Properties of the Nickel(III) Complex with 1,4,8,11-Tetraazacyclotetradecane-1,4,8,11-tetraacetate in Aqueous Solution

Abstract

Oxidation of trans-I−NiIIL, or NiIILout, by •OH radicals was carried out by irradiating N2O saturated solutions containing the complex, prepared by mixing equimolar concentrations of the metal ion and the ligand at pH 3.50. The intermediate thus formed has a strong absorption band at 310 nm and is stable for hours. That this unstable complex is a nickel(III) species was verified by EPR spectroscopy and its chemical reduction with ascorbic acid, which was found to be instantaneous. The most striking feature of the oxidation by •OH radicals, which are powerful single electron oxidizing agents, is that it produces a nickel(III) species which is different from the electrochemically produced one as manifested by their absorption spectra and EPR signals. The radiolytically produced nickel(III) species undergoes decarboxylation leading to the production of CO2, CH2O, NiIIL‘ and NiIIL (L‘ = the new ligand produced after oxidative degradation of one of the N-acetate groups of the ligand). The electrochemical oxidation of trans-I−NiIIL, or NiII outL, proceeds via the degradation of two of the acetate arms on average. The yield of CH2O is ∼2.0 mol per mole of the nickel(II) complex in electrochemical oxidations. These observations point out that the two techniques produce different nickel(III) complexes which do not interconvert. The mechanisms leading to the production of NiIIL‘ (oxidation by •OH radicals, radiolytically) and NiIIL‘‘ (electrochemically) differ from that proposed in the literature.

Modern chemistry of nitrous oxide

“…294,295 In addition, the ability of N 2 O to react with solvated electrons attracts attention of researchers engaged in the application of ionising radiation to purification of sewage. It is well known that radiation treatment (cathode-ray or gamma radiation) in combination with other chemical or biological methods for the purification of liquid waste often proves to be convenient for the decomposition of harmful impurities.…”

Luminescence and Magnetic Properties of Tb(III) Complexes with TETA and Synergistic Effect by 1,10‐Phenanthroline

“…On the other hand, less attention has been paid to lanthanide complexes with 1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetraacetate (TETA) . Other metals complexed with TETA include copper, nickel, and uranium . TETA ligands form very stable complexes by encapsulating lanthanide ions through coordination with the four N atoms and four carboxylate O atoms attached to the nitrogen atoms .…”

Kinetics of oxidation of benzenediols by (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)nickel(III) in aqueous acidic media

“…Macrocyclic complexes containing pendant donors are capable of forming intra-or intermolecular coordination. Pendant arms, usually bound to the nitrogen donor atoms, with substituents such as -CH 2 CH 2 NH 2 , -CH 2 COOH [4][5][6], and -CH 2 CH 2 OH [7] that can axially bind to the central nickel ion, shift the redox potential of the complex cathodically, i.e., stabilize the trivalent complex. Stabilization of such Ni(III)-hexaazamacrocyclic complexes has been studied in neutral and slightly alkaline aqueous solutions in the presence of stabilizing anionic ligands through the formation of Ni III LX 2 complexes (where X = F -, SO 4 2-, HPO 4 2-, HCO 2 -, C 6 H 5 CO 2 -, CH 3 CO 2 -and (CH 3 ) 3 CCO 2 -) [8].…”

“…The oxidations of quinol, QH 2 , by Fe III [15][16][17][18], Co III [19][20][21][22], Ce IV [20], and Mn III [23,24], are all rapid reactions. Quinols have also been studied as reductants for IrCl 6 2- [25][26][27][28], V(V) [29], Np(VI) [30] and Mo(CN) 8 3- [31]. An extensive work has been carried out with substitution inert Ni(III) and Ni(IV) macrocyclic complexes as an oxidant [11,[32][33][34][35][36].…”