Anomalous magnetic properties in the solid state of salts of the Bis[2-(2-pyridylamino)-4-(2-pyridyl)thiazole]iron(II) ion

Abstract

The magnetism of nine salts containing the bis[2-(2-pyridylamino)-4-(2- pyridyl)thiazole]iron(II) ion has been investigated over the temperature range c. 100-350�K. All salts were obtained hydrated and in some instances the magnetism of the anhydrous salts was also investigated. The magnetism was found to be markedly dependent on the anion of the salt. Two distinct classes of compounds were recognized- those obeying a simple Curie-Weiss law and having magnetic moments corresponding to the expected value for spin-free iron(II); and those whose temperature dependence of magnetism was found to be anomalous. For these compounds the magnetic moments varied from almost spin-paired to almost spin-free values. The anomalous behaviour has been qualitatively interpreted in terms of a thermal equilibrium between the nearly equi-energetic spin-paired and spin-free states of the iron atom. The differences in the behaviour of different salts have been ascribed to differences in crystal lattice forces. The presence of hydrate water in the crystal lattice has been shown in some instances to have a marked influence on the magnetism. Two magnetically isomeric forms of the anhydrous chloride salt have been obtained. It has been shown that there is an association between the magnetism and colour of the compounds.