Abstract: The title compounds are members of the M2O-CuO-P2O5 system (M = Li, Na, K and Rb), where the lithium, sodium, potassium, rubidium and cesium phases have already been structurally characterized. The studied diphosphates LiNaCuP2O7, LiKCuP2O7 and Rb0.5Na1.5CuP2O7 belong to a large family of materials of general formula, MM’CuP2O7 (M, M’ = Monovalent cation) where the elements M and M’ ionic radii are decisive in the structural type determination. They were synthesized by solid-state reactions. The X-ray structur…