Isomerism in Coordination Complexes - Video Tutorials & Practice Problems
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concept
Isomers
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Now recall that isomers are molecules with the same molecular formula, but different connectivity or spatial orientation. Here in the middle, we have our coordination complex, which is comprised of our coordination I a complex ion and this counterion of bromide. With a structural isomer, you'd have the same exact formula, overall formula, but different connections. The way we could do this is we could take one of the chlorines here and this bromide and have them swap places. So now our bromine would be here and our chloride ion would be out here. Both structures have the same formula, but they have different connectivity because now we're connected to the bromine instead of 2 chlorines. With sterile isomers, we're talking about differences in spatial orientation. So the connections are the same, they're just represented differently in terms of spacing. So what I could do here is I have 2 chlorines on the same side here and 2 ammonia on the same side. I can just swap that. Now I have an ammonia on this side, and I have a chlorine on this side. The connections are still the same. Our metal cation is still connected to 2 chlorides and 2 ammonium ammonia molecules. It's just now they're not on the same side with each other. So this will count as a stereo isomer. So keep this in mind when we're talking about isomers, overall we'll take taking a look at differences in connectivity or in spatial orientation.
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concept
Structural Isomers
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Now when we talk about structural isomers, we're gonna say it consists of 2 types. We have coordination isomers or linkage isomers. In coordination isomers, we're gonna say these these are molecules where the anionic ligand and a counter ion have switched places. So if we take a look here at these 2, what can make them coordination isomers? Well, we have an anionic ligand. Let's say our ligand here that's anionic is the bromide ion, and it's gonna switch places with a counter ion. Now the charges of them both have to be the same. So if I have a minus one here, I need to have a minus one ligand attached to the metal. So let's put a chlorine here. For for us to make its isomer, I just have those switch places. Now my bromide ion has come here and my chloride ion is out here. So we swapped in an anionic ligand for another one. Now linkage isomers. These are molecules where the connectivity between the ligand and the metal is different. So one example we can have here is with thionocyanate. Remember, thionocyanate has resonance involved. And because of that, we could either have the nitrogen be the negative end or the sulfur being the negative end. When we talked about donor atoms, we said that the negatively charged atom within a ligand would act as a donor atom, And because nitrogen or sulfur can be negatively charged, either one could be the donor atom. This will result in linkage isomers. One where we have these sulfurs directly connecting to our silver ion, or one where the nitrogen directly connects to our silver ion. So these will be 2 linkage isomers, and it's a result of the ligand itself possessing resonance, meaning multiple elements could be the donor atom. Right? So just keep in mind when we talk about structural isomers, we're talking either about coordination isomers or linkage isomers.
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example
Isomerism in Coordination Complexes Example
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Draw 1 coordination isomer and 1 linkage isomer of the following complex. Alright. So here we have our coordination complex. If we wanna draw a coordination isomer, that means we have to substitute a counter ion for a ligand that's attached to the metal. Here, we could do that, we have still have our platinum here, it would still be connected to the ammonias, and it's the thiocyanate ion that's negatively charged like the bromide counter ion that's negatively charged. So I would just switch out the thiocyanide or thiocyanate anion, and bring in the bromide, and then your thiocyanate ion is on the outside. This will represent a coordination isomer. For our linkage isomer, the ammonias are still there, And what we're doing here, remember, thiocyanide has resonance involved. Here we show the sulfur directly connecting to the metal cation, but I could easily have the nitrogen directly connecting to it instead. And the bromide ion would still be on the outside as a counter ion. So this here would represent a linkage isomer. Right? So these are examples of a coordination isomer and a linkage isomer based on the original coordination complex given.
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concept
Geometric Isomers
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With geometric isomers, we're gonna say this is where a ligand has different spatial orientation around the metal. Now this occurs in complexes of formula, mx2y2and mx2y4. Here we're going to say sys equals the ligand pair on the same side, and trans equals ligand pair on opposite sides. So if we take a look here at m x two y two, here we could say that x could represent the ammonia, and then y could represent the chlorine. If we want to make this cis, that means same side, we'd have to put a chlorine here, so that they're both on the same side. And we put an ammonia here. So they're on the same side. Trans here, they would have to be opposite, so they have to be on different sides. So the chlorine would be here, and now they're kind of opposite of each other, opposite sides. And the ammonia would be here, again, opposite sides. With mx2y4, here let's say we're using, as our x 2 chloride ions again. For them to be cis, they'd have to be on the same side, so I put a c l here. Actually, let me just make this yeah. We'll put a c l here and a c l here. They're both on the same side. And to make them trans to each other, they'd have to be on opposite sides, so a c l would go here and a c l would go here. Now they're on opposite sides of each other. So again, geometric isomers, we're talking about different spatial orientation around the metal, and this happens when the formula is mx2y2 or mx2y4. So keep that in mind when looking at different types of geometric isomers.
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example
Isomerism in Coordination Complexes Example
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Identify the following pairs of complexes as coordination, linkage, or geometric isomers. For the first one, look for where the difference is. The difference is here and here. In the first one, we have n o 2, where the nitrogen is connecting directly to the cobalt metal cation. But then next to it, it's the oxygen within the nitrite ion that's connecting to the metal cation. How is this possible? Through resonance. So we'd say the first one is a linkage pair, or a pair of linkage isomers. For the next one, look to see where is the change, where is the difference here. Well, in both, they're connected to nickel's connected to 2 waters, and it's connected to 2 ammonia. But as we can see in the first one, the waters are on the same side, the ammonia is on the same side, but the iceberg next to it, they're opposite of each other now, so this would be a geometric pair of isomers. So next, let's see. Next we have what? What's the difference? Well, the chlorines here are next to each other, making them cis, and now they're opposites of each other, making them trans to each other. Also remember, in this first example, if we look, the formulas are what? Mx2y2, and these 2 are mx2y4. They'll those tell us that these are geometric isomers as well. Then finally the last one, what's the difference between these 2? Well, it looks like we have a BR here and a CL here, and it looks like they swapped places. We substituted out the counter ion and the, basically anionic ligand here. This is an example of coordination isomers. So that's what we can say about each of the following pairs given to us within this example problem.
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Problem
Problem
Which of the following complexes cannot have geometric isomers?
i) [PtCl2(NH3)2]
ii) K4[Fe(CN)4(OH)2]
iii) [Ag(NH3)2]Cl
iv) [Ni(H2O)2(NH3)2]Br2
A
i, ii, and iv
B
ii and iv
C
iii only
D
i and iii
E
iv only
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Problem
Problem
The complex [Fe(NH3)5OCN]2+ has two isomers. Draw their structures.
A
B
C
D
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Problem
Problem
How many isomers are possible for [Cu(H2O)2(NH3)2]SO4? Draw their structures.