What characterizes a low spin complex?

A low spin complex is characterized by an arrangement in which more electrons are paired than unpaired. This phenomenon occurs when the crystal field splitting energy (Δ) is large enough to overcome the pairing energy, which leads to the pairing of electrons in the lower energy orbitals before occupying the higher energy orbitals. As a result, you have a higher likelihood of finding paired electrons, which is typical for transition metal complexes with strong field ligands.

In such complexes, the larger splitting energy favors the occupancy of the lower energy orbitals over the higher ones, resulting in fewer unpaired electrons. This situation is frequently observed with ligands that create a strong field, such as CN⁻ or CO, as opposed to weaker field ligands that would result in a high spin configuration where more unpaired electrons are present.

The presence of paired electrons also has implications for the magnetic properties of the complex, typically leading to a diamagnetic character in low spin complexes, as opposed to paramagnetic character seen in high spin complexes that have a higher number of unpaired electrons. The low spin characteristic is essential in determining the stability, reactivity, and magnetic behavior of the inorganic complexes involved.