Lanthanide carboxylates

Another lanthanide carboxylate complex that also contains nonacoordinated lanthanide ion in a monocapped square antiprismatic arrangement of nine oxygens is the erbium oxalate trihydrate with the composition Er(OOCCOO) (HOOCCOO) (OH2)3. This complex crystaUizes (767) in space group P4/ with 0 = 8.664, c =6.4209 A and Z=2, when the precipitate of erbium oxalate, ob-... 

Although heterobimetallic complexes with alkylated rare-earth metal centers were proposed to promote 1,3-diene polymerization via an allyl insertion mechanism, details of the polymerization mechanism and of the structure of the catalytically active center(s) are rare [58,83,118-125]. Moreover, until now, the interaction of the cationizing chloride-donating reagent with alkylated rare-earth metal centers is not well-understood. Lanthanide carboxylate complexes, which are used in the industrial-scale polymerization of butadiene and isoprene, are generally derived from octanoic, versatic, and... 

Chart 2 Symmetrically substituted benzoate ligands used as model ligands in order to investigate the alkylation behavior of lanthanide carboxylates... 

Similar products were obtained via the reaction of carboxylates Ln(02CArl Pr)3 x (Ln = La, Nd) with 3-4 equivalents of triethylaluminum. Highly soluble heterobimetallic lanthanide carboxylates were crystallized in low yields and fully characterized. In the case of the smaller metal centers... 

Scheme 22 [Carboxylate]- -[alkyl] exchange a mechanistic scenario of the formation of differently alkylated lanthanide carboxylate complexes (except for Ij, and I2 all Ln complexes were completely characterized ArR = C6H2R 3-2,4,6 or C6H3R 2-2,6) [148]...

Table 5 Polymerization of isoprene with plex Ln[(02CAr -Pr)2(AlR2)]2[AlR4] (R = mono-alkylated lanthanide carboxylate com-Me, Et) ...

Table 6 Polymerization of isoprene with bis-alkylated lanthanide carboxylate complexes [Ln(AlMe4)2(/x-02CArt"Bu)]2...

The reaction of Cp2LnCl with sodium carboxylates yields the corresponding dicyclopen-tadienyl lanthanide carboxylates, which on the basis of molecular weight determinations are dimers with /i-carboxylate bridges [57]. Some of the carboxylic acid complexes are summarized. 

Evans, W.J., Giarikos, D.G, and Ziller, J.W. (2001) Lanthanide carboxylate precursors for diene polymerization catalysis syntheses, structures, and reactivity withEt2Aia. Orgarwmetallics, 20, 5751-5758. 

Vadura, R. and Kvapil, J. (1971) Growth and lattice parameters of the lanthanide carboxylates 1. Tetrahydrated lanthanide acetates. Materials Research Bulletin, 6, 865-873. 

Alternatively, hydrolysis of presumably not so soluble lanthanide carboxylate complexes may be possible by carrying out the hydrolysis under hydrothermal conditions. It appears that such conditions (high temperature and high pressure) are particularly conducive to the formation of polynuclear lanthanide complexes, often with unpredictable but nevertheless interesting structure. Under ambient pressure, analogous synthesis generally produces complexes with carboxylate coordination only and without any involvement of hydroxo groups. 

It is interesting to note that the mesomorphic behavior of these lanthanides carboxylates is much closer to the behavior of alkaline and alkaline earth soaps than to the transition metal soaps described above. However, it is less complex since only one smectic A mesophase is observed, although sometimes a second mesophase, which has not been identified by X-ray diffraction, is present for the short-chain homologs. Such a simple behavior has been attributed to the high carboxylate-to-metal ratio, which makes the ionic layer more rigid. 

It is appropriate to consider the relative stability of lanthanide conq)lexes as a first indicator of a ligand s potential applicability for lanthanide separations. In fig. 9 is shown a plot of the relative stability of a variety of lanthanide carboxylate complexes (normalized to log/ (Gd )=0) of importance in ana ical separations. The 1 2 complexes of the lanthanides with glycolate and digjtycolate exhibit similarly poor discrimination of lanthanide ions between Gd and Ho, though the overall slope is greater for diglycolate. The 1 2 lactate complexes vary more regularly than these species, but... 

Different modes are frequently present in the same complex, adding complexity to the lanthanide-carboxylate coordination. The large size, flexible coordination geometry, and oxophilicity of the lanthanide ions are responsible for... 

Han Y, Li X, Li L et al (2010) Structures and properties of porous coordination polymers based on lanthanide carboxylate building units. Inorg Chem 49 10781-10787... 

---