Isostructural species have the same shape and geometry.

1. XeF4: Xenon undergoes sp3d2 hybridization (4 bond pairs + 2 lone pairs) and has a square planar geometry.
2. XeO4: Xenon undergoes sp3 hybridization (4 bond pairs + 0 lone pairs) and has a tetrahedral geometry. Since their shapes are different, they are not isostructural. In contrast, SiCl4 and PCl4+ are both tetrahedral (sp3); Diamond and Silicon carbide both have a similar tetrahedral network solid structure; NH3 and PH3 are both trigonal pyramidal (sp3 with 1 lone pair).