Studies of Thermal Annealing of Neutron‐Irradiated Tris(dipyridyl)Cobalt (III) Perchlorate. Redistribution of Electrons among the Donors

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Abstract
Thermally treated and untreated anhydrous samples of tris (dipyridyl) Co(III) perchlorate were ``hydrated'' at 30° in air at a relative humidity of 93%. Some of them were chilled at −78° while others were kept at 30° for a prolonged period before chilling at −78°. The chilled samples were neutron irradiated at −78°. Thermally treated samples chilled immediately after hydration exhibit a much faster rate of thermal annealing as compared to the latter and to the trihydrate. These observations have been interpreted on the basis of the ``variable‐depth‐electron‐donors—isotopic‐exchange'' model which postulates an annealing rate proportional to the free‐electron density. Evidence is presented for the creation of electron traps and electron—hole ``recombination centers'' during thermal treatment of the anhydrous form and for populating of the electron traps with electrons to form shallow donors during hydration through exo‐electron emission. Hence, in the freshly hydrated samples kept at 30° for prolonged periods before chilling and irradiation, a considerable amount of depopulation of the shallow donors takes place resulting in a slower rate of postrecoil thermal annealing. In contrast, the hydrated complex prepared by hydrating the untreated anhydrous sample exhibits a faster rate of annealing on storage at 30° after hydration and prior to irradiation as compared to the samples chilled immediately after hydration. For the trihydrate it has been shown that the electron traps constituted by the crystal imperfections are largely filled up with electrons during crystallization from aqueous solution. However, the process of filling up continues slowly during storage of Co(dipy)3‐(ClO4)3·3H2O at 30°C (or at higher temperatures). Consequently, the stored samples show a faster rate of annealing as compared to the freshly prepared ones.