The paper presents the results of a study of MIMn(SO4).~ compounds with M I = K, Rb, Cs orT1, and M rI = Cu or Ni, in the interval from room temperature to the melting temperature. All the compounds studied show endo-or exothermic excursions in their DTA curves, corresponding to phase transitions connected with colour changes of the compounds. For M~Cu(SO4)2, where M I is K or T1, several modifications could be prepared at laboratory temperature, probably distortion isomers. No modifications of this type could be prepared, however, for Mt~Ni(SQ)2 compounds.Many complex compounds of Cu(II) and Ni(II) are characterized by a reversible thermochromism. Study of the structures of Cu(II) complexes at different temperatures showed that this thermochromism was connected with changes of the tetragonal distortion of the coordination polyhedra, and in some cases a change of the ligand conformation also took place [1][2][3].It is known from older literature that, depending on the temperature of its preparation, potassium copper(II) sulphate forms three different coloured modifications. This compound is also characterized by thermochromism [5]. Since the literature contains only a few data on the theimochromism structure and other properties of compounds of the type M~Cu(SO4)2 and M2Ni(SO4)2, or they are even entirely missing, this study was aimed at obtaining further experimental information.
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