Abstract The appearance energy (the threshold energy for stable fragment formation by hot atoms produced after nuclear transformation) was determined using the (γ, γ′) reaction. For the indium hedta complex it is about 45 eV, which is lower than that for the indium edta complex. A slight effect of water of crystallization was also observed. The order of the complex yield in the plateau region is found as follows; Na[In·edta(H 2O)]>H[In·edta(H 2O0]>[In·hedta] which is the same order as the appearance energy. A model for hot atom reactions in solids is proposed and the chemical effect on the shape of the energy dependence of the complex yield interpreted.