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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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Table 18. Comparison of precipitation pH values, solubility product and solubility of the rare earth hydroxides from perchlorate [294], nitrate, sulphate and acetate [295] media
56
Compounds of Europium
<D o c3 <D
’fl O <1
O 1 e*
b O o
£ Pi U1
«4H ^ 1 «0
.-fi ft o
o U1 1* o
o CO <N lO vH © r-* CO CO
00 ic CD CO c4 c4 ei d o d ▼H
CO CO 00 (M © CO CO CO CO
ic *o CO c4 d d d o ▼H
o o <M 00 ▼H 00 o i> CO iq CO 05
00 Tji Tj5 ▼H ▼H © o o o d d d
00 1 <N °J CO 00 05 CO t 1C lO 05
00 1 <N ▼H © d o i d d d
Ol o o H H Cl 00 c*
iH 1 ■ CJ 1 Cl 1 Cl ■ Cl 1 Cl 1 Cl 1 Cl 1 Cl 1 Cl 1 Cl 1
1 o i o 1 o 1 o i O 1 O 1 O O I o 1 o 1 o 1 O
▼H ▼H ▼H ▼H ▼H ▼H ■H ▼H ▼H
X X X X X X X X X X X X
tH 00 CO 00 o o <M 05
▼H H Tji oi ▼H ▼H to CO d d CO ▼H
o o o H Cl 09 09 »o «o lO 00
Cl 1 M 1 M 1 Cl 1 Cl 1 Cl I Cl I Cl ■ Cl 1 d 1 Cl ■ Cl I
1 o 1 O 1 o 1 O 1 o 1 o 1 o i o 1 O I O 1 o 1 O
▼H ▼H ▼H ■H ▼H ▼H ▼H i—i
X X X X X X X X X X X X
<N o CO O 05 00 CO o 00
t> c4 CO c4 CO ©4 l> <N 00 CO CO CO
a» iH H Cl 09 CO 00 00
vH N Cl Cl ct Cl Cl Cl Cl Cl Cl Cl
1 1 1 1 1 1 1 1 1 1 1
O o o O o o o O o o o o
fH H ▼H ▼H ▼H ▼H ▼H ▼H ■»H iH tH
X X X X X X X X X *X X X
iH o T* lH CO CO 00 ic o (N 05
fH 00 CO Tj5 t> CO ci CO
til Cl Cl CO CO 00 00
iH 1 CJ ■ Cl 1 Cl 1 Cl 1 Cl 1 Cl 1 Cl I Cl ■ I
1 O i o 1 o 1 o 1 O 1 o i o I O I o 1 O
▼H 1 ▼H ▼H ■H ■H 1 ▼H
X 1 X X X X X X 1 X X X
t- cq °5 00 io 05 CO
▼H co CO 00 d ▼H tj5
CO t> CO o* o 00 o 05 CO o CO CO
OJ t> CO *0 ▼H lO lO ic 00
t> I> I> I> d d d d d
IQ ic o oo io o 00 00 CO
CO ▼H o t> CO I> IO <M 00
l> CO CO CO CO d d d d d
cq o to ▼H <N <N CO CO o o o io
00 CO CO CO 05 00 00 tH CO CO 05
CO CO d d d d d d
o o o CO \o io
1 i CO 05 00 CO | tH tH 00
00 CO d d d d d
c3
vl
<D
Ü
U
P4
§
s
GO
ss
O
w
I
Inorganic Coordination Compounds
57
Few workers [288, 290] have determined the stability constants of rare earth-nitrate complexes. The stability constants for the MX2+ species of several rare earths are compared in Table 19. It will be noticed from the table that the k\ values for the species MX2+ show a definite increase in the light rare earth region reaching the highest value at europium and then slowly decreasing.
Table 19. Stability constants for the MX2+ species of several rare earth nitrate [288] complexes (n = 1.0 at 22° C)
M3+ kt
La 1.3 ± 0.3
Ce 1.3 ± 0.3
Pr 1.7 ± 0.3
Eu 2.0 ± 0.3
Tm 0.7 ± 0.2
Yb 0.6 ± 0.2
Lu 0.6 ± 0.2
The M—O stretching frequency for the anhydrous rare earth nitrates is found to occur [297a] between 237 and 265 cm-1. In the case of Eu(N0s)3 this particular frequency occurs at 239 cm-1.
Oxides and Mixed Oxides
The oxides of the rare earths have long been of great interest to the scientist. Goldschmidt et al. [298] in 1925 made systematic studies on the crystal structures of the trivalent rare earth oxides, M2O3. They classified the oxides into three polymorphic forms (i) hexagonal symmetric (type A), (ii) monoclinic (type B), and (iii) cubic (type C). From time to time various authors have contributed to the knowledge of the rare earth oxides, their polymorphism and formation of mixed oxides. According to Templeton and Dauben [286] the oxides (M2O3 type) of Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu possess a cubic Mn2C>3 type structure. The recent classification of the rare earth oxides by Roth and Schneider [299] differs somewhat from the classic one of Goldschmidt. The Roth-Schneider classification of the M2O3 type oxides is as follows
A-type: La203 and Ndg03 B-type: Sm203, Eu2Os and Gd203
C-type: Dy2Os, Ho203, Er203, Tm203, Yb203, Lu203, Y2Os and Sc203.
They concluded that each oxide exists stably in one form only and that the C forms of Nd203, Sm203, EU2O3 and Gd2C>3 are metastable at lower temperatures. They also believe that all low-temperature forms transform irreversibly to the most stable form at higher temperature. However, Warshaw and Roy [300] have shown that Sm203, EU2O3, Gd2C>3, Tb203 and Dy203 can exist in both B- and C-type polymorphs and the trans-
58
Compounds of Europium
formation is reversible. The B—C transformation temperature of EU2O3 as found by various workers is listed below.
B—C transformation temp, of Eu2Os(° C)
Goldschmidt et al. [298] 800
Roth and Schneider [299] 1075
Warshaw and Roy [300] 1100
Iandelli [301] 1350
Recently, Tsagareishvtli and Gvelesiani [302] measured the heat capacities and enthalpies of Eu20s(B and C form),Tm203 and Yb2C>3 in the temperature range 298—1600° K.
The lattice parameter of C-type EU2O3 was reported as a = 10.842 A by Bommer [303] and a — 10.866 ± 0.005 A by Templeton and Dauben [286]. Guentert and Mozzi [304], and Curtis and Tharp [305] have shown that B-type EU2O3 (see Roth-Schneider classification) and B-type Gd2C>3 are isotypic with B-type Sn^Os. The monoclinic Sm203 (B-type) belongs [306] to the space group 02/m with 12 Sm-atoms and 18 O-atoms in the unit cell. The lattice parameters for polymorphic rare earth oxides obtained by various investigators are collected in Table 20 for comparison.
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