STUDY ON PHYSICAL AND CHEMICAL STABILITIES OF METALLOFULLERENES PROVED BY NUCLEAR PHENOMENA

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The unique problem posed by nuclear phenomena is the stability of carbon cages against nuclear reactions and nuclear decay. Knowledge of such property of carbon cages is important not only for radioactive labeling of fullerenes but also for investigating the physical and chemical stability of fullerene cages against sudden jerks and/or a sudden supply of a hung amount of recoil energy, and against the sudden change of nuclear charge of the cage or that of endohedral metal atoms.It can be considered that such "retention yield" is a complicated product of not only the survivability of the metallofullerenes against the recoil energy in the (n, γ) reaction, but also the stability against the gamma dose in the reactor of the fullerene molecules and chemical yield in each step of the chemical procedure applied to the sample after neutron irradiation. The ratios of retention yield observed for ィイD1169ィエD1Yb/ィイD1175ィエD1Yb and ィイD1153ィエD1Gd/ィイD1161ィエD1Gd have led to the conclusion that the thre … More shold energies for destruction of their M@CィイD282ィエD2 metallofullerenes following the recoiling phenomena associated with (n, γ) reaction are about 27-29 eV. The overall retention yield of 20 % in the reactor irradiation was deduced by the experiments on La@CィイD282ィエD2 that were aimed to cancel out the corrections requires for chemical yields during the chemical treatment.It is to further investigate the influence of radioactive decay process on the physical and chemical stability of metallofullerenes. It is concluded that the metallofullerenes which are stable during the chemical process of ordinary solvent extraction and HPLC separations in air are also stable against the β-decay and EC-decay process of the metal atom in the cage, as long as the oxidation state of the daughter nuclide remains the same with that of the parent nuclide within the same carbon cage. But if the oxidation state is changed by nuclear transformation, it is appeared to form chemically unstable metallofullerenes are formed as demonstrated in the β-decay of ィイD1177ィエD1Yb-ィイD1177ィエD1Lu where the oxidation state is likely to have changed from +2 to +3. However, the existence of a special kind of CィイD282ィエD2 carbon cage that forms chemically stable metallofullerenes with metal atoms of both +2 and +3 oxidation state is experimentally found for the first time by the study of EC decay of ィイD1146ィエD1Gd-ィイD1146ィエD1Eu. Less