On the structure and reactivity of small iron clusters with benzene, [Fen–C6H6]0,+,−, n⩽7: A theoretical study

Kinetics of stepwise nitrogen adsorption by size-selected iron cluster cations: Evidence for size-dependent nitrogen phobia

We present a study of stepwise cryogenic N₂ adsorption on size-selected Fe_n ⁺ (n = 8-20) clusters within a hexapole collision cell held at T = 21-28 K. The stoichiometries of the observed adsorption limits and the kinetic fits of stepwise N₂ uptake reveal cluster size-dependent variations that characterize four structural regions. Exploratory density functional theory studies support tentative structural assignment in terms of icosahedral, hexagonal antiprismatic, and closely packed structural motifs. There are three particularly noteworthy cases, Fe₁₃ ⁺ with a peculiar metastable adsorption limit, Fe₁₇ ⁺ with unprecedented nitrogen phobia (inefficient N₂ adsorption), and Fe₁₈ ⁺ with an isomeric mixture that undergoes relaxation upon considerable N₂ uptake.

Cyclotrimerization of Acetylene under Thermal Conditions: Gas-Phase Kinetics of V+ and Fe+ + C2H2

The kinetics of successive reactions of acetylene (C₂H₂) initiated on either vanadium or iron atomic cations have been investigated under thermal conditions using the variable-ion source and temperature-adjustable selected-ion flow tube apparatus. Consistent with the literature results, the reaction of Fe⁺ + C₂H₂ primarily yields Fe⁺(m/z = (C₂H₂)₃); however, analysis via quantum chemical calculations and statistical modeling shows that the mechanism does not form benzene upon the third acetylene addition. The kinetics are more consistent with successive addition of three acetylene molecules, yielding Fe⁺(C₂H₂)₃, followed by an addition of a fourth acetylene molecule, initiating cyclotrimerization, yielding either Fe⁺(C₂H₂) + neutral benzene or Fe⁺(Bz) + acetylene, where Bz is a benzene ligand. In contrast, the reaction of V⁺ + C₂H₂ yields products via successive associations V⁺(m/z = (C₂H₂)_n) either with or without a bimolecular step involving loss of one H₂ and V⁺C₂(m/z = (C₂H₂)_m), where n and m extend at least up to 11 under conditions of 0.32 Torr at 300 K. Stabilized V⁺(Bz) is not a significant intermediate in the association mechanism. We propose a plausible mechanism for the generation of neutral benzene in this reaction and compare with the Fe⁺ results. The reaction steps that produce benzene result in turnover of the single-atom catalyst, and the large hydrocarbons produced that remain associated to the catalyst are proposed to be polycyclic aromatic hydrocarbons.

Uniform, Anticorrosive, and Antiabrasive Coatings on Metallic Surfaces for Cation-Metal and Cation-π Interactions

Metals are widely used, from daily life to modern industry. Great efforts have been made to protect the metals with various coatings. However, the well-known conventional electrochemical corrosion induced by cations and the ubiquitous nature of the coffee-ring effect make these processes very difficult. Here, a scheme by two bridges of cations and ethylenediamine (EDA) is proposed to overcome the coffee-ring effect and electrochemical corrosion and experimentally achieve uniform, anticorrosive, and antiabrasive coatings on metallic surfaces. Anticorrosive capability reaches about 26 times higher than that without cation-controlled coatings at 12 h in extremely acidic, high-temperature, and high-humidity conditions and still enhances to 2.7 times over a week. Antiabrasive capability also reaches 2.5 times. Theoretical calculations show that the suspended materials are uniformly adsorbed on the surface mediated by complexed cations through strong cation-metal and cation-π interactions. Notably, the well-known conventional electrochemical corrosion induced by cations is avoided by EDA to control cations solubility in different coating processes. These findings provide a new efficient, cost-effective, facile, and scalable method to fabricate protective coatings on metallic materials and a methodology to study metallic nanostructures in solutions, benefitting practical applications including coatings, printing, dyeing, electrochemical protection, and biosensors.