Lanthanide-acylpyrazolone complexes

Complexation rate constants for tervalent lanthanide-acylpyrazolone complexes in the toluene-water phase pair... 

The lanthanide complexes lack distinct ultraviolet-visible spectra and, hence, kinetic information on their complex formation and dissociation reactions was obtained indirectly by the metallochromic indicator method. These studies indicate that in the case of the Cyanex 272 complexes, the CPC efficiencies are mainly limited by the slow dissociation of the M(HL2)HL complex at the heptane-H20 interface. In the case of the complexes of the acylpyrazolones, the CPC efficiencies are again limited by the dissociation of the lanthanide-pyrazolone complexes at the organic-aqueous interface with the rate-limiting step being the dissociation of the ML complex. It was also shown that because the dissociation reactions are interfacial separations, efficiencies can be dramatically improved by the addition of surfactants like Triton X-100 to the organic phase and by... 

A similar limitation has been recently reported for the synthesis of unsaturated triple-stranded binuclear lanthanide helicates with bis-bidentate acylpyrazolone ligand strands and some analogues of bis- S-diketonate ligands, for which only the ethyl spacer was found to form the targeted helical complex (Semenov et al., 2008). 

Significant differences are seen between Cyanex 272 and the acylpyrazolones. The extractibility of the trivalent lanthanides is higher with Cyanex 272 than with the acylpyrazolones, where HPMBP shows better extraction than HPMCP. The stability constants of the lanthanides increases from the light to heavy, and the values for the Cyanex 272 and HPMCP complexes are larger than those of HPMBP. The separation factor (or selectivity) for a pair of lanthanides is much better with Cyanex 272 than with HPMBP or HPMCP, which have similar separation factors. 

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