DSC Investigations of the Phase Transitions of [M(NH3 )6](ClO4)2 and [M(NH3)6](BF4)2 , where M = Co and Cd

Abstract

Solid polymorphism of four compounds of the type [M(NH3)6](XY4)2 , where M = Co2+ or Cd2+ , and XY4 = ClO4 - or BF4 - has been studied at 100 -300 K by DSC. One or two phase transitions of the investigated compounds have been found. For the compounds with M = Co the phase transitions have not yet been described in the literature. For the compounds with M = Cd the phase transition-temperature is in good agreement with the results obtained by NMR and EPR. Generally, for [M(NH3)6](BF4)2 compounds (M = Mg, Fe, Co, or Ni) the phase transition temperature TCl is lower than that for the corresponding [M(NH3)6](ClO4)2 , but for compounds with M = Cd it is higher. However, the enthalpy and entropy changes at the TCI phase transitions of [M(NH3)6](BF4)2 are always lower than those for [M(NH3)6](ClO4)2. Moreover, for the compounds of this type a correlation between the transition temperature TCl and the crystal lattice parameter a has been found.