Iron(II) and Nickel(II) Complexes of N-Alkylimidazoles and 1-Methyl-1H-1, 2, 4-Triazole: X-ray Studies, Magnetic Characterization, and DFT Calculations

Synthesis and crystal structure of an iron triazole complex resulting from the unexpected ligand cleavage of a triazolium carbene precursor

Typically reactions of N-heterocyclic carbenes with transition metals are straightforward and require a carbene salt, a base strong enough to deprotonate such a salt and a metal. Yet when carbene precursors are in the form of triazolium salts, reaction may not proceed as easily as expected. In our work, we intended to obtain a triazolylidene complex of iron(II) chloride, but due to the presence of small amounts of water in the tetrahydrofuran solvent used, bis(acetonitrile)tetrakis(1-benzyl-1H-1,2,4-triazole-κN4)iron(II) μ-oxido-bis[trichloridoferrate(III)] acetonitrile disolvate, [Fe(C9H9N3)4(CH3CN)2][Fe2Cl6O]·2CH3CN - an interesting anion with a linear geometry of the O atom - was formed instead of the iron carbene complex. Reaction proceeded via cleavage of the alkyl N-substituent of the triazolium salt. The formation of the product was confirmed by X-ray crystallography. The crystal structure and possible reaction pathways are discussed.

Thin Films of a Complex Polymer Compound for the Inhibition of Iron Alloy Corrosion in a H3PO4 Solution

The etching of iron alloy items in a H3PO4 solution is used in various human activities (gas and oil production, metalworking, transport, utilities, etc.). The etching of iron alloys is associated with significant material losses due to their corrosion. It has been found that an efficient way to prevent the corrosion of iron alloys in a H3PO4 solution involves the formation of thin complex compound films consisting of the corrosion inhibitor molecules of a triazole derivative (TrzD) on their surface. It has been shown that the protection of iron alloys with a mixture of TrzD + KNCS in a H3PO4 solution is accompanied by the formation of a thin film of coordination polymer compounds thicker than 4 nm consisting of TrzD molecules, Fe2+ cations and NCS-. The layer of the complex compound immediately adjacent to the iron alloy surface is chemisorbed on it. The efficiency of this composition as an inhibitor of iron alloy corrosion and hydrogen bulk sorption by iron alloys is determined by its ability to form a coordination polymer compound layer, as experimentally confirmed by electrochemical, AFM and XPS data. The efficiency values of inhibitor compositions 5 mM TrzD + 0.5 mM KNCS and 5 mM TrzD + 0.5 mM KNCS + 200 mM C6H12N4 at a temperature of 20 ± 1 °C are 97% and 98%, respectively. The kinetic parameters of the limiting processes of hydrogen evolution and permeation into an iron alloy in a H3PO4 solution were determined. A significant decrease in both the reaction rate of hydrogen evolution and the rate of hydrogen permeation into the iron alloy by the TrzD and its mixtures in question was noted. The inhibitor compositions 5 mM TrzD + 0.5 mM KNCS and 5 mM TrzD + 0.5 mM KNCS + 200 mM C6H12N4 decreased the total hydrogen concentration in the iron alloy up to 9.3- and 11-fold, respectively. The preservation of the iron alloy plasticity in the corrosive environment containing the inhibitor under study was determined by a decrease in the hydrogen content in the alloy bulk.

The crystal structure of hexakis(1-ethylimidazole-κ1 N)nickel(II) dichloride – 1-ethylimidazole (1/2), C40H64Cl2NiN16

C40H64Cl2NiN16, monoclinic, P21/c (no. 14), a = 8.2320(9) Å, b = 16.2902(16) Å, c = 17.3843(17) Å, α = 90°, β = 101.773(3)°, γ = 90°, V = 2282.2(4) Å3, Z = 2, R gt (F) = 0.0448, wR ref (F 2) = 0.1181, T = 298(2) K.

Thin Benzotriazole Films for Inhibition of Carbon Steel Corrosion in Neutral Electrolytes

This article investigates the modification of a carbon steel surface by benzotriazole (BTA), and the structure and properties of the formed layers. Adsorption was studied by surface analytical methods such as X-ray photoelectron spectroscopy (XPS) and reflecting infrared microscopy (FTIR). It has been established that a polymer-like film containing iron-azole complexes that are 2 nm thick and strongly bonded to the metal is formed on the surface as a result of the azole interacting with a steel surface. This film is capable to inhibit uniform and localized corrosion of steel in neutral aqueous electrolytes containing chloride ions. It is shown that the iron-azole layer located at the interface acts as a promotor of adhesion, increasing the interaction of polymeric coatings with the steel surface. Taking into account these properties, the steel pretreatments can be used for improving the anticorrosion properties of polymeric coatings applied for the protection of steel constructions.

Crystal structure of di-aqua-tris-(1-ethyl-1H-imidazole-κN (3))(sulfato-κO)nickel(II)

In the title complex, [Ni(SO4)(C5H8N2)3(H2O)2], the Ni(II) ion is coordinated by three facial 1-ethyl-1H-imidazole ligands, one monodentate sulfate ligand and two water mol-ecules in a slightly distorted octa-hedral coordination environment. In the crystal, two pairs of O-H⋯O hydrogen bonds link complex mol-ecules, forming inversion dimers incorporating R 2 (4)(8), R 2 (2)(8) and R 2 (2)(12) rings. The dimeric unit also contains two symmetry-unique intra-molecular O-H⋯O hydrogen bonds. In addition, weak C-H⋯O hydrogen bonds, weak C-H⋯π inter-actions and π-π inter-actions with a centroid-centroid distance of 3.560 (2) Å combine to form a three-dimensional network. One of the ethyl groups is disordered over two sets of sites with occupancies in the ratio 0.586 (7):0.414 (7).

Mechanochemical Synthesis of 3d Transition-Metal-1,2,4-Triazole Complexes as Precursors for Microwave-Assisted and Thermal Conversion to Coordination Polymers with a High Influence on the Dielectric Properties

The complexes [MCl2 (TzH)4] (M=Mn (1), Fe (2); TzH=1,2,4-1H-triazole) and [ZnCl2 (TzH)2] (3) have been obtained by mechanochemical reactions of the corresponding divalent metal chloride and 1,2,4-1H-triazole. They were successfully used as precursors for the formation of coordination polymers either by a microwave-assisted reaction or by thermal conversion. For manganese, the conversion directly yielded 1∞ [MnCl2 TzH] (4), whereas for the iron-containing precursor, 1∞ [FeCl2 TzH] (6), was formed via the intermediate coordination polymer 1∞ [FeCl(TzH)2]Cl (5). For cobalt, the isotypic polymer 1∞ [CoCl(TzH)2]Cl (7) was obtained, but exclusively by a microwave-induced reaction directly from CoCl2 . The crystal structures were resolved from single crystals and powders. The dielectric properties were determined and revealed large differences in permittivity between the precursor complexes and the rigid chain-like coordination polymers. Whereas the monomeric complexes exhibit very different dielectric behaviour, depending on the transition metal, from "low-k" to "high-k" with the permittivity ranging from 4.3 to >100 for frequencies of up to 1000 Hz, the coordination polymers and complexes with strong intermolecular interactions are all close to "low-k" materials with very low dielectric constants up to 50 °C. Therefore, the conversion procedures can be used to deliberately influence the dielectric properties from complex to polymer and for different 3d transition-metal ions.