Crystal Field Theory: Octahedral Complexes - Video Tutorials & Practice Problems
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1
concept
The crystal field splitting pattern for octahedral complexes has the d orbitals on or along the axes as having the higher energy.
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3m
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Now, crystal field splitting is the separation of degenerate d orbitals into non degenerate sets. So remember the word degenerate means same energy. So we're taking the five D orbitals that are on the same level, same energy and we're basically separating them, creating one tier that's lower in energy and one that's higher in energy. Now, the splitting patter complex depends upon its geometry. So we'll see based on the geometry of our our complex ion, these five D orbitals can orient themselves in different ways. Now, here with octahedral crystal field splitting, we're gonna say recall that in octahedral complexes, the liga orbital interactions are on the, on the axis or along the axions are the strongest ones. We're gonna say uh this increases the energies of the orbitals that are oriented on the axis. So if we take a look here, we have our six lends that are the green dots. And remember the two orbitals that lie on the axis or along the axes are DX squared minus Y squared or DZ squared, they have the greatest energy. So we would orient them up here. And then these other three are the ones that lie in between the axes, they have less interaction and therefore would have lower energy. So we're placing them down here. Now, we're gonna say that the difference in energy between these three bottom ones and then these two top ones, it is designated as delta delta represents our crystal field splitting energy. And we're gonna say that this is the energy difference between the two sets which are E and T two of orbitals. All right. So which one is uh E, which one is T two? Well, in terms of this optic Hero complex, we're gonna say that our E equals doublet, which means it's the pair of orbitals are two orbitals. So these two would be our E set and then T here stands for triplet which is our three orbitals. So this would be our T set here. So just remember when we talk about crystal field splitting, we're looking at our five original de orbitals and we're separating them. One on the bottom is lower in energy. And then up here higher in energy for all Toral species. It's the ones that lie on the axis or along the axes that have greater energy because of greater interaction. That's why D sub X squared minus Y squared and D sub Z squared are up here. The other ones lie in between the axes, less interaction, less energy. That's why they're lower down here. And again, their difference in levels is our delta, our crystal field splitting energy
2
example
Example
Video duration:
43s
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For which of the following complexes, the energy of the T two set is lower than the E set. So this question is actually easier than it appears. What they're really asking us to determine is which one of these complex ions represents an octahedral complex. So remember to be octahedral, you need your metal cion to be connected to six ligands. And if we look the only option that has our metal cion connected to six ligands is option D. Here we have Cobalt three plus ion connected to six water molecules. This would give us an octahedral orientation, which in turn would mean that our T two set of three orbitals is lower in energy than our E set of our pair of orbitals.
3
Problem
Problem
The following diagram shows crystal field splitting pattern for a complex. Which one of the complexes given below should best match the given diagram?
A
[Ag(NH3)2]+
B
[Cu(ox)2]2–
C
[Cr(en)3]3+
D
[Fe(CO)5]
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