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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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Thermal decomposition studies [469] indicate that the onset of weight loss for most of those complexes is rather abrupt. For the Eu3+-complex complete decomposition occurs between 400 and 500° C.
7 Sinha, Europium
98
Compounds of Europium
The stability constants [470] of La- and Ce-8-quinolinol complexes we*e studied in a dioxane-water mixture. Freasier et al. [471] reported the stability and thermodynamic data for La, Ce, Pr, Nd, Sm, Gd and Er complexes of 8-quinolinol-5-sulphonic acid. These complexes were found to be less stable than those of 8-quinolinol and 2-methyl-8-quinolinol.
D. Ligands Having Donors other than Nitroge n j and Oxygens
Apart from a few thio-acids and cyclopentadiene, organic ligands having donors other than nitrogens and oxygens have not been fully investigated. On page 82 the mercaptoacetate (thioglycolate) complex of Eu8+ was mentioned. In Table 38 the stability constant [472, 473] data for several thiocarboxylates viz. mercaptoacetate (MAC, HSCH2 COOH), s-ethylthioghycolate (SETG, H3CCH2-S-CH2COOH), a-mercaptopropio-
(a-MP, H8C—CH—COOH) nate j and p-mercaptopropionate (P-MP,
SH
HS—CH2CH2—COOH) complexes are compared. For these complexes
Table 38. Stability constants of the thiocarboxylates of rare earths
Ligand La Ce Nd Sm Eu Gd Tb Ho Er Yb
MAC
log kx 1.42 1.43 1.49 1.81 1.75 1.64 1.63 1.32 1.28 1.32
log k2 0.70 0.70 0.78 0.90 0.78 0.78 0.78 0.85 0.90 0.90
SETG
logfci 1.70 - 1.72 1.85 1.79 1.70 1.53 1.43 1.42 1.40
log k2 0.85 - 0.85 0.90 0.90 0.90 0.95 0.95 1.00 1.00
a-MP
log kx 1.49 - 1.56 1.83 1.81 1.62 1.60 1.45 1.38 1.43
logfc- 0.70 - 0.78 0.90 0.85 0.78 0.90 0.95 1.04 1.00
ß-MP
log *i 1.82 - 1.94 2.19 2.15 2.03 1.79 1.68 1.70 1.75
log k2 1.26 - 1.30 1.32 1.34 1.32 1.32 1.32 1.38 1.32
log k\ values increase from La8+ to Sm3+. Starting at Eu3+ however, the log k\ values steadily decrease through the series. The values for the stability constants of these thiocarboxylate complexes are very low and are not comparable to those of the hydroxycarboxylates. Evidently no chelate formation takes place in the case of thiocarboxylate ligands. However, a slight increase of log ki values over the carboxylate complexes for a-MP complexes can be conveniently explained assuming the +/ contribution of the methyl group. The larger values of stability constants for the p-MP ligand compared to the a-MP are rather difficult to rationalize. Cydopentadienyl complexes. — Rare earth-tricyclopentadienyl complexes
Coordination Compounds Containing Organic Ligands
99
were prepared by Wilkinson and Birmingham [474, 475] by reacting anhydrous chlorides withNa-cyclopentadiene (NaCsHs) in tetrhydrofuran. Manastybskyj and Dubeck [476] were able to prepare a europium complex having the composition (CsHsJaEu-THF. The room temperature magnetic susceptibility of this mahogany-brown compound (5589 X 10-6 e.g.s.) indicates a trivalent oxidation state for europium. Although a dichloroeuropium-cyclopentedienide complex can be isolated [477] the monochloro europium-dicyclopentadienide is still unknown.
Reaction of metallic europium with cyclopentadiene in liquid ammonia yields [478] a yellow europous-dicyclopentadienyl (eq. 41) complex. Magnetic measurements on this compound (fi = 7.62 Bohr magneton) and its infrared spectrum definitely confirm the divalent state of europium.
Eu + 3CjHj > Eu(C5H5)9 -f C5H8
liq.NH3
(41)
id I
Chapter 6
Spectroscopic Properties of Europium
Part I
Absorption Spectra of the Europium Ion and Its Complexes
Considerable attention has been paid in the past few years to the study of both the absorption and emission spectra of the rare earths. This has been boosted further by the development of the new branch of physics, the Laser (light amplification through stimulated emission of radiation). The study of the optical spectra of ions yields valuable information about the energy levels of normal configurations and of excited states, and also about the nature of their environment. However, a detailed analysis of optical spectra demands a considerable knowledge of theoretical techniques. Recent advances in paramagnetic resonance techniques [479] have enabled us to understand the nature of the ground states of the rare earth ions in crystalline environments.
Although most of the complex chemistry is concentrated in the triva-lent oxidation state of the rare earth ions, it is possible to ionize the rare earths by successive removal of electrons. We have earlier tabulated the ground state electronic configurations (Table 6 and 10) of the rare earth atoms and trivalent ions, and those of the mono- and divalent (M+, M2+) ions1 are given below. In this chapter we shall concern our-
Ion Ce Pr Nd Pm Sm Eu Gd
M+ *■^7/2 m2 8^l/2 10A/2
M2+ 3H4 4^9/2 *#5/2 7^o 8S7/2 °d2
Ion Tb Dy Ho Er Tm Yb Lu
M+ 7H6 ®-^17/2 5*8 4tf13/2 *Ft zsl/2
M2+ ‘#15/2 5Ib 8#e 2F7/2 lS0 2S7l2
selves mainly with the di- and trivalent oxidation states and especially
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