Magnetic Properties of Complex Ions - Video Tutorials & Practice Problems
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1
concept
Low-Spin Complexes are associated with large Δ values and High-Spin Complexes are associated with small Δ values.
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Now the magnetic properties of complexes depends on how the transition metal valence electrons fill d orbitals. Now here we're gonna 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, it's gonna 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 6 electrons. Those 6 electrons, if we're talking about a low spin structure, we're gonna fill in the lower energy orbitals. So we take our 6 electrons, and following Hund's rule, we'd fill up halfway first. Up, up, up. But remember, we have 6 electrons we need to fill. So we're gonna 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 5 orbitals here have been split. We have here d x, d y z, and d x z, these are in between the axes, they're the ones that are belonging to t 2 sets, and then we have d x squared minus y squared, and then d z squared, these are along or on the axes, 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 where we have these 3 on the lower part and these 2 on the higher part, because their difference in energy is so small so much smaller, we're gonna treat them as the same. So it's not gonna 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 gonna start filling. Up, up, up. That's 3, 4, 5, and then we still have that 6th one, so we come back down, down. So we've filled in our 6 electrons. We can see here that the difference in crystal field splitting energy between t 2 and esat are 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 1 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 2 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 half fill all of them first before you start filling up the lower row. Right? So just keep this in mind, the differences between high and low complexes in relation to crystal field splitting energy.
2
concept
Finding tetrahedral and square planar geometries helps to determine the low vs high spin of complexes.
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Finding 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 delta. Now that just means that the energy level between your two rows of orbitals is pretty high. So it'll be a high cost for electrons to fill in the 1st row, and then try to go up to the 2nd 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 gonna stay in the lower level, so we're gonna say this is a low spin complex. We're gonna say because it's a low spin complex, for square planar this will give us a diamagnetic electron orbital diagram. Now if you're 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 delta. A small delta 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 paramagnetic species. So the takeaway 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.
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example
Example
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2m
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Determine the geometry and spin of a following complex ion. Alright. So if we take a look here, we have palladium involved. Palladium would have to have a charge of 2 plus, and that's because the bromide ion, there's 4 of them, which collectively is minus 4, but our overall charge is 2 minus. The palladium would have to be 2+ 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 as a neutral atom is krypton, and the thing with it is it cannot have any electrons in its 5 s orbital. Those 2 electrons are promoted up to the 4 d orbitals, so it's really 4d10. 2 plus means we've lost electrons from our highest shell number here, so now it's gonna be Krypton 4d8. So this is a d 8 ion. Remember, if you're d 8, that means your geometry is square planar. So we know the 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 splitting 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 paramagnetic 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 kinda throws everything out of whack. So here in this particular case, all we need to know is that this is a squares square planar species, and that it has a low spin complex.
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Problem
Problem
Determine if the following complex ion is either paramagnetic or diamagnetic: [CoF4]2–.
A
Paramagnetic
B
Diamagnetic
C
Cannot be determined
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