Samarium cluster

FIGURE 78 Syntheses of hexanuclear and octanuclear samarium cluster complexes and their reaction with dinitrogen to afford tetranuclear cluster species containing a N2 ligand derived from dinitrogen reduction (top). The crystal structures of the hexanuclear (bottom left) and octanuclear (bottom right) clusters are shown (redrawn after Ganesan et al 2001). 

Electrochemical properties of samarium(ii) iodide are very sensitive to the nature of solvents. Reduction potential increases by replacing THE with a more polar solvent, such as DME or CH3CN. Addition of HMPA to a THE solution of samarium(ii) iodide leads to a substantial increase in the electron-donating nature of samarium(ii). The principal samarium(ii) species in a mixed solvent of THE and HMPA is an ionic cluster of [Sm(HMPA)4(THE)2] 2I in HMPA-THF (4 1) or [Sm(HMPA)6] 2I in HMPA-THE (>10 1). The reactivity order of the samarium(ii) complexes is [Sm(HMPA)6] 2I > [Sm(HMPA)4(THF)2] 2P > Sml2 in the reaction with 1-iodobutane. 

An inversion temperature was found for the ring opening of meso-epoxides by amines in dichloromethane.23 These reactions, which were catalysed by samarium iodobinaphthoxide, gave amino alcohols in high enantiomeric excess. The inversion temperature was thought arise because the reaction can occur with two different solvation clusters. 

This chloro-containing cluster also failed to react with nitrogen despite the fact that all of the metal ions are formally divalent. These observations provide further support to the conclusion that halide ions, by coordinating the samarium atoms, prevent the reaction of the cluster with nitrogen from occurring. 

FIGURE no Crystal structure of a nonanuclear samarium hydroxide cluster supported by acac ligands (redrawn after Addamo et al., 2004). 

Molecular orbital study of Robinson s compound New ways of synthesizing cluster compounds of samarium Cu complex that reproduces the essential reactivity of galactose oxidase Nitrogen fixation by stepwise reduction of N2 to form nitride dimer complex Nb 2(/r-N2)Na2(thf)i2... 

Fig. 3. Comparison between the 3d spectra of Sm vapor, SmS solid and Sm in clusters for two different concentrations R (argon to samarium ratio). Notice that at very low concentrations multiplets are present. (By courtesy of Drs. R.C. Kamatak and J.M. Esteva).

The cluster system of reactivity compensation is used to compensate for temperature and power reactivity effects, reactivity margins for core poisoning by xenon-135 and samarium-149, operating margins to change reactivity during reactor power changes, and to provide core sub criticality under reactor shutdown. 

Radu NS, Hollander FJ, Tilley TD, Rheingold AL (1996) Samarium-mediated redistribution of silanes and formation of tiinuclear samarium-silicon clusters. Chtan Ctnnmun 2459... 

---