Mounim Lebrini

Manganese(III)-Containing Wells–Dawson Sandwich-Type Polyoxometalates: Comparison with their Manganese(II) Counterparts

We present the synthesis and structural characterization, assessed by various techniques (FTIR, TGA, UV-vis, elemental analysis, single-crystal X-ray diffraction for three compounds, magnetic susceptibility, and electrochemistry) of five manganese-containing Wells-Dawson sandwich-type (WDST) complexes. The dimanganese(II)-containing complex, [Na(2)(H(2)O)(2)Mn(II)(2)(As(2)W(15)O(56))(2)](18-) (1), was obtained by reaction of MnCl(2) with 1 equiv of [As(2)W(15)O(56)](12-) in acetate medium (pH 4.7). Oxidation of 1 by Na(2)S(2)O(8) in aqueous solution led to the dimanganese(III) complex [Na(2)(H(2)O)(2)Mn(III)(2)(As(2)W(15)O(56))(2)](16-) (2), while its trimanganese(II) homologue, [Na(H(2)O)(2)Mn(II)(H(2)O)Mn(II)(2)(As(2)W(15)O(56))(2)](17-) (3), was obtained by addition of ca. 1 equiv of MnCl(2) to a solution of 1 in 1 M NaCl. The trimanganese(III) and tetramanganese(III) counterparts, [Mn(III)(H(2)O)Mn(III)(2)(As(2)W(15)O(56))(2)](15-) (4) and [Mn(III)(2)(H(2)O)(2)Mn(III)(2)(As(2)W(15)O(56))(2)](12-) (6), are, respectively, obtained by oxidation of aqueous solutions of 3 and [Mn(II)(2)(H(2)O)(2)Mn(II)(2)(As(2)W(15)O(56))(2)](16-) (5) by Na(2)S(2)O(8). Single-crystal X-ray analyses were carried out on 2, 3, and 4. BVS calculations and XPS confirmed that the oxidation state of Mn centers is +II for complexes 1, 3, and 5 and +III for 2, 4, and 6. A complete comparative electrochemical study was carried out on the six compounds cited above, and it was possible to observe the distinct redox steps Mn(IV/III) and Mn(III/II). Magnetization measurements, as a function of temperature, confirm the presence of antiferromagnetic interactions between the Mn ions in these compounds in all cases with the exception of compound 2.

Study of Temperature Effect on the Corrosion Inhibition of C38 Carbon Steel Using Amino-tris(Methylenephosphonic) Acid in Hydrochloric Acid Solution

Tafel polarization method was used to assess the corrosion inhibitive and adsorption behaviours of amino-tris(methylenephosphonic) acid (ATMP) for C38 carbon steel in 1 M HCl solution in the temperature range from 30 to 60∘C. It was shown that the corrosion inhibition efficiency was found to increase with increase in ATMP concentration but decreased with temperature, which is suggestive of physical adsorption mechanism. The adsorption of the ATMP onto the C38 steel surface was found to follow Langmuir adsorption isotherm model. The corrosion inhibition mechanism was further corroborated by the values of kinetic and thermodynamic parameters obtained from the experimental data.

Synthesis, Structure, and Magnetic Electrochemical Properties of a Family of Tungstoarsenates Containing Just CoII Centers or Both CoII and FeIII Centers

The three polyoxotungstates [(NaOH2)2CoII2(As2W15O56)2]18- (1), [(NaOH2)(CoIIOH2)CoII2(As2W15O56)2]17- (2), and [(CoIIOH2)2CoII2(As2W15O56)2]16- (3) have been prepared in aqueous solution upon mixing cobalt(II) salts with the ligand [As2W15O56]12-. The reaction of 1 or 2 with the Fe3+ ion leads invariably to the same species [(FeIIIOH2)(CoIIOH2)CoII2(As2W15O56)2]15- (4) possessing three cobalt atoms and a single iron atom. However, if the Fe-containing homologue of compound 1, that is, the polyoxotungstate [(NaOH2)2FeIII2(As2W15O56)2]16- (5), is employed instead to react with the Co2+ ion, the species [(CoIIOH2)2FeIII2(As2W15O56)2]14- (6) is obtained, having two cobalt atoms and two iron atoms. The compounds 1, 2, 3, 4, and 6 are described for the first time and have been characterized by several physicochemical methods such as FTIR, UV-visible, ATG, and elemental analysis. Structural analysis by single-crystal X-ray diffraction has been carried out with compounds 2 (monoclinic space group P21/c, a = 17.0622(5) Å, b = 15.0828(4) Å, c = 32.0872(8) Å, β = 91.170(1)°, and Z = 2) and 3 (triclinic space group P1̅, a = 13.6137(7) Å, b = 13.8836(8) Å, c = 22.9276(6) Å, α = 89.906(3)°, β = 78.356(2)°, γ = 61.451(2)°, and Z = 1). Electrochemical studies undertaken with all the above-mentioned compounds and some of their homologues shed light on the influence of the chemical composition on their electrocatalytic properties toward substrates such as the nitrite ion and dioxygen. Magnetic measurements evidence anisotropic ferromagnetic interactions between Co2+ ions and antiferromagnetic interactions between Fe3+ ions. The nature and the strength of the Co2+-Fe3+ interactions depend on the relative orientations of their 3d orbitals. The effective magnetic moment of the Co2+ ions varies with the temperature and with the distortion of the octahedral sites in which they are located.

Crown Compounds Containing a 1,3,4-Thiadiazole Moiety: Microwave Assisted Synthesis, Crystal Structure and Quantum Calculations

A number of macrocyclic polyether compounds containing a 2,5-bis(2-hydroxyphenyl)-1,3,4-thiadiazole moiety are quickly prepared by a nucleophilic substitution reaction involving ethylene or polyethyleglycol ditosylate anda biphenol, the 2,5-bis(2-hydroxyphenyl)-1,3,4-thiadiazole, with solid anhydrous carbonate as a base under microwave irradiation. The quantum calculations at DFT level and the structure of different conformations of the 2,5-bis(2-hydroxyphenyl)-l,3,4-thiadiazole were performed both in vacuum and acetonitrile solvent using PCM method. The structures are ascertained by spectroscopic properties. The crystal structure of one of the crown compounds has been determined and shows the sufur atom to be inside the macroring cavity.

Adsorption Properties and Inhibition of C38 Steel Corrosion in Hydrochloric Solution by Some Indole Derivates: Temperature Effect, Activation Energies, and Thermodynamics of Adsorption

The corrosion rates in the presence of some indole derivates, namely, 9H-pyrido[3,4-b]indole (norharmane) and 1-methyl-9H-pyrido[3,4-b]indole (harmane), as inhibitors of C38 steel corrosion inhibitor in 1 M HCl solution, were measured by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, in the range of temperatures from 25 to 55∘C. Results obtained revealed that the organic compounds investigated have inhibiting properties for all temperatures. The inhibition was assumed to occur via adsorption of the indole molecules on the metal surface. Adsorption of indole derivates was found to follow the Langmuir isotherm. The apparent activation energies, enthalpies, and entropies of the dissolution process and the free energies and enthalpies for the adsorption process were determined by potentiodynamic polarization and electrochemical impedance. The fundamental thermodynamic functions were used to collect important information about indole inhibitory behaviour.