Electrochemical and X-ray studies of nickel(II) Schiff base complexes derived from salicylaldehyde: Structural effects of bridge substituents on the stabilisation of the +3 oxidation state

• Published in: Polyhedron Vol. 19; no. 6; pp. 655 - 664
• Main Authors: Santos, I.C, Vilas-Boas, M, Piedade, M.F.M, Freire, C, Duarte, M.T, de Castro, B
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 30.03.2000; Elsevier
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Crystal structures; Crystallography; Electrochemistry; EPR; Nickel(II)/(III) complexes; Physical Sciences; Schiff base complexes; Science & Technology; Electrochemistry; Crystal structures; Nickel(II)/(III) complexes; EPR; Schiff base complexes; nickel(II)/(III) complexes; electrochemistry; MOLECULAR-STRUCTURE; PARAMETERS; crystal structures; LIGANDS; SALEN; ELECTRODE; REDOX; COBALT(II) COMPLEXES; UNITS
• ISSN: 0277-5387
• DOI: 10.1016/S0277-5387(00)00300-4

The oxidative chemistry of three Ni(II) complexes with Schiff base ligands derived from salicylaldehyde and diamines with different steric demands, N, N′-2-methylpropane-2,3-diyl-bis(salicylideneiminate)nickel(II) ( 1), N, N′-1,2-cyclohexyl-1,2-dyil-bis(salicylideneiminate)nickel(II) ( 2) and N, N′-2,3-dimethylbutane-2,3-diyl-bis(salicylideneiminate)nickel(II) ( 3), was studied by cyclic voltammetry and chronoamperometry in N, N′-dimethylformamide and (CH 3) 2SO. The electrogenerated species were characterised by EPR spectroscopy. All three complexes exhibited metal-centred oxidised processes and the oxidised products were low-spin six-coordinate Ni(III) species (d z 2 ground state) with two solvent molecules axially coordinate. Addition of pyridine resulted in the replacement of solvent molecules with no changes in the ground state. The crystal structures of compounds 1 and 3 were determined from single crystal X-ray diffraction data, and the crystal packing for any of the complexes did not show any systematic parallel orientation of any part of the molecules. X-ray structural data for the Ni(II) complexes provided a rationale for the E 1/2 values obtained in the oxidation processes and for the relative energy of the low-lying excited duplets of the electrogenerated Ni(III) species.