While additives play an important role in the reactions of samarium iodide, ligand-SmI2 complexation constants are scarce. Here, VIS spectroscopy was harnessed along with NMR to determine the first complexation constant for most of the alcohols and amines used in SmI2 reactions. The second equilibrium constant was determined for selected ligands. In cases where both methods could be applied, in general, a good correlation between the equilibrium constants was obtained.