The state of iron atoms and their interatomic interactions were investigated by the method of magnetic dilution in Bi₂SrNb_2−2xFe_2xO_9−δ with a layered perovskite-like structure. It was found that the solid solutions are characterized by increased values of the magnetic moment of iron atoms, compared with purely spin values of Fe(III). This was explained by the presence of exchange-bound aggregates of Fe(III) atoms with antiferro- and ferromagnetic types of exchange. The dependencies of the exchange parameters and cluster distribution on the iron content of Bi₂SrNb_2−2xFe_2xO_9−δ solid solutions were calculated.