Thiosemicarbazone complexes with cobalt(II), nickel(II), and copper(II) metal ions are studied in ethanol solutions. The stability constants of all the identified complexes are calculated, and we found that stability increases from cobalt to copper. The stability of the complex is increased by the presence of a donor group like methyl, whereas it is not affected by the length of the thiosemicarbazone side chain. A further study of the cobalt(II) complexes in the solid state permits the identification of the coordinating atoms. With the help of additional results from electronic spectra structures of the cobalt(II) complexes are proposed.