A tellurium-125 Mössbauer study of bis(trifluoromethyl)- and bis(pentafluorophenyl)- tellurides and their dihalides

Abstract

The 125Te Mössbauer spectra for (CF3)2Te and (C6F5)2Te have been recorded and exhibit significantly larger quadrupole splittings (14.02 and 13.40 mm s−1 respectively) than those of Me2Te (10.5 mm s−1) and Ph2Te (11.0 mm s−1). The dihalides (CF3)2TeX2 and (C66F5)2TeX2 (X = F, Cl,Br) have consistently smaller quadrupole splittings than the dihalides Me2Tex2 and Ph2TeX2. These observations are consistent with the greater electronegativity of the CF3 and C6F5 ligands. The 125Te nmr chemical shifts of (C6F5)Te and its dihalides show a consistent trend to more positive values (increased deshielding) as the electronegativity of the ligands attached to tellurium increases ((C6F5)Te, 297.6 ppm; (C6F5)2TeF2, 1060 ppm). However, for (CF3)2Te and its dihalides a more complex pattern is observed which may be explained by changes in the mean electronic excitation term in the Ramsey paramagnetic shielding term.