Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 2 / Section H / 33 / b / iii / Solution

The central silicon contributes four electrons to the delocalized metal-core count. Six monovalent Cp* ligands each withdraw one electron, givingThis is a jellium closed shell, through the filled 2P shell. The ${\mu }_8$ label identifies an encapsulated silicon with eight aluminium contacts; it should not be counted as an ordinary exterior Wade vertex with an outward lone pair. The gross electron count rationalizes shell closure but does not alone reconstruct every Al–Al bond or all ligand positions.