SYNTHESIS, STRUCTURE AND OXIDATION OF [NIL1]2+ [L1=5-(4-AMINO-2-AZABUTYL)-5-METHYL-3,7-DIAZANONANE-1,9-DIAMINE] - EVIDENCE FOR REARRANGEMENT WITHIN THE COMPLEXED NICKEL(III) SPECIES

The ligand 5-(4-amino-2-azabutyl)-5-methyl-3,7-diazanonane-1,9-diamine, L1, has been synthesised and a nickel(II) complex, [NiL1]Br2, characterized by X-ray crystallography (monoclinic, space group P2(1)/n, a = 14.143, b = 9.618, c = 13.552. beta = 106.14-degrees, Z = 4, R = 0.0429, R' = 0.0418). The cation adopts a distorted octahedral geometry typical of similar nickel(ii) complexes. The complex [NiL1]2+ can be oxidized, under neutral conditions, either electrochemically or by use of S2O82- to a moderately stable nickel(III) complex. By monitoring the reaction with S2O82- using ESR spectroscopy, evidence has been obtained for three species, with characteristic ESR signals, g1, g2 and g3. These represent the initial nickel(III) complexed ion and two structural modifications formed through substitution by sulfate. The final product is a distorted tetragonal complex with axial sulfate ligation. These reactions represent a rare example of ligand substitution at an NiN63+ chromophore. A second-order rate constant of 0.26 +/- 0.05 dM3 mol-1 s-1 for the reaction of [NiL1]2+ with S2O82- has been obtained.