Abstract
A series of lanthanide nitrate hydrate:urea “Type IV” deep eutectic solvents (DES; Ln = Ce, Pr, Nd) were prepared and their physical properties measured, showing very high surface tension and densi...
Highlights
Deep eutectic solvents (DES) are gaining attention as inherently tunable and potentially more environmentally friendly drop-in replacements for traditional organic solvents.[1]DES are extensively H-bonding eutectic mixtures of molecular and ionic compounds, forming a partially ionic liquid phase at desirable temperatures, and they are very often based around choline chloride (ChCl) and/or urea.[2]
Lanthanide DES (LnDES) were found to form homogeneous room-temperature liquids over a wide mixing range
The Tg was determined using extrapolation of the viscosity/temperature relationship with the Vogel−Fulcher−Tammann (VFT) equation and differential scanning calorimetry (DSC), shown in the Supporting Information.[45,46]. Both techniques suggest a Tg of 215 K, which is a significant eutectic depression when compared with the melting points of the urea (406 K) and lanthanide precursors i.e. Ce(NO3)3·6H2O (369 K), and relatable to the more extreme eutectic depressions such as that of ChCl:urea.[47]
Summary
Deep eutectic solvents (DES) are gaining attention as inherently tunable and potentially more environmentally friendly drop-in replacements for traditional organic solvents.[1]DES are extensively H-bonding eutectic mixtures of molecular and ionic compounds, forming a partially ionic liquid phase at desirable temperatures, and they are very often based around choline chloride (ChCl) and/or urea.[2]. ChCl:ZnCl2·3H2O), “Type III” DES are the most commonly studied and are made of ionic-molecular eutectic mixtures ChCl:urea), and “Type IV” DES are mixtures of metal salts with molecular components In the initial framework of DES, all “Type I−IV” systems were said to contain some form of complex-ion, based on mass spectrometry data.[7,16] this technique is regarded as inappropriate for characterization of ionic liquids and speciation; MS destructively ionizes the bulk liquid, and analysis of the gas-phase products usually leads to spurious conclusions.[17] For example, understanding of “Type III” DES nanostructure has evolved from a complex-ion model Understanding of “Type III” DES nanostructure has evolved from a complex-ion model (ie. [(urea)2·Cl]− + [cholinium]+) as concluded from MS,[18] to an “alphabet soup” model with multifaceted disorder,[19,20] with Hbonding contributions from all the various species,[21−23] and minimal evidence for the initially posited charge delocalization and complex-ion formation as the driver for eutectic formation.[18,24,25] Studies have investigated the effect of Received: October 27, 2018 Revised: December 28, 2018 Published: January 28, 2019
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