Experimental X-ray Electron Density Study of Atomic Charges, Oxidation States, and Inverted Ligand Field in Cu(CF₃)₄

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 d _x orbital is only 1.26. Using topological analysis combined with theoretical calculations, the depopulation of d _x 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.