Two novel three-dimensional lanthanum coordination polymers have been prepared with the phosphonic acid H2O3PCH2N(C2H4)2 NCH2PO3H2 (LH4). La2(LH2)2(LH4)Cl2 (I) and La2(LH2)2(LH3)Cl (II) arise from similar hydrothermal reactions but differing sources of La. A one-dimensional "lanthanum-phosphate" chain, comprising corner-linked LaO7 and PO3C polyhedra, forms the basis for the two different structures. The two structures differ in the mode of connectivity of the inorganic chains via the phosphonate groups. Both materials include extraframework chloride ions, the different amounts of which apparently direct the polytypic structures. In II, the chloride ions are incorporated in a noncentrosymmetric manner leading to a polar framework topology.