Geometries of the ScC2, ScC3 molecules and their anions have been optimised at the CASSCF level. For the first time a cyclic structure is predicted as the ground state for ScC2-. Ab initio adiabatic electron affinities have been obtained by performing single point CASPT2 calculations. The resulting adiabatic electron affinities are in good correspondence with experimental data. The ground states of the two neutral clusters result from a transfer of two metal valence electrons to the ligands. The additional electron of the corresponding anionic clusters occupies a non-bonding sp-hybrid metal orbital. (C) 2004 Elsevier B.V. All rights reserved.