Strong-Field vs Weak-Field Ligands - Video Tutorials & Practice Problems

Strong-Field Ligands result in a large Δ and Weak-Field Ligands result in a small Δ.

Here, we can say that the crystal field splitting energy or delta of the octahedral complexes depends on the liam. Now, depending on the type of Ln attached to a metal cation, it can influence the magnitude and size of our crystal field splitting energy. Here, we're going to say that strong field Liang attached to metal CS result in large crystal field splitting energy. So if we take a look here, we see that the distances between our lower orbitals to our higher level orbitals, there's a bigger gap that's a larger delta. Next, we'd say that weak field ligands typically have result in a smaller or small crystal field splitting energy. So here are delta much smaller and we say in these cases, we'd have orbitals that are more degenerate, similar or same energy. Now, here when we're talking about strong field versus weak field li ans, we have these ones in particular, these are the ones that you need to commit to memory. So over here, we have our large delta. These are the largest delta with Sinai being at the, at the very end. And over here, we have our smallest delta with iodine. Over here on this end. Now our s our strong field ligands, how do we memorize the order of them? Well, all you have to recall is this memory tool and it is that Larry cannot enter the neighborhood. So Larry large cans and cyanide no deals with nitrate enter is ethylene diamine the neighborhood. So here we have ammonia. These represent our strong field like adds and then our weak field logans, we started with water And then you might notice that the rest of the ions are halogens. If you look at group seven A on the periodic table, you'll see you have fluorine, chlorine, bromine and iodine. So this is listed as we go down group seven A. So fluoride chloride bromide and iodide. So just remember that Larry cannot enter the neighborhood. Then for the week we have water and then look at group seven A flooring down to iodine. This gives us the order from strong field ligands to weak field ligands.

Example

Identify the complex with the largest crystal field splitting energy otherwise known as delta. So when it comes to delta, remember that tetrahedral has the smallest, then octahedral in the middle and then square planar is the highest. Now, if we take a look, the first three each has iron connected to six ligands. So all of these are octahedral in nature. The last one though has four chlorides connected to copper. So there's the potential of it being tetrahedral or square planar. So let's figure that one out first. So here this has to do with the copper plus one ion because here it's trying to basically work with the four chloride ions. But since there's more negative charge, that's why we have a remainder of three minus neutral copper. Its electron configuration is argon four S 1 3d 10. Remember is an exception. Plus one means we've lost one electron from the highest shell number. So the four S electron will be gone. So copper one is argon 3d 10, we have ad 10 ion. And because it's D 10, that means that it is tetrahedral tetrahedral has the smallest crystal field splitting energy. So this would not be our answer. It's gonna be one of these three. Here, they're all octahedral. So how do we determine? Well, remember for octahedral species, the Ln that attaches determines or affects our crystal field splitting energy. So all you have to remember is that Larry cannot enter the neighborhood. So here, the strongest field liad would give us the highest or largest crystal field splitting energy and cannot is the beginning of our memory tool. So cyanide here would be the strongest field liga when compared to water and ammonia. So here the answer would have to be option C so C would be our answer. It would produce the largest crystal field splitting energy.

Arrange the following complexes in an ascending order of the magnitude of Δ.

a) [Cr(NH₃)₆]²⁺

b) [Cr(en)₃]²⁺

c) [Cr(NO₂)₆]^4–

d) [Cr(H₂O)₄Cl₂]

• A. a < c < b < d
• B. c < b < a < d
• C. d < a < b < c
• D. b < c < d < a