Chapter 5: Magnetism of Metal Complexes

One of the important features of transition metal complexes is that they often have open-shell electronic configurations and are paramagnetic, due to the spin and/or orbital angular momentum of the metal ions. The magnetic properties of transition metals are discussed in this chapter. The Zeeman effect in magnetic fields is first described, then magnetisation and molar susceptibility (χ_M) are formulated and Curie law is introduced. The Van Vleck formula derived here is the most important equation to formulate the temperature dependence of χ_M based on the zero- to second-order Zeeman coefficients. Then, two cases where the magnetic susceptibility does not follow the Curie law are discussed, namely the presence of magnetic anisotropy and the presence of magnetic interactions between metal ions. In both cases, the nature and magnitude of each can be estimated by precise analysis of the χ_M vs. T plots, and their mechanism will also be discussed. The last two sections will introduce the spin crossover phenomena and complex-based magnets, such as single molecule magnets. Research on molecular magnets has been very active in recent years, and it will be useful to learn ideas about the aforementioned magnetic anisotropy and magnetic interactions in order to understand molecular magnetism.