Two novel core–shell-like molecular composites, [Ni(dap)₃]₄[HV^IV₁₂V^V₆O₄₂(PO₄)] (1) and [Ni(dap)₂]₄[HV^IV₁₂V^V₆O₄₂(PO₄)]·4H₂O (2) (dap = 1,2-diaminopropane), were obtained from the supermolecular assembly of polyoxoanions and metal–organic cationic units. These two inorganic–organic hybrids were prepared under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, PXRD and single crystal X-ray diffraction analysis. In the well defined molecular core–shell structure of composite 1, the sphere-like anion [PV₁₈O₄₆]⁹⁻ was surrounded by a shell composed of eight windmill-type [Ni(dap)₃]²⁺ cationic units. In 2, ten sheet-like [Ni(dap)₂]²⁺ metal–organic groups surrounded the sphere-like anion [PV₁₈O₄₆]⁹⁻, which was achieved by the easy alteration of the chemical composition of the core–shell structure by simply adjusting the feeding amount of dap. The resulting core–shell-like molecular composites represent a promising structural model toward core–shell nanostructures and exhibit electrocatalytic activity for the reduction of H₂O₂ and oxidation of NO₂⁻.