Formation, stability, and structures of antimony oxide cluster ions

The formation of positively charged antimony oxide clusters has been invest igated as a function of oxygen partial pressure using time of flight mass s pectrometry. With increasing oxygen partial pressure magic number patterns are observed, which can be attributed to the clusters of (Sb2O3)(n)(+) and (Sb2O3)(n)(SbO)(+) with 2 less than or equal to n < 7 and 1 less than or eq ual to n < 7, respectively. Oxygen rich clusters, i.e., clusters formed by the addition of one or more oxygen atoms to the above observed series, gain in intensity with increasing cluster size and increasing oxygen partial pr essure. To obtain information about structures and general building princip les of these clusters we have performed ab initio quantum chemistry calcula tions for the series (Sb2O3)(n), (Sb2O3)(n)(+), (Sb2O3)(n)(SbO)(+), (Sb2O3) (n)(SbO2)(+), and (Sb2O3)(n)(SbO3)(+). Except from a defect center in the c ationic series, antimony atoms are trivalent and oxygen atoms divalent. For the cationic series (Sb2O3)(n)(SbO)(+), an open valence atone antimony ato m is avoided by the formation of an additional Lewis-donor Lewis-acceptor S b-O bond with a trivalent oxygen atom. Open structures with terminal oxygen atoms or with Sb-Sb bonds are very high in energy, expressing a principle of the formation of a maximum number of Sb-O bonds. In the series (Sb2O3)(n )(SbO2)(+), an excess oxygen valence leads to structures with a central SbV O-4 unit (i.e., without terminal oxygen). For n greater than or equal to 3, such structures have a very pronounced energetic stability compared to i somers with a terminal oxygen atom or with an O-O bond. Characteristic buil ding blocks in the neutral and in the cationic series are eight-membered ri ngs, which are also found in the bulk antimony(III)oxide modification senar monite, as well as Sb4O5 units bridged by oxygen atoms. (C) 1999 American I nstitute of Physics. [S0021-9606(99)00102-6].