Small angle neutron scattering investigation of the species formed in the extraction of Sr(II) by mixtures of di-n-octylphosphoric acid and dicyclohexano-18-crown-6
R. Chiarizia et al., Small angle neutron scattering investigation of the species formed in the extraction of Sr(II) by mixtures of di-n-octylphosphoric acid and dicyclohexano-18-crown-6, SOLVENT EXT, 18(3), 2000, pp. 451-478
Deuterated toluene solutions of di-n-octylphosphoric acid, HDOP, containing
Sr+2 extracted from 0.1 M LiNO3 aqueous solutions, were investigated by sm
all angle neutron scattering (SANS). The extractions were also performed in
the presence of either the cis-syn-cis or the cis-anti-cis stereoisomer of
dicyclohexano-18-crown-6 (DCH18C6) in combination with HDOP in the toluene
phase. The addition of the crown ether increased metal extraction into the
organic phase over that observed with HDOP alone (synergistic extraction).
The cis-syn-cis isomer was more effective than the cis-anti-cis isomer in
enhancing Sr(II) extraction in the synergistic system. The SANS results con
firmed that when the metal cation is extracted by HDOP present in large sto
ichiometric excess, the predominant species formed in the organic phase can
be described as Sr(H(DOP)(2))(2) with 2 extra HDOP molecules solvating the
complex. In the synergistic crown ether-HDOP system, the SANS data are con
sistent with solvent extraction data suggesting the formation of complexes
containing one crown ether and two HDOP dimers. In the extraction of Sr(II)
by HDOP alone, the SANS data reveal the presence of small amounts of large
aggregates. Both the cis-syn-cis and cis-anti-cis isomers of DCH18C6 inhib
it the formation of these aggregates. The cis-anti-cis isomer, however, des
pite its weaker complexation of strontium, is more effective in preventing
aggregate formation.