A Moessbauer spectroscopic study of the iodides of europium

The enthalpy of formation of europium(III) iodide from its elements at 298 K has been estimated to be -534 kJ mol-1 lending encouragement to attempts at the preparation of this substance. Accordingly some reactions which might be expected to lead to its formation have been examined. Thermal decomposition of europium(III) iodide nonahydrate in a closed system gives europium(II) iodide monohydrate and then the impure anhydrous di-iodide. Displacement of water by ammonium iodide in an open system under vacuum leads only to anhydrous europium(II) iodide and heating the latter with excess iodine does not unequivocally yield any anhydrous tri-iodide. A linear relation is observed between the Moessbauer spectroscopic isomer shift and ionicity for the anhydrous europium(II) halides. (author)