A new pillared layered phosphonate, cadmium 2-aminoethylphosphonate, Cd(O3PC2H4NH2) (1), has been synthesized, and its structure was solved ab initio from X-ray powder diffraction data and refined by Rietveld methods. Compound 1 is orthorhombic: space group Pna2(1), a = 15.4643(2) Angstrom, b = 5.16512(7) Angstrom, c = 6.27650(8) Angstrom, and Z = 4. Its layer arrangement is similar to that in Cd(O3PR). H2O, except that the water molecule coordinated to cadmium in Cd(O3PR). H2O is replaced by the nitrogen atom from the amino ends of the ethyl chains borne by phosphorus of the upper and lower layers. The strong similarity of the IR, P-31, and Cd-113 NMR data for Cd(O3PC2H4NH2) and Cd(O3PCH3). n-NH2C4H9 clearly shows the topotactic character of the intercalation of n-alkylamines in the dehydrated form of Cd(O3PR). H2O to yield Cd(O3PR). n-NH2R'.