¹²⁷I Mössbauer Spectroscopic Studies of Some Cations and Anions of Iodine

Abstract

<p>The ¹²⁷I Mössbauer spectra have been recorded at liquid-helium temperature for several series of iodine compounds. The Mössbauer spectra of a number of apparently cubic inorganic iodine compounds were measured and many were found to give abnormally broad lines. This was attributed to distortions from true cubic symmetry present in the compounds. KI gave the narrowest line and it was selected as the reference compound for ¹²⁷I Mössbauer spectroscopy.</p> <p>The Mössbauer spectra of a series of linear iodine compounds, including the trihalide [X-I-Y]ˉ anions were measured and the magnitude of the quadrupole coupling constant was found to vary with the electronegativity of the attached ligands. Semi-empirical relationships had been developed to convert isomer shifts and quadrupole coupling constants into s- and p-orbital populations and these relationships have been re-established using the data for these linear iodine compounds. It was found that these semi-empirical relationships do not have general applicabilty when they were tested with a series of interhalogen cations and some iodine-chalcogen cations.</p> <p>Several new interhalogen cations of iodine were also prepared and characterized. The ¹²⁷I Mössbauer parameters for these square planar iodine (I:I) cations revealed that, while secondary or bridging interactions are important in determining the sign of the quadrupole coupling constant, it is the primary bonds to iodine which determine the magnitude of the quadrupole coupling constant.</p> <p>Finally, ¹²⁷I Mössbauer spectroscopy was applied to some interesting chemical problems. Mössbauer measurements on frozen solutions of [I₂]⁺ suggest that the new species formed is a square or rectangular dimer of [I₂]⁺, namely [I₄]²⁺. ¹²⁷I Mössbauer measurements in conjunction with recent ¹²⁹Xe and ¹²⁵Te NMR and ¹²⁹Xe Mössbauer have conclusively shown that the 0TeF₅ ligand is less electronegative than -F.</p>