From an Al4-Cluster to Al+ Complexes: Lessons on Metalloidal Clustering

Low-valent aluminium compounds are among the most reactive and widely researched main-group compounds. Since the isolation of [(AlCp*)4] in 1991 as the first stable, molecular AlI compound, a variety of highly reactive neutral or anionic low-valent aluminium complexes were developed. In particular, the strongly basic aluminyl anions allowed for nucleophilic activation of a large variety of small molecules and formation of elusive transition-metal complexes. By contrast, an accessible cationic, low-valent aluminium compound combining the nucleophilicity of low-valent compounds with the electrophilicity of aluminium is hitherto unknown. Here, we report the synthesis of [Al(AlCp*)3]+[Al(ORF)4]– (RF = C(CF3)3) via a simple metathesis route. Unexpectedly, the complex ion forms a dimer in the solid state and in concentrated solutions. Addition of Lewis bases results in monomerization and coordination to the unique formal Al+ atom giving [(L)xAl(AlCp*)3]+ salts with L = hexaphenylcarbodiphosporane (cdp; x = 1), tetramethylethylenediamine (tmeda; x = 1) and 4-dimethylamino-pyridine (dmap; x = 3). Depending on the donor strength of the ligand added, the Al+–AlCp* bonds in the [(L)xAl(AlCp*)3]+ cluster cations can be finely tuned between very strong (L = nothing) to very weak and approaching isolated [Al(L)3]+ ions (L = dmap). We anticipate our easily accessible low-valent aluminium cation salts to be the starting point for investigation and potential application of this unusual compound class. In particular, the ambiphilic reactivity of the cationic, low-valent compounds will be studied. Moreover, knowledge gained from the stabilization of the reported complex salts is expected to facilitate the isolation and application of novel cationic, low-valent Al complexes.

Electrochemical Mechanism of Al Metal–Organic Battery Based on Phenanthrenequinone

Al metal-organic batteries are a perspective high-energy battery technology based on abundant materials. However, the practical energy density of Al metal-organic batteries is strongly dependent on its electrochemical mechanism. Energy density is mostly governed by the nature of the aluminium complex ion and utilization of redox activity of the organic group. Although organic cathodes have been used before, detailed study of the electrochemical mechanism is typically not the primary focus. In the present work, electrochemical mechanism of Al metal-phenanthrenequinone battery is investigated with a range of different analytical techniques. Firstly, its capacity retention is optimized through the preparation of insoluble cross-coupled polymer, which exemplifies extremely low capacity fade and long-term cycling stability. Ex situ and operando ATR-IR confirm that reduction of phenanthrenequinone group proceeds through the two-electron reduction of carbonyl groups, which was previously believed to exchange only one-electron, severely limiting cathode capacity. Nature of aluminium complex ion interacting with organic cathode is determined through multiprong approach using SEM-EDS, XPS, and solid-state NMR, which all point to the dominant contribution of AlCl2+ cation. Upon full capacity utilization, Al metal-polyphenanthrenequinone battery utilizing AlCl2+ offers an energy density of more than 200 Wh/kg making it a viable solution for stationary electrical energy storage.

Solubility and Complex-Ion Equilibria

Solubility and Complex-Ion Equilibria broadens the previous chapter’s coverage of equilibria to include aqueous systems containing two or more solutes of slightly soluble ionic compounds and the formation of metal complexes in solution. Solubility equilibria which allow quantitative predictions of how much of a compound will dissolve under given conditions are covered. The meaning of the solubility product constant (K sp) and how to calculate it from molar solubility values is presented. Also discussed is determination of molar solubility from K sp. Calculations demonstrate how to predict the formation of a precipitate by comparing the ion product or solubility quotient (Q) with K sp. Formation constants of complex ions and calculations involving complex ion equilibria are explained.

INFLUENCE OF SURFACE PRE-HEATING ON THE NITRIDING DEPTH OF STEEL 25CrMoVA USED COMPLEX ION-PLASMA TREATMENT

In the method of nitriding elements, various methods of their thermal heating are used. The simplest heating method in ion-plasma nitriding is heating by bombarding the surface first with low-energy gas ions and then with metal ions with energies up to several kiloelectronvolt. Elements exposed to ion bombardment have a welldeveloped surface that is free from contaminants and facilitates the diffusion of nitrogen into the depth of the metal during nitriding. The paper studies the effect of various preliminary heating methods on the nitriding depth in the complex ion-plasma hardening technology of 25CrMoVA steel. A JSM 7000-1F scanning electron microscope equipped with an X-ray spectral energy dispersive microanalysis attachment was used to diagnose changes occurring on the surface of the samples and at depth; the hardness was measured using a Nanoindentor G200 device. The preliminary heating of the samples was carried out both with the use of bombardment with Ti or Mo ions, and without its direct effect on the heated surface. In the experiment, differences in the depth of hardening of the nitrided layer of steel are observed when it is heated in different ways. When bombarded with Mo ions, the greatest depths of hardening were obtained in comparison with other preliminary heating conditions. It is shown that these differences are associated with the features of the morphology of the steel surface formed as a result of sputtering processes. The formation of nitride compounds in its surface layer can serve as a barrier that slows down the penetration of nitrogen into the metal. It is shown that with complex treatment in the process of deposition of a nitride coating on the surface of nitrided steel, an additional increase in the depth of hardening of the nitrided layer occurs.

Towards Chloride-Free Organic Electrolytes for Rechargeable Aluminum Batteries

The corrosivity of chloride-based electrolytes is a major shortcoming in the practical realization of rechargeable aluminum batteries. Herein, the effect of Cl- on Al speciation and electrochemistry in tetrahydrofuran was measured by employing theoretical and experimental approaches for three systems: Al(OTF)3/THF, Al(OTF)3 plus LiCl in THF, and AlCl3/THF. The high consistency between measured and computed spectroscopic aspects associated with Al(OTF)3/THF electrolyte provided both a rationale for understanding Al complex-ion formation in a Cl- free environment and an approach for examining the effect of Cl- on Al speciation. Room-temperature Al plating was achieved from dilute solutions ([Al] = 0.1M) at potentials ≥ 0V (vs. Al⁄Al3+). Cl- is found to enable facile Al plating and SEM reveals that Al is electrochemically deposited as nanocrystalline grains.

Towards Chloride-Free Organic Electrolytes for Rechargeable Aluminum Batteries

The corrosivity of chloride-based electrolytes is a major shortcoming in the practical realization of rechargeable aluminum batteries. Herein, the effect of Cl- on Al speciation and electrochemistry in tetrahydrofuran was measured by employing theoretical and experimental approaches for three systems: Al(OTF)3/THF, Al(OTF)3 plus LiCl in THF, and AlCl3/THF. The high consistency between measured and computed spectroscopic aspects associated with Al(OTF)3/THF electrolyte provided both a rationale for understanding Al complex-ion formation in a Cl- free environment and an approach for examining the effect of Cl- on Al speciation. Room-temperature Al plating was achieved from dilute solutions ([Al] = 0.1M) at potentials ≥ 0V (vs. Al⁄Al3+). Cl- is found to enable facile Al plating and SEM reveals that Al is electrochemically deposited as nanocrystalline grains.

On the Electrochemical Migration Mechanism of Gold in Electronics—Less Reliable Than Expected?

Electrochemical migration (ECM) forming dendritic short circuits is a major reliability limiting factor in microcircuits. Gold, which is a noble metal, has been regarded as a metallization that can withstand corrosion and also ECM, therefore its application in high-reliability metallization and surface finishing systems became widespread although it has a relatively high and fluctuating price. Gold electrochemical short circuits have been found only in the case of halogen (e.g., chloride containing) contaminants that can initiate the anodic dissolution of gold via complex ion formation. The experimental results of the study demonstrate that gold can form dendritic shorts even without the presence of halogen contaminants, therefore the direct anodic dissolution of gold must also be supposed. This could also be a serious reliability influencing factor even when applying gold metallization systems and must be taken into consideration. The theoretical background of the classical (contaminant-free) model of gold is also discussed in the paper.

Crystal structure and magnetic study of the complex salt [RuCp(PTA)2–μ-CN-1κC:2κN–RuCp(PTA)2][Re(NO)Br4(EtOH)0.5(MeOH)0.5]

A new RuII–ReII complex salt, μ-cyanido-κ2 C:N-bis[(η5-cyclopentadienyl)bis(3,5,7-triazaphosphaadamantane-κP)ruthenium(II)] tetrabromido(ethanol/methanol-κO)nitrosylrhenate(II), [Ru(CN)(C5H5)2(C6H12N3P)4][ReBr4(NO)(CH4O)0.5(C2H6O)0.5] or [RuCp(PTA)2–μ-CN–1κC:2κ2 N-RuCp(PTA)2][Re(NO)Br4(EtOH)0.5(MeOH)0.5] (PTA = 3,5,7-triazaphosphaadamantane) was obtained and characterized by single-crystal X-ray diffraction, elemental analysis and infrared spectroscopy. The title salt was obtained by liquid–liquid diffusion of methanol/DMSO solutions of (NBu4)[Re(NO)Br4(EtOH)] and [(PTA)2CpRu–μ-CN–1κC:2κ2 N-RuCp(PTA)2](CF3SO3). The RuII and ReII independent moieties correspond to a binuclear and mononuclear complex ion, respectively. A deep geometrical parameter analysis was performed, and no significant differences were found with earlier reports containing similar molecules. The magnetic properties were investigated in the temperature range 2.0–300 K, and the complex behaves as a quasi-magnetically isolated spin doublet with weak antiferromagnetic interactions.