The electronic structures and static dipole polarizabilities of M3N@C-2n fullerenes (M = Sc and Y; 2n = 68-98) were studied by using density functional theory. Unlike nonmetal endohedral fullerenes, M3N@C-2n show smaller static dipole polarizabilities than the corresponding C-2n ones do. It is because the induced electric field of carbon cages is reduced by inserting M3N cluster. The mean dipole polarizabilities of M3N@C-2n fullerenes were found to correlate closely to their chemical hardness and electron delocalization volume. The refractive indexes of the face-centered-cubic crystals assembled by M3N@C-2n fullerenes were also estimated. (c) 2009 Elsevier B.V. All rights reserved.