Study of the structural changes occurring during the reduction process of the Sr 2 RhO 4d (214), n 1 term of the Ruddlesden and Popper series, shows that for d `0.02 values, this material dissociates into the Sr 4 RhO 6 (416) monodimensional phase, a I , b 0 compound of the (A 3 B 2 O 6 ) a -(A 3 B 3 O 9 ) b family, and Rh metal. During the first stage, this process occurs by the formation of an intergrowth between the ( 214) and ( 416) materials which can be only detected by high resolution electron microscopy and is easily interpreted on the basis of the structural relationship established between them. Further reduction allows the segregation of both phases as separated entities, which coexist with Rh metal. The dissociation process is reversible and, under oxidizing conditions, a layered ma-terial with anionic composition d 0.06 is always obtained. This behaviour seems to be a general way of accommodating the compositional changes in layered A 2 BO 4 phases where the B cation is always in a octahedral environment. The structural mechanism of this transformation is proposed, and the structural relationship between these two low-dimensional oxides is established.