The infrared spectrum and the 13C NMR chemical shifts were
calculated with the Gaussian 09 software [13]. All calculations
were made with the B3LYP method. The 6-31+G⁄ basis was chosen for all atoms except for antimony for which the LanL2DZ pseudopotential was used. In all cases the positions of the atoms were
those determined by the X-ray diffraction study except for the
hydrogen atoms which were first optimized at the above level of
theory. Indeed the positions determined by X-ray do not correspond to the location of the proton but to that of the barycenter
of charges. The 13C NMR chemical shifts were then calculated by
use of the GIAO method.