Neodymium(III) Complexes of Dialkylphosphoric and Dialkylphosphonic Acids Relevant to Liquid–Liquid Extraction Systems

The
complexes formed during the extraction of neodymium­(III) into hydrophobic
solvents containing acidic organophosphorus extractants were probed
by single-crystal X-ray diffractometry, visible spectrophotometry,
and Fourier-transform infrared spectroscopy. The crystal structure
of the compound Nd­(DMP)3 (1, DMP = dimethyl
phosphate) revealed a polymeric arrangement in which each Nd­(III)
center is surrounded by six DMP oxygen atoms in a pseudo-octahedral
environment. Adjacent Nd­(III) ions are bridged by (MeO)2POO– anions, forming the polymeric network. The
diffuse reflectance visible spectrum of 1 is nearly identical
to that of the solid that is formed when an n-dodecane
solution of di­(2-ethylhexyl)­phosphoric acid (HA) is saturated with
Nd­(III), indicating a similar coordination environment around the
Nd center in the NdA3 solid. The visible spectrum of the
HA solution fully loaded with Nd­(III) is very similar to that of the
NdA3 material, both displaying hypersensitive bands characteristic
of an pseudo-octahedral coordination environment around Nd. These
spectral characteristics persisted across a wide range of organic
Nd concentrations, suggesting that the pseudo-octahedral coordination
environment is maintained from dilute to saturated conditions.