Nickel(II) complexes with Schiff-bases obtained by condensation of 1,3-propanediamine with salicylaldehyde and thiosalicylaldehyde, which present a N₂OS or N₂S₂ co-ordination sphere, were synthesized and studied. The molecular and crystal structure of the asymmetric complex [2-({3-[(3,5-dichloro-2-hydroxyphenyl)methyleneamino]propyl}iminomethylene)benzenethiolato-O,N,N′,S]nickel(II) [Ni(t-salCl₂salpd)] has been determined by X-ray crystallography and shows a tetrahedrally distorted square-planar co-ordination geometry for the nickel center. The complexes were characterized by spectroscopic and electrochemical techniques and the results were used to assess the influence of the donor-atoms on their chemical properties. The results obtained show that the compounds may be reduced, either chemically or electrochemically, to Ni(I) complexes. Reduction potentials were found to be strongly dependent on the tetrahedral distortion of the Ni(II) complexes. EPR parameters for Ni(I) complexes, although not very sensitive to ligand substituents, show a regular dependence on the co-ordination set and the tetrahedral distortion of the complexes.