The effects of the nonbonding lone pair in the tin and lead anions in compounds such as Sr(MX₃)₂.5H₂O (M = Sn or Pb, X = Cl or Br) have been studied by crystallography and by electronic structure calculations (I. Abrahams et al., Polyhedron, 2006, 25, 996). Briefly outline the synthetic method used to prepare the compounds and indicate which compound could not be prepared. Explain how this compound was handled in the electronic structure calculations as no experimental structural data were available. State the shape of the [MX₃]⁻ anions and describe how the effect of the nonbonding lone pair varies between Sn and Pb in the gas phase and the solid phase.