An efficient multi-gram access in a two-step synthesis to soluble, nine-atomic, silylated silicon clusters

Silicon is by far the most important semiconducting material. However, solution-based synthetic approaches for unsaturated silicon-rich molecules require less efficient multi-step syntheses. We report on a straightforward access to soluble, polyhedral Si₉ clusters from the binary phase K₁₂Si₁₇, which contains both [Si₄]^4- and [Si₉]^4- clusters. [Si₄]^4- ions, characterised by a high charge per atom ratio, behave as strong reducing agents, preventing [Si₉]^4- from directed reactions. By the here reported separation of [Si₄]^4- by means of fractional crystallisation, Si₉ clusters of the precursor phase K₁₂Si₁₇ are isolated as monoprotonated [Si₉H]^3- ions on a multi-gram scale and further crystallised as their 2.2.2-Cryptate salt. 20 grams of the product can be obtained through this two-step procedure - a new starting point for silicon Zintl chemistry, such as the isolation and structural characterisation of a trisilylated [^MeHyp₃Si₉]^- cluster.