[en] Results of investigation of Mo⁶⁺ complexing with salicylhydroxamic acid in water-acetone solution by the PMR method are presented. Processes of protonation and complexing are studied on the basis of signal shift of aromatic ring protons in free and bound ligand depending on solution pH. It is shown that depending on solution pH the ligand is in different tautomeric forms. Formation of the complexes of the compositions 1:1 and 1:2 is ascertained. Stability constant of diprotonated complex of the composition 1:2 is calculated