Crystal Field Theory: Square Planar Complexes - Video Tutorials & Practice Problems
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1
concept
Square planar complexes show the most complex splitting pattern.
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Square planar complexes show the most complex splitting pattern. We're gonna say orbitals on and between the x and y axis 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 first three 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 axes. The x axis interacts with 2 lobes here as it cuts through, and then the y axis interacts with 2 lobes as it cuts here. The next one should have the 2nd highest energy because it interacts with both x and y axis still, just not as much as the first one. D z squared might seem misplaced here, but there is some interaction occurring with the x and y axis. If you look in closely, you'll see this ring or kind of disc. This one lies and interacts with the x and y axis. 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 2 orbitals, so that's why it's here. The last 2, they are degenerative, they have the same energy because they're each only interacting with 1 of the 2 axes that we care about, x and y. D y z is interacting with the y axes, and d x z is interacting with the x axes. 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 or with the x and y axes, it all starts to make sense.
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example
Example
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Which one of the following complexes shows the most complex splitting pattern energy? Remember, this occurs with square planar complexes. If we look at our options, b and d are both out because in both, we have 6 donor atoms connecting to our metal cation. Those could not give us a square planar complex. The answer is gonna be either a or c, because in both of those, we have 4 ligands which have the potential of being either tetrahedral or square planar. In the first one, if we take a look at the cadmium ion, it's cadmium 2+. Its electron configuration, when you look at it, would be Krypton 4d10. Now here it is a d 10 ion, and remember if you're d 10, you are tetrahedral. So this would not give us the correct geometry. For c, we have nickel here connected to 4 ammonias, which are neutral, so the 2 plus charge is coming from the nickel itself. If we do its electron configuration, it would be argon 3d8. Now it is a d 8 ion, and that means that its geometry is square planar. So option c would give us a square planar geometry, which results in the most complex splitting pattern energy.
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Problem
Problem
Which of the following complexes will have the largest crystal field splitting energy?
A
[Co(NH3)6]2+
B
[Cr(NH3)3(H2O)3]2+
C
[ZnCl4]2–
D
[Ni(CN)4]2–
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