Coordination Structures and Supramolecular Architectures in a Cerium(III)-Malonamide Solvent Extraction System

The process chemistry and solution structures investigated in the title system bridge the three ostensibly disparate fields of separation sciences, soft matter research, and coordination chemistry. We have explored this subject with synchrotron radiation, research and advanced analyses leading to original insights into aggregation phenomena in solvent extraction. Herein we present findings showing the coagulation of reverse micelles into wormlike aggregates in organic phases (N,W-dimethyl-N,W-dibutyltetradecylmalonamide abbreviated as DMDBTDMA-in n-dodecane) obtained by liquid liquid extraction following contact with acidic and neutral aqueous media containing trivalent cerium. The growth of solute architectures was shown to prelude phase transition (i.e., the formation of a "third phase"). The presence of acid was shown to promote the growth of these micellar chains and, therefore, promoted third-phase formation. Acid was also shown to hydrate and swell the reverse micelle units, preorganizing them to allow for incorporation of cerium, leading to different coordination structures and enhanced metal extraction. The approach of linking both the coordination environment and supramolecular structures to the process properties of a solvent extraction system in a single study provides perspectives that are not available from independent, uncorrelated experimentation. Moreover, the analysis of small-angle X-ray scattering data from a solvent extraction system using the generalized indirect Fourier transform method to gain real-space information led to insights not otherwise available, showing that micellar assemblies are larger and more ordered than previously thought. This multipronged and multidisciplinary investigation opens new avenues in the evolving understanding of solute architectures in organic phases of practical relevance to solvent extraction and, simultaneously, of fundamental relevance to structured fluids and, in particular, phase transition phenomena.