The electron density distribution of the complex monoanion Cu(CF3)4 in (Bu4N)[Cu(CF3)4] has been studied by high-resolution X-ray single-crystal diffraction and augmented with theoretical calculations. The study finds that the central copper bears an atomic charge of close to +1, while the occupancy of its dx2-y2 orbital is only 1.26. Using topological analysis combined with theoretical calculations, the depopulation of dx2-y2 is shown to be due to significant covalency in the Cu-C bonds. The combination of the monovalent picture and the covalency is interpreted as a confirmation of an inverted ligand field.
