The first tetrameric cation-cation neptunyl(v) cluster, [NpO 2(salen) 4(μ 8-K) 2][K(18C6)Py] 2, has been synthesized in non-aqueous solution from the reaction of [(NpO 2Py 5)(KI 2Py 2)] n with K 2salen and its structure determined in the solid state and in solution where the complex retains its tetrameric form. © 2012 The Royal Society of Chemistry.