Question

${\left[Si{F}_6\right]}^{2-}$ is known whereas ${\left[SiC{l}_6\right]}^{2-}$ not. Give possible reasons.

Answer 1

Reasons for non-existence of ${\left[SiC{l}_6\right]}^{2-}$:

(i) Due to smaller size of $F$, steric repulsions will be less in ${\left[Si{F}_6\right]}^{2-}$. In ${\left[SiC{l}_6\right]}^{2-}$, six large chloride ions cannot be accommodated around $S{i}^{4+}$ due to limitation of its size.

(ii) Interaction between lone pair of fluoride with $S{i}^{4+}$ is stronger while interaction between lone pair of chloride ion with $S{i}^{4+}$ is not very strong.