A novel complex with the stoichiometry [(NH2)2CSSC(NH2)2]2[OsIVCl6]Cl2·3H2O (1) is isolated as a product of the reaction of H2[OsCl6] with thiourea in concentrated HCl under deliberately optimized conditions favoring a partial thiourea oxidation to α,α′-dithiobisformamidinium dication but preserving hexachloroosmate [OsCl6]2 - anions. A bromide analogue [(NH2)2CSSC(NH2)2]2[OsIVBr6]Br2·3H2O 2 is afforded by a similar reaction. A counter synthesis of 1 is accomplished via the direct ion-exchange reaction between H2[OsCl6] and [S2C2(NH2)4]Cl2. Crystal structures of 1 and 2 are unambiguously established by synchrotron radiation-based single-crystal X-ray diffraction at 100 K. The two compounds are isostructural and are crystallized in the orthorhombic space group Cmcm, Z = 4. Unit cell parameters are for 1: a = 11.279(2) Å b = 13.611(3) Å c = 16.731(3) Å; for 2: a = 11.695(2) Å b = 14.005(3) Å c = 17.015(3) Å. The osmium atoms in [OsX6]2− (X = Cl or Br) anions adopt slightly distorted octahedral coordination. The α,α′-dithiobisformamidinium cations are paired into rings via the NH…Cl− hydrogen bonds. The rings are further linked into a spatial network by H-bonds with water molecules and S…Cl nonvalence interactions. © 2018 Elsevier B.V.