Kinetics and thermal decomposition of Fe(III) and UO2(II) complexes with embelin (2,5-dihydroxy-3-undecyl-P-benzoquinone)

The thermal decomposition of the complexes: [Fe(C₁₇H₂₄O₄)_1.5·2H₂O]_n and [UO₂(C₁₇H₂₄O₄·2H₂O]_n, and evaluation of kinetic parameters (E, Z andS) by making use of Piloyan-Novikova, Coats-Redfern and Horowitz-Metzger equations are reported. The complexes are found to decompose in three well defined steps involving random nucleation mechanism. The intermediates formed during decomposition usually undergo further decomposition without remaining stable over a considerable range of temperature.

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Zusammenfassung Es wird über die thermische Zersetzung der Komplexe [Fe(C₁₇H₂₄O₄)_1.5·2H₂O]_n und [UO₂(C₁₇H₂₄O₄)·2H₂O]_n und über die Ermittlung der kinetischen Parameter durch Anwendung der Piloyan-Novikova, der Coats-Redfern und der Horowitz-Metzger-Gleichungen berichtet. Die Komplexe werden in drei gut definierten Stufen mit Random-Keimbildungsmechanismus zersetzt. Die während der Zersetzung gebildeten Zwischenprodukte unterliegen stets einer weiteren Zersetzung, ohne in einem erheblichen Temperaturbereich Stabilität zu zeigen.

     

Kinetics of the Fe(II) reduction of trans-halogenopyridinebis(dimethylglyoximato)Co(III) complexes

The kinetics of the Fe(II) reduction of trans-chloro, bromo and iodopyridinebis(dimethylglyoximato)Co(III) have been studied at 30.0±0.1°C and I = 1.0 mol. dm⁻³(NaClO₄) in the [H⁺] range 0.0043–0.115 mol. dm⁻³. The reaction showed an inverse dependence on [H⁺]. The second order rate constant could be expressed in the form k_II = k₁ + k₂(1 + K_B[H⁺])^{−1. The kinetic data were found to be:} Co(DH)₂(py)Cl−k₁ = 0.051 ±0.003 dm³ mol⁻¹s⁻¹, 0.051±0.003 dm³ mol⁻¹ s⁻¹,k₂ = 0.76±0.04 dm³ mol⁻¹ s⁻¹ K_B = 325±8 dm³ mol⁻¹;Co(DH)₂(py)Br-k₁ = 0.071±0.004 dm³mol⁻¹ s⁻¹,k₂ = 1.21±0.04 dm³ mol⁻¹ s⁻¹ K_B = 460±15 dm³ mol⁻¹; Co(DH)₂(py)I-k₁ = 0.075±0.006 dm³ mol⁻¹ s⁻¹,k₂ = 1.91±0.09 dm³ mol⁻¹ s⁻¹ K_B = 625±30 dm³ mol⁻¹. The inverse dependence on [H⁺] suggests an inner-sphere mechanism involving protonated and unprotonated species of the complex. The order of rates for the three complexes was found to be Co(DH)₂(py)I > Co(DH)₂(py)Br > Co(DH)₂(py)Cl.     

The mechanism of thermal decomposition of Co(NO3)2 · 2H2O

The mechanism of thermal decomposition of Co(NO₃)₂ · 2H₂O was found to involve stages in which Co(NO₃)₃ and Co₂O₃ · H₂O are formed both of which decompose to Co₃O₄. During the process, the total cobalt enters the +3 oxidation state, which is consistent with the results reported by Mehandjiev [2].

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Zusammenfassung Es wurde gefunden, daß der Zersetzungsmechanismus von Co(NO₃)₂ · 2H₂O Schritte umfaßt, bei denen Co(NO₃)₃ sowie Co₂O₃ · H₂O gebildet werden, beides weiterzerfallend zu Co₃O₄. Während des Vorganges erreicht das Gesamtkobalt die Oxidationsstufe +3, was mit Ergebnissen von Mehandjiev übereinstimmt [2].

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, , CO₃O₄. , .

     

Crystal structure and heat capacity of the mixed-valence trinuclear iron monoiodoacetate complex, [Fe(III)2Fe(II)O(O2CCH2I)6(H2O)3][Fe(III)3O(O2CCH2I)6(H2O)3]I

The crystal structure of a trinuclear iron monoiodoacetate complex was determined. Although it has been incorrectly characterized as [Fe₃O(O₂CCH₂I)₆(H₂O)₃], the correct chemical formula turned out to be [Fe(III)₂Fe(II)O(O₂CCH₂I)₆(H₂O)₃]-[Fe(III)₃O(O₂CCH₂I)₆(H₂O)₃]I (1). The two kinds of Fe₃O molecules (Fe(III)₂Fe(II)O and Fe(III)₃O) are crystallographically indistinguishable. All the Fe atoms are crystallographically equivalent because of a crystallographic threefold symmetry. Heat capacities of 1 seem to exhibit no thermal anomaly in the temperature range 5.5–309 K, although the valence detrapping phenomenon has been observed in this temperature range. This fact indicates that the valence-detrapping phenomenon in 1 occurs without any phase transition, leading 1 to a glassy state, probably because the crystal of 1 is just like a solid solution of distorted mixed-valence Fe(III)₂Fe(II)O molecules and permanently undistorted Fe(III)₃O molecules which may act as an inhibitor for a cooperative valence-trapping.     

The mass spectra of 1,1,1-trichloro-2,4-pentanedione and its Al(III), Cr(III), Fe(III), Mn(II), Co(II) and Cu(II) complexes

The compounds 1,1,1-trichloro-2,4-pentanedione, Cu(II)tca₂, Co(II)tca₂, Mn(II)tca₂, Al(III)tca₃, Cr(III)tca₃ and Fe(III)tca₃ (tca?1,1,1-trichloro-2,4-pentanedionato, [CCl₃COCHCOCH₃]^?) have been prepared and their mass spectra have been obtained. The mass spectral results have been compared with findings for comparable fluorinated and nonhalogenated compounds. Comparisons are made in terms of internal redox reactions and hard and soft acid base theory. Rearrangement of chloride from ligand to metal accompanied by the elimination of CO or other neutral even electron fragments emerges as an important reaction for the ions of these compounds. While the internal redox reactions characteristic of all previous β-diketonate complex mass spectra still occur, their importance appears reduced to some degree by the facility of the chlorine rearrangement.     

Schiff-Basen aus 1,3-Dicarbonylverbindungen und Triaminen und ihre Fe (III)-, Co (III)-, Ni(II)- und Cu(II)-Komplexe

Schiff bases of 1,3-dicarbonyl compounds with triamines and their Fe(III), Co(III), Ni(II) and Cu(II) complexes The preparation of new hexadentate ligands obtained by the reaction of cis, cis-1,3,5-triaminocyclohexane (tach) or 1,1,1-tris (aminomethyl)ethane (tame) with an 2-ethoxymethylidene-1,3-dicarbonyl compound as well as their Fe(III), Co(III), Ni(II) and Cu(II) complexes is reported. Fe(III) and Co(III) yield neutral complexes with an octahedral N₃O₃-coordination sphere, Ni(II) and Cu(II) complexes with a square-planar coordination-sphere. In the later complexes one of the bidentate branches of the ligand is not deprotonated and stays uncoordinated.     

Mixed-metal sandwich complexes [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (M(II) = Co, Mn): synthesis and stability. The molecular structure of [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14-

Two new mixed-metal sandwich complexes [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (abbreviated [M2Fe2P4W30], M(II) = Co(II), Mn(II)) were obtained at pH 3 by addition of M2+ to [Na2(H2O)2Fe(III)2(P2W15O56)2]16- (abbreviated [Na2Fe2P4W30]) without substitution in the alpha-[P2W15O56]12- (abbreviated [P2W15]) units. Their X-ray structures are reported. At lower pH, back conversion to [Na2Fe2P4W30] was followed by 31P NMR, electrochemistry and UV-visible spectroscopy. The preparation and the characterization in solution of the lacunary intermediate [NaCo(II)(H2O)2Fe(III)2(P2W15O56)2]15- (abbreviated [NaCoFe2P4W30]) is also described.     

Ferromagnetism in malonato-bridged copper(II) complexes. Synthesis,crystal structures,and magnetic properties of [[Cu(H2O)3][Cu(mal)2(H2O)]]n and [[Cu(H2O)4]2[Cu(mal)2(H2O)]][Cu(mal)2(H2O)2][[Cu(H2O)4][Cu(mal)2(H2O)2][(H2mal = malonic acid)

Three malonato-bridged copper(II) complexes of the formulas [[Cu(H2O)3][Cu(C3H2O4)2(H2O)]]n (1), [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]] [Cu(C3H2O4)2(H2O)2][[Cu(H2O)4][Cu(C3H2O4)2(H2O)2]] (2), and [Cu(H2O)4][Cu(C3H2O4)2(H2O)2] (3) (C3H2O4 = malonate dianion) have been prepared, and the structures of the two former have been solved by X-ray diffraction methods. The structure of compound 3 was already known. Complex 1 crystallizes in the orthorhombic space group Pcab, Z = 8, with unit cell parameters of a = 10.339(1) A, b = 13.222(2) A, and c = 17.394(4) A. Complex 2 crystallizes in the monoclinic space group P2/c, Z = 4, with unit cell parameters of a = 21.100(4) A, b = 21.088(4) A, c = 14.007(2) A, and beta = 115.93(2) degrees. Complex 1 is a chain compound with a regular alternation of aquabis(malonato)copper(II) and triaquacopper(II) units developing along the z axis. The aquabis(malonato)copper(II) unit acts as a bridging ligand through two slightly different trans-carboxylato groups exhibiting an anti-syn coordination mode. The four carboxylate oxygens, in the basal plane, and the one water molecule, in the apical position, describe a distorted square pyramid around Cu1, whereas the same metal surroundings are observed around Cu2 but with three water molecules and one carboxylate oxygen building the equatorial plane and a carboxylate oxygen from another malonato filling the apical site. Complex 2 is made up of discrete mono-, di-, and trinuclear copper(II) complexes of the formulas [Cu(C3H2O4)2(H2O)2]2-, [[Cu(H2O)4] [Cu(C3H2O4)2(H2O)2]], and [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]]2+, respectively, which coexist in a single crystal. The copper environment in the mononuclear unit is that of an elongated octahedron with four carboxylate oxygens building the equatorial plane and two water molecules assuming the axial positions. The neutral dinuclear unit contains two types of copper atoms, one that is six-coordinated, as in the mononuclear entity, and another that is distorted square pyramidal with four water molecules building the basal plane and a carboxylate oxygen in the apical position. The overall structure of this dinuclear entity is nearly identical to that of compound 3. Finally, the cationic trimer consists of an aquabis(malonato)copper(II) complex that acts as a bismonodentate ligand through two cis-carboxylato groups (anti-syn coordination mode) toward two tetraaqua-copper(II) terminal units. The environment of the copper atoms is distorted square pyramidal with four carboxylate oxygens (four water molecules) building the basal plane of the central (terminal) copper atom and a water molecule (a carboxylate oxygen) filling the axial position. The magnetic properties of 1-3 have been investigated in the temperature range 1.9-290 K. Overall, ferromagnetic behavior is observed in the three cases: two weak, alternating intrachain ferromagnetic interactions (J = 3.0 cm-1 and alpha J = 1.9 cm-1 with H = -J sigma i[S2i.S2i-1 + alpha S2i.S2i+1]) occur in 1, whereas the magnetic behavior of 2 is the sum of a magnetically isolated spin doublet and ferromagnetically coupled di- (J3 = 1.8 cm-1 from the magnetic study of the model complex 3) and trinuclear (J = 1.2 cm-1 with H = -J (S1.S2 + S1.S3) copper(II) units. The exchange pathway that accounts for the ferromagnetic coupling, through an anti-syn carboxylato bridge, is discussed in the light of the available magneto-structural data.     

Kinetics of decomposition of hydrogen peroxide on Fe(III)?Al(III) hydroxide-oxide systems

The kinetics of decomposition of hydrogen peroxide have been studied on mixed Fe(III)–Al(III) hydroxide and oxide catalysts. While iron hydroxide possesses considerable catalytic activity, aluminium hydroxide has very little activity. The rate of decomposition on mixed hydroxides increases with increasing concentration of aluminium hydroxide up to about 1.5 mol% and decreases thereafter. The mixed oxides possess negligible activity compared to the corresponding hydroxides. The energy of activation, as calculated from the Arrhenius equation, is 10.1 kcal/mol for sample S4, containing 1.52 mol% of alumina. The rate of decomposition of S4 increases with increasing pH up to 6.8 and decreases thereafter. The rate is first order in all these cases. A suitable mechanism is suggested.

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Fe(III)–Al(III). , . , 1,5 , . . , , 10,1 / S4, 1,52 . S4 pH 6,8, . . .

     

Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The R_N and/or A_M models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol^–1 (R_1.575, stage I); 101 kJ mol^–1 (Ain1.725 stage II); 185 kJ mol^–1 (A _2.9, stage III) and in argon: 66 kJ mol^–1 (A _1.25, stage I); 87 kJ mol^–1 (A _1.825, stage II); 133 kJ mol^–1 (A _2.525, stage III).     

Kinetics and mechanism of the [Ru(III)(edta)(H2O)](-)-mediated oxidation of cysteine by H2O2

The kinetics and mechanism of the [Ru(III)(edta)(H(2)O)](-)-mediated oxidation of cysteine (RSH) by hydrogen peroxide (edta(4-) = ethylenediaminetetraacetate), were studied in detail as a function of both the hydrogen peroxide and cysteine concentrations at pH 5.1 and room temperature. The kinetic traces reveal clear evidence for a catalytic process in which hydrogen peroxide reacts directly with cysteine coordinated to the Ru(III)(edta) complex in the form of [Ru(III)(edta)SR](2-). A parallel process in which [Ru(III)(edta)(H(2)O)](-) first reacts with H(2)O(2) to produce [Ru(V)(edta)O](-) and subsequently oxidizes cysteine, is orders of magnitude slower than the [Ru(III)(edta)(H(2)O)](-)-mediated oxidation in which cysteine rapidly coordinates to [Ru(III)(edta)(H(2)O)](-) prior to the reaction with H(2)O(2). HPLC product analyses revealed the formation of cystine (RSSR) as major product along with cysteine sulfinic acid (RSO(2)H) in the reaction system, and established the catalytic role of [Ru(III)(edta)(H(2)O)](-). Simulations were performed to account for the rather complex kinetic traces in terms of the suggested reaction mechanism. The results of the simulations support the proposed reaction mechanism that involves the oxidation of coordinated cysteine to cysteine sulfenic acid (RSOH), which subsequently rapidly reacts with H(2)O(2) and RSH to form RSO(2)H and RSSR, respectively.     

Salisaldehyde-2-aminobenzimidazole schiff base complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)

New metal complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with salicylidine-2-aminobenzimidazole (SABI) are synthesized and their physicochemical properties are investigated using elemental and thermal analyses, IR, conductometric, solid reflectance and magnetic susceptibility measurements. The base reacts with these metal ions to give 1:1 (Metal:SABI) complexes; in cases of Fe(III), Co(II), Cu(II), Zn(II) and Cd(II) ions; and 1:2 (Metal:SABI) complexes; in case of Ni(II) ion. The conductance data reveal that Fe(III) complex is 2:1 electrolyte, Co(II) is 1:2 electrolyte, Cu(II), Zn(II) and Cd(II) complexes are 1:1 electrolytes while Ni(II) is non-electrolyte. IR spectra showed that the ligand is coordinated to the metal ions in a terdentate mannar with O, N, N donor sites of the phenloic -OH, azomethine -N and benzimidazole -N3. Magnetic and solid reflectance spectra are used to infer the coordinating capacity of the ligand and the geometrical structure of these complexes. The thermal decomposition of the complexes is studied and indicates that not only the coordinated and/or crystallization water is lost but also that the decomposition of the ligand from the complexes is necessary to interpret the successive mass loss. Different thermodynamic activation parameters are also reported, using Coats-Redfern method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-salicydene-o-hydroxymethyleneaniline

The new Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes with tridentate Schiff base, the product of condensation of o-aminobenzyl alcohol with salicylaldehyde have been synthesized and characterized by elemental analysis, IR, electronic, EPR and Mössbauer spectra, thermal analysis, magnetic susceptibility and molecular weight measurements. Dimeric or polymeric structures for the investigated complexes were proposed. The interaction of the cobalt complex with dioxygen is also described.     

Encapsulation of Fe(III) and Cu(II) complexes in NaY zeolite

The use of nonporphyrin complexes encapsulated in zeolites as catalysts for oxidation reactions has been improved in the past decades by the discovery of increasing numbers of nonheme monoxygenases. The zeolite lattice can change the oxidative chemistry of the metallocomplexes, resulting in a catalytic effect different from those observed in homogeneous reactions. We report the encapsulation of iron and copper metallocomplexes with the ligand (2-hydroxybenzyl)(2-methylpyridyl)amine, Hbpa, and iron complexes with the ligand N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl) ethylenediamine, H(2)bbpen. The zeolite-encapsulated metallocomplexes were prepared by diffusion of the ligands through the pores of the zeolites, already exchanged with the respective metal. The syntheses were performed in methanol and toluene solutions. Elemental analysis of solids with the Hbpa ligand have indicated better complexation for synthesis in toluene, where 74% of the iron atoms were coordinated by the ligand, against 37% for the synthesis in methanol. For the immobilization with the H(2)bbpen ligand in toluene it was observed that 46% of the iron atoms are coordinated, showing that the diffusion of the small ligand Hbpa through the zeolite cage was facilitated. The EPR spectra of the solids show signals at g = 2.0, which was attributed to an Fe-Fe interaction from the noncoordinated atoms, and g = 4.3 attributed to iron (III) in a rhombic geometry.     

Synthesis and magnetic properties of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)]2 (M(II) = Zn,Cu, Ni,Co, Fe,Mn; H3L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane; Hhfac = hexafluoroacetylacetone)

A series of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)](2) (M(II) = Zn (1), Cu (2), Ni (3), Co (4), Fe(5), and Mn (6)) have been synthesized by the assembly reaction of K[CuL] and [M(II)(hfac)(2)(H(2)O)(2)] with a 1:1 mole ratio in methanol, where H(3)L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane and Hhfac = hexafluoroacetylacetone. The crystal structures of 2, 4, and [Cu(II)LMn(II)(acac)](2) (6a) (Hacac = acetylacetone) were determined by single-crystal X-ray analyses. Each complex has a cyclic tetranuclear Cu(II)(2)M(II)(2) structure, in which the Cu(II) complex functions as a "bridging ligand complex", and the Cu(II) and M(II) ions are alternately arrayed. One side of the planar Cu(II) complex coordinates to one M(II) ion at the two phenoxo and the methoxy oxygen atoms, and the opposite side of the Cu(II) complex coordinates to another M(II) ion at the amido oxygen atom. The temperature-dependent magnetic susceptibilities revealed spin states of S(M) = 0, 1/2, 1, 3/2, 2, and 5/2 for the Zn(II), Cu(II), Ni(II), Co(II), Fe(II), and Mn(II) ions, respectively. Satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a rectangular arrangement with two different g-factors for the Cu(II) and M(II) ions, two different isotropic magnetic exchange interactions, J(1) and J(2), between the Cu(II) and M(II) ions, and a zero-field splitting term for the M(II) ion. In all cases, the antiferromagnetic coupling constants were found for both exchange interactions suggesting nonzero spin ground states with S(T) = 2/S(M) - S(Cu)/, which were confirmed by the analysis of the field-dependent magnetization measurements.     

Co(II) and Co(III) complexes of m-benziphthalocyanine

The syntheses and structural elucidations of three different cobalt complexes of m-benziphthalocyanine are reported; both Co(II) and Co(III) complexes can be generated, and the ring undergoes partial oxidation upon metalation with Co(OAc)2x4H2O.