Mixed-valent tri- and tetranuclear complexes of neptunium, [{NpIVCl4}{NpVO2Cl(THF)3}2]·THF and [{NpIVCl3}{NpVO2(μ2-Cl)(THF)2}3{μ3-Cl}] (THF = tetrahydrofuran), were synthesised and characterised. Both the complexes are formed via the cation-cation interactions between the Np(iv) centre and the axial oxygens of the neptunyl(v) unit (i.e. trans-dioxo NpO2+ cation), demonstrating the potential of cation-cation interactions for further exploring the oligomer/cluster chemistry of actinides.