The first structurally characterised example of silicon in an S 6 coordination sphere

The reaction of sodium hydro-tris(phenylthioimidazolyl)borate (NaTm) with silicon tetraiodide gives rise to the first crystallographically characterised molecular silicon compounds, [Si(Tm)2] 2X (X = I and I3 ), in which the silicon is found in a regular S6 environment. The [Si(Tm)2] 2+ cation is subjected to analysis using DFT methods to explain why an S6 coordination motif is preferred to an S4 coordination motif.