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Europium - Sinha S.P.

Sinha S.P. Europium - Springer-Verlag, 1967. - 88 p.
Download (direct link): europium1967.djvu
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Oxyhydroxide. — Europium oxyhydroxide, EuOOH, was first reported by Rau and Glover [293] as an intermediate in the thermal decomposition of Eu(OH)3. They also investigated it’s crystal structure and thought it to be orthorhombic. The crystal parameters reported by these authors are a — 8.235, b = 11.626 and c = 7.453 A. Recent investigation by Barnighausen [336], however, showed the compound to be monoclinic with a = 6.109 ± 0.005, b = 3.748 ± 0.003, c = 4.347 ± 0.0003 A and {} = 108.6 ± 0.2°. He obtained this compound as an intermediate during the thermal decomposition of Eu(OH)2 • H2O.
Oxysulphide. — Europium oxysulphide EU2O2S, can be prepared [337] by heating the oxide at 800° in a stream of CS2, and reducing the product
Inorganic Coordination Compounds 69
by hydrogen at a higher temperature (1200°). EU2O2S belongs to the space group D\d—P 3 m and has the following lattice constants a = 3.8716 ± 0.0002, c = 6.6856 ± 0.0007 A.
Phosphate. — In addition to being found in nature the phosphates of the rare earths have been synthesized in the laboratory by fusion methods [338, 339], hydrothermal crystallization from aqueous solutions [340, 341] and chemical reactions [28, 263, 342]. The phosphates of the lighter rare earths (La—Gd) have the monoclinic monazite structure whilst those of heavier ones (Dy—Lu) have the tetragonal xenotime structure. Terbium orthophosphate exhibits dimorphism. Feigelson [343] has synthesized single crystals of some rare earth orthophosphates using molten lead pyrophosphate (Pb2P20?) as solvent, and studied their crystal structures. The lattice constants for EUPO4 reported by Feigelson [343] are a = 6.63, b = 6.83, c = 6.31 A and 0 = 103° 05'.
Sulphate.—Europous sulphate, E11SO4, can be conveniently prepared by reducing Eu3+ to Eu2* and treating with H2SO4. The reduction is best done in a Jones reductor, and the following proceedure is recommended [344]. A Jones reductor 2 cm in diameter and 40 cm high containing amalgamated zinc is flushed out with 200 ml 0.1 M HC1 enough acid being left to cover the amalgam. The outlet of the reductor is dipped into a vessel containing 50 ml of 8 M H2SO4 under an inert atmosphere. About 200 ml of a 0.1 M EuCl3 solution is passed slowly through the reductor, and then followed by washing with 150 ml of 0.1 M HC1. A feathery white precipitate of EuS04 (a-form) is first formed which can be converted to the more stable /9-form by heating at 80° under a carbon dioxide atmosphere. This procedure gives about a 90% (4.4 gm) yield of pure E11SO4. The /?-form of EuS04 unlike the a-form is only slightly soluble in H2SO4 solution. Recently Sklyarenko and Stroganova [345] measured the solubility of E11SO4 with great accuracy using radioactive isotopes and obtained a value of 0.0185 g/1 at 20° C. This value is smaller by three orders of magnitude than that for Eu2(S04)3 -8H20. However, the solubility of EuSC>4 compares well with BaSC>4 (0.0022 g/1), SrSC>4 (0.1143 g/1) and CaS04 (2.080 g/1). The microcrystalline EuSC>4 salt has a density [344] of 4.98 at 25° C. Sklyarenko et al. [346] however, reported the density as 5.38.
EuS04 belongs [270] to the space group Pnma {D™h). The orthorhombic lattice constants are a = 8.333, b = 5.326, and c = 6.861 A. Sklyarenko et al. [346] have recently redetemined the lattice constants and report the following values, a = 8.364, b = 5.356 and c = 6.871. They claim a high degree of purity for their sample. They have also studied the thermal decomposition of EuSC>4, and found that it is stable up to 550° C. Above this temperature it is oxidized and the thermal reaction can be represented
70
Compounds of Europium
as follows
550° 750°
2EuS04 _> Eu20(S04)2 Eu202S04 (33)
• 12^2 —wUj
The end product, EU2O2SO4, has been identified completely reliably, but the presence of Eu20(S04)2 was inferred only by chemical means. These workers tend to disagree ever the complete oxidation of EuSC>4 to Eu2(S04)3. The high temperature decomposition of Eu202S04 may possibly be represented by analogy [350] as
Eu202S04 ——>■ Eu2Os (34)
—b\J3
Measurement [347] of the magnetic susceptibility of EuS(>4 gave a value Xg(106) = 21900. This value compares reasonably well with that for Gd2(S04)3 ■ 8H2O i.e. 25710.
EU2O3 dissolves in sulphuric acid to give europic sulphate, which crystallizes with eight molecules of water of crystallization, Eu2(S04)3 • 8H2O. The crystals belong [348] to one of the two space groups
—A2ja or C\—Aa. The latticc constants are a = 18.25 ± 0.04, b = 6.74 ± 0,02, c = 13.49 ± 0.03 A, and ft = 102° 15' ± 15', and the unit cell consists of four formula units.
The formation constants for the europium sulphate, EuSOJ, complex at various ionic strengths {fi = 0.05 to 0.1) were reported by Manning and Monk [349]. Recently, Bansal et al. [290] and Sekine [291] have reinvestigated the sulphate system along with their studies on several other inorganic ligands. A comparison of the stability constants of the sulphate complexes of Eu3+ and Am3+ is presented in Table 24. Here again, as for the chloride, the k values for Eu3+ are comparable in magnitude with
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