Europium(III) acetate explained

Europium(III) acetate is an inorganic salt of europium and acetic acid with the chemical formula of Eu(CH₃COO)₃. In this compound, europium exhibits the +3 oxidation state. It can exist in the anhydrous form, sesquihydrate and tetrahydrate.^[1] Its hydrate molecule is a dimer.^{[2] [3]}

Preparation

Europium acetate can be obtained by stirring reaction of acetic acid and europium oxide under heating, and then diluting with water and crystallizing:^[4]

Eu₂O₃ + 6 CH₃COOH → 2 Eu(CH₃COO)₃ + 3 H₂O

Europium can also directly participate in the reaction:^[5]

2 Eu + 6 CH₃COOH → 2 Eu(CH₃COO)₃ + 3 H₂↑

Properties

Physical properties

The anhydrous europium acetate crystallizes monoclinically in the space group C2/c (space group no. 15) with the lattice parameters a = 1126.0(3), b = 2900.5(6), c = 799.1(2) pm and β = 132.03(2)° with four formula units per unit cell. The sesquihydrate crystallizes monoclinically in the space group Cc (No. 9) with the lattice parameters a = 1608.7(2), b = 1665.6(2), c = 839.1(1) pm and β = 115.75(9)° with four formula units per unit cell. The heat capacity at 280 K is 803±16 J/(mol∙K).

Chemical properties

Europium acetate can be dissolved in water, acidified with acetic acid, and the compound of divalent europium [Eu(CH₃COO)₂(CH₃COOH)(H₂O)₂] can be obtained by electrochemical reduction.^[6]

Europium acetate can be crystallized in excess glacial acetic acid to give the salt [Eu(H(CH₃COO)₂)₃](H₂O).^[5]

Decomposition

Europium acetate can be decomposed by heating, and the hydrate first loses water to obtain anhydrous, and then passes through basic acetate EuOCH₃COO, basic carbonate Eu₂O₂CO₃, and finally obtains europium oxide.^[7] The tetrahydrate of europium acetate decomposes in air over 6 stages to europium oxide.

Stage 1 at 135 °C:

Eu(CH₃COO)₃·4H₂O → Eu(CH₃COO)₃·H₂O + 3H₂O

Stage 2 at 170 °C:

Eu(CH₃COO)₃·3H₂O → Eu(CH₃COO)₃·0.5 H₂O + 0.5 H₂O

Stage 3 at 210 °C:

Eu(CH₃COO)₃·0.5H₂O → Eu(CH₃COO)₃ + 0.5 H₂O

Stage 4 at 310 °C:

Eu(CH₃COO)₃ → EuO(CH₃COO) + C₃H₆O + CO₂

Stage 5 at 390 °C:

2EuO(CH₃COO) → Eu₂O₂[CO₃] + C₃H₆O

Stage 6 at 670 °C:

Eu₂O₂[CO₃] → Eu₂O₃ + CO₂

Notes and References

1. The Salts of Europium. 1939-09-01. 10.1021/ja01878a055. Journal of the American Chemical Society. 2455–2456. 61. 9. 0002-7863. 2019-02-01. Herbert N. McCoy.
2. P. Starynowicz . 1995-12-01 . Structure and spectroscopy of diaqua(μ3-acetato)(acetato-O)(acetic acid-O)europium(II), [Eu(OAc)2(AcOH)(H2O)2] ]. Polyhedron . 14 . 23 . 3573–3577 . 10.1016/0277-5387(95)00174-Q . 0277-5387 . 2019-02-01.
3. Australian Journal of Chemistry. 52. 6. en. 0004-9425. 1999. 437. 10.1071/CH98041. Structural Systematics of Rare Earth Complexes. X ('Maximally') Hydrated Rare Earth Acetates. 2020-01-18. Cameron J. Kepert, Lu Wei-Min, Peter C. Junk, Brian W. Skelton, Allan H. White.
4. Tang, Huian; Liu, Yanzhi; Zhao, Aiping. A preparation method of europium acetate [Patent]. CN104387254A. 2015.
5. Sonia Gomez Torres, Ingo Pantenburg, Gerd Meyer . 2006 . Direct Oxidation of Europium Metal with Acetic Acid: Anhydrous Europium(III) Acetate, Eu(OAc)3, its Sesqui-hydrate, Eu(OAc)3(H2O)1.5, and the "Hydrogendiacetate", [Eu(H(OAc)2)3](H2O) ]. Zeitschrift für anorganische und allgemeine Chemie . en . 632 . 12–13 . 1989–1994 . 10.1002/zaac.200600154 . 1521-3749 . 2019-02-01.
6. Structure and spectroscopy of diaqua(μ3-acetato)(acetato-O)(acetic acid-O)europium(II), [Eu(OAc)2(AcOH)(H2O)2]]. 14. 23. 3573–3577. 1995-12-01. 0277-5387. 10.1016/0277-5387(95)00174-Q. Polyhedron. 2019-02-01. P. Starynowicz.
7. Ogawa M, Manabe K. Thermal Decomposition of Europium (III) Acetate Tetrahydrate （酢酸ユウロピウム(III)4水和物の熱分解）. Journal of the Ceramic Society of Japan, 1988, 96(1117): 890-893.