Answer
See explanation below.
Work Step by Step
Square planar coordination can be imagined to result when two ligands on the z-axis of an octahedron are removed from the complex, leaving only the ligands in the x-y plane. As the z-ligands move away, the ligands in the square plane move a little closer to the metal.
The orbital splitting diagram for square planar coordination can thus be derived from the octahedral diagram. As ligands move away along the z-axis, d-orbitals with a z-component will fall in energy. The dz2 orbital falls the most, as its electrons are concentrated in lobes along the z-axis. The dxz and dyz orbitals also drop in energy, but not as much. Conversely, the dx2-y2 and the dxy orbitals increase in energy. The splitting diagram for square planar complexes is more complex than for octahedral and tetrahedral complexes, and is shown below with the relative energies of each orbital.
