Electron-gain and -loss centres in irradiated periodates: an electron spin resonance study

Abstract

Exposure of octahedrally co-ordinated periodates (H₃IO₆^2–, H₅IO₆, or H₆IO₆⁺) to ⁶⁰Co γ-rays at 77 K results in electron-capture centres having large, almost isotropic ¹²⁷I hyperfine coupling constants corresponding to ca. 21% 5s character. On annealing to ca. 120 K these centres decompose to give axially symmetrical centres with a reduced 5s character, thought to be five-co-ordinate iodine(VI) complexes [e.g. ˙I(OH)₅⁺ or ˙IO(OH)₄]. The electron-loss centres in these systems, exhibiting weak coupling to ¹²⁷I nuclei, have their unpaired electron confined to one or more oxygen ligands. For H₅IO₆, a dimeric centre having two equivalent ¹²⁷I nuclei is obtained. The tetrahedral periodate ion, IO₄^–(in K[IO₄] and Na[IO₄]), gives similar electron-loss centres, but markedly different electron-gain centres, having low spin density on iodine (a_s²ca. 0.038, a_p²ca. 0.16). These centres are thought to be the anion ˙IO₄^2–. The results are comparable with those previously reported for ˙BrO₄^2– and ˙ClO₄^2– anions.