Lanthanides ordinal numbers

Codeposition of lanthanide atoms with CO in argon matrices has afforded41 a series of metal carbonyls, M(CO)x (x = 1 — 6) (M = Pr, Nd, Eu, Gd, Ho, and Yb). The final product upon controlled annealing of the matrices was M(CO)6. It was found that vco varies with co-ordination number in much the same way as in other compounds, but that it is relatively independent of the nature of M. 

Bradley, D.C., Ghotra, J.S., and Hart, F.A. (1973) Low co-ordination numbers in lanthanide and actinide compounds. Part I. The preparation and characterization of tris bis(trimethylsilyl)-amido lanthanides. Journal cf of the Chemical Society, Dalton Transactions, 1021. 

By this term we refer to the accumulation of many configurations, both even and odd, at about the same height, thus leading to a high density of energy levels. This competition is a direct result of the above mentioned competition between electrons. In order to describe the structure of the lanthanide spectra in terms of these competitions, each lanthanide, characterized by its atomic number Z, has been assigned an ordinal number... 

No reports of studies of metal ions with high co-ordination numbers have appeared apart from the lanthanide exchange reactions noted in Sections 7 and 8. 

Apart from the lanthanide and actinide exchange reactions described in Sections 7 and 8, the photochemical investigations of the cyano-complexes of molybdenum(iv) mentioned in Section 4,i <-i and the n.m.r. investigations outlined above, no further kinetic studies of metal ions with high co-ordination numbers have appeared. 

We conclude this section by referring to recent work on metals, in which co-ordination-number changes have for some time been regarded as important, namely zinc and the lanthanide ions. 

The 1 1 complexes between the lanthanides and edta form stable associates with the anions of 8-hydroxyquinoline-5-sulphonic acid (oxs), iminodiacetic acid (ida), and nitrilotriacetic acid (nta) since the characteristic co-ordination number of the Ln ions is generally greater than six. In Figure 6 the free-energy changes associated with the formation of these... 

All of the kinetic studies of substitution and related reactions of inert metal complexes with co-ordination numbers greater than six reported in the present volume are concerned with eight-co-ordinate complexes. The relevant references are collected together in Table 29. It is likely that the co-ordination numbers of the lanthanide and actinide cations whose complexes are mentioned in Sections 7 and 8 of this chapter are greater than six, but as knowledge of the precise co-ordination number in each case is lacking, these are not included in Table 29. 

Speculation and discussion of the co-ordination numbers of lanthanide cations in various media continue. The effects of a series of Ln + cations on rates of oxygen exchange between edta and water have been interpreted in terms of a change from a co-ordination number of nine to one of eight in the complexes [Ln(edta)(OHa) ] about two-thirds of the way along the lanthanide series. Ultrasonic absorption studies on solutions of erbium nitrate and erbium chloride in water-methanol mixtures suggest that a difference in coordination number of the erbium cation in nitrate and in chloride media has an effect on kinetic behaviour. ... 

A number of complexes of urea and substituted ureas with various lanthanide salts have been isolated. The lanthanide acetates give both anhydrous and hydrated complexes with urea (67, 68). The hydrated complexes could be dehydrated by drying the complexes over CaCl2 or P4Oi0 (68). It is interesting to note that in the complexes of substituted ureas like EU (70) and CPU (71), the L M is independent of the anion. The anions in these complexes with a L M of 8 1 are apparently nonco-ordinated. Seminara et al. (72) have reported complexes of lanthanide chlorides with DMU and DEU which contain five and three molecules of the ligand respectively per... 

General Chemistry of the Lanthanides.—By using a n.m.r. method, the number of water molecules co-ordinated directly to the metal ion in aqueous solutions of La(C10J3 was found to be six, in Ce(C10j3 at least six and possibly higher, but the accurate number associated with ErfClOJj could not... 

Scheme I and, in more detail, Table 4 represent the trend of ionic radii of these large cations which prefer formal coordination numbers in the range of 8-12 [77]. For example, considering the effective Ln(III) radii for 9-co-ordination, a discrepancy of 0.164 A allows the steric fine-tuning of the metal center [60]. The structural implications of the lanthanide contraction can be visually illustrated by the well-examined homoleptic cyclopentadienyl derivatives (Fig. 2) [78], Three structure types are observed, depending on the size of the central metal atom A, [( j5—Cp)2Ln(ji— 5 rf — Cp)] x, 1 < % < 2 B Ln(fj5 —Cp)3 C, [fo -CpJjLnCi- 1 ff1—Cp)], these exhibit coordination numbers of 11 (10), 9, and 8, respectively. Also a small change in ligand substitution leads to a change in coordination behavior and number (10), as...

Fig. 7.37. Plots of lanthanide ion luminescence decay constants, k (ms 1), vs. mole fraction of H2O (/h->o) ln HtO-DtO mixtures for Eu(III) and Tb(III). The number of coordinated H20 s, n, for the indicated complexes is given on the right-hand ordinates aquo ions ( ) NTA complexes (pH 6.0) (O) EDTA (1 1) complexes (pH 6.0) (V) EDTA (2 1) complexes (pH 7.5) (A) 11231.

---