Erbium molecules

The erbium ion is coordinated to eight carboxyhc oxygens [2.362—2.415 A)] from four oxalate (acid oxalate) moieties which forms a square antiprism around Er(III). A water molecule forms the cap (Er—OH2 =2.441 A) above the large square face of the antiprism. The acid oxalates (HOOCCOO) and oxalate ions occupy the crystallographic sites at random. The statistically averaged oxalate groups are centrosymmetric and planar. A very short H-bond (2.43 A) has been observed between two water molecules in two equivalent molecules, but the physical significance is difficult to assess because these waters are disordered in the molecule. 

Fig. 14. The separation of the RDF for the 1 M erbium(III) chloride solution in Fig. 13 into a RDF involving only the metal ions (upper curve) and a reduced RDF for the remaining nonmetal interactions (lower curve). Theoretical peaks for eight water molecules (1st coordination sphere) and 16 water molecules (2nd coordination sphere) are shown for comparison (upper curve).

The heavier rare earths form a second type of isonicotinate dihydrate structure typified by [Er(C5H4NC02)3(H20)2]2 oo in which chains of erbium atoms are linked by pairs of bridging carboxylate groups. Eight-coordination is achieved at each metal atom by a chelating carboxylate and two water molecules [97]. 

Oxalic acid is a precipitation agent for rare earth ions. The solubility of rare earth oxalates range from 10 to lO" mol in neutral solutions. The precipitate usually contains coordinated and/or lattice water molecules, RE2(C204)3 n H2O, where = 10 for lanthanum to erbium and yttrium while n = 6 for holmium, erbium, thulium, ytterbium to lutetium and scandium. 

Besides the substances mentioned so far, functionalized fuUerenes like the simple Bingel adduct can be intercalated into nanotubes as well (Section 2.5.5.2). The formation of peapods has further been described for metallocenes (e.g., ferrocene), porphyrines (e.g., erbium phthalocyanine complex) and small fragments of nanotubes. The most important prerequisite for the feasibility of inclusion is always a suitable proportion of sizes of both the tube and the structure to be embedded. For example, this effect can be observed for the intercalation of different cobaltocene derivatives into SWNT. The endohedral functionalization only takes place at an internal diameter of 0.92nm or above (Figure 3.100). But there is also an upper limit to successful incorporation. When the diameter of the nanotube is too large, the embedded species can easily diffuse away again from the host. Only few molecules are consequently found inside such a wide tube. 

The 5-nitro-2-anthranilates of lanthanum(III), samarium(III), terbium(III), erbium(III) and lutetium(III) were obtained as hydrates having 2.5 mol of water molecules per 1 mol of compound [167]. The compounds are isostructural. The processes of dehydration and rehydration were investigated. The first step of dehydration does not cause a change of crystal structure. The entire dehydration gives anhydrous compounds wifii different structures to the structures of hydrates. The dehydration of the La, Sm, Tb and Br compounds was reversible and rehydration gives complexes having the same crystal structures as the initial compounds. 

The first compounds containing bonds between dicyclopentadienyl rare earth moieties and elements of group IV have been prepared by Schumann and Cygon (1978). Dicyclopentadienyl erbium chloride and dicyclopentadienyl ytterbium chloride react with lithium triphenylgermane or triphenylstannane with formation of dicyclopentadienyl erbium triphenylgermane and -stannane and dicyclopentadienyl ytterbium triphenylstannane, the latter containing two tetrahydrofuran molecules coordinated to ytterbium ... 

Porphyrin molecules form stable complexes with lanthanide ions, these complexes have intensive absorption in a visible range of spectrum. Erbium, ytterbium and neodymium complexes are characterized by a 4f-luminescence in near IR-range of spectrum [1]. The most studied complexes with porphyrins are ytterbium complexes since Yb has smaller ionic radius in comparison with lanthanum (radius of Yb ion is 1.01 A), which determines higher stability of these metallocomplexes. Distinctive feature of Yb porphyrin complexes is a characteristic narrow and rather intensive luminescence band located in the IR-range at 975-985 nm, in so-called therapeutic window of tissue transparency. ... 

All the radionuclides listed in O Table 46.3 emit 3 particles with relatively short tissue ranges. Erbium-169 colloids have found application for the treatment of arthritis in small joints (Menkes et al. 1982). Three other radionuclides that have been explored in clinical radionuclide therapy studies are Cu, and Lu. All of the others have not been pursued either due to problems with their production in sufficient specific activity and radionuclidic purity, or lack of suitable chemistry for attaching them to carrier molecules of interest. Nonetheless, all the radionuclides listed in O Table 46.3 would be suited, from an energetic perspective, to the treatment of small tumor metastases (O Donoghue et al. 1995). 

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