From non-innocent ionic liquids to reactive agents in the synthesis of chalcogenido metalate compounds

Chalcogenido metalate compounds are an exceptional class of inorganic materials, ranging from discrete clusters and simple binary solids to complex multinary three-dimensional structures with open frameworks. This structural and compositional diversity generally enables a wide range of applications, including opto-electronics, ion separation and catalysis. Traditionally, chalcogenido metalates have been synthesized using flux synthesis or high-temperature solid-state reactions as well as solvothermal approaches. More recently, this was shifted towards lower-temperature approaches, not only for economic and environmental reasons, but also to access previously inaccessible compounds. In this context, ionic liquids (ILs) have become important reaction media. However, while ILs have been famous for their role as inert reaction media that provide a controlled environment for crystallization, they can also be actively involved in the reactions under certain conditions and thus influence the formation and stabilization of the new chalcogenido metalate compounds. This can take place by adopting a templating role or through the transfer of (functional) groups, which enables access to modifications and variations of the corresponding substructures. This dual role of ILs-as reaction media and reactive agents-provides new opportunities for fine-tuning the structural and electronic properties of chalcogenido metalate compounds. In this review, the multifaceted roles of non-innocent ILs in the synthesis of chalcogenido metalate compounds are explored, with particular attention on their effects on cluster formation, cluster stability, and their ultimate effect on the compounds' properties.