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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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M3+
La Ce Pr Nd Sm Eu Gd Dy Ho Er Lu Y
pH | 4.9 4.7 4.3 4.1 3.7 3.7 3.2 3.4 3.45 3.45 3.7 3.3
These hexavanadates, like the ortho and meta vanadates, are sparingly soluble in water.
Part II
Coordination Compounds Containing Organic Ligands
A. Ligands Having Nitrogens as Donors
It has been mentioned before (p. 54) that ammonia and certain amines are basic enough to precipitate the practically insoluble hydroxides of the rare earths when added to aqueous solutions of their salts. Ammonia and amines in fact behave more as OH" generators than as ligands. For the formation of a Eu3+ complex with methylamine (CH3NH2, fcdiss = 5.6 X 10-4), it is neccessary [361] that the instability constant of the europium-amine complex should not be higher than 1013. Pyridine (C5H5N) is less basic (fcdiss = 2.3 X 10 9) than methylamine and the expected instability constant for a hexapyridino complex of Eu3+ should be of the order of ~10-7. However, in aqueous solution no pyridine complex of the rare earths has yet been realized. Serebrennixov et al. [362] have recently studied in some detail the reaction between pyridine and cerium trichloride or sulphate. Ryabcbjkov and Terentyeva [363] were able to isolate complexes of the composition [MAn] [Cr(NCS)e] (where A = pyridine, pyramidone or antipyrine and n = 3—6) by adding potassium hexathiocyanatochromate to a solution containing rare earth ions and amine molecules. It has been suggested [364] that anions of large dimensions favour the precipitation of amine-containing cations from aqueous solution.
Several adducts of amine hydrochlorides with rare earth trichlorides of the type [MCI3] [AHCl]x containing varied amounts of solvent molecules have been isolated [365, 366] from alcoholic solution.
2,2'-dipyridyl complexes. — It often happens in the history of a rapidly developing subject that the same sort of observation is made independently in two countries almost at the same time. Both the present author [367] and two Russian chemists Lobanov and Samirnova [368] reporled the existence of the 2,2'-dipyridyl complexes of rare earths. Although the
74 Compounds of Europium
work of Lobanov and Samirnova [368] appeared in Russian in September 1963, the English translation was not available until the end of 1964. Lobanov and Samirnova [368] said that the fo’s-dipyridyl rare earth chlorides could not be isolated from an alcoholic solution of the components. The author, however, was able to prepare [367] the fo's-dipyridyl
2,2'-dipyridyl
complexes as chlorides and nitrates. These complexes have the general formula M(Dip)2(H20)»X3 (X being Cl- or NO3 and n varying from 0 to 4). A displacement of the “breathing mode” from 990 cm-1 to higher wavenumber, and the appearance of two new infrared bands between 1480 and 1600 cm-1 in these chelates were observed [367]. Recently
Table 26. M—N stretching vibrations (cmr1) in rare earth chloride complexes of 2,2'-dipyridyl and 1,10-phenanthroline [369]
M3+ Dipyridyl Phenanthroline
La 210 (s) 178 (m)
197 (8)
218 (m)
Nd 214 (8) 175 (m)
196 (m)
218 (m)
Sm 215 (8) 175 (m)
199 (m)
216 (m)
Eu 217 (8) 235 (8)
Gd 222 (Sh) 224 (sh)
233 (8) 235 (s)
249 (sh)
r>y 233 (8) 238 (8)
249 (sh) 247 (sh)
Ho 224 (sh) 224 (sh)
231 (8) 235 (8)
249 (sh) 246 (sh)
Er 234 (8) 225 (sh)
254 (8) 238 (s)
248 (sh)
Tm 224 (Sh) 224 (sh)
235 (8) 237 (8)
256 (8) 248 (sh)
Lu 243 (8) 224 (sh)
260 (8) 238 (s)
248 (sh)
Coordination Compounds Containing Organic Ligands
75
Ferraro et al. [369] examined the infrared spectra of several rare earth dipyridyl and phenanthroline complexes with chloride as anion and confirmed the above results. They also studied the low frequency region (650—70 cm-1) where M—N vibrations are expected. The dipyridyl complexes show the M—N stretching vibrations (Table 26) between 210—243 cm-1. It is quite interesting that for the lighter members of the rare earth series (La—Sm) the M—N stretching frequency in the dipyridyl complexes occurs at higher wavenumber than the corresponding phenanthroline complexes. For the heavier members (Eu—Lu) this is reversed. Phenanthroline was expected [370\ to form stronger complex than dipyridyl. No evidence for M—Cl vibrations in either the dipyridyl or the phenanthroline complexes was obtained from the infrared spectra, and the metal-chloride linkages in these complexes should be considered as ionic. There is however, strong infrared evidence [367] for covalently bonded nitrates in the case of the foVdipyridyl nitrate complexes.
Recently, Hart and Laming [371] have prepared ftis-dipyridyl complexes of rare earth containing chloride, nitrate and thiocyanate as anions.
4,4'-dimethyl-2,2'-dipyridyl complexes. — Sinha [372, 373] has reported the preparation and spectroscopic properties of bis-4,4'-dimethyl-2,2'-dipyridyl (Dimp) complexes of Nd, Eu and Tb. The fo's-Dimp-complexes for the whole rare earth series have been prepared by the author (unpublished results). In the para position both the inductive
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