Lanthanum divalent complexes

Divalent complexes can also be synthesised by the reductive pathway. This method is less direct, since it involves two steps instead of one for the metathesis reaction (a) synthesis of a suitable trivalent complex as precursor and (b) chemical reduction of this trivalent complex. This method has a number of advantages, however, since, in addition to organothu-lium(II) complexes, it has permitted to isolate compounds that could not be synthesised by the metathesis pathway, such as lanthanum(II),... 

Separation Processes. The product of ore digestion contains the rare earths in the same ratio as that in which they were originally present in the ore, with few exceptions, because of the similarity in chemical properties. The various processes for separating individual rare earth from naturally occurring rare-earth mixtures essentially utilize small differences in acidity resulting from the decrease in ionic radius from lanthanum to lutetium. The acidity differences influence the solubiUties of salts, the hydrolysis of cations, and the formation of complex species so as to allow separation by fractional crystallization, fractional precipitation, ion exchange, and solvent extraction. In addition, the existence of tetravalent and divalent species for cerium and europium, respectively, is useful because the chemical behavior of these ions is markedly different from that of the trivalent species. 

Pyrazolin-5-ones form complexes with both inorganic and organic compounds much more readily than do the 2-pyrazolin-5-ones. The most extensive series of complexes is that formed with a variety of metallic salts. Antipyrine (2,3-dimethyl-l-phenyl-3-pyrazolin-5-one) forms a series of complexes with salts of divalent, trivalent and tetra-valent metals. Two molecules of antipyrine form a complex with one molecule of copper, cadmium, cobalt and zinc salts.266,866,1116 Complexes prepared from metallic nitrates are usually hydrated.1322 There also exists a series of complexes in which three molecules of antipyrine form a complex with one or two molecules of metallic salts. Such complexes form with two molecules of simple ferric salts272 or with one of complex iron cyanides.608 Nitrates of thorium, lanthanum, cerium and samarium also give such complexes.841 This ratio also occurs in some antipyrine complexes with cadmium and zinc thiocyanate.266 A number of salts of rare earths and iron which have complex anions such as thiosulfate, thiocyanate, dithionic acid and complex iron cyanides form complexes in which six molecules of antipyrine are present.405,408 608,841,950 Stannic chloride forms salts containing three or four molecules of antipyrine and hydrochloric acid.46... 

Rate constants have been obtained for the aquation of a series of pentaammine(carboxylato)cobalt(III) complexes [Co(NH3)5L] in UCIO4-HCIO4 media. " In many cases the values of fc<>bs are not proportional to [H ]. The data have been used to calculate association constants of protonated forms of the complexes and the corresponding rate constants for aquation. Association constants (Xml) of ion pairs formed by a series of divalent metal ions and also lanthanum(III) ions with [Co(NH3)sOOCC02] have been determined from spectrophotometric UV absorbance data at 50 and Rate constants for aquation of the... 

---