JEE Main · 2021 · 25 Jul 2021 · Shift 1 · p-Block Elements

Silicon can expand its coordination number beyond four by using $3d$ orbitals, but only with ligands small enough for six of them to pack round so small an atom. Fluoride meets that condition, so $[\mathrm{Si}{\mathrm{F}}_6{]}^{2-}$ is a well known ion, while six chloride ions, which are much larger, cannot be fitted about silicon without severe crowding. Germanium and tin are bigger atoms and take six chlorides or six hydroxides comfortably, so $[\mathrm{GeC}{\mathrm{l}}_6{]}^{2-}$ and $[\mathrm{Sn}(\mathrm{OH}{)}_6{]}^{2-}$ both exist. The species that is not known is $[\mathrm{SiC}{\mathrm{l}}_6{]}^{2-}$.