Editing Coordination complex (section)

===Colors of lanthanide complexes===
Superficially [[lanthanide]] complexes are similar to those of the transition metals in that some are colored. However, for the common Ln<sup>3+</sup> ions (Ln = lanthanide) the colors are all pale, and hardly influenced by the nature of the ligand. The colors are due to 4f electron transitions. As the 4f orbitals in lanthanides are "buried" in the xenon core and shielded from the ligand by the 5s and 5p orbitals they are therefore not influenced by the ligands to any great extent leading to a much smaller [[Crystal field theory|crystal field]] splitting than in the transition metals. The absorption spectra of an Ln<sup>3+</sup> ion approximates to that of the free ion where the electronic states are described by [[Angular momentum coupling#Spin-orbit coupling|spin-orbit coupling]]. This contrasts to the transition metals where the ground state is split by the crystal field. Absorptions for Ln<sup>3+</sup> are weak as electric dipole transitions are parity forbidden ([[Laporte rule|Laporte forbidden]]) but can gain intensity due to the effect of a low-symmetry ligand field or mixing with higher electronic states (''e.g.'' d orbitals). f-f absorption bands are extremely sharp which contrasts with those observed for transition metals which generally have broad bands.<ref name = "C&W6th">{{Cotton&Wilkinson6th}}</ref><ref name=CottonSA2006>{{cite book |last=Cotton |first=Simon |year=2006 |title=Lanthanide and Actinide Chemistry|publisher= John Wiley & Sons Ltd}}</ref> This can lead to extremely unusual effects, such as significant color changes under different forms of lighting.