This work reports the structure investigation of organometallic complexes formation between nickel and cobalt and the extractants Cyanex 272, Versatic 10 and their mixtures. For a better understanding of nickel and cobalt purification from solvent extraction technique, the experiments were carried out with a synthetic leach solution similar to the nickel laterite leach liquor. The coordination number of the metal complexes was evaluated by the ultraviolet–visible (UV–vis) absorption spectra of the organic phases after extraction. The results indicated that the nickel complexes exhibited an octahedral coordination geometry in all investigated organic phases. The cobalt-Versatic 10 complex showed an octahedral geometry, while for Cyanex 272 and the extractants mixture of 15% (v/v) Cyanex 272 and 5% (v/v) Versatic 10 (C15V5), the cobalt complexes presented a tetrahedral structure. Attenuated total reflectance with Fourier transform infrared spectroscopy (ATR/FTIR) was used to identify the interactions between the functional groups of the extractant and the metal ions. Thermogravimetric analysis (TGA) was used to examine the hydration of the complexes. The continuous variation method (Job’s method) was applied to determine the number of molecules involved in the metal-extractant complexes. The Ni-Versatic 10 complex was formed by three molecules of the extractant. For Ni-C15V5 complex, one molecule of Cyanex 272, one of Versatic 10 and two molecules of water formed the complex. For Co-Cyanex 272 and Co-C15V5, the complex was formed with two molecules of Cyanex 272, indicating that in this experimental condition there was no interaction of the extractant Versatic 10 in the extraction. After the stoichiometry of all the organometallic complexes formed had been defined, a structure was proposed for each metal-extractant complex.