121Sb Isomer Shifts in Antimony Halides

Mössbauer spectra of ¹²¹Sb in all the binary antimony halides have been obtained, as well as in cubic Sb₂O₃. The isomer shifts relative to the ¹²¹SnO₂ source are − 11.3 mm/sec (Sb₂O₃), − 13.8 (SbCl₃), − 13.9 (SbBr₃), − 15.9 (SbI₃), − 14.6 (SbF₃), + 2.2 (SbF₅), and − 3.12 (SbCl₅). Quadrupole splittings were obtained for most of the antimony(III) compounds. The linear variation of isomer shift with ligand–metal electronegativity difference for Sb₂O₃, SbCl₃, SbBr₃ and SbI₃ is interpreted as due to a constant $s$ character in the ligand–metal bonds. The SbF₃ does not obey this relationship due to its radically different geometry.