Highly concentrated "solutions" of metal cations in ionic liquids: current status and future challenges.

In this article we summarize a series of conditions that allow highly concentrated "solutions" of metal cations in ionic liquids to be obtained, evidencing structural features and some of the most important physico-chemical properties of these systems. We try to emphasize aspects and problems that are not conventionally discussed in detail in the literature. In particular, we provide a full length discussion on the topics of: (i) solvation of metal salts in ionic liquids, (ii) anion coordinating ability and homologous and heterogeneous complexes. A brief outlook into future perspectives of metal containing ILs is also provided.