Rational Construction of Porous Polymeric Cadmium Ferrocene-1,1′-disulfonates for Transition Metal Ion Exchange and Sorption

Porous pillared bilayer open coordination polymer {[Cd(bpp)₂(O₃SFcSO₃)]·(CH₃OH)₂ ·(H₂O)₆}_n 1 (Fc = ferrocene) and 3D porous coordination polymer {[Cd(bpy)₂(O₃SFcSO₃)]·(CH₃OH)₄}_n 2 have been assembled from Cd(NO₃)₂, ferrocene-1,1′-disulfonate, and bridging ligands 1,3-bis(4-pyridyl)propane (bpp) or 4,4′-bipyridine (bpy). Both of them show very special adsorption properties to copper salts. Along with the increase in the solution concentration of Cu(NO₃)₂, the percentage of adsorbed copper ions falls, but the percentage of exchanged central cadmium ions and the amount of adsorbed copper ions rises. In dilute solution, there mainly exists metal ion sorption, whereas both ion sorption and exchange are in charge of the whole progress in strong solution. Meanwhile, such materials could be used as ideal metal ion adsorbent toward some other metal cations, including of Pb²⁺, Zn²⁺, Mn²⁺, Co²⁺, Ni²⁺. However, when all these metal ions coexist in a mixture solution, the two ferrocenyl complexes selectively adsorb large amounts of only Pb²⁺ (for 1, 88.54%; for 2, 75.80%) and Cu²⁺ (for 1, 90.94%; for 2, 79.45%). Ion sorption and central cadmium ion exchange might be considered as being dominated by the coordination ability of metal ions to free functional groups, ionic radii of adsorbed metal ions, and the solution concentration of adsorbed metal salts. On the basis of the recognition of ion exchange, the center metal ion-exchange product of 2, {[Cd_0.5Cu_0.5(bpy)₂(O₃SFcSO₃)]·(CH₃OH)₄}_n 3, could be obtained by ion-exchange-induced single crystal to single crystal transformation.