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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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M(DBM)S • HzO (HO)M(DBM)2 (40)
anhydrous fm-complexes of Nd and Eu of any purity were obtained by Charles and Perrotto [431] after careful heating of the hydrated complexes in vacuo for 1 hr. at 100° C.
Whan and Crosby [636], and Metlay [642] showed the existence of an extra dibenzoylmethane molecule in the complexes.
A few mixed compounds of Eu3+ containing dibenzoylmethide ion and carboxylate anions (acetate, propionate and benzoate) of the general formula, (DBM)2EuOCOR, have been isolated [432]. Thermogravimetric investigations on these complexes show that their heat stability decreases in the order acetate > propionate > benzoate. The melting points of
Coordination Compounds Containing Organic Ligands
89
these mixed complexes are reported to be 269 — 70°, 268 — 70° and 223 — 25° C respectively.
When the p-diketonate complexes are prepared in the presence of a Lewis base, mixed complexes containing three or four moles of the P-diketone and one or two moles of the Lewis base are obtained [433]. The composition of these mixed complexes presumably depends on the nature and concentration of both the Lewis base and p-diketone. The following europium complexes have been isolated by Lee and Nugent [433]. [Eu(Benzoylacetone)4]~ (Piperidine H+), m.p. 125°; [Eu(Benzoyl-acetone)4]~ (Morpholine H+), m.p. 127 — 28°; [Eu(Benzoylacetone)4]~ (Diethylamine H+); m.p. 128 — 30°; [Eu(Benzoylacetone)3] (NH3)2, m.p. 120 — 22°; [Eu(Dibenzoylmethide)4]“ (Morpholine H+), m.p. 179 — 80°; [Eu(Dibenzoylmethide)4]_ (Diethylamine H+), m.p. 196 — 204°; [Eu(Dibenzoylmethide)3]- (Diethylinetriamine), m.p. 164 — 66°. Several other adducts of Lewis bases with Eu(DBM)3 have recently been prepared [434]. Adducts of the general formula Eu(DBM)3 • A2 are obtained when A is 1,4-dioxane, n-butylamine, piperidine, pyridine, quinoline, whereas a mono-adduct, Eu(DBM)3 • A is formed when A is aniline, pyridine-N-oxide and dimethylformamide. The thermal stability of these adducts have been investigated. Many of the p-diketon-ates and the mixed chelates are very useful laser material.
ThenoyUrifluoroacetonates. — The dihydrated complex of europium, Eu(CsH402F3S)3 • 2H2O, was prepared [434a] by reacting an ethanolic solution of anhydrous thenoyltrifluoroacetone1 with aqueous EuCl3 and neutralizing with ammonia. It’s thermogravimetric analysis shows a weight loss of 2.4 per cent at 110° C corresponding to the loss of one water molecule and the formation of EutCsEUOsFsS^ * H20. Further heating would possibly hydrolyse the monohydrate complex to give Eu(C8H402F3S)2 • OH. The anhydrous complex cannot be obtained by the usual drying process.
The fluorescence properties of the fris-chelate have also been investigated [434a].
2,2,6,6-tetramethyl-3,5-hepatanedione complexes. — The tris complexes of the rare earths, M(THD)s, were prepared by Eisentraut and Sievers [125] in connection with separation studies using gas chromatography (p. 17). These complexes are volatile, and are eluted without decomposition.
Adducts
Alcohols, especially the higher ones enter into the solvation sphere of the rare earths. Several ketones and ethers are found to form adducts with rare earth perchlorates [435, 436] and nitrates [437]. Although perchlor-
1 The systematic name for this reagent is 4,4,4-trifluoro-l-(2-thienyl)-1,3-butanedione.
90
Compounds of Europium
atesform complexes with the general formula M(C104)3 * 9H2O • (C4Hs02)4, for tHoxane (C4H8O2) X-ray powder diagrams show two series of isomor-phous substances [436]. The adducts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy are all isomorphous and belong to the first series. The second series includes the Ho, Tm, Er, Yb and Lu adducts. Infrared spectra reveal no change of the dioxane frequencies.
Some anhydrous adducts of rare earth perchlorates with N,N-di-methylacetamide (DMA) have been prepared [438]. The complexes, M(C10)4 • xDMA, are found to contain varied amounts of DMA. Those with M = La to Nd crystallize with 8 DMA, those from Sm to Er with 7 DMA and those of Tm, Yb and Lu with 6 DMA. The acetates of Ce, Pr, Nd, Sm, Eu and Gd form [355] monosolvates, M(CHsCOO)3 * DMF, with N,N'-dimethylformamide.
. ligands Having both Nitrogen and Oxygen as Donors
Although complexes of rare earths with various substituted multi-dentate amino acids have been extensively investigated, only a limited number of rare earths have been used in studying the complexes with simpler amino acids. There is still considerable scope for investigation among the simpler members of the amino acid series. The stability constants of the rare earth amino acid complexes are compared in Table 34 and are also discussed below.
Complexes with EDTA and similar ligands. — Ethylenediamine-N,N, N',N'-tetraacetic (EDTA) acid forms complexes of exceptional stability [113, 439—445], and the difference in stability constants between the complexes of adjacent rare earths is sufficient to render this reagent very useful in ion exchange processes [113]. This exceptional stability is ascribed [446] to the large increase in entropy of complexation (see Table 37). Prom considerations of their entropy changes on formation, the complexes can be divided into two groups about gadolinium. These two groups differ by 6 —10 e.u. This difference has been accounted for by assuming a change in multidentate character of the ligand after gadolinium. Bates and Dahlinger [446] considered a change from pentacoordination to tetracoordination after gadolinium as explaining the break that occured in the Eu — Gd region, rather than from hexa to pentacoordination as proposed by Wheelwright et al. [111]. It is not unreasonable that such a change in dentate-character may occur, considering the steric hindrance by the carboxylate groups of the bulky EDTA anion when complexed to heavier rare earths with their smaller ionic size. In solution EDTA complexes are stabilized by hydrogen bonding. The high strain involved in a hexadentate EDTA chelates is somewhat released by hydrogen bonding through carbonyl oxygens [447].
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