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Chemistry LibreTexts

Paramagnetic Properties of Fe, Fe2+ and Fe3+

Chemical Concepts Demonstrated

  • Paramagnetic properties of iron metal and its salts
  • High-spin and low-spin complexes
  • Strong-field and weak-field ions and ligands

Demonstration

  • Use a magnet to assess whether or not the sample in each test tube is paramagnetic.
  • Compare results.
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Sample Paramagnetic?
Iron metal Paramagnetic. Iron metal has 2 lone electrons.
Iron(II) Usually, paramagnetic.  However because there are an even number of electrons in Fe2+, it is possible that all of the electrons could end up paired in certain situations (see explanation below).
Iron(III) Paramagnetic (1 lone electron).
Salt Diamagnetic.
Sugar Diamagnetic.
Water Diamagnetic.

Explanation

Compounds in which all of the electrons are paired are diamagnetic. Technically, they are repelled by the poles of a magnet, but this repulsion is usually too small to notice. Paramagnetic compounds contain one or more unpaired electrons and are attracted to the poles of a magnet.

Elemental iron and iron (III) are paramagnetic because of the necessity of unpaired electrons in their orbitals.  Iron (II) is also in this same position most of the time. When iron (II) is bonded to certain ligands, however, the resulting compound may be diamagnetic because of the creation of a low-spin situation.

If the ligands attached to the Fe (II) metal are strong-field ligands in an octahedral configuration, a low-spin situation is created in the d orbitals.  All of the electrons are paired and, as a result, the complex is diamagnetic.

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