RbCuO2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Rb1+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. There are two shorter (2.83 Å) and four longer (3.00 Å) Rb–O bond lengths. Cu3+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Cu–O bond lengths are 1.85 Å. O2- is bonded in a 5-coordinate geometry to three equivalent Rb1+ and two equivalent Cu3+ atoms.