The electronic structure and electronic spectra of [Mo2Sn]2-(n = 6-9) with Mo-Mo single bond are studied by SCF-CI. The changes of Mo-Mo bond order and atomic charges with n increasing are discussed. The unusual sequence of d-d interactions in the cluster anions and the nature of some bonds (Mo-Mo, Mo-S't) are analyzed. The calculated values of wave no. and transition intensity of the spectra correspond with the experimental results. The bands are assigned and the properties of their charge transfer are discussed. Some transitions are interesting, for instance, the transition between bonding orbitals, sx2-y2 ?pxy.

Key words: ELECTRONIC STRUCTURE, ELECTRON TRANSITION, METALLIC BONDS, CHARGE TRANSFER, ELECTRONIC SPECTROSCOPY