[en] The structure of the complex AgxTBDTPP (tetrabutyl S-dithiopyrophosphate) formed in HNO₃ medium was studied by IR and NMR methods. The complex is involved in the isomerization of TBDTPP in the presence of Ag⁺ and NO₃^- ions. In the IR spectra, the authors observed the disappearance of P-O-P band and the occurrence of new absorption bands associated with P-S-P and P-O bonds. The silver ion is coordinated to the thiophosphoryl group of the isomer molecule. The influence of HNO₃ concentration on complex formation is discussed. The results of the NMR measurements fully confirmed those of the IR spectroscopic measurements. (author)