We report on the synthesis of C2n-qSiq clusters with 2n = 32 -100 and
q < 4. The analysis of the abundance distribution and photofragmentati
on spectra provides clear evidences that such clusters remain in the f
ullerene geometry and that the Si atoms are located close to each othe
r in the fullerene network. These results are corroborated by ab initi
o calculations within the density functional theory. The stability and
electronic properties of these heterofullerenes are discussed.