New 2D undulating layer pure inorganic polymers H2[{M(H2O)8 M(H2O)7M(H2O)6}P2W18Ce3O70(OH) (H2O)2]∙xH2O; M = Ce3+ (1), Nd3+ (2) and Sm3+ (3) were synthesized by routine synthetic reactions in aqueous solution and characterized by elemental analysis, IR spectra, cyclic voltammetry, XRPD, magnetic susceptibility, TG analysis, and X-ray single-crystal diffraction. The 2D framework of 1–3 were built by tri-Ce4+ substituted sandwich-type polyoxoanions modified by six trivalent lanthanide cations M(H2O)x (x = 6–8) units. The M(H2O)x (x = 6–7) groups act as bridges to form 2D undulating layer, but the M(H2O)8 groups link the 2D layers together via hydrogen bonds to form a 3D supra-molecular framework.
