With the motivation of searching for highly selective ferric ion sorbents, two open-framework and microporous materials, {[Pb-7(HEDTP)(2)(H2O)]-7H(2)O}(n) (1) and {[Zn-2(H4EDTP)]-2H(2)O}(n) (2) [H8EDTP = N,N,N',N'-ethylenediaminetetrakis(methylenephosphonic acid)], have been synthesized and structurally characterized. The structure of compound 1 results from the seven crystallographically different lead atoms that are bridged by two HEDTP7-ligands to yield a three-dimensional microporous framework with tunnels along the a and b axes. Compound 2 features a layer architecture built of square waves along the a axis. The layers are connected by hydrogen bonds between uncoordinated phosphonate oxygen atoms to form a three-dimensional supramolecular network, with one-dimensional tunnels along the a axis. Both compounds 1 and 2 exhibited high ion sorption and exchange capacities for millimolar concentrations of Fe-III. Specifically, when 0.01 g of 1 (or 2) was added to 5 mL of a 1 mM metallic chloride aqueous solution and the mixture was allowed to stand for 2 days at room temperature, compound 1 adsorbed nearly 100% of Fe-III and compound 2 adsorbed 96.8% of Fe-III. They were also found to adsorb ferric ions selectively over other metal ions, such as Ca-II, Cr-II, Mn-II, Cu-II, Zn-II, Cd-II, etc. Their special ferric ion uptake capacities may be attributed to the cation exchange, coordination bonding, and electrostatic attraction between ferric ions and metal phosphonates.