SYSTEMATICS IN ELECTRON-TRANSFER ENERGIES FOR LANTHANIDES AND ACTINIDES

Literature data and data from the electronic absorption spectra of dif ferent S-ions in MX(6)(3-) (M = Ln, An, X = Cl, Br), AnCl(3), YF3: Ln( 3+), O2-, LaF3: Ln(3+), O2- and ThF4: Ln(3+), O2- systems are consider ed. Calculations and experimental determination of the pi --> f and f --> d transitions are analysed and indicate that the transition energi es have the relationship pi --> d = f + f --> d. This corresponds to a redox process for elements in the same oxidation state across the var ious series and for the same set of ligands. This represents a new kin d of systematics. With increasing atomic number, the values of pi --> d transition energy follow two parabolic variations with a sharp maxim um for the f(7) electron configuration. We propose to call this ''hump -peak-hump'' systematics. This is a characteristic feature of pi --> d energy transitions and also of the physical and chemical properties r elated to the disproportionation reaction 2M(3+) --> M(4+) + M(2+) for Ln and An in the trivalent state and for higher oxidation states in t he case of An (IV, V, VI).