Mono-ammine complexes of trivalent f(0), f(7), and f(14) ions were investigated by using all-electron four-component relativistic calculations based on the Dirac-Hartree-Fock (DHF) method. Relativistic second-order Mphiller-Plesset perturbation (RMP2) calculations were also performed to incorporate electron correlation for the closed-shell systems. A comparison with the previous data of the aqua complexes showed that the ammine complex provides longer metal-ligand distance, larger stabilization energy, and larger amount of electron donation than the aqua complex does for a certain metal ion. (C) 2002 Elsevier Science B.V. All rights reserved.