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.