Imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium, and quaternary ammonium bis(trifluoromethylsulfonyl)imide salts were functionalized with a carboxyl group. These ionic liquids are useful for the selective dissolution of metal oxides and hydroxides. Although these hydrophobic ionic liquids are immiscible with water at room temperature, several of them form a single phase with water at elevated temperatures. Phase separation occurs upon cooling. This thermomorphic behavior has been investigated by (1)H NMR, and it was found that it can be attributed to the temperature-dependent hydration and hydrogen-bond formation of the ionic liquid components. The crystal structures of four ionic liquids and five metal complexes have been determined.
A new twist: Structural twisting by about 32° between the semiquinoneiminecopper(II) entities in 2 caused by weak Cu–S interaction results in a different spin arrangement (↑,↓,↑) than for planar 1 (↑,↑,↓). Most revealingly, 2 has an EPR spectrum typical for a radical whereas 1 displays a signal for a CuII center. Oxidation state distributions for the 22+,+,0,−,2− forms are assigned on the basis of UV/Vis/NIR spectroelectrochemistry.
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