Cyclic voltammetry and electrochemical admittance were used to characterize the self-assembly process of nano-scaled spheres of polyoxomolybdate (NH4)(42)[(MO72Mo60O372)-Mo-VI-O-V(CH3COO)(30)(H2O)(72)]center dot ca.300H(2)O.ca. 10CH(3)COONH(4)) or {MO132} . Cyclic voltammetry indicated that the self-assembly process could be detected after 8 h and completed after one day. Electrochemical admittance showed that the molybdenum species in the CH3COONH4-CH3COOH buffer (pH 4.46) were totally different from those in the pure (NH4)(6)Mo7O24 solution (pH 5.54) and the (NH4)(6)Mo7O24 solution (pH 4.21) acidified by hydrochloric acid. However, the molybdate species in the latter two solutions should be mixtures of non-protonated and/or protonated [Mo7O24](6-) and [Mo8O26](4-) anions. Detailed analysis of admittance results could support the existence of the molybdate species related to the {Mo-6(VI)} fragment which was one of the components Of {MO132} clusters. Admittance results on the self-assembly process were coincident with those from cyclic voltammetry. (C) 2007 Elsevier Ltd. All rights reserved.