The polyoxo-22-palladate [Na₂PdII22O₁₂(As^VO₄)₁₅(As^VO₃OH)]^25- (1), which represents a novel polyoxo-noble-metalate structural type, was synthesized by reaction of Pd²⁺ and AsO₄^3- ions in aqueous solution. Polyanion 1 comprises two {NaPd₁₁} units linked by two arsenate bridges, and hence represents the first example of a defect, monolacunary {Pd₁₁} polyoxopalladate nanocube with arsenate capping groups. The title polyanion was characterized in the solid state as well as by theoretical calculations.