Explain the structures of ${\mathrm{SF}}_4\text{ and }{\mathrm{SF}}_6$.

In SF₆ central atom sulphur undergoes sp³d²  hybridization so that it has octahedral geometry. In SF₄ central atom sulphur undergoes sp³d hybridization.
Out of the five hybrid orbitals fifth orbital occupied by lone pair of electrons. The molecule possess distorted trigonal bipyramidal structure.