Layered sodium manganese bronzes, Na2/3MO2 (M = Mn(1-x)A(x), A = Co, Li, Ni) with the P2-structure were investigated. A phase diagram (composition-structure-temperature diagram) for materials synthesized in air is presented. Substitution extends the stability region of P2 phases toward lower temperatures. Na2/3MnO2 exhibits a monoclinic distortion. Weakly substituted samples exhibit an orthorhombic distortion of the ideal P2-structure whereas heavily substituted bronzes adopt the ideal P2-structure. Dry samples exhibit larger distortions than samples exposed to air. The layered sodium bronzes were used to prepare layered Li-transition metal oxides by ion-exchange. Layered Li-Mn oxides with O2-structures were prepared from these bronzes for the first time. As an example crystalline Li-2/3[Ni1/3Mn2/3]O-2 with the O2 structure was prepared.