Europium(II) oxalate is an inorganic compound of europium in the +2 oxidation state and the oxalate ion, with the formula EuC2O4. It is a reddish-brown solid and is known both as an anhydrous compound and as a monohydrate, EuC2O4·H2O.
Preparation Europium(II) oxalate monohydrate can be prepared by reacting europium(II) sulfate with ammonium oxalate in aqueous solution:
EuSO4 + (NH4)2C2O4 + H2O → EuC2O4·H2O↓ + (NH4)2SO4
The preparation must be carried out under conditions that preserve europium in the divalent state.
Properties Hydrate and structure Europium(II) oxalate forms a monohydrate that is isomorphous with strontium oxalate monohydrate.
The crystal water is lost on heating to about 160 °C, producing anhydrous EuC2O4 without oxidation of Eu2+ to Eu3+.
This retention of divalent europium during dehydration distinguishes it from many other europium compounds, in which oxidation to Eu(III) can occur relatively easily.
Magnetic properties Both anhydrous europium(II) oxalate and its monohydrate order magnetically only at very low temperature.
Mössbauer and magnetic measurements found transition temperatures of approximately 1.9 ± 0.1 K for anhydrous EuC2O4 and 2.8 ± 0.1 K for EuC2O4·H2O.
The 151Eu Mössbauer isomer shift is about −13.9 mm/s for both forms relative to a 151Sm2O3 source, consistent with divalent europium.
Uses Europium(II) oxalate can be used as a precursor for preparing europium monochalcogenides such as europium(II) sulfide, europium(II) selenide and europium(II) telluride.
Pink reported that europium oxalate was a more suitable starting material for obtaining phase-pure EuS, EuSe and EuTe than europium chloride.
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