Four Ni II chloro complexes were identi®ed spectrophotometrically in aprotic media such as DMSO, DMF and propylene carbonate for the ®rst time. An original multiwavelength numerical treatment, based on a Marquardt method, results in the determination of the individual electronic spectra of the mononuclear chloro complexes and of their stability constants, the values of which indicate the presence of rather weak complexes in DMSO and DMF, much stronger in the less solvating propylene carbonate solvent. The overall stability constants calculated for the Ni II chloro complexes are: b 1 52, b 2 140, b 3 160, b 4 210 in DMSO, b 1 60, b 2 110, b 3 900, b 4 15000 in DMF, b 1 1.6´10 9 , b 2 6.4´10 15 , b 3 2.7´10 21 , b 4 5.1´10 26 in PC. The solvent eect is discussed in terms of the quantitative results obtained from this spectrophotometric study and reveals that the stability of the complexes is an inverse function of the donor properties of the solvent. This result illustrates the general behavior of complex formation in dipolar aprotic solvents, i.e. the substitution of one solvent molecule in the inner coordination sphere by the ligand is easier if the solvation strength of the solvent is lower. The solvent eect is also described in terms of the variation of shifts of the calculated absorption maxima for the individual electronic spectra of the chloro complexes. This result is used to identify clearly at which step of coordination the octahedral con®guration of the nickel ion changes to the tetrahedral con®guration, by comparison with the well-known structural properties of these complexes in the solid state.