Octahedral and tetrahedral configuration changes of nickel(II) chloro complexes from spectrophotometric studies in aprotic solvents

Four NiII chloro complexes were identified spectrophotometrically in aprotic media such as DMSO, DMF and propylene carbonate for the first 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 NiII chloro complexes are: β1=52, β2=140, β3=160, β4=210 in DMSO, β1=60, β2=110, β3=900, β4=15000 in DMF, β1=1.6×109, β2=6.4×1015, β3=2.7×1021, β4= 5.1×1026 in PC.