Kinetics of stepwise oxidation of manganese(II) by peroxodisulphate in phosphoric acid medium

Summary The oxidation of Mn^II by S₂O₈ ^2– to Mn^VII in phosphoric acid medium proceeds via a stable Mn^III and Mn^IV species. The reaction is catalysed by Ag⁺ and exhibits first order dependence on [S₂O₈ ^2–], [Ag⁺] and, is independent of [Mn^II]. The [H⁺] has no significant effect on the reaction. It is observed that the PO₄ ^3– ion stabilises the transient manganese(III) and manganese(IV) species by forming a stable and soluble phosphato-complexes. The activation parameters for the two stages of oxidation, namely Mn^II Mn^IV and Mn^IVMn^VII at 25° C are E_a=52 ±4 kJ mole^–1, S^*=–57±2 JK^–1 mole^–1 and E_a =56±4 kJ mole^–1, S^*=–44±2 JK^–1 mole^–1, respectively. A mechanism consistent with the experimental observations is proposed.Presented at the National Symposium on Reaction Kinetics and Mechanism, Department of Chemistry, University of Jodhpur, Jodhpur, India, Nov. 15–18, 1986.     

Unusual stabilization of manganese(III) during the cooxidation of dimethylformamide and manganese(II) by chromium(VI)

The kinetics of the formation and decomposition of Mn^III have been investigated spectrophotometrically in acidic media at 25 °C. The complete rate law for Mn^III formation isCr^VI + DMF + Mn^II {H⁺} Mn^III + CO₂ + Me₂NH + Cr^III ... (1)Mn^III + DMF {H⁺} Mn^II + CO₂ + Me₂NH ... (2)expressed by k _obs1 = k ₁ k₁ K _a1[H⁺][DMFH⁺][Mn^II]/{1 + K _a1[H⁺]}. Mn^III reduction by DMF follows the rate law k _obs2 = k ₂ K _h[DMF][H⁺]²/{[H⁺] + K _h}. The above results are accounted for by a mechanism involving the intermediacy of Cr^IV.     

Synthesis and magnetic properties of tetrabromophthalato-bridged manganese(II) binuclear complexes

Summary Four novel Mn^II binuclear complexes have been prepared and characterized, namely: [Mn₂(TBPHTA)(L)₄](ClO₄)₂ [L = 2,2-bipyridyl (bipy), 1,10-phenanthroline (phen), 4,4-dimethyl-2,2-bipyridyl (Me₂bipy) and 5-nitro-1,10-phenanthroline (NO₂-phen), respectively], and TBPHTA = the tetrabromophthalate dianion. Based on i.r. spectra, elemental analyses and conductivity measurements, extended tetrabromophthalato-bridged structures consisting of two Mn^II ions, in which each Mn^II ion has a distorted octahedral environment, are proposed for these complexes. The temperature dependence of the magnetic susceptibility for [Mn₂(TBPHTA)(phen)₄] (ClO₄)₂·H₂O was measured over the 4–300 K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator ( = -2J _{1 2}), giving the exchange integral J = -1.22 cm^–1. This result indicates a weak antiferromagnetic spin exchange interaction between the metal ions.     

Redox chemistry of mononuclear manganese(II), binuclear manganese(III) and binuclear mixed manganese(II)-manganese(III) complexes with 3-aminopyrazine-2-carboxylate in dimethylsulphoxide

Summary Mn^II forms a yellow mononuclear species with the title ligand having a 12 stoichiometry and whose conditional stability constant is 8.9 × 10¹⁰ m ^–2. The c.v. of this complex shows an oxidation at +0.78V versus s.c.e. Controlled-potential electrolysis at +0.80V versus s.c.e. yields a binuclear species of Mn^III with a 12 metal:ligand stoichiometry.The addition of Mn^III(urea)₆(ClO₄)₃ to a solution of the ligand produces a mononuclear complex of Mn^III if the concentration of the metal ion is less than 1 mM. At higher concentrations a binuclear species is obtained. The latter is reduced in two steps, at +0.24 and –0.58 V versus s.c.e. Controlled-potential electrolysis at 0.0 V produces a dark green complex after the transfer of 0.5 equivalents of charge per mole of Mn. This binuclear L₂Mn^II-Mn^IIIL₂ mixed-valence complex can be obtained only by electrolysis of the binuclear L₂Mn^IIIMn^IIIL₂ species. Attempts to prepare the complex chemically were unsuccessful - the binuclear Mn^III species was obtained in every case.Author to whom all correspondence should be directed.     

Synthesis,spectroscopy and thermal properties of the nickel(II), palladium(II) and copper(II) complexes of bis(aminoalkyl)-oxamides (=LH2) including the crystal structure of Cu2L(NO3)2

Summary The synthesis of the Ni^II, Pd^II and Cu^II complexes of N, N-bis(aminoalkyl)oxamides (LH₂) is described and structures are proposed on the basis of their physical and spectroscopic properties. With Ni^II and Pd^II only one complex is formed with general formula NiL or PdL, characterised by coordination through two deprotonated amide N-atoms and two terminal NH₂ groups. With Cu^II it proved possible to obtain three structurally different compounds, depending on the pH, with general formulae Cu(LH₂)X₂, Cu₂(L)X₂ and CuL in which X=Cl, Br or NO₃. The structure of [Cu₂(C₈O₂N₄H₁₆](NO₃)₂ was solved by means ofx-ray diffraction; Mr=451.33, monoclinic, space group P2₁/n, a=9.503(4), b=7.614(1), c=10.407(3) Å, =98.43(3)°, V=744.3(7)ų, Z=2, Dx=1.202 g cm^–3, =1.33 cm^–1, (MoK)=0.71073 Å, F(000)=520, room temperature, R=0.043, wR=0.047 for 1080 observed [I>-3(I)] not systematically absent reflections out of 1423 measurements and 137 variables. The compound has a conformational chair/boat disorder with 82% in the more stable chair form.     

Synthesis and characterization of some methyl complexes of palladium(II). Part 2(1)

Summary Dichloro complexes of Pd^II, [Pd(L–L)Cl₂], where L–L=1-(thiomethyl)-2-(diphenylarsino)ethane (S–As) or 1-(thiomethyl)-2-(diphenylphosphino)ethane (S–P) andtrans-[PdL₂Cl₂], where L=diphenyl(2-phenylethyl)-phosphine (PE), diphenyl(1-naphthyl)phosphine (PN) orN-methyl-2-thiophenealdimine (SN), have been prepared and characterized. The reactions of these complexes with MeLi were investigated. The dimethyl complexes [Pd(L–L)Me₂] (L–L=S–As, S–P) and [Pd(PE)Me₂] were isolated and characterized. Reaction of [Pd(L–L)Me₂] (L–L=S–As, S–P) with HCl affords the monomethyl derivatives [Pd(L–L)Me(Cl)]. In contrast to the Pt analogues, [Pd(L–L)Me₂] and [Pd(L–L)Me(Cl)] are relatively less stable than [Pt(L–L)Me₂] and [Pt(L–L)Me(Cl)].     

Oxalate-bridged mixed-valence trinuclear manganese(II)-manganese(III)-manganese(II) complexes: synthesis and magnetism

Summary Two novel Mn^II-Mn^III-Mn^II oxalato complexes have been synthesized and characterized, namely [Mn₂Mn(ox)₃(L)₄](ClO₄) [L = 1,10-phenanthroline (phen) or 5-nitro-1,10-phenanthroline (NO₂-phen), respectively], where ox stands for the oxalate dianion. Based on i.r., elemental analyses and electronic spectra, these complexes are proposed to have extended oxalatobridged structures consisting of Mn^II and Mn^III ions, in which Mn^III and each Mn^II ion has a distorted octahedral environment. The temperature dependence of magnetic susceptibility for [Mn₂Mn(ox)₃(phen)₄] (ClO₄) was measured over the 4.1–300 K range and the observed data were successfully simulated by an equation based on the spin-Hamiltonian operator ( = -2J( _{1 2} + _{2 3})), giving the exchange integral J = -1.57cm^–1. This indicates weak antiferromagnetic spin exchange interaction between Mn^II and Mn^III ions.     

Rate constant of unimolecular decomposition of the radical (CH3)2juvyCCH(CH3)2

The energy of activation of CH ₃ ^. radical rupture from the radical (CH₃)₂juvyCCH(CH₃)₂ is 142.2 kJ mol^–1; the selfcombination rate constant is k_c {(CH₃)₂juvyCCH(CH₃)₂}=10^7.3 dm³ mol^–1 s^–1.

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CH ₃ ^. (CH₃)₂juvyCCH(CH₃)₂ 142,2 /, k_c {(CH₃)₂juvyCCH(CH₃)₂}=10^{7,3 3–1 –1}.

     

Synthesis,spectroscopy and electrochemistry of mono and dinuclear complexes of a peripherally mixed ligand and the interaction of (E,E) Ni(LH)2 with Pd2+ and Ag+

We describe the synthesis, characterization and electrochemistry of a new family of peripherally functionalised vic-dioxime, 5,6-bis-(hydroxyimino)-1,2,9,10-hydroxy-4,7-dithiadecane (LH₂), with bis-(thiopropandiol) moieties attached to the oxime. Thiopolyalcohol groups containing two different heteroatoms (—S— and —O—) serve as weak exocyclic binding sites for Pd⁺² and Ag⁺ ions. Novel mononuclear (LH)₂M, (M = Ni^II, Cu^II, Co^II, Mn^II and Fe^II), homodinuclear (LH)₂(UO₂)₂(OH) and heterotrinuclear (LH)₂MM₂ (M = Ni^II and M = Pd^II and Ag^I) species have been obtained with the metal:ligand ratios of 1:2, 2:2, and 3:2 respectively. Metal ions coordinate through N,N of the oxime and S,O donor sites of the peripherally attached groups in the presence of the base. The heterotrinuclear complexes were prepared by the interaction of the mononuclear complex, (LH)₂Ni, with Pd(C₅H₅)₂ and AgNO₃ in an appropriate solvent. The complexes were characterized by elemental analysis, ¹H-n.m.r., u.v.–vis. spectroscopy, FT-IR., and by f.a.b-m.s. The redox properties of the complexes were studied by cyclic voltammetry.     

Synthesis,spectral and magnetic studies on mixed-ligand complexes M(DIAFO)2(NCS)2 and M(DIAFH)2X2 (M = FeII,CoII, NiII). The crystal structure of Co(DIAFO)2(NCS)2

Summary A series of mixed-ligand complexes of group VIII metals, M(DIAFO)₂(NCS)₂ and M(DIAFH)₂X₂ (M = Fe^II, Co^II, Ni^II, X = NCS^–, Cl^–) with the 3,3-bridged derivative of 2,2-bipyridyl (bipy) (1) were prepared, where DIAFO (2) and DIAFH (3) are 4,5-diazafluoren-9-one and 4,5-diazafluoren-9-hydrazone, respectively. These complexes were investigated by i.r., u.v.-vis-near i.r. spectroscopy and by variable-temperature magnetic susceptibility measurements. The electronic spectra show that the two ligands exert a field strength far removed from the Fe^II cross-over value. All the complexes are paramagnetic, following the Curie-Weiss law in the 77–300 K range. A typical crystal structure of Co(DIAFO)₂(NCS)₂ for these compounds was determined with orthorhombic, space group Pcan, a = 10.377(5) Å, b = 13.289(6) Å, c= 16.629(7) Å, V = 2293(2) ų, D _c = 1.563 g cm^–3, F(000) = 1091.74, Z = 4, R = 0.043, R = 0.047. Steric effects are thought to be operative in both ligands studied, but are weaker than those of the typical bidentate diimine ligand bipy.Author to whom all correspondence should be directed.     

Preparation and electrochemical study of manganese(II) macrocycles containing terpyridine

The macrocycle, L, prepared by template condensation of bis-6,6-(-methylhydrazino)-4-phenyl-2,2:6,2-terpyridine with glyoxal, forms a stable crystalline Mn^II complex, [Mn(L)(H₂O)₂][PF₆]₂, which has been used as a starting material for electrochemical studies on a series of seven coordinate Mn^II complexes [Mn(L)X₂]²⁺ (X = pyridine, 4-cyanopyridine, 4-aminopyridine, 4-dimethylaminopyridine, pyrazine, imidazole 1-methylimidazole, 2-dimethylimidazole or Ph₃P). Cyclic voltammetry of the complexes in MeCN shows a reversible one electron reduction wave in the range –1.32 to –1.42 V versus the Ag/AgBF₄ reference electrode.     

A novel (E,E)-dioxime and its mono-, di- and trinuclear complexes bearing tetradentate octyl sulfanyl phenylamino substituents. Synthesis,characterization and electrochemical properties of its transition metal complexes

A new vic-dioxime, 13,14-bis-(hydroxyimino)-9,12,15,18-diazadithiaoctacosane, has been synthesized from 2-octylsulfanylaminobenzene and (E,E)-dichloroglyoxime. Mononuclear transition metal complexes of Ni^II, Cu^II, Co^II and Fe^II have been prepared and were found to have a metal–ligand ratio of 1:2. The synthesis of di- and trinuclear complexes was achieved with U^IVO₂ and Cu^II depending on the stoichiometry of the reactants. The complexes were characterized by elemental analysis, ¹H-n.m.r., u.v.–vis, i.r., f.a.b.-m.s. and by cyclic voltammetry.     

Complexes of N-nicotinoyl-N′-2-furanthiocarbohydrazide with oxovanadium(IV), manganese(II), iron(II & III), cobalt(II), nickel(II), copper(II) and zinc(II)

A new potential tetradentate ligand, N-nicotinoyl-N-2-furanthiocarbohydrazide (H₂Nfth), and its complexes with VO^IV, Mn^II, Fe^II,III, Co^II, Ni^II, Cu^II and Zn^II have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, u.v.–vis, i.r., n.m.r., ES⁺ and FAB mass spectral data. The room temperature e.s.r spectra of the VO^IV and Fe^III complexes yield g values, characteristic of octahedral complexes. The Mössbauer spectra of [Fe(HNfth)₂] and [Fe₂(Nfth)₃] at room temperature and at 78 K suggest the presence of high-spin iron(II) and iron(III), respectively. The complexes are electrically insulating at room temperature, however, their conductivities increase as the temperature increases from 333–383 K, with a band gap of 0.46–0.77 eV, indicating their semiconducting behaviour. H₂Nfth and its soluble complexes have been screened against several bacteria and fungi.     

ESR study of SO2 on MnO2-alumina

SO ₃ ^– radicals are formed during the reaction between SO₂ and MnO₂-alumina, which suggests that SO ₃ ^– take part in the reduction of Mn⁴⁺ to Mn²⁺.

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SO₂ MnO₂/Al₂O₃ SO ₃ ^– , , SO ₃ ^– Mn⁴⁺ Mn²⁺.

     

Study of the oxidation-reduction reactions of manganese and cobalt in alkaline triethanolamine medium

Summary It has been found that in alkaline triethanolamine medium the complex of bivalent manganese is oxidised by hexacyanoferrate(III), hydrogen peroxide or lead dioxide to the red-coloured complex of Mn^IV, which can be titrated potentiometrically with ferrous salt solution (Mn^IV Mn^III and Mn^III Mn^II). The stability of this complex has been studied in dependence on the oxidant employed, and it has been found that lead dioxide is best suited for this oxidation process. Similarly the oxidation of the complex Co^II Co^III has been studied in the same medium, and conditions have been found for the reductometric determination of the Co^III complex formed.The possibilities for determining manganese in the presence of cobalt and of other accompanying elements are discussed. The results obtained have been applied to the determination of manganese in ores and alloys.

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Zusammenfassung Bei Untersuchungen zum Oxydations-Reduktions-Verhalten von Mangan und Kobalt in alkalischer Triäthanolaminlösung wurde gefunden, daß der Mn^II-Komplex durch Hexacyanoferrat(III), Wasserstoffperoxid oder Bleidioxid zum rotgefärbten Mn^IV-Komplex oxydiert wird, der potentiometrisch mit, Fe^II-Lösung titriert werden kann (Mn^IV Mn^III; Mn^III Mn^II). Die Stabilität des Komplexes wurde in Abhängigkeit von der Art des Oxydationsmittels geprüft und Bleidioxid als am günstigsten gefunden. Analog wurden auch die Oxydation des Co^II- zum Co^III-Komplex untersucht und Bedingungen zur reduktometrischen Bestimmung des letzteren ausgearbeitet. Die Möglichkeiten zur Manganbestimmung in Gegenwart von Kobalt sowie anderen Begleitelementen werden diskutiert, und als praktische Anwendung wird die Manganbestimmung in Erzen und Legierungen beschrieben.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.     

Synthesis and characterisation of some complexes of manganese(II) and iron(II) picrates with heterocyclic amines

Summary Complexes of manganese(II) and iron(II) picrates with various bidentate (L) and monodentate (L) heterocyclic bases have been synthesised; their compositions have been established as [ML₃]A₂ (1), [ML₂ · 2 H₂O]A₂ (2), [ML₆]A₂ (3) and [ML4 · 2 H₂O]A₂ (4), where M = Fe^II and Mn^II, L = 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) in (1), A = picrate anion; M = Mn^II, L = bipy and phen in (2); M = Fe^II, L = pyridine (py), 4-picoline (4-pic) and 3-picoline (3-pic) in (3); M = Mn^II, L = py, 4-pic, quinoline (quin) and 2,6-lutidine (2,6-lut) in (4) and also M = Fe^II, L = quin and 2,6-lut.     

Complexes of 2-(2-hydroxyacetophenone)imino-5-(p-anisyl)-1,3,4-oxadiazole with some bivalent metals ions

Summary The metal complexes of the type [M(SB)₂(H₂O)₂] and [M(SB)₂][where M = Mn^II, Co^II, Ni^II or Cu^II, M = Zn^II Cd^II, Hg^II and Pb^II and SBH = 2-(2-hydroxyacetophenone)imino-5-(p-anisyl)-1,3,4-oxadiazole] have been prepared and characterised by elemental analyses, thermal analyses, magnetic measurements, electronic and infrared spectral studies. The complexes [M(SB)₂(H₂O)₂] possess octahedral structures, whereas complexes [M(SB)₂] are tetrahedral. The crystal field parameters of the Co^II and Ni^II complexes are also calculated.     

CO hydration over catalysts prepared via supporting Fe3(CO)12 and (NEt4)2[Fe2Mn(CO)12] on oxide supports

A comparison of the properties of iron-containing catalysts prepared through carbonyl clusters Fe₃(CO)₁₂ and (NEt₄)₂[Fe₂Mn(CO)₁₂] and iron and manganese nitrates in CO hydration indicates that the addition of Mn incorporated in (NEt₄)₂[Fe₂Mn(CO)₁₂] decreases the methane yield and increases the portion of higher hydrocarbons.

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, Fe(CO)₁₂ (NEt₄)₂[Fe₂Mn(CO)₁₂] , CO. Mn (NEt₄)₂[Fe₂Mn(CO)₁₂] .

     

Complex formation between nickel(II) and 2-(2-aminoethyl) benzimidazole: A kinetic and equilibrium study

Summary The reversible complex formation between 2-(2-aminoethyl) benzimidazole (AEB) and nickel(II) was studied by stopped flow spectrophotometry at I = 0.30 mol dm^–3. Both the neutral and monoprotonated form of AEB reacted to give the NiAEB²⁺ chelate. At 25 °C, the rates and activation parameters for the reactions Ni_II + AEB NiAEB²⁺ and Ni^II + AEBH⁺ NiAEB²⁺ + H⁺ are k _f ^L(dm^–3 mol^–1 s^–1) = (2.17 ± 0.24) × 10³, H (kJ mol^–1) = 40.0 ± 0.8, S (JK^–1 mol^–1) = – 47 ± 3 and k _inff ^pHL (dm³ mol^–1 s^–1) = 33 ± 10, H (kJ mol^–1) = 42.0 ±2.7, S (JK^–1 mol^–1) = – 72 ± 9. The dissociation of NiAEB²⁺ was acid catalysed and k _obs for this process increased linearly with [H⁺] in the 0.01–0.15 mol dm^–3 (10–30 °C) range with k _H(dm³ mol^–1s^–1) (25 °C) = 329 ± 6, H (kJ mol^–1) = 40 ± 2 and S (JK^–1 mol^–1) = – 61 ± 8. The results also indicated that the formation of NiAEB²⁺ involves a chelation-controlled, rate-limiting process. Analysis of the S ° data for the acid ionisation of AEBH _inf2 ^p2+ and the formation of NiAEB²⁺ showed that the bulky AEBH⁺ ion has a solvent structure breaking effect as compared to AEB [s _aqS ° (AEBH⁺) – s _aq ° (AEB) = 69 JK^–1 mol^–1], while AEBH _inf2 ^p2+ is a solvent ordering ion relative to NiAEB²⁺ [s _aq° (NiAEB²⁺) – ovS _aq ° (AEBH _inf2 ^p2+ ) = 11 JK^–1 mol^–1].Author to whom all correspondence should be directed.     

Naphthyl-(2-pyridylmethylene)amine complexes of silver(I) and ruthenium(II): synthesis,spectral studies and electrochemical behaviour

Pyridine-2-carboxaldehyde reacts with /-naphthylamine to give /-naphthyl-(2-pyridylmethylene)amine [-L (1), -L (2)]. L belongs to the unsymmetric diimine (—N=C—C=N—) family which can form five–membered chelate rings with metal ions. {donor centers are abbreviated as N[N(Py)] and N [N(nap)]} [Ag(L)₂]⁺ complexes were prepared and characterized by spectroscopic data. The reaction between L and RuCl₃ in boiling EtOH yielded green and blue–green compounds of composition RuCl₂(L)₂. I.r., u.v.–vis. and ¹H-n.m.r. data determined the stereochemistry of the complexes as trans-cis-cis (green) and cis-trans-cis (blue–green) according to the sequence of the coordination pair of Cl, N [N(Py)] and N [N(nap)]. Upon treatment of Ag(L)₂ ⁺ with Ru(bpy)₂Cl₂ in alcoholic suspension the ternary complexes, [Ru(bpy)₂(L)](ClO₄)₂, were isolated and characterized by spectroscopic data. [Ru(bpy)(L)₂](ClO₄)₂ complexes were synthesized similarly from ctc-Ru(L)₂Cl₂ and 2,2-bipyridine (bpy) in the presence of AgNO₃ and NaClO₄. These complexes show well-defined m.l.c.t transitions in the visible region. The sterochemistry of the complexes was established by ¹H-n.m.r. data. Cyclic voltammetry shows a high potential Ru^III/Ru^II couple and follows the order: [Ru(bpy)(L)₂]²⁺ > [Ru(bpy)₂(L)]²⁺ > Ru(-L)₂Cl₂ > Ru(-L)₂Cl₂.