Magnetic Properties of Complexes

An atom’s size and electron configuration are factors that affect the magnetic properties of a compound. The number of unpaired electrons in a compound determines its magnetic properties because magnetism is based on electron spin. The magnetism of the transition metals (or d-block elements) is examined in this section. They are characterised by having many unpaired electrons.

Transition Metals

Transition metals can form magnets, which is one of their interesting properties. They are magnetic when they contain unpaired electrons. This magnetism is caused by having unpaired d electrons since the last electrons reside in the d orbitals. The quantum number indicates the spin of a single electron. 

When the electron is paired with another, this spin is negated, but when it is unpaired, this spin produces a weak magnetic field. The number of unpaired electrons increases the paramagnetic effects. When electrons in ligands and electrons in the compound repel each other, the electron configuration of a transition metal (d-block) changes. 

A compound may be paramagnetic or diamagnetic depending on the strength of its ligand.

Bulk Magnetism: Ferromagnetism

A permanent magnet is formed when materials (such as iron) undergo ferromagnetism. Rather than exhibiting magnetic properties only when it is exposed to a magnetic field, this type of compound shows permanent magnetic properties. Electrons are grouped into domains in a ferromagnetic element, with each domain having the same charge.

A magnetic field causes these domains to align so that all charges are parallel throughout the compound. The number of unpaired electrons in a compound and the size of the atom determine if it is ferromagnetic or not.

It is common in everyday life for nickel, cobalt, and iron to exhibit ferromagnetism or permanent magnetism. Ferromagnetism was known and applied by Aristotle in 625 BC, the compass in 1187, and the refrigerator today. The special relativity theory of Einstein asserts the inextricable link between electricity and magnetism.

Molecules and ions have magnetic moments

The theory of high- and low-spin complexes is supported by experimental evidence of magnetic measurements. You must remember that unpaired electron molecules such as O2 behave like paramagnetic molecules. Magnetic fields are attracted to paramagnetic substances. The unpaired electrons in transition metal complexes cause them to be paramagnetic There is a slight tendency for magnetic fields to repel diamagnetic substances.

The magnetic moment due to the spin of an unpaired electron in an atom or ion causes the entire atom or ion to be paramagnetic. A system containing unpaired electrons has a magnetic moment whose size is directly related to the number of unpaired electrons. A large magnetic moment is caused by an excess of unpaired electrons. To calculate the number of unpaired electrons in a system, magnetic moments are observed.

The Hunds’ Rule states that before pairing up, electrons must fill all of their orbitals with single electrons while maintaining parallel spins (paired electrons are oppositely spun). Before combining, an uncomplex metal atom with five degenerate orbitals is paired with electrons that fill all five orbitals. When ligands are added, however, the process gets more complicated.

In the higher-energy orbitals, a single electron requires more energy to be placed into d-orbitals because of the splitting energy. 

Having filled half of the lower-energy orbitals with electrons (one electron per orbital), one can place an electron in a higher-energy orbital or pair it with an electron in a lower-energy orbital. 

Which alternative is chosen is determined on the strength of the ligands. The electrons will pair up if the splitting energy is larger than the pairing energy; if the pairing energy is greater, unpaired electrons will occupy higher energy orbitals.

To put it another way, when a strong-field ligand is used, low-spin complexes are formed; with a weak-field ligand, a high-spin complex is formed.

Low-spin complexes contain more paired electrons because the splitting energy is larger than the pairing energy. These complexes, which include [Fe(CN)6]3-, often exhibit diamagnetic characteristics or are weakly paramagnetic. 

A high-spin complex typically contains more unpaired electrons than a lower-spin complex because the pairing energy of the high-spin complex is higher than the splitting energy. Because they have more unpaired electrons, complexes with high spin are often paramagnetic. Paramagnetic compounds have tiny magnetic fields created by unpaired electrons, similar to ferromagnetic materials’ domains. 

When a coordination complex has unpaired electrons, its paramagnetism is stronger; a complex with more spin is more paramagnetic. Paramagnetisms and their relative strengths can be predicted based on the type of ligand and whether it is a weak or strong field ligand.

Conclusion

There are differences in the electrical configurations of transition elements and other transition metals, such as zinc, cadmium, and mercury that are not considered transition elements. There is, however, a similarity between the properties of another element in the d-block, and this similarity can be seen down each row of the periodic table.