An IR-spectroscopy method is used to examine the state of nonane diluted bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HR) in the presence of various electron-donor additives (L). Trioctyl amine (TOA), n-octanol, trioctylphosphine oxide (TOPO), tributylphosphate (TBP), and triisobutylphosphine sulfide (TIBPS) were used as additives. The formation of hydrogen bonded complexes (H-complexes) via proton transfer and a TOAH + R − ion pair was shown to occur in the system containing HR and TOA. For the other additives, except n-octanol, during the formation of the H-complexes, hydrogen bonding without proton transfer takes place. In the HR and n-octanol mixture H-complexes having a structure in which the acid exhibits both proton and electron-donor properties are formed. The concentrations of the monomers (C HR ) and the activity coefficients for the dithiophosphinic acid (γ HR(tot) ) in the presence of the additives were calculated. It was shown that C HR and γ HR(tot) depend essentially on the type of additive and that their values decrease when passing from n-octanol to TOA. The strength of the interaction between HR and L decreases in the series TOA > TOPO > TBP > TIBPS > n-octanol. This series coincides with the basicity series of the additives. An antagonistic effect takes place when zinc is extracted with the HR and L mixture, where L is the trialkyl amine (TAA), the trialkyl phosphine oxide (TAPO), TBP, and n-octanol. A decrease in extraction is observed in the series TAA > TAPO > TBP > n-octanol. This series coincides with the series for decreasing HR activity in the presence of additives. Thus a decrease in the extractant activity resulting from the interaction between HR and L is the determinant factor during zinc extraction with bis(2,4,4-trimethylpentyl)dithiophosphinic acid in the presence of the electron-donor additives.