Chapter 3, Problem 3.26P

${\text{SeCl}}_{\text{6}}{}^{\text{2}-},{\text{TeCl}}_{\text{6}}{}^{\text{2}-}$ , and ${\text{CIF}}_{{\text{6}}^{-}}$ are all octahedral, but ${\text{SeF}}_{\text{6}}{}^{\text{2}-}$ and ${\text{IF}}_{{\text{6}}^{-}}$ are distorted, with a lonepair on the central atom apparently influencing the shape. Suggest a reason for the difference inshape of these two groups of ions. (See J. Pilmé, E. A. Robinson, R. J. Gillespie,Inorg. Chem.,2006, 45, 6198.)