Magnetic Properties of Complex Ions - Online Tutor, Practice Problems & Exam Prep

• Crystal field splitting energy determines the magnetic properties of complexes, influencing whether electrons fill lower or higher energy orbitals first.
• Large crystal field splitting energy results in low spin complexes where electrons fill lower energy orbitals first, leading to diamagnetic species with paired electrons.
• Small crystal field splitting energy results in high spin complexes where electrons are more likely to occupy higher energy orbitals, leading to paramagnetic species with unpaired electrons.
• Square planar geometries are associated with large crystal field splitting energies, typically resulting in low spin, diamagnetic complexes.
• Tetrahedral geometries are associated with small crystal field splitting energies, typically resulting in high spin, paramagnetic complexes.
• The geometry of a complex ion (square planar vs tetrahedral) can help predict its magnetic properties and the arrangement of electrons in its orbitals.

Low-Spin Complexes are associated with large Δ values and High-Spin Complexes are associated with small Δ values.

Now, the magnetic properties of complexes depends on how the transition metal valence electrons fill D orbitals. Now here we're going to talk about large crystal field splitting energy and small crystal field splitting energy. Well, with large crystal field splitting energy, we're going to say that lower energy orbitals fill first. This is what gives us what we call a low spin complex.

Now think of it like this. If your difference in energy is pretty high, going to cost you a lot of energy as an electron to try to go up to a higher energy level. The easier thing to do is just to stay on the same energy level as your other orbitals and continue to fill them out. If we take a look here, we have our metal cation with no ligands attached, and let's say that it has six electrons. Those six electrons, if we're talking about a low spin structure, we're going to fill in the lower energy orbitals.

So we take our six electrons, and following Hun's rule, we'd fill up halfway, First up, up. But remember we have 6 electrons we need to fill O. We're going to go down, down, down. So there's a couple things we can say here. We did this again because the cost of energy to go up to the higher level is pretty high. There's a large change in our crystal field splitting energy. Easier to just stay on that lower row of orbitals.

If we take a look, every single electron is paired up here, so within this low spin example we have a diamagnetic species. Remember diamagnetic means you have no unpaired electrons. And also remember we have our basically our five orbitals here have been split. We have here dx, dyz and dxz. These are in between the axes, they're the ones that are belonging to T2 sets. And then we have dx2 - y2 and then dz2. These are along or on the axis, they're higher up in energy and the difference between them is our crystal field splitting energy.

Now, what happens if the difference is small? Well, if you have a small crystal field splitting energy difference, then the orbitals are treated as degenerate. Remember we've talked about this word in earlier chapters, It just means that they're at the same energy. So although they're tiered where we have these three on the lower part and these two are on the higher part because their difference in energy is so, so much smaller, we're going to treat them as the same. So it's not going to cost as much energy for an electron to try to fill up the higher levels.

So here we call this also a high spin complex. So here we have high spin. We have these same 6 electrons originally, so we're going to start filling up op, op. That's three 4-5. And then we still have that 6th 1:00. So we come back down down O. We've filled in our six electrons. We can see here that the difference in crystal field splitting energy between T2 and esat arm is much smaller. That's why we can do this.

Another thing we should notice here is that we have some electrons that are not paired up. If we have a species that has at least one unpaired electron, we say that is called paramagnetic. So just keep in mind when we're talking about differences in crystal field energy splitting energy, if it's too large, electrons rather just stay on the bottom level. That's more stable, less energetic. Fill that out as much as it can before even attempts to go up to a higher level.

In this case you'll have a low spin complex. In this example here we have it as a diamagnetic species. If you have a very small difference in your two sets of orbitals then treat them as the same in terms of energy or degeneracy. So you'd have a high spin complex and you would have fill all of them first before you start filling U the lower row. So just keep this in mind the differences between high and low complexes in relation to crystal field splitting energy.

Finding tetrahedral and square planar geometries helps to determine the low vs high spin of complexes.

Find tetrahedral and square planar geometries helps to determine the low versus high spin of complexes. Here we can say that if you have a square planar geometry that is associated with a large crystal field splitting energy or Δ. Now that just means that the energy level between your two rows of orbitals is pretty high. So it would be a high cost for electrons to fill in the first row and then try to go up to the second row. They'd rather stay there on the bottom row and fill in as much of the orbitals as they can.

In this case, they're going to stay in the lower level. So we're going to say this is a low spin complex. We're going to say because it's a low spin complex for squared planar, this will give us a diamagnetic electron orbital diagram. Now if you're a tetrahedral, so we can assume since square planar is that way, tetrahedral would be what the opposite. So here with tetrahedral, that's associated with a small Δ.

A small Δ here would mean that there's not much difference between the energy levels, so you would treat all the orbitals as degenerate having the same energy. So that would give us a high spin complex, and we'd say with a high spin complex we typically are a pair of magnetic species. So the take away from this is if you have square planar, we have low spin complexes and they are diamagnetic, and if you have tetrahedral they tend to be high spin complexes that lead to paramagnetic species, right?

So keep this in mind when we're looking for the geometry of different types of complex ions.

Example

Determine the geometry and spin of the following complex ion. Alright, so if we take a look here, we have Palladium involved. Palladium would have to have a charge of two plus and that's because the bromide ion, there's four of them, which collectively is -4. But our overall charge is 2 minus. The Palladium would have to be two plus in order to secure this 2 minus overall charge.

Alright, so we have the ion. Remember, Palladium is one of those exceptions that exists. Palladium is a neutral atom is Krypton, and the thing with it is it cannot have any electrons in its 5S orbital. Those two electrons are promoted up to the 4D orbitals, so it's really 4D₁₀. Two plus means we've lost electrons from our highest shell number here, so now it's going to be Krypton 4D₈. So this is AD₈ ion.

And remember, if your D₈, that means your geometry is square planar. So we know that geometry is square planar, and then we have to talk about the spin. Here we'd say because it's square planar, they typically have high crystal field slitting energy, which means that they will result in a low spin complex. So here this is what we can say in terms of this particular complex ion.

Now if we were to fill this out, we would see that there would be some unpaired electrons which would actually give us a perimagnetic orientation. But remember, with square planar and basically with our tetrahedral species, we could talk about the spins of them and typically square planar should have a diamagnetic orientation, but that's not always certain as we can see here. And that's because Palladium is one of those elements. That's just an exception to the electron configuration setup. So it kind of throws everything out of whack.

So here in this particular case, all we need to know is that this is a square square planar species and that it has a low spin complex.

Determine if the following complex ion is either paramagnetic or diamagnetic: [CoF₄]^2–.

• A. Paramagnetic
• B. Diamagnetic
• C. Cannot be determined