`[SiF_6]^(2-)` is known but `[SiCl_6]^(2-)` is not. Why?

Explanation

Possible reasons for the non-existance of `[SiF_6]^(2-)`are:
1. Six fluorine atoms can be easily accommodated around silicon atom due to smaller size while six larger chlorine atoms cannot be accommodated around silicon atom.
2. The unshared pair of electrons present in a relatively small 2p -orbital of F interacts with the d -orbitals of Si better than the unshared pair of electrons present in a relatively large 3 p -orbital of Cl.