DOS) of s and three p (px, py and pz) states of the OII atom not only shift toward lower energy region but also drive down in higher energy region and drive up in lower energy region. No crystal-field splitting is observed among three p (px, py and pz) states of anions OI and OII as well as among three p (px, py and pz) states and five d (dxy, dyz, dxz, dz2 and dx2−y2) states of cation Zr as the arrangements of the surrounding cations (anions) do not have any symmetry. The additional covalent character of Zr–O ionic bonds is attributed to the hybridization of itinerant Zr(5s) and less filled Zr(4d) states to the separated O(2s) and O(2p) states.

Acidifying effect of removal of tree stumps and logging residues as compared to atmospheric deposition

Harvesting of stumps and logging residues for bioenergy can be expected to increase in the future. An increased biomass export from the forest will increase the biological acidification, measured as net cation (cations–anions) export. The aim of this study is to estimate the acidifying effect that various levels of harvesting of tree stumps and logging residues will have in Sweden, and compare this with the acidification currently caused by acid deposition. Estimations of yearly logging of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and birch (Betula spp.) on county-level were made based on scenario data from forestry consequence analyses and data from the Swedish National Forest Inventory. Data of cation and anion contents in tree parts were used to calculate the net cation extraction per area unit resulting from harvesting of stumps, stem-wood and logging residues, respectively. County-level data were merged into data for three different regions representing a gradient in deposition and climate.Results indicate that harvesting of stumps constitutes 13–24% of total (stumps+stem-wood+logging residues) excess cation extraction, depending on harvest intensity and tree species. Harvesting of logging residues constitutes 27–45% of total net cation extraction. The higher acidifying effect of logging residues can be explained by the higher contents of base cations in needles and branches compared to stem-wood. In a comparison between total net cation extraction by tree harvesting and maximum levels of current acid deposition the acidifying effect of pine harvesting is 57–108% of that of acid deposition, the acidifying effect of spruce harvesting is 114–263% while the acidifying effect of birch harvesting is 60–171%. Concerning the amount of acid input to the soil per unit heating value as biofuel, stump harvesting generates 12–27eqH+ MWh−1 while logging residue harvesting generates 39–66eqH+ MWh−1.Stump harvesting generates a higher heating value per area unit than logging residue harvesting and results in a lower acid input to the soil per unit heating value generated. Thus, from a strict nutrient balance and acidification perspective stump harvesting is a better alternative than harvesting of logging residues.

Ligand Redox Non‐Innocence in Transition‐Metal σ‐Alkynyl and Related Complexes

AbstractTransition‐metal σ‐alkynyl complexes are valuable functional materials that have found application as sructural units in the assembly of polymetallic arrays and large molecular structures, reagents for the transfer, oligomerisation or functionalisation of alkynes, magnetic or optical materials and putative components for use in a future molecular‐based electronics platform. Many σ‐alkynyl complexes are redox‐active, undergoing facile oxidation (reduction) at moderate potentials to generate radical cations (anions) in which the charge and spin density can be tuned from being largely metal‐centred to alkynyl ligand‐centred by variation of the nature of the metal, supporting ligands and alkynyl substituents. This review summarises the diverse chemical behaviour of metal‐supported σ‐alkynyl radicals, and some selected closely related systems, which can often be rationalised in terms of the distribution of electron‐spin density over the metal–alkynyl scaffold.