TY - JOUR
T1 - Oxidation of first-row bivalent transition-metal complexes containing ethylenediaminetetra-acetate and nitrilotriacetate ligands by free radicals
T2 - A pulse-radiolysis study
AU - Lati, Joseph
AU - Meyerstein, Dan
N1 - Funding Information:
In the copper complex :Lfurther electron transfer, or a direct two-electroxitransfer, is expected yielding Cu' (N=CH,) which is tlicnhydrolyzed. The exact fate of NiLL(NCH2') is difficult todetermine since the rate-determining step is the electron-transfer reaction producing this radical. Plausibledecomposition paths of similar radicals were discussedfor the corresponding iron(ir) and cobalt(r1) radical^.^^?^^Similar meclianisnis for the thermal oxidative tiegrad-ation of edta by Ce1V,44 or photochemical degradation of[Fe(edta)] - and [Co(edta)]--,42y43 have been proposed.Another plausible mechanism for the oxidation of theligand by the central cation is the reverse of reaction (20).This mechanism was ruled out for the decomposition ofcopper(r1r) complexes containing amino-ligands, since[Cu(en),I3+ (en = ethylenediamine) decomposes slowlyvia a second-order process.26 Furthermore, the resultsindicated that complexes containing a-, p-, and y-amino-acids and a-aminoisobutyric acid as ligands decomposedat similar rates, suggesting that the rate-deterniining stepis the electron transfer from the carboxylateWe therefore believe that the mechanism of decom-position is better described by tlie electron-transfermechanism. *( P ) Mcchanisnas of decomposition of the free Yadicdsobtained by hydrogen abstvactiopa from the ligaiads. This4O C. H. Langforcl and V. S. Sastri, ' Reaction Mcchanisms inInorganic Chemistry,' ser. 1, vol. 9, M.T.P. Intrrnat. IZcv. Sci.,Butterworths, Oxford, 1972, p. 203.41 P. Natarajan and J. I;. Endicott, J . I'liys. Clieiq~., 1973, 77,1823, 2049.42 P. Natarajan and J. I;. Endicott, J . Anger. Chcm. Suc., 1973,95, 2740.43 J. Lati and D. Meyerstein, Inorg. Chern., 1972, 11, 2393.44 S. R. Hanna, W. R. Caroll, S. A. Attiya, and W. €1. Webb,2. Natuvforsch., 1976, B30, 409 and refs. thereinIt118 J.C.S. Dalton(compare M = Co to Mn or Zn). (iv) We have no explan-ation at the moment for the first-order process observed[MII(NR1R2[CH(OH)COd-]}]in these systems. The most probable path would besome hydrolysis of the [M11{NR1R2(CHCOb-)}] radicals.However, the kinetic data or the product analysisavailable give no indication as to the exact nature of thisprocess.H,C[MIT(NR1R2H)] + CHOC0,- (or CH,O + CO,) (24)subject was not the aim of this study but several pointsshould be noted. (i) All these intermediates react with0, in a fast reaction indicating that they are free radicals.(ii) In all the systems studied, [MII{NR1R2(tHC0O-))](M = Zn, Mn, or Co), the decomposition reaction involvestwo steps, a fast first-order process followed by a slowersecond-order process. (iii) The second-order processinvolves most probably a disproportionation reaction (23)as would be expected for similar aliphatic radicals.Such a mechanism is also in agreement with the final2 [MII{NR1R2(CHCOb-)}] PHZO[MIJ{NR1R2(CH2COO-)}] +[ MIr(N R1R2 [C H (0 H) CO 0 -1 }] (23)products ob~erved.~~-,~ Reaction (23) is most probablyfollowed by (24). It is of interest to note that the natureof the central cation affects the rate of reaction (23)We thank Dr. M. S. Matheson for his interest and forreading the manuscript, Dr. I. Michaeli for encouragement,Mr. Y . Ogdan for the care in operating the LINAC and themaintenance of the electronic equipment, and Miss M. Haikfor technical assistance. This study was partially financedby a grant from the United States-Israel Binational ScienceFoundation, Jerusalem, Israel.[7/1157 Hrceii~ed, 4th July, 1977
PY - 1978
Y1 - 1978
N2 - The kinetics of reaction of OH radicals with the ligands (L) ethylenediaminetetra-acetate (edta) and nitrilotriacetate (nta), and their complexes [ML] (M = ZnII, CuII, NiII, CoII, FeII, and MnII), have been studied. All these reactions have similar rate constants, although a hydrogen-abstraction reaction from the ligand is observed for the free ligands and their complexes with ZnII, MnII, and CoII. For [Co(edta)]2- a partial oxidation to [Co(edta)]- is observed. On the other hand, when M = NiII, CuII, or FeII the metal is oxidized by the OH radicals. The reasons for these observations are discussed in detail. The spectra, and kinetics of decomposition, of the unstable intermediates formed by the reactions of the OH radicals are reported and discussed. The reactions of nickel(III) complexes with I-, Br-, and O2 are reported. The kinetics of oxidation of the complexes (M = FeII, MnII, or CoII) by [O2]-., .O2CH2CMe2OH, [Br2]-., [(NCS)2]-., and [I2]-., the latter only with M = FeII, have also been studied. The kinetics indicate an inner-sphere mechanism for these reactions. The kinetics of hydrolysis of [MnIIIL(X)] and [CoIIIL(X)] thus formed are reported.
AB - The kinetics of reaction of OH radicals with the ligands (L) ethylenediaminetetra-acetate (edta) and nitrilotriacetate (nta), and their complexes [ML] (M = ZnII, CuII, NiII, CoII, FeII, and MnII), have been studied. All these reactions have similar rate constants, although a hydrogen-abstraction reaction from the ligand is observed for the free ligands and their complexes with ZnII, MnII, and CoII. For [Co(edta)]2- a partial oxidation to [Co(edta)]- is observed. On the other hand, when M = NiII, CuII, or FeII the metal is oxidized by the OH radicals. The reasons for these observations are discussed in detail. The spectra, and kinetics of decomposition, of the unstable intermediates formed by the reactions of the OH radicals are reported and discussed. The reactions of nickel(III) complexes with I-, Br-, and O2 are reported. The kinetics of oxidation of the complexes (M = FeII, MnII, or CoII) by [O2]-., .O2CH2CMe2OH, [Br2]-., [(NCS)2]-., and [I2]-., the latter only with M = FeII, have also been studied. The kinetics indicate an inner-sphere mechanism for these reactions. The kinetics of hydrolysis of [MnIIIL(X)] and [CoIIIL(X)] thus formed are reported.
UR - https://www.scopus.com/pages/publications/37049096538
U2 - 10.1039/DT9780001105
DO - 10.1039/DT9780001105
M3 - ???researchoutput.researchoutputtypes.contributiontojournal.article???
AN - SCOPUS:37049096538
SN - 1472-7773
SP - 1105
EP - 1118
JO - Journal of the Chemical Society. Dalton Transactions
JF - Journal of the Chemical Society. Dalton Transactions
IS - 9
ER -