Molecular and crystal structure of diaqua-sulphato(pyridoxal semicarbazone-ONO)iron(II) and dichloroaqua(pyridoxal semicarbazone-ONO)iron(III) complexes with tridentate ONO pyridoxal semicarbazone ligand, PLSC, of formula [FeII(PLSC)(H2O)2SO4] and [FeIII(PLSC)(H2O)Cl2]Cl is reported. Thermal decomposition of the compounds was followed in argon and air gas carriers. The dequation mechanism is discussed in the view of the crystal structure, emphasizing the complexity of the related parameters and processes.