Spectroscopic and structural studies on polyfluorophenyl tellurides and tellurium(IV) dihalides

Bis(fluorophenyl) tellurides R2Te (R = C6F2H3 (1), CF3C6F4 (2), CF3C6F4OC6F4 (3), and C6F5 (4)) are synthesized by the facile reaction of Na2Te with bromo-fluorobenzenes, RBr. The corresponding bis(fluorophenyl)tellurium(IV) dihalides, R2TeHal2 (Hal = F, Cl, and Br) (5-16), are obtained by the oxidation of 1-4 with mild halogenating agents (XeF2, SO2Cl2, and Br2). The dihalides show temperature-dependent NMR spectra. On the basis of the 19F NMR spectra of the two series, (C6F2H3)2TeHal2 (Hal = F (5), Cl (9), and Br (13)) and R2TeCl2 (R = C6F2H3 (9), CF3C6F4 (10), CF3C6F4OC6F4 (11), and C6F5 (12)), the coalescence temperatures, T(c), and free enthalpies, DeltaG, of rotation of the TeC bonds are determined. The activation enthalpies for the dichlorides/dibromide 9-13 are in the range of 14.4-15.2 kcal mol(-1) and that for the difluoride 5 is considerably lower at 10.7 kcal mol(-1). In addition to thorough spectroscopic characterization of 1-16, the crystal structures of the monotellurides 2 and 4 as well as of the tellurium(IV) dihalides 5, 6, 9, 10, and 13 were determined. The dihalides show interesting intermolecular Te...Hal contacts, significantly shorter than the sum of the van der Waals radii, leading to different networks of association.