A classmate says, “A weak-field ligand usually means the complex is high spin.” Is your classmate correct? Explain.

Video transcript

All right. Hi everyone. So this question says that a complex with a strong field ligand is usually high spin, is this claim correct? And to briefly explain. So on the screen right now is an example of an energy diagram for an octahedral complex, meaning that there are two higher energy D orbitals and three lower energy D orbitals. Now the crystal field splitting energy abbreviated here as delta is the energy difference between these higher energy and lower energy orbitals. The specific value for delta for the crystal field splitting energy is dependent on the complex itself or more specifically the ligands themselves. Now, just for a moment, I am going to go ahead and copy and paste this diagram because I want to showcase two different possibilities. Alright. So here I've continued the recording and I have two separate energy diagrams right now. One of them specifically the one to the right has a higher energy difference between the higher and lower energy orbitals. In cases like this, when the value for delta is larger, this is going to be an example of when a strong field thickened is present. On the other hand, when the value for delta is smaller. This is going to be an example of a weak field ligand. Now, it just so happens that a particular complex can be either high spin or low spin. And that's going to depend on the value of the pairing energy relative to delta. Recall that the pairing energy or P is the amount of energy associated with pairing electrons in one single orbital. And electrons are going to prefer to be in the lowest available energy state as often as possible. This means that in cases where P is greater than delta, this is considered to be high spin. And so what that means is that electrons are going to occupy all of the orbitals first, including higher energy orbitals before any electrons are paired. On the other hand, if the value for P is less than delta, then this is an example of a low spin complex. And so what that means is that electrons would rather pair up and occupy all of the lower energy orbitals before moving to those higher energy orbitals. So going back to the diagram for a strong field ligand, strong field ligands are going to result in larger values for delta. That's the crystal field splitting energy. If the splitting energy is larger than the pairing energy, then that's more likely to result in a low spin complex. Meaning that electrons would rather occupy the lower energy orbitals first before jumping to those higher energy orbitals on the other hand, when having a weak field ligand and therefore a smaller value for delta, then the opposite can be observed. And a high spin complex can be observed. Meaning that if I am accommodating four electrons, then the first three would it be unpaired within the lower energy orbitals? And the forest can jump towards the higher energy orbitals? So going back to our claim here, this claim is not correct. So I'm going to briefly pause the recording so I can write out the final answer and summarize what we discussed. All right. So now the recording has resumed and I'm going to scroll down. So you can see the final answer. The final answer reads as follows. No, the statement is incorrect. A complex with a strong field ligand will influence large crystal field splitting energy or delta. If the splitting energy is larger than the pairing energy P electrons will be, will more likely pair up first before filling the higher energy orbitals resulting in a low spin complex. And there you have it. So with that being said, thank you so very much for watching. And I hope you found this helpful.