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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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Borohydride. — By reacting anhydrous rare earth chlorides with lithium borohydride (L1BH4) in THF, their chloroborohydrides (eq. 21) can be isolated [264—266]. In the case of europium no borohydride was
THF
MC1S + 2LiBH4 -► MC1(BH4)2 + 2LiCl (21)
obtained [265] by the same procedure. Instead ЕиСЛз was reduced to the dichloride according to eq. 22.
THF
EuCls + LiBH4 —EuC12 (22)
However, compounds with the empirical formula М(ВШ)з, where M = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, have been reported by Zange [267]. These compounds are presumably of the МНз-ЗВНз type. They can easily be prepared by reacting rare earth methylates with diborane in THF (eq. 23), under nitrogen and are very soluble in THF.
1 Compare this value with that of solvated electron from potassium in
liquid ammonia, gTK-^H, = 2.0012 ± 0.0002 (C. A. Hutchinson and
R. C. Pastor: J. Chem. Phys. 21, 1959 (1953)).
4 Sinha, Europium
60
Compounds of Europium
THF
M(OCH3)3 + 2 (BH3)2 -> MH3 • 3BH3 (23)
Bromate. — Singh [268] has studied the crystal structure of europium bromate, Еи(ВгОз)з * 9НгО and found it to be hexagonal bipyramidal with an а/с ratio of 0.5714. Еи(ВгОз)з * 9НгО was found to be isostruc-tural with Gd(BrOs)s * 9НгО, having an а/с ratio of 0.5690. The sample of europium bromate was prepared by the reaction of europium sulphate with barium bromate and concentration of the filtrate to crystallization point.
Carbonates. — EuS(>4 (p. 69) can be converted to the carbonate according to the metathetical reaction
EuS04 + Na2COs ^ EuCOs + Na2S04 (24)
By adding solid EuS04 slowly to a vigorously boiling solution of NaHCOs and NaOH (in the absence of air) ЕиСОз can be prepared [269] in a lemon yellow crystalline form. It is insoluble in water but dissolve in acids yielding the corresponding Eu2+ salts in the absence of oxygen. The orthorhombic crystals of EuCOs belong [270] to the space group Pmcn (Pnma) (DgS) with a = 5.102, b = 8.422 and c = 6.030 A.
Carbonates of the type Мг(С0з)з are conveniently prepared by homogeneous precipitation from solution using the trichloroacetate ion [271, 272]. Charles [273] has recently used a modified version of
M(Cl3CCOO)3 -f 3H20 + M2(COs)3 + 3C02 + 6CHC13 (25)
this method to prepare rare earth carbonates. Normal carbonates are obtained with La, Nd, Sm, Eu, Gd, Tb, Dy and Ho whilst Ce, Pr, Er, Tm, Yb and Lu give basic carbonates under the same experimental conditions. The normal and basic carbonates have different degrees of hydration e. g., La2(C03)s * 8H2O, М2(С0з)з*2Н20, 8т2(С0з)з-2Н20, Еи2(СОз)з • 2H20, Gd2(COs)3 • 2H20, Т2(С03)з*2Н20, Бу2(С0з)з-2Н20, Ног(СОз)з • 2НгО, Се(СОз)і.о4(ОН)о.92*0.7Н20, Рг(СОз)і.і7(ОН)о.вв*0.5 Н2О, Ег(СОз)і.2з(ОН)о.82 • І.7Н2О, Тт(СОз)і.із(ОН)о.74 • 1.7НгО, Yb(COs)i.oe(OH)o.88 • І.7Н2О and Lu(COs)i.i3(OH)o.74* 1.5НгО. The infrared spectrum of La2(C0s)3 • 8H20 differs from those of other normal carbonates with two molecules of water of crystallization. The infrared spectra of the basic carbonates differ from the normal carbonates and may contain OH and MOH vibrations in addition to the water and carbonate absorption bands.
The thermal decomposition (TGA) curves for La, Nd, Sm, Eu and Gd carbonates show weight plateaus corresponding to the intermediate composition M2O3.CO2.
Inorganic Coordination Compounds
51
The system 35SO|~— C0|~ contaning several trivalent rare earths has been studied [274] and the exchange constants Kr, were measured. A complex species of the type [M(COs)4]5“ was shown to be present in solution. Poluektov and Kononenko [275] showed a displacement of the 393.5 m/i peak of the europium aquo ion to 394.5 mju and a decrease of intensity of about 1.45 times due to complexation with carbonate ion.
M3+ Pr Nd Pm Sm Eu
Kr 0.39 0.448 0.751 0.861 1.47
Halides
Europous Halides
In 1939 Klemm and Doll [276] prepared all the halides of divalent europium and studied the magnetic characteristics of these compounds. The magnetic susceptibilities (Xg) and effective moments (jiett) of the fluoride, chloride, bromide and iodide are tabulated in Table 15. Except for the
Table 15. The magnetic susceptibilities (%g) and effective moments (juett) of europous halides [276]
Halide Temperature Xg juett
(Abs)
EuF2 292 125 7.46
195 187 7.47
90 400 7.42
EuC12 292 119 7.92
90 385 7.90
EuBr2 292 86 7.93
90 281 7.97
Eul2 292 64 7.85
90 211 7.88
fluoride the temperature independent effective moment of ~7.9 is in good agreement with the expected theoretical value of 7.94 for the isoelectronic Gd3+ ion.
Although EuF2 has been reported to be antiferromagnetic, a recent study [276a] by electron spin resonance has shown that this compound is paramagnetic down to 1.6° K. In some samples Lee et al. [276a] observed magnetically ordered inclusions in the paramagnetic host. Electron spin resonance at the X-band indicated a transition temperature of 19.5° K. It is believed that the magnetically ordered inclusions are oxyfluoride. The single crystal samples varied in stoichiometry from EuFi.82 to E11F2.39 with a lattice constant varying from 5.838 to 5.798 A.
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