Radioisotope generators comprising inorganic layered hydroxide composition, such as magnesium aluminates and lithium aluminates. These inorganic layered hydroxides form anion exchange materials that exhibit surprisingly high selective affinities for certain radioisotopes. Inorganic layered hydroxides have been prepared and shown to have high affinity for tungstate anions, the anion form of tungsten-188, yet low affinity for perrhenate anions, the anion form of rhenium-188.