The re-determination of the molecular structure of antimony(iii) oxide using very-high-temperature gas electron diffraction (VHT–GED)

Abstract

The molecular structure of a fundamental binary compound [antimony(III) oxide] has been re-determined to a far higher accuracy and precision than previously reported. The structure is compared to those determined by various ab initio methods, X-ray diffraction and to a previous gas-phase structure determined by electron diffraction prior to modern-day developments for data extraction and manipulation. The experiments utilised a new very-high-temperature (VHT) inlet nozzle system that has been designed and constructed for the gas electron diffraction (GED) apparatus now based at the University of Canterbury (formerly at the University of Edinburgh). The VHT–GED system is capable of heating samples to temperatures of up to 1100 K. The VHT system was tested by studying the gas-phase structure of antimony(III) oxide. Data were collected at 750 K and the contents of the gas flow analysed by mass spectrometry. In the gas phase at this temperature, antimony(III) oxide (Sb₂O₃) exists as a dimer (Sb₄O₆) with tetrahedral symmetry. The Sb–O bond length (r_a3,1) was determined to be 195.66(4) pm and the O–Sb–O bond angle was 98.15(3)°. Unusually, the Sb–O bond length observed from X-ray diffraction investigation of Sb₄O₆ was longer than the gas phase bond length [197.7(1) pm as compared to 195.66(4) pm].