Synthesis and structure of some Co(III)–Bi(III) heterometallic complexes: [Co(NH3)5NCS][Bi(EDTA)]2·4H2O, trans-[Co(NH3)4(NO2)2][Bi(EDTA)(H2O)]·2H2O, and [Co(NH3)4(CO3)][Bi(EDTA)]·3H2O

Three Co(III)–Bi(III) heterometallic complexes: pentaammine-thiocyanato-cobalt(III) ethylenediaminetetraacetatobismuthate(III) dihydrate, [Co(NH3)5NCS](Bi(EDTA)]2·4H2O, (I), trans-tetraamminedinitrocobalt(III) ethylenediaminetetraacetato(aqua)bismuthate(III) dihydrate (trans-[Co(NH3)4(NO2)2][Bi(EDTA)(H2O)]·2H2O, (II), and tetraammine(carbonato)-cobalt(III) ethylenediaminetetraacetatobismuthate(III) trihydrate [Co(NH3)4(CO3)][Bi(EDTA)]·3H2O, (III) were synthesized and characterized by X-ray crystallography. Thermal decomposition of the complexes proceeds in several stages, dehydration, deamination, and finally pyrolysis of ligands leaving sillenite and traces of Co3O4 in the case of (II) and (III), and an unknown phase in the case of (I). Complex (II) is thus a potential precursor for Bi/Co mixtures in the ratio of 1/1.