In an octahedral complex, when Δ is large (strong field ligand), the electrons will first fill the lower energy d orbitals before any electrons are placed on the higher energy d orbitals. It is then classified as low spin because there is a minimal amount of unpaired electrons.

What are the low spin complexes?

What are Low Spin Complexes? Low spin complexes are coordination complexes containing paired electrons at low energy levels. Since there are no unpaired electrons in the low spin complexes (all the electrons are paired), they are diamagnetic. This means these compounds cannot be attracted to an external magnetic field.

Can tetrahedral complex be low spin?

CFSE of tetrahedral complexes is less than the pairing energy. The electrons are occupied in the higher energy levels. Thus its CFSE will not be enough for pairing of spin to occur. Thus it rarely forms low spin complexes, but forms high spin complexes.