Formation of antimony oxide clusters in a molecular beam

The formation of positively charged antimony oxide clusters has been investigated as a function of oxygen partial pressure. At low oxygen concentration oxide clusters with a large variety of stoichiometries are observed. With increasing oxygen pressure some mass peaks become prominent. The special stability of these antimony oxide clusters can be explained by simple valence bond arguments, all the antimony atoms being in a formal +III and all the oxygen atoms being in a formal −II oxidation state. A further increase in the oxygen partial pressure shifts the distribution to mixed valence oxide clusters with one or more of the antimony atoms in the formal +V oxidation state. According to this model it is possible to predict discrete structures for these clusters. They have no direct Sb–Sb bonds, instead all the Sb-atoms are bridged by O-atoms. Further oxygen can then be added in a terminal position to form the mixed valence oxides. This model is also supported by bulk and gas-phase data of antimony oxides.