Ok, und unsere zweite Aufgabe ist, what is the crystal field theory?

Ok, dieses Thema oder diese Theorie ist relevant für Metallkomplexe.

Es sind Strukturen, wo es einen Zentralatom gibt, zum Beispiel einen Übergangsmetall, und der wird von mehreren Ionen oder Liganden umgeben.

Die Wechselwirkungen zwischen einem Übergangsmetall und einer Gruppe von Liganden ergibt sich aus der Anziehungskraft zwischen dem positiv geladenen Metallkarton und der negativen Ladung der Liganden.

Hier im Metallkarton kann man insgesamt fünf verschiedene Deorbitale finden, das heisst fünf verschiedene rundliche Orientierungen, die sind hier in Lille markiert.

Im freien Metalljohn sind die Deorbitale entartet, das heisst sie besitzen die gleiche Energie.

Diese Theorie sagt, dass wenn man dieses Karton in ein Ligandenfeld bringt, gibt es repulsive Wechselwirkungen zwischen den Elektronen der äußeren Deorbitale und den freien Elektronenpaaren der Liganden.

Wegen dieser repulsiven Wechselwirkungen steigt der Energieinhalt der Deorbitalen.

Das Problem ist, dass diese Ionen oder Liganden einige Deorbitalstärke destabilisieren können.

In this case, the deelectrons that are closer to the ligands contain a higher energy compared to the other deelectrons that are further away.

What is the consequence of this? The consequence is that these deorbitales lose their degeneration and an energy separation of the orbitals occurs.

For example, this is how the orbitals look like in a normal ion. This would be a perfect case if you put this ion in a symmetrical ligand field.

Here, the energy content rises due to the repulsive Wechselwirkungen, but it is degeneration and stays.

The influence would be symmetrical. But here we have a real case where the effect of ligands is not so perfectly symmetrical.

Therefore, the energy content of the orbitals is very different and the sparsity occurs. For example, here, in the example of the image, these deorbitales are closer to the ligands.

Because they are closer, the repulsive Wechselwirkungen are also higher and therefore these orbitals contain a higher energy.

Why is this theory so important? Because of this theory, many important properties of complexes are explained. For example, the color, which is a striking characteristic of this transition metal complex.

The structures are also explained, such as magnetism, stability and reaction ability.

What is a high spin? First of all, a small fraction of basic chemistry. Each orbital can contain a maximum of two electrons, where these electrons can show magnetic spin quantities.

Another important thing is the Hund rule. Each of these orbitals is first occupied with an electron with parallel spin.

For example, for an atom that has six electrons in total in the orbital, as shown here, the five electrons are first occupied by the empty orbitals, the five with a parallel spin.

The remaining electron would then fill up an energy-less orbital, as I said, with a opposite spin.

It should also be noted that there are repulsive Wechselwirkungen between two electrons in the same orbital.

This means that a certain energy is needed for these two electrons to remain in the same orbital.

If this energy separation is not so big, because the ligands are simply weak, this energy is less than the energy of the two energies in the orbitals.

In this case, we speak of a high spin configuration.

Each orbital is occupied by at least one electron and the Hund rule is then kept.

But if the effects of the ligands are very strong, it can also be seen that the energy is greater than the spin-parameter energy and so we have a low spin configuration.

This happens when the energy difference here is so high that it is more energy efficient for the electrons to occupy the entire energy-less orbital in double.

In this case, the Hund rule was not kept.

In summary, the separation can be very small or very large and is always very dependent on the discharge of the electrons of the deorbital and the ligands.

A stronger discharge increases the energy of the deorbital and then this energy separation is also large and the low spin complexes arise.

You can also find different complexes of geometry, that is, the ways in which the ligands occupy my orbital.

Typically, there are tetra-aedra complexes, which are usually very small in this configuration. Therefore, they have the largest number of electrons and they mostly exist in high spin complexes.

In the case of quadratic planar complexes, it is something different. In this geometry, the separation is large and the connections exist as low spin complexes.

We also have octa-aedra complexes, which are the most common found complexes. They have high spin and low spin conditions.

This is dependent on the ligands and the oxidation levels of the metal center.

Here we have the expecsochemical ranges of the ligands.

Here are the ligands and their field strength. From the weakest to the strongest ligand.

For example, CO and NO-cations have the better ability to split the deorbital and to solve spin complexes.

On the other hand, J and Jn are very weak and the ligands are usually called spin complexes.

Here we have some examples of complex geometries that can be found in general.

That's all for this second exercise.