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1.
A comparative kinetic study of the reactions of two mixed valence manganese(III,IV) complexes of macrocyclic ligands, [L1MnIV(O)2MnIIIL1], 1 (L1 = 1,4,8,11‐tetraazacyclotetradecane) and [L2MnIV(O)2MnIIIL2], 2 (L2 = 1,4,7,10‐tetraazacyclododecane) with thiosulfate has been carried out by spectrophotometry in aqueous buffer at 30°C. Reaction between complex 1 and thiosulfate follows a first‐order rate saturation kinetics. The pH dependency and kinetic evidences suggest the participation of two complex species of MnIII(μ‐O)2MnIV under the experimental conditions. Detailed kinetic study shows that reduction of 2 proceeds through an autocatalytic path where the intermediate (MnIII)2 species has been assumed to catalyze the reaction. The difference in the reaction mechanisms is ascribed to the difference in stability of the intermediate complex species, the evidence for which comes from the electrochemical behavior of the complexes and time dependent EPR spectroscopic measurements during the reduction of 2 . © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 119–128, 2004  相似文献   

2.
A comparative kinetic study of the reactions of two mixed valence manganese(III,IV) complexes with macrocyclic ligands, [L1MnIV(O)2MnIIIL1], 1 (L1 = 1,4,7,10‐tetraazacyclododecane) and [L2MnIV(O)2MnIIIL2], 2 (L2 = 1,4,8,11‐tetraazacyclotetradecane) with 2‐mercaptoethanol (RSH) has been carried out by spectrophotometry in aqueous buffer at (30 ± 0.1)°C. Rate of the reactions between the oxidants and the reductant was found to be negligibly slow with no systematic dependence on either redox partners. Externally added copper(II) (usually 5 × 10?7 mol dm?3), however, increases the rate of the reduction of 1 and 2 significantly. In the presence of catalytic amount of copper(II), the rate of the reaction is nearly proportional to [RSH] at lower concentration of the reductant but follows a saturation kinetics at higher concentration of the latter for the reaction between 1 and the thiol. Reaction rate was found to be strongly influenced by the variation of acidity of the medium and the observed kinetics suggests that the two reductant species ([Cu(RSH)]2+ and [Cu(RS)]+) are significant for the reaction between 1 and the thiol. The dependence of the rate on [RSH] for the reduction of 2 by the thiol was complex and rationalized considering two equilibria involving the catalyst (Cu2+) and the reductant. The pH rate profile suggests that both the μ‐O protonated [MnIII(O)(OH)MnIV] and the deprotonated [MnIII(O)2MnIV] forms of the oxidant 2 become important. The kinetic results presented in this study indicate the domination of outer‐sphere path. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 129–137, 2004  相似文献   

3.
This study deals with the unprecedented reactivity of dinuclear non‐heme MnII–thiolate complexes with O2, which dependent on the protonation state of the initial MnII dimer selectively generates either a di‐μ‐oxo or μ‐oxo‐μ‐hydroxo MnIV complex. Both dimers have been characterized by different techniques including single‐crystal X‐ray diffraction and mass spectrometry. Oxygenation reactions carried out with labeled 18O2 unambiguously show that the oxygen atoms present in the MnIV dimers originate from O2. Based on experimental observations and DFT calculations, evidence is provided that these MnIV species comproportionate with a MnII precursor to yield μ‐oxo and/or μ‐hydroxo MnIII dimers. Our work highlights the delicate balance of reaction conditions to control the synthesis of non‐heme high‐valent μ‐oxo and μ‐hydroxo Mn species from MnII precursors and O2.  相似文献   

4.
The title dinuclear di‐μ‐oxo‐bis­[(1,4,8,11‐tetra­aza­cyclo­tetra­decane‐κ4N)­manganese(III,IV)] diperchlorate nitrate complex, [Mn2O2(C10H24N4)2](ClO4)2(NO3) or [(cyclam)Mn­O]2(ClO4)2(NO3), was self‐assembled by the reaction of Mn2+ with 1,4,8,11‐tetra­aza­cyclo­tetra­decane in aqueous media. The structure of this compound consists of a centrosymmetric binuclear [(cyclam)MnO]3+ unit, two perchlorate anions and one nitrate anion. While the low‐temperature electron paramagnetic resonance spectra show a typical 16‐line signal for a di‐μ‐oxo MnIII/MnIV dimer, the magnetic susceptibility studies also confirm a characteristic antiferromagnetic coupling between the electronic spins of the MnIV and MnIII ions.  相似文献   

5.
Reactions of nonheme FeIII–superoxo and MnIV–peroxo complexes bearing a common tetraamido macrocyclic ligand (TAML), namely [(TAML)FeIII(O2)]2? and [(TAML)MnIV(O2)]2?, with nitric oxide (NO) afford the FeIII–NO3 complex [(TAML)FeIII(NO3)]2? and the MnV–oxo complex [(TAML)MnV(O)]? plus NO2?, respectively. Mechanistic studies, including density functional theory (DFT) calculations, reveal that MIII–peroxynitrite (M=Fe and Mn) species, generated in the reactions of [(TAML)FeIII(O2)]2? and [(TAML)MnIV(O2)]2? with NO, are converted into MIV(O) and .NO2 species through O?O bond homolysis of the peroxynitrite ligand. Then, a rebound of FeIV(O) with .NO2 affords [(TAML)FeIII(NO3)]2?, whereas electron transfer from MnIV(O) to .NO2 yields [(TAML)MnV(O)]? plus NO2?.  相似文献   

6.
The crystal structure of the low‐spin (S = 1) MnIII complex [Mn(CN)2(C10H24N4)]ClO4, or trans‐[Mn(CN)2(cyclam)](ClO4) (cyclam is the tetradentate amine ligand 1,4,8,11‐tetra­aza­cyclo­tetra­decane), is reported. The structural parameters in the Mn(cyclam) moiety are found to be insensitive to both the spin and the oxidation state of the Mn ion. The difference between high‐ and low‐spin MnIII complexes is that a pronounced tetragonal elongation of the coordination octahedron occurs in high‐spin complexes and a slight tetragonal compression is seen in low‐spin complexes, as in the title complex.  相似文献   

7.
A mononuclear nonheme manganese(IV)–oxo complex binding the Ce4+ ion, [(dpaq)MnIV(O)]+–Ce4+ ( 1 ‐Ce4+), was synthesized by reacting [(dpaq)MnIII(OH)]+ ( 2 ) with cerium ammonium nitrate (CAN). 1 ‐Ce4+ was characterized using various spectroscopic techniques, such as UV/Vis, EPR, CSI‐MS, resonance Raman, XANES, and EXAFS, showing an Mn?O bond distance of 1.69 Å with a resonance Raman band at 675 cm?1. Electron‐transfer and oxygen atom transfer reactivities of 1 ‐Ce4+ were found to be greater than those of MnIV(O) intermediates binding redox‐inactive metal ions ( 1 ‐Mn+). This study reports the first example of a redox‐active Ce4+ ion‐bound MnIV‐oxo complex and its spectroscopic characterization and chemical properties.  相似文献   

8.
Mononuclear metal–dioxygen species are key intermediates that are frequently observed in the catalytic cycles of dioxygen activation by metalloenzymes and their biomimetic compounds. In this work, a side‐on cobalt(III)–peroxo complex bearing a macrocyclic N‐tetramethylated cyclam (TMC) ligand, [CoIII(15‐TMC)(O2)]+, was synthesized and characterized with various spectroscopic methods. Upon protonation, this cobalt(III)–peroxo complex was cleanly converted into an end‐on cobalt(III)–hydroperoxo complex, [CoIII(15‐TMC)(OOH)]2+. The cobalt(III)–hydroperoxo complex was further converted to [CoIII(15‐TMC‐CH2‐O)]2+ by hydroxylation of a methyl group of the 15‐TMC ligand. Kinetic studies and 18O‐labeling experiments proposed that the aliphatic hydroxylation occurred via a CoIV–oxo (or CoIII–oxyl) species, which was formed by O? O bond homolysis of the cobalt(III)–hydroperoxo complex. In conclusion, we have shown the synthesis, structural and spectroscopic characterization, and reactivities of mononuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands.  相似文献   

9.
Mononuclear MnIII–peroxo and dinuclear bis(μ‐oxo)MnIII2 complexes that bear a common macrocyclic ligand were synthesized by controlling the concentration of the starting MnII complex in the reaction of H2O2 (i.e., a MnIII–peroxo complex at a low concentration (≤1 mM ) and a bis(μ‐oxo)MnIII2 complex at a high concentration (≥30 mM )). These intermediates were successfully characterized by various physicochemical methods such as UV–visible spectroscopy, ESI‐MS, resonance Raman, and X‐ray analysis. The structural and spectroscopic characterization combined with density functional theory (DFT) calculations demonstrated unambiguously that the peroxo ligand is bound in a side‐on fashion in the MnIII–peroxo complex and the Mn2O2 diamond core is in the bis(μ‐oxo)MnIII2 complex. The reactivity of these intermediates was investigated in electrophilic and nucleophilic reactions, in which only the MnIII–peroxo complex showed a nucleophilic reactivity in the deformylation of aldehydes.  相似文献   

10.
Proton transfer reactions are of central importance to a wide variety of biochemical processes, though determining proton location and monitoring proton transfers in biological systems is often extremely challenging. Herein, we use two‐color valence‐to‐core X‐ray emission spectroscopy (VtC XES) to identify protonation events across three oxidation states of the O2‐activating, radical‐initiating manganese–iron heterodinuclear cofactor in a class I‐c ribonucleotide reductase. This is the first application of VtC XES to an enzyme intermediate and the first simultaneous measurement of two‐color VtC spectra. In contrast to more conventional methods of assessing protonation state, VtC XES is a more direct probe applicable to a wide range of metalloenzyme systems. These data, coupled to insight provided by DFT calculations, allow the inorganic cores of the MnIVFeIV and MnIVFeIII states of the enzyme to be assigned as MnIV(μ‐O)2FeIV and MnIV(μ‐O)(μ‐OH)FeIII, respectively.  相似文献   

11.
The molecule of the title compound, [Mn4Al(CH3)2(C3H7O2)4I5(C4H8O)], contains one AlIII and four MnII ions. Two Mn atoms are five‐coordinate in the form of a trigonal bipyramid or a square pyramid. The two other Mn atoms are six‐coordinate with an octahedral geometry. The fourcoordinate Al atom is linked to the manganese core by μ‐Oalkoxo bridges, forming an almost planar five‐membered ring.  相似文献   

12.
13.
Reaction of the trivalent uranium complex [((Ad,MeArO)3N)U(DME)] with one molar equiv [Na(OCAs)(dioxane)3], in the presence of 2.2.2‐crypt, yields [Na(2.2.2‐crypt)][{((Ad,MeArO)3N)UIV(THF)}(μ‐O){((Ad,MeArO)3N)UIV(CAs)}] ( 1 ), the first example of a coordinated η1‐cyaarside ligand (CAs?). Formation of the terminal CAs? is promoted by the highly reducing, oxophilic UIII precursor [((Ad,MeArO)3N)U(DME)] and proceeds through reductive C?O bond cleavage of the bound arsaethynolate anion, OCAs?. If two equiv of OCAs? react with the UIII precursor, the binuclear, μ‐oxo‐bridged U2IV/IV complex [Na(2.2.2‐crypt)]2[{((Ad,MeArO)3N)UIV}2(μ‐O)(μ‐AsCAs)] ( 2 ), comprising the hitherto unknown μ:η11‐coordinated (AsCAs)2? ligand, is isolated. The mechanistic pathway to 2 involves the decarbonylation of a dimeric intermediate formed in the reaction of 1 with OCAs?. An alternative pathway to complex 2 is by conversion of 1 via addition of one further equiv of OCAs?.  相似文献   

14.
A new MnIII‐Schiff base complex, [MnL(OH2)](ClO4) ( 1 ) (H2L = N, N′‐bis‐(3‐Br‐5‐Cl‐salicylidene)‐1, 2‐diimino‐2‐methylethane), an inorganic model of the catalytic center (OEC, Oxygen Evolving Complex) in photosystem II (PSII), has been synthesized and characterized by elemental analysis, IR and EPR spectroscopy, mass spectrometry, magnetic susceptibility measurement and the study of its redox properties by cyclic and normal pulse voltammetry. This complex mimics reactivity (showing a relevant photolytic activity), and also some structural characteristics (parallel‐mode MnIII EPR signal from partially assembled OEC cluster) of the natural OEC. The complex 1 was found to rearrange in solution into a crystallographically solved square‐pyramidal complex, [MnLL′] ( 2 ) (HL′ = 6‐bromo‐4‐chloro‐2‐cyanophenol), through a process, which probably liberates radical species (detected by EPR), and provokes a C—N bond cleavage in the ligand. A photo‐radical mechanism is discussed to explain this rearrangement.  相似文献   

15.
In the title one‐dimensional complex, {[MnIII(C9H10NO2)2]Cl}n, the Schiff base ligand 2‐[(2‐hydroxy­ethyl)­imino­methyl]­phenolate (Hsae) functions as both a bridging and a chelating ligand. The MnIII ion is six‐coordinated by two N and four O atoms from four different Hsae ligands, yielding a distorted MnO4N2 octahedral environment. Each [MnIII(Hsae)2]+ cationic unit has the Mn atom on an inversion centre and each [MnIII(Hsae)2]+ cation lies about another inversion centre. The chain‐like complex is further extended into a three‐dimensional network structure through Cl⋯H—O hydrogen bonds and C—H⋯π contacts involving the Hsae rings.  相似文献   

16.
Metal‐superoxo species are involved in a variety of enzymatic oxidation reactions, and multi‐electron oxidation of substrates is frequently observed in those enzymatic reactions. A CrIII‐superoxo complex, [CrIII(O2)(TMC)(Cl)]+ ( 1 ; TMC=1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane), is described that acts as a novel three‐electron oxidant in the oxidation of dihydronicotinamide adenine dinucleotide (NADH) analogues. In the reactions of 1 with NADH analogues, a CrIV‐oxo complex, [CrIV(O)(TMC)(Cl)]+ ( 2 ), is formed by a heterolytic O−O bond cleavage of a putative CrII‐hydroperoxo complex, [CrII(OOH)(TMC)(Cl)], which is generated by hydride transfer from NADH analogues to 1 . The comparison of the reactivity of NADH analogues with 1 and p ‐chloranil (Cl4Q) indicates that oxidation of NADH analogues by 1 proceeds by proton‐coupled electron transfer with a very large tunneling effect (for example, with a kinetic isotope effect of 470 at 233 K), followed by rapid electron transfer.  相似文献   

17.
The title compound, [Mn2O2(C14H18N4)2](ClO4)3·6H2O, contains a mixed‐valent MnIII/MnIV complex. In accordance with a previous report [Collins, Hodgson, Michelsen & Towle (1987). J. Chem. Soc. Chem. Commun. pp. 1659–1660], the structure at 295 K is best described in the space group C2/c, with the complex exhibiting twofold rotational symmetry, and with half site occupancy for one perchlorate anion and several solvent water molecules. At 180 K, the structure is ordered in the subgroup P21/n and is clearly shown to be a hexahydrate, rather than the previously reported trihydrate. The origin of the order–disorder phase transition lies in the thermal motion of the perchlorate anions.  相似文献   

18.
Reactions of CeIII(NO3)3?6 H2O or (NH4)2[CeIV(NO3)6] with Mn‐containing starting materials result in seven novel polynuclear Ce or Ce/Mn complexes with pivalato (tBuCO ) and, in most cases, auxiliary N,O‐ or N,O,O‐donor ligands. With nuclearities ranging from 6–14, the compounds present aesthetically pleasing structures. Complexes [CeIV6(μ3‐O)4(μ3‐OH)4(μ‐O2CtBu)12] ( 1 ), [CeIV6MnIII4(μ4‐O)4(μ3‐O)4(O2CtBu)12(ea)4(OAc)4]?4 H2O?4 MeCN (ea?=2‐aminoethanolato; 2 ), [CeIV6MnIII8(μ4‐O)4(μ3‐O)8(pye)4(O2CtBu)18]2[CeIV6(μ3‐O)4(μ3‐OH)4(O2CtBu)10(NO3)4] [CeIII(NO3)5(H2O)]?21 MeCN (pye?=pyridine‐2‐ethanolato; 3 ), and [CeIV6CeIII2MnIII2(μ4‐O)4(μ3‐O)4(tbdea)2(O2CtBu)12(NO3)2(OAc)2]?4 CH2Cl2 (tbdea2?=2,2′‐(tert‐butylimino]bis[ethanolato]; 4 ) all contain structures based on an octahedral {CeIV6(μ3‐O)8} core, in which many of the O‐atoms are either protonated to give (μ3‐OH)? hydroxo ligands or coordinate to further metal centers (MnIII or CeIII) to give interstitial (μ4‐O)2? oxo bridges. The decanuclear complex [CeIV8CeIIIMnIII(μ4‐O)3(μ3‐O)3(μ3‐OH)2(μ‐OH)(bdea)4(O2CtBu)9.5(NO3)3.5(OAc)2]?1.5 MeCN (bdea2?=2,2′‐(butylimino]bis[ethanolato]; 5 ) contains a rather compact CeIV7 core with the CeIII and MnIII centers well‐separated from each other on the periphery. The aggregate in [CeIV4MnIV2(μ3‐O)4(bdea)2(O2CtBu)10(NO3)2]?4 MeCN ( 6 ) is based on a quasi‐planar {MnIV2CeIV4(μ3‐O)4} core made up of four edge‐sharing {MnIVCeIV2(μ3‐O)} or {CeIV3(μ3‐O)} triangles. The structure of [CeIV3MnIV4MnIII(μ4‐O)2(μ3‐O)7(O2CtBu)12(NO3)(furan)]?6 H2O ( 7 ?6 H2O) can be considered as {MnIV2CeIV2O4} and distorted {MnIV2MnIIICeIVO4} cubane units linked through a central (μ4‐O) bridge. The Ce6Mn8 equals the highest nuclearity yet reported for a heterometallic Ce/Mn aggregate. In contrast to most of the previously reported heterometallic Ce/Mn systems, which contain only CeIV and either MnIV or MnIII, some of the aggregates presented here show mixed valency, either MnIV/MnIII (see 7 ) or CeIV/CeIII (see 4 and 5 ). Interestingly, some of the compounds, including the heterovalent CeIV/CeIII 4 , could be obtained from either CeIII(NO3)3?6 H2O or (NH4)2[CeIV(NO3)6] as starting material.  相似文献   

19.
The complex [MnIV(napbh)2] (napbhH2 = N-(2-hydroxynaphthalen-1-yl)methylenebenzoylhydrazide) reacts with activated ruthenium(III) chloride in methanol in 1 : 1.2 molar ratio under reflux, giving heterobimetallic complexes, [MnIV(napbh)2RuIIICl3(H2O)] · [RuIII(napbhH)Cl2(H2O)] reacts with Mn(OAc)2·4H2O in methanol in 1 : 1.2 molar ratio under reflux to give [RuIII(napbhH)Cl2(H2O)MnII(OAc)2]. Replacement of aquo in these heterobimetallic complexes has been observed when the reactions are carried out in the presence of pyridine (py), 3-picoline (3-pic), or 4-picoline (4-pic). The molar conductances for these complexes in DMF indicates 1 : 1 electrolytes. Magnetic moment values suggest that these heterobimetallic complexes contain MnIV and RuIII or RuIII and MnII in the same structural unit. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that the napbhH2 ligand coordinates in its enol form to MnIV and bridges to RuIII and in the keto form to RuIII and bridging to MnII.  相似文献   

20.
The bitopic ligand 1,2‐bis(1,2,4‐triazol‐4‐yl)ethane (tr2eth) provides an unprecedented short‐distance N1:N2‐triazole bridging of CuI and VIV ions in poly[bis[μ4‐1,2‐bis(1,2,4‐triazol‐4‐yl)ethane]di‐μ2‐fluorido‐tetrafluoridodi‐μ2‐oxido‐dicopper(I)divanadium(IV)], [Cu2V2F6O2(C6H8N6)2]n. The CuI ions and tr2eth linkers afford a two‐dimensional square‐grid topology involving centrosymmetric (tr)Cu(μ‐tr)2Cu(tr) [tr is triazole; Cu—N = 1.9525 (16)–2.0768 (18) Å] binuclear net nodes, which are expanded in a third dimension by centrosymmetric [V2O2F6]2− pillars. The concerted μ‐tr and μ‐O bridging between the CuI and VIV ions allows a multi‐centre accommodation of the vanadium oxyfluoride moiety on a cationic Cu/tr2eth matrix [Cu—O = 2.1979 (15) Å and V—N = 2.1929 (17) Å]. The distorted octahedral coordination of [VONF4] is completed by two terminal and two bridging F ions [V—F = 1.8874 (14)–1.8928 (13) and 2.0017 (13)–2.1192 (12) Å, respectively]. The resulting three‐dimensional framework has a primitive cubic net topology and adopts a threefold interpenetration.  相似文献   

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