Erbium coordination number

Fig. 13. The RDF (upper curve) and the reduced RDF (lower curve) for a 1 M aqueous erbium(III) chloride solution. The peak at 2.36 A, corresponding to the first coordination sphere of the erbium(III) ion, is compared with a theoretical peak, calculated for a coordination number of eight.

The lanthanide or rare earth elements (atomic numbers 57 through 71) typically add electrons to the 4f orbitals as the atomic number increases, but lanthanum (4f°) is usually considered a lanthanide. Scandium and yttrium are also chemically similar to lanthanides. Lanthanide chemistry is typically that of + 3 cations, and as the atomic number increases, there is a decrease in radius for each lanthanide, known as the lanthanide contraction. Because bonding within the lanthanide series is usually predominantly ionic, the lanthanide contraction often determines the differences in properties of lanthanide compounds and ions. Lanthanide compounds often have high coordination numbers between 6 and 12. see also Cerium Dysprosium Erbium Europium Gadolinium Holmium Lanthanum Lutetium Praseodymium Promethium Samarium Terbium Thulium Ytterbium. 

The first stage of oirr work was the synthesis of lanthanide elements salts (ytterbium and erbium) in a form of acetylacetonates. The rare-earth elements (REE) complexes in most cases have the coordination number (CN) more than six (7, 8, 9, 10 and even 12). CN of REE ions in complexes with organic poly dentate ligands are high and variable [10]. The reason of this phenomenon lies in the big ionic radius, which decreases from 1.06 A (La " ) to 0.88 A (Lu " ) (the effect of lanthanide compression ). The empty site of the coordination sphere is occupied by other ligands water, hydroxyl ions, etc. In IR-spectrum the hydroxyl ion is characterized by a narrow strip at 3700-3600 cm, it has higher frequency than water. Frequency v of water is located in a region of about 3600-3200 cm". ... 

The results of three ultrasonic investigations on lanthanide salts have been reported. The studies on erbium(iii) perchlorate in aqueous methanol suggest that inner-sphere perchlorate complexes occur at water mole fractions of less than 0.9. On that basis, the rate constant for the formation of the inner-sphere complex from the outer-sphere complex at 25 °C is 1.2 x 10 s. The case of erbium(m) nitrate in aqueous methanol is more complicated and it is suggested that the mechanism involves the existence of two forms of the solvated lanthanide ion, differing in coordination number, in equilibrium with the outer- and inner-sphere complexes. The results for aqueous yttrium nitrate, on the other hand, represent a simplification over those of previous ultrasonic studies on the lanthanides. The authors reject the normal multistep mechanism in favour of a single diffusion-controlled process. Unfortunately, the computed value for the formation rate constant kt of 1.0 x 10 1 mol s is at least two orders of magnitude lower than the value calculated on the Debye-Smoluchowski approach, but the discrepancy is attributed to steric effects. 

The structures of the Nd, Y, and La compounds have been reported by Safyanov and Belov (1976) and Safyanov et al. (1977, 1978a,b, 1979) while the erbium and ytterbium compounds have been studied by Rivero et al. (1984, 1985). In all structures the decavanadate is formed by ten edge-sharing VOg octahedra. The coordination number of R is either nine (La and Nd) or eight (Y and Er). The structure of the La compound is unique in that it has two bonds between the R " central ion and decavanadate oxygens. In all other cases the coordination polyhedra around the rare earth is exclusively formed by water oxygens (fig. 116). 

The lanthanides have high coordination numbers and more variable coordination geometries, so it was expected that Ln AMFFs could show more various structure characters and topologies (Figure 2f-h), compared to the TM ones with fixed octahedral coordination geometry. Indeed, several chiral erbium-formate... 

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. ... 

The only complexes of lanthanum or cerium to be described are [La(terpy)3][C104]3 175) and Ce(terpy)Cl3 H20 411). The lanthanum compound is a 1 3 electrolyte in MeCN or MeN02, and is almost certainly a nine-coordinate mononuclear species the structure of the cerium compound is not known with any certainty. A number of workers have reported hydrated 1 1 complexes of terpy with praseodymium chloride 376,411,438), and the complex PrCl3(terpy)-8H20 has been structurally characterized 376). The metal is in nine-coordinate monocapped square-antiprismatic [Pr(terpy)Cl(H20)5] cations (Fig. 24). Complexes with a 1 1 stoichiometry have also been described for neodymium 33, 409, 411, 413, 417), samarium 33, 411, 412), europium 33, 316, 411, 414, 417), gadolinium 33, 411), terbium 316, 410, 414), dysprosium 33, 410, 412), holmium 33, 410), erbium 33, 410, 417), thulium 410, 412), and ytterbium 410). The 1 2 stoichiometry has only been observed with the later lanthanides, europium 33, 411, 414), gadolinium, dysprosium, and erbium 33). 

Among seven-coordinate structures, many involve dike-tonate complexes Ln(diket)3 L these generally have either capped-octahedral or capped trigonal prismatic geometry. A considerable number of complexes with neutral donors (e g. thf) of the type LnX3L4 (X = halide, NCS), however, have structures closest to pentagonal bipyramidal, similarly found in the erbium perchlorate complex with 2,6-dimethyl-4-pyrone (Section 3.7.4). 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

Prior to 1968 a number of complexes of the thiocyanate ion had been prepared but each of them contained additional adduct molecules (such as dioxane or alcohol) that were most likely coordinated as well (Golub and Borsch, 1967). In 1968 the preparation of the complexes [(C4H9)4N]3R(NCS)6 was reported along with the crystal structure of the erbium complex (Martin et al., 1968). This was the first six-coordinate, discrete, anionic complex for which an X-ray diffraction study had been made. These compounds are quite stable, non-hygroscopic, soluble in many organic solvents, and melt without decomposition (Burmeister et al., 1969). The corresponding selenocyanates have also been prepared and, as expected, they are considerably less stable decomposing quite rapidly in moist air or in solution (Burmeister and Deardorff, 1970). 

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