Synthesis and characterization of divalent metal–betaine–bistriflimide complexes: a property comparison with metal bistriflimide salts

A panel of metal-betaine-bistriflimide complexes (with minimum formula M[Bet]2[Tf2N]2, where M = Mg, Ca, Zn, Cu and Ni) has been prepared in high purity and a quantitative yield. In parallel, a series of metal bistriflimide salts (sharing the same metal cations) has been synthesized and characterized though the same set of techniques. The current work presents a first comprehensive investigation of the physical-chemical properties of these two classes of metal systems, whose importance in a variety of applicative fields was not yet matched, to the best of our knowledge, by an adequate study of their characteristics. All the considered compounds have been spectroscopically, thermally and electrochemically characterized, and their solubility characteristics assessed, gaining insights into the role of metal cations in the definition of their properties. On the other hand, the evident effect of the betaine coordination on the prepared complexes’ solubility, thermal stability, melting point, glass and solid-solid transitions, redox behaviour and electrochemical window was ascertained, providing results which would allow a more informed use and application of these classes of divalent metal complexes.