Square planar complexes show the most complex splitting pattern. We're going to say orbitals on and between the X&Y axes have the strongest interactions with ligands. Remember, the stronger the interaction with the ligands, the higher the energy of the orbital. If we take a look here at this image, we can see that there's a gradient that forms with the 1st 3 orbitals. It starts off very shaded initially, and then it tapers off and gets lighter as we move towards the right, signifying a lesser interaction with the ligands and therefore lower energy for our orbitals.
The first will make sense because in this one we're dealing with interactions that are on or along the axis. The X axis interacts with two lobes here as it cuts through, and then the Y axis interacts with two lobes as it cuts here. The next one should have the second highest energy because it interacts with both X&Y axes, still just not as much as the first one. dz² might seem misplaced here, but there is some interaction occurring with the X&Y axis. If you look in closely, you'll see this ring or kind of disk. This one lies and interacts with the X&Y axes. If you look, you can see the Y cutting through it, and here you can see the X cutting through it. So it's along the axis. It just doesn't have as great interaction as the previous two orbitals, so that's why it's here.
The last two, they are degenerative. They have the same energy because they're each only interacting with one of the two axes that we care about. X&Y dyz is interacting with the Y axis and dxz is interacting with the X axis. Now as you can see, this crystal field splitting pattern is pretty tall, and the difference in height here is why square planar complexes have the largest delta values. Now again, their splitting pattern is a bit more complex, but as you go through each one and see how they interact on the organ with the X&Y axes, it all starts to make sense.
