The first example of an inverted ligand field was demonstrated in paper form 1995 by James Snyder. In this theoretical paper, Snyder proposed that the [Cu(CF)] complexes reported by Naumann et al. and assigned a formal oxidation state of 3+ at the copper would be better thought of as Cu(I). By comparing the d-orbital occupation, calculated charges and orbital population of [Cu(CF)] "Cu(III)" complex and the formally Cu(I) [Cu(CH)] complex, they illustrated how the former could be better described as a d10 copper complex experiencing two electron donation from the CF ligands. The phenomenon, termed an inverted ligand field by Roald Hoffman, began to be described by Aullón and Alvarez as they identified this phenonmenon as being a result of relative electronegativities. Lancaster and co-workers later provided experimental evidence to support the assignment of this oxidation state. Using UV/visible/near IR spectroscopy, Cu K-edge X-ray absorption spectroscopy, and 1s2p resonant inelastic X-ray scattering in concert with density functional theory, multiplet theory, and multireference calculations, they were able to map the ground state electronic configuration. This showed that the lowest unoccupied orbital was of primarily trifluoromethyl character. This confirmed the presence of an inverted ligand field and started building experimental tools to probe this phenomenon. Since the Snyder case, many other complexes of later transition metals have been shown to display inverted ligand field through both theoretical and experimental methods.