Heavy Chalcogenide-Based Ionic Liquids in Syntheses of Metal Chalcogenide Materials near Room Temperature

This minireview describes two strategically different and unexplored approaches to use ionic liquids (IL) containing weakly solvated and highly reactive chalcogenide anions [E-SiMe₃ ]^- and [E-H]^- of the heavy chalcogens (E=S, Se, Te) in materials synthesis near room temperature. The first strategy involves the synthesis of unprecedented trimethylsilyl chalcogenido metalates Cat⁺ [M(E-SiMe₃ )_n ]^- (Cat=organic IL cation) of main group and transition metals (M=Ga, In, Sn, Zn, Cu, Ag, Au). These fully characterized homoleptic metalates serve as thermally metastable precursors in low-temperature syntheses of binary, ternary and even quaternary chalcogenide materials such as CIGS and CZTS relevant for semiconductor and photovoltaics (PV) applications. Furthermore, thermally and protolytically metastable coinage metalates Cat⁺ [M(ESiMe₃ )₂ ]^- (M=Cu, Ag, Au; E=S, Se) are accessible. Finally, the use of precursors BMPyr[E-SiMe₃ ] (E=Se,Te; BMPyr=1-butyl-1-methylpyrrolidinium) as sources of activated selenium and tellurium in the synthesis of high-grade thermoelectric nanoparticles Bi₂ Se₃ and Bi₂ Te₃ is shortly highlighted. The second synthesis strategy involves the metalation of ionic liquids Cat[S-H] and Cat[Se-H] by protolytically highly active metal alkyls or amides R_n M. This rather general approach towards unknown chalcogenido metalates Cat_m [R_n-1 M(E)]_m (E=S, Se) will be demonstrated in a research paper following this short review head-to-tail.