The nephelauxetic effect is a term used in the inorganic chemistry of transition metals. It refers to a decrease in the Racah interelectronic repulsion parameter, given the symbol B, that occurs when a transition-metal free ion forms a complex with ligands. The name "nephelauxetic" comes from the Greek for cloud-expanding and was proposed by the Danish inorganic chemist C. K. Jorgensen. The presence of this effect highlights the disadvantages of crystal field theory, which treats metal-ligand interactions as purely electrostatic, since the nephelauxetic effect reveals the covalent character in the metal-ligand interaction.