Heat capacity of iron(II) and cobalt hexafluorosilicates from 8 to 298 K

Abstract

The heat capacity, Cp, of the salts FeSiF6· 6H2O and CoSiF6· 6H2O has been measured from ca. 8 to ca. 298 K. Below ca. 35 K Cp of the iron compound is anomalously high compared with Cp of the cobalt salt and of the four other fluorosilicates for which Cp has been determined. This anomaly is a Schottky effect which arises from the triplet nature of the ground state of the Fe(H2O)2+6 ion in the fluorosilicate. The measured Cp values of the iron salt are shown to be quantitatively consistent with the information about the triplet ground state derived from magnetic susceptibility studies, which therefore supports the conclusion reached from the magnetic work that the octahedral cation in the salt FeSiF6· 6H2O is distorted by being compressed along the crystal axis.