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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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(c) It often happens that on complexation some of the absorption bands of the rare earths are intensified and frequently the extinction coefficient (e) for such hypersensitive bands is an order of magnitude higher in comparison with the aquo ion. It should be pointed out here that we have especially mentioned the extinction coefficients (c) because these are reported in the literature and not the oscillator strengths except in few cases. The reader will realize that the very narrow absoption bands of the rare earths covering as they do only a small area (dv xh where dv in cm-1 and h is the height of the peak) almost invariably suffer narrowing (i.e. decrease in dv) when intensified although the value of h is increased. Thus the effective area covered by a hypersensitive band in many cases is in no way greater than those of the aquo ion, even though the e is increased considerably due to increase in h.
Absorption Spectra of the Europium Ion and Its Complexes 123
However, a theoretical treatment by J0rgensen and Jtjdd [580] points out that these hypersensitive transitions occur due to the inhomogeneity of the dielectric and obey the selection rule AJ = 2. These authors believe that these transitions are pseudoquadrupole in nature. The author [581] has pointed out that the selection rule proposed by J0BGENSEN - Judd is not rigorously obeyed as they have claimed. Some comments on the validity of J0rgensen - Judd’s theory may also be found elsewhere [582, 583]. Recently Judd [584] tried “to air a certain uneasiness” caused by the theory [580], and pointed out that only the following symmetry classes will give rise to hypersensitive transitions.
Cgt Glt C2, Gz, C^sr» C4» C±v, Cg and Cj
Hence it is left to the experimentalist to verify another theoretical prediction put forward before the results were obtained.
The following /—/ transitions are usually intensified due to complexation.
Ma+ Transition Wavenumber ( x 10-8 cm-1)
Nda+ 4A/2 4£*5/2 17.3
4^»/2 4^7/2 19.2
Sm8+ 6®5/2 "*■ ^^l/2 |6.2
Eu3+ 7F0 + *D2 21.5
Dy3+ 6^15/2 ^F 1112 7.7
Ho®+ - 3^e 22.2
- 5o6 26.2
Er*+ 5-^15/2 2Hlll2 19.2
5-^15/2 4^ll/2 26.5
Tms+ 3H6 - 12.6
The Spectrum of Eu3+ ion in Solution
Stewart [505, 585] was the first to investigate systematically the spectra of the rare earth aquo ions, and he reported the following absorption maxima for the Eu3+ ion. It will be seen that the absorption bands in the visible region are of very weak intensity. Later Banks and Klengman [586] measured the same spectra using a Cary 14 spectrophotometer and their results for the Eu3+ ion are also reproduced below. A broad band at 1880 A (53190 cm-1) has been observed [587] for 0.03 M europium perchlorate in 0.1 M HCIO4 which may possibly be due to a 4/ 5d transition of the /6 configuration.
124
Spectroscopic Properties of Europium
Eu8+ aquo ion [585]
-X5- Wave- length (A) Wave- number (cm-1) Wave- length (A) Wave- number (cm-1) є
2220 45045 17.1 3617 27647 0.418
2513 39793 1.84 3749 26674 (sh)
2562 39032 1.20 3760 26596 0.346
2674 37397 0.686 3809 26253 0.288
2856 35014 0.601 3853 25954 0.320
2935 34071 0.268 3943 25361 2.36
2978 33579 0.673 4650 21505 0.052
3168 31565 (ah) 5262 19004 0.078
3177 31479 0.739 5360 18657 0.029
3260 30675 0.124
Eu3+ aquo ion [<5#6]
Wavelength Wavenumber Molar
 cm-1 absorptivity*
2728 36657 0.335
2870 34843 0.132
3611 27693 0.053
3650 27397 0.062
3796 26343 0.299
3942 25368 3.06
4015 24906 0.097
liters/mole-cm
Sayre et al. [5&S, 589] investigated the nature of the effective symmetries around Eu3+ ions in water, methanol and ethanol and found that the Eu3+ aquo ion has a Dzn symmetry whereas in an anhydrous alcohol the symmetry proved to be C2v- In a methanolic solution the 4643 and 5790 A lines became highly intense. The changes in intensities are only noticeable after the addition of 2—3 per cent water. However, after the addition of 15 per cent water in either methanolic or ethanolic solution no further change was observed and the spectrum in either solution was indistinguishable from that in pure water.
The absorption spectra of some rare earths and actinides in a molten LiNOs—KNO3 eutectic have been measured [590, 591]. A comparison of the oscillator strength of the 4650 A band (7Fo -*■ 5Dz) in DCIO4 and the molten nitrate eutectic shows an increase [510] of ~18 times in the latter solvent. Incidentally, the 7F0 5jD2 transition is a hypersensitive transition [580]. Carnall et al. [591] were able to observe some transitions between the ground state multiplets viz. 7Fo -*•7 F в, 7F і 7Fe and 7Fo -*■ 7Fb at 4610,4930 and 3910 cm-1 respectively in the nitrate eutectic.
Absorption Spectra of the Europium Ion and Its Complexes 125
Intensification of the 7Fo 5 Do, 7Fq 5Di and 7F0 -*■ 5L7 bands in the somewhat unstable Eu3+-diethyldithiocarbamate has been reported by J0RGENSEN [592]. He has also observed genuine electron transfer bands from the highest filled molecular orbital to the partly filled 4/ shell in the bromo complexes of Nd3+, Sm3+, Eu3+, Tm3+ and Yb3+. In the case of Eu3+ the electron transfer bands occur [592] at 3200, 2660 and 2300 A corresponding to 31250, 37594 and 43478 cm-1 respectively.
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