gamma-rays and pulse radiolysis of aqueous solutions of Ni2+ ions in the presence of polyacrylate (PA(-)) and 2-propanol leads to the formation of metastable species absorbing at 540 nm that are ascribed to "pink" oligomeric clusters of a few nickel atoms only. The molar absorption coefficient is evaluated as epsilon(540nm) = 3300 +/- 300 L mol(-1) cm(-1) per Ni-0 atom. The successive steps from the reduction of Ni2+ into Ni+ ions to the formation of the pink clusters at 540 nm under conditions of complexation by PA- are investigated by pulse radiolysis. The yield of the formation of pink clusters increases markedly with the irradiation dose rate, demonstrating the occurrence of the disproportionation of the [Ni+, PA(-)] complex after a single electron pulse. The reduction and nucleation mechanisms, including rate constants, in competition with the back oxidation by protons, particularly at low dose rate, are discussed.