(a) Draw possible stereoisomers for the trigonal bipyramidal [SiF₃Me₂]⁻ anion (Me = CH₃). An X-ray diffraction study of a salt of [SiF₃Me₂]⁻ shows that two F atoms occupy axial sites. Suggest why this stereoisomer is preferred over the other possible structures that you have drawn.

(b) Account for the fact that members of the series of complexes [PtCl₄]²⁻, [PtCl₃(PMe₃)]⁻, [PtCl₂(PMe₃)₂] and [PtCl(PMe₃)₃]⁺ do not possess the same number of stereoisomers.