Intro to Crystal Field Theory - Video Tutorials & Practice Problems
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1
concept
The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.
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In this video on the intro to crystal field theory, we're going to see that transition metal coordinations compounds form crystalline solids. Now, if we take a look here, we see this beautiful gem, this red gem. Well, crystal field theory was developed to explain the color as well as the magnetism or magnetic properties of cordination compounds. In fact, we're gonna say that coordinating compounds form crystals. When we say crystal song, we're talking about crystals, hence the name for color within the name. And we're going to say it also focuses on the effects of ligands electric field around the metal cations. Now ligands surround and create this type of magnetic. Well, this electric field around a metal cion. That's why the word field is also in the name. Later on. This helped to create what's known as li and field theory. It's just a combination of crystal field theory with molecular orbital theory. So that's the origins of this whole idea of crystals and colors and magnetic properties. So as we delve into different types of complexes, we'll be touching on a little bit of each of these ideas within our videos
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concept
The greater the interaction between the metal and its ligands then the greater the energy of its d orbitals
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When it comes to l an orbital interactions, we're going to say that the interaction between them is electrostatic. And we're gonna say we're gonna have an increase in the energies of metal de orbitals, which in turn causes an increase in their interactions, which increases our energy. Just understand that we are gonna have like charges and light charges repel one another. So we're gonna have the electrons of the metal cion interacting with the electrons of our ligands. This repulsion between them causes this increase in energy. So if we take a look here, we have our up arrow which is showing an increase in energy. And we have here initially are five orbitals, five D orbitals. We're gonna say these are metal D orbitals without a Ln attached. Once we bring in A L in and attach it to the metal cion. Again, we have to compete, we have this repulsive behavior between the electrons of the metal cion and the electrons of the ligand. This is gonna cause an increase between the interactions of their electrons. So these higher energy orbitals here are just the metal D orbitals with the ligand or ligands attached. So take from this as, as we add ligands to our metal cations, we're gonna see an uptick in the energy of the de orbital electrons of the metal cion.
3
concept
For octahedral complexes, the greatest ligand-metal interactions occur on or along the axes.
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Now, in terms of the interactions in octahedral complexes, we're going to say that the strength of light and orbital interactions depend on complex geometry and de orbital orientation. We're gonna say here that for octahedral complexes, the ligands are on the axes. So remember we say on the axes or along the axes, they're both synonymous with one another. We're gonna say on the axes orbitals have the greatest interaction interactions with the ligands. So if we take a look here, what we have is a representation of our octahedral species. So think of it like two square pyramids that are stacked on top of each other or stacked inversely to each other, their base is touching one another. So we have these six points which represents our lances and in the center, we have our metal cion in theory. Now, on the axis, we'd say that the greatest interaction again happens on the X and y axis here for this one. So it's DX squared minus Y squared. And then this one, we have the most interactions happening on the Z axis. So DZ squared in these two on the axes examples, we'd say that an increase in interaction causes an increase in energy. Now, in between the axis, we have our other three orbitals. These don't line up in the correct orientation to have the greatest interaction. So we're gonna say we have less interaction in this setup which would cause a decrease in energy or less energy involved. So just remember when it comes to octahedral species themselves, the greatest interaction is happening on the axis or along the axis. So in particular, we're talking about D sub X squared minus Y squared and D sub Z squared. So just keep that in mind.
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example
Example
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Here, it says which set of de orbitals below will interact the most with the ammonia ligands in within this coordinations complex. All right. So remember this is our complex ion portion and this is what we care about. A chlorine over here is just a counter ion. Now, here we have six ammonia molecule ligands attached to our iron. So this is an octahedral complex. And when it comes to octahedral complexes, the greatest interactions are happening along the axes or on the axes. And that only happens for two types of orbitals. And they would be D sub X squared minus Y squared and D sub Z squared. If we look at our options, the only one that has only those two orbitals and nothing else would be option. E so here, option E would be our final answer.
5
concept
For tetrahedral complexes, the greatest ligand-metal interactions occur in between the axes.
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Now with interactions in tetrahedral complexes, we're going to say that the ligands are lined in between the axes. And we're gonna say in between the axes, the orbitals there have the greatest interactions with the lances. So if we take a look here, think of a cube, the cube here we have are four points in terms of this cube. And we're gonna say that this point and this point are the ones that are nearest us. And you can see that these two dots here are smaller because they're in the back. If you were to take those four points and have them represent our four li ends, you couldn't shift this over and put it amongst all of these axes, your xy and Z axis. Now remember in between the axis deals with Dxydyz and DXZ along or on the axis. Well, that's reserved for D sub X squared minus Y squared and D sub Z squared. Now remember for tetrahedral complexes, the greatest interaction is in between the axes. So here we have the greatest interaction amongst these three orbitals which will result in the greatest amount of energy for the ones on the axes. They don't quite line up in the way that has the greatest interaction between the LG and the metal cion. Because of this, we're gonna see a decrease in interaction which is gonna result in a decrease in energy. So remember with tetrahedral complexes, the greatest interaction between the metal cion and the liga um lies in between the axes and keep in reference these particular D orbitals, dxydyz and DXZ.
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example
Example
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Identify the de orbital or orbitals with the highest energy in the complex show below. Here we have zinc as our metal cion connected to four hydroxide ions doing this gives us an overcharge of two minus. Now, the way that it's depicted shows that this is a tetrahedral complex and with tetrahedral complexes, the greatest interaction happens in between the axes. Remember the orders that lie in between the axes would be dxydyz and DXZ. These remaining two are the ones that are along the axes or on the axis. So they would not have the greatest interaction. So A B and C are the correct orbitals. And because of that, the answer would have to be option G. So we're talking about A B and C as being the D orbitals with the highest energy in this tetrahedral complex.
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Problem
Problem
For an octahedral complex, which set of d orbitals is expected to be at the lowest energy?
A
dxy, dyz, dz2
B
dyz, dxz, dz2
C
dxy, dyz, dxz
D
dxy, dyz, dx2–y2
E
dyz, dx2–y2, dz2
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