Presence of vacant $d$-orbitals in $\mathrm{Si}, \mathrm{Ge}$ and $\mathrm{Sn}$, makes the existence of species $\left[\mathrm{SiF}_6\right]^{2-},\left[\mathrm{GeCl}_6\right]^{2-}$ and $\left[\mathrm{Sn}(\mathrm{OH})_6\right]^{2-}$ feasible. But $\left[\mathrm{SiCl}_6\right]^{2-}$ cannot exist as six large $\mathrm{Cl}^{-}$cannot be accomodated around $\mathrm{Si}^{4+}$ ion due to smaller size of cation.