Lanthanide complex, tetranuclear

Gerasko, O.A., Mainicheva, E.A., Naumova, M.I., Neumaier, M., Kappes, M.M., Lebedkin, S. et al. (2008) Sandwich-type tetranuclear lanthanide complexes with cucurbit[6]uril from molecular compounds to coordination polymers. Inorganic Chemistry, 47, 8869-8880. 

A TETRANUCLEAR LANTHANIDE HYDROXO COMPLEX FEATURING THE CUBANE-LIKE [Ln4(Ai3-OH)4] + CLUSTER CORE, [Nd4(/i3-OH)4(H20)io(alanine)6][Ci04]8... 

The lanthanide metals, with their larger coordination numbers, invariably have the ligand coordinated in either a trismonodentate or a tetrakismonodentate fashion (42, 55, 57) (see Figs. 10 and 11). Thus, the ligand apparently tends toward the maximization of its coordinating capacity where circumstances allow, giving rise in many cases to the formation of sheet or cage structures. Limited chain formation was observed in the platinum, palladium, and rhodium complexes described, while the molybdenum complexes described by Hilbers et al. consist of dinuclear and tetranuclear units. 

Tetranuclear complexes are the most abundant amongst all reported lanthanide hydroxides. Three distinct core motifs have been identified, namely the cubane, the rhombus, and the square. 

Reaction of tetranuclear lanthanide octahydrides with styrene provides lanthanide benzylic allyl heptahydride complexes through the insertion of a styrene molecule into one Ln-H bond. The lanthanide benzylic allyl complexes can be considered as the intermediates of styrene hydrogenation. Indeed, both the lanthanide octahydrides and the lanthanide benzylic allyl complexes can catalyze styrene hydrogenation efficiently in the presence of H2 [89]. Lanthanide hydrides react with 1,3-cyclohexadiene to form lanthanide allylic complexes via 1,4-addition [90]. However, these lanthanide hydride clusters can not catalyze the polymerization of styrene and 1,4-cyclohexadiene. 

Kido, T., Ikuta, Y, Sunatsuki, Y. et al. (2003) Nature of Copper(II)-lanthanide(lll) magnetic interactions and generation of a large magnetic moment with magnetic anisotropy of 3d-4f cyclic cylindrical tetranuclear complexes [Cu LLn (hfac)2]2, (H3L = l-(2-hydroxybenzamido)-2-(2-hydroxy-3- methoxyben-zylideneamino)ethane and Hhfac = hexafluoroacetylacetone, Lnlll = Eu, Gd, Tb, Dy). Inorganic Chemistry, 42, 398 08. 

The reaction of the same lanthanide starting material with the steri-cally more hindered benzenethiol afforded an anionic tetranuclear complex Li[R4 (/i4-Cl)Nd4(/t-SPh)g] wherein a /t4-Cl group rather than a /t4-SPh as in the example above was found to form a square pyramid with four basal lanthanide atoms (Eigure 67). Good catalytic activity of this cluster in the ROP of 8-caprolactone has been demonstrated (Li et al., 2005). 

FIGURE 90 Proposed mechanism for the self-assembly of a tetranuclear lanthanide-hydroxo complex with EDTA from its corresponding mononuclear aqua complex (redrawn after Zheng, 2001). 

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