On the Coordination Chemistry of the lanthanum(III) Nitrate Salt in EAN/MeOH Mixtures.

A thorough structural characterization of the La(NO) salt dissolved into several mixtures of ethyl ammonium nitrate (EAN) and methanol (MeOH) with EAN molar fraction χ ranging from 0 to 1 has been carried out by combining molecular dynamics (MD) and X-ray absorption spectroscopy (XAS). The XAS and MD results show that changes take place in the La first solvation shell when moving from pure MeOH to pure EAN. With increasing the ionic liquid content of the mixture, the La first-shell complex progressively loses MeOH molecules to accommodate more and more nitrate anions. Except in pure EAN, the La ion is always able to coordinate both MeOH and nitrate anions, with a ratio between the two ligands that changes continuously in the entire concentration range. When moving from pure MeOH to pure EAN, the La first solvation shell passes from a 10-fold bicapped square antiprism geometry where all the nitrate anions act only as monodentate ligands to a 12-coordinated icosahedral structure in pure EAN where the nitrate anions bind the La cation both in mono- and bidentate modes. The La solvation structure formed in the MeOH/EAN mixtures shows a great adaptability to changes in the composition, allowing the system to reach the ideal compromise among all of the different interactions that take place into it.