Thermal properties of four Co/Fe complexes based on amine-type and cyanido ligands

Four ionic cobalt hexacyanidoferrate(II) complexes with formulae [Co(NH3)6]4[Fe(CN)6]3·12H2O (1) [Co(NH3)6]2Cl2[Fe(CN)6]·4H2O (2), [Co(dien)2][Fe(CN)5(CNH)]·3H2O (3) and [Co(dien)2]4[Fe(CN)6]3·23H2O (4), where dien is 1,4,7-triazaheptane, have been synthetized and chemically and spectroscopically (IR and Mössbauer) characterized. X-ray single-crystal study of complex 3 revealed that its crystal structure is ionic and is built up of mer-[Co(dien)2]3+ complex cations, scarce [FeII(CN)5(CNH)]3− complex anions with one protonated cyanide group and water molecules of crystallization. The thermal properties (TG and DTA) on air of all complexes were studied. The thermal decompositions of all studied complexes are stepwise starting with dehydration at 60 (1), 130 (2), 70 (3) and 55 °C (4). Further decomposition of the respective complexes involves (with possible overlapping of the respective processes) deamination and redox decomposition of the cyanido ligands yielding metals which upon further heating are re-oxidized. The solid residue for 1 was identified using powder X-ray diffraction, SEM and EDX methods as inverse spinel oxide.