Teaching old compounds new tricks: efficient N2 fixation by simple Fe(N2)(diphosphine)2 complexes

The Fe(0) species Fe(N2)(dmpe)2 exists in equilibrium with the previously unreported dimer, [Fe(dmpe2)2(μ-N2)]. For the first time these complexes, alongside Fe(N2)(depe)2, are shown unambiguously to produce N2H4 and/or NH3 upon addition of triflic acid; for Fe(N2)(depe)2 this represents one of the highest electron conversion efficiencies for Fe complexes to date

Ionic liquids at electrified interfaces

Until recently, “room-temperature” (<100–150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)–(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of “first-generation” room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the “later generation” RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in “cocktails” of one’s choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost “universal” solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) “sister-systems”.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules

Selective Removal of Alkali Metal Cations from Multiply-Charged Ions via Gas-Phase Ion/Ion Reactions Using Weakly Coordinating Anions

Selective removal of alkali metal cations from mixed cation multiply-charged peptide ions is demonstrated here using gas-phase ion/ion reactions with a series of weakly coordinating anions (WCAs), including hexafluorophosphate (PF6 (-)), tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BARF), tetrakis(pentafluorophenyl)borate (TPPB), and carborane (CHB11Cl11 (-)). In all cases, a long-lived complex is generated by dication/anion condensation followed by ion activation to compare proton transfer with alkali ion transfer from the peptide to the anion. The carborane anion was the only anion studied to undergo dissociation exclusively through loss of the metallated anion, regardless of the studied metal adduct. All other anions studied yield varying abundances of protonated and metallated peptide depending on the peptide sequence and the metal identity. Density functional theory calculations suggest that for the WCAs studied, metal ion transfer is most strongly favored thermodynamically, which is consistent with the experimental results. The carborane anion is demonstrated to be a robust reagent for the selective removal of alkali metal cations from peptide cations with mixtures of excess protons and metal cations

Synthesis and characterization of an Al(69)(3-) cluster with 51 naked Al atoms: analogies and differences to the previously characterized Al(77)(2-) cluster

A disproportionation process of a metastable AlCl solution with a simultaneous ligand exchange-Cl is substituted by N(SiMe(3))(2)-leads to a [Al(69)[N(SiMe(3))(2)](18)](3-) cluster compound that can be regarded as an intermediate on the way to bulk metal formation. The cluster was characterized by an X-ray crystal structural analysis. Regarding its structure and the packing within the crystal, this metalloid cluster with 4 times more Al atoms than ligands is compared to the [Al(77)N(SiMe(3))(2)](20)](2-) cluster that has been published four years ago. Although there is a similar packing density of the Al atoms in both clusters as well as in Al metal, the X-ray structural analysis shows significant differences in topology and distance proportions. The differences between these-at a first glance almost identical-Al clusters demonstrate that results of physical measuring, e.g., of nanostructured surfaces which carry supposedly identical cluster species, have to be interpreted with great caution. [on SciFinder (R)

Poly(oxymethylene) dimethyl ether synthesis: A combined chemical equilibrium investigation towards an increasingly efficient and potentially sustainable synthetic route

Polyoxymethylene dimethyl ethers (denoted hereon as OME) are potential sustainable fuels (e.g. as a diesel substitute). In this paper, the fundamental analysis of a potentially, sustainable synthetic OME system is presented (i.e. based on CH3OH synthesised from H2 and recycled CO2). In this context, a multicomponent thermodynamic vapour–liquid equilibrium model, based on CH3OH as the educt and source of H2CO for OME synthesis, is described. A thermodynamic equilibrium mathematical model for this complex (i.e. a 29 reaction network) CH3OH–H2CO equilibrium system is presented, capable of solving the sequential chemical and phase equilibrium, importantly considering all components in the reaction system including poly(oxymethylene) hemiformals and poly(oxymethylene) glycols. A theoretical efficiency evaluation indicates that the proposed anhydrous route is potentially more attractive than the conventional synthesis (i.e. based on dimethoxymethane and trioxane). To substantiate these theoretical investigations, a complimentary experimental batch OME synthesis is also presented, providing validation for the presented thermodynamic model. An initial kinetic analysis of the OME synthesis over different commercial catalysts is also highlighted. Our presented findings reliably describe the synthesis equilibrium with respect to our experimentally obtained results. The presented work supports further an operating OME synthesis framework based on CH3OH and H2CO and highlights the requirement for innovative process design regarding feed preparation, reactor technology, and product separation/fractions recycling

Understanding the effect of lattice polarisability on the electrochemical properties of lithium tetrahaloaluminates, LiAlX4 (X = Cl, Br, I)

Establishing links between the structure and physical properties of solid-state ionic conductors contributes not only to a rationale of their fundamental nature, but also provides design principles to accelerate the discovery of new materials. Lithium ion conduction in complex halides is not well-elucidated and so the interplay between lattice dynamics, electronic structure and electrochemical properties in such halides has been explored in the isostructural family of lithium tetrahaloaluminates LiAlX4 (X = Cl, Br, I). Using a combination of experimental methods (Diffuse reflectance UV-Vis spectroscopy, Pulse-Echo Speed of Sound measurements, Raman spectroscopy, Inelastic Neutron Scattering) and periodic density functional theory (DFT) based calculations, we demonstrate that softer lattices (quantified in terms of Debye frequencies or Li-phonon band centres as a function of X) provide lower activation energies for Li+ migration. However, the relationship between polarisability and Li+ conductivity is not straightforward. In line with expectations emergent from the Meyer-Neldel rule, the activation energy for Li+ hopping, Ea, and the pre-exponential terms collated as σ0 in the Arrenhius equation for activated conductivity, correlate. It is also evident that the electrochemical oxidative potential limit correlates with the X– phonon band centre in the vibrational density of states (VDOS) and that the electrochemical stability window (EW) and optical band gap are interlinked, as expected