I. Kawabe et A. Masuda, The original examples of lanthanide tetrad effect in solvent extraction: Anew interpretation compatible with recent progress in REE geochemistry, GEOCHEM J, 35(4), 2001, pp. 215-224
Geochemical studies reporting lanthanide tetrad effects in natural samples
often cite the original examples of tetrad effect depicted by logK(d)(org/a
q) for Ln(III) in the two solvent-extraction systems (Peppard et al., 1969)
and its theoretical interpretation (Jorgensen, 1970; Nugent, 1970). An imp
roved equation for the refined spin-pairing energy theory (RSPET), which ha
s been developed in pursuing tetrad effects in geochemical studies, makes i
t possible to examine more thoroughly the original examples of tetrad effec
t by using the digitized logK(d)(org/aq) data. The logK(d)(org/aq) values a
re found to be successfully described by the RSPET equation. Our analyses s
how that the ratios of relative differences in Racah parameters for Ln(3+)
ions in aqueous and organic phases, DeltaE(3)/DeltaE(1), are 0.29 +/- 0.07
and 0.25 +/- 0.06 for the two extraction systems. They are comparable with
the spectroscopic observations of nephelauxetic effect in Nd(III) compounds
(DeltaE(3)/DeltaE(1) = 0.23 +/- 0.02). The tetrad effects in logK(d)(org/a
q) are experimental evidence for the thermochemical consequence of the neph
elauxetic effect in Ln(III) complexes. Although Ln(3+) ions in condensed ph
ases are atomic-like, it is rather surprising that logK(d)(org/aq) can easi
ly be reproduced by the simple RSPET equation derived from the Slater-Condo
n-Racah theory for free Ln(3+) ions in vacuum. The effect of coordination c
hange of Ln(3+) ion across the Ln(3+)(aq) series is not obvious in the seri
es variations of logK(d)(org/aq), suggesting that the coordination changes
in the two Ln(III) complex series in the extraction systems are significant
ly canceled out in DeltaG(r)degrees. The two sets of logK(d)(org/aq) are an
alogous to the Masuda-Coryell plot in REE geochemistry with respect to thei
r coordinates. This gives an insight into the fact that the Masuda-Coryell
plot also depicts tetrad effects in the REE patterns for geochemical sample
s.