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, {[Cd0.5Cu0.5(bpy)2(O3SFcSO3)]·(CH3OH)4}n 3, could be obtained by ion-exchange-induced single crystal to single crystal transformation.

多孔柱状双层开放配位聚合物{[Cd(bpp)₂(O₃SFcSO₃)]·(CH₃OH)₂·(H₂O)₆}ₙ 1（其中Fc为二茂铁（ferrocene））与三维多孔配位聚合物{[Cd(bpy)₂(O₃SFcSO₃)]·(CH₃OH)₄}ₙ 2，均由硝酸镉（Cd(NO₃)₂）、二茂铁-1,1'-二磺酸盐以及桥联配体1,3-双(4-吡啶基)丙烷（bpp）或4,4'-联吡啶（bpy）组装得到。二者对铜盐均展现出极为特殊的吸附性能。随着硝酸铜溶液浓度升高，吸附的铜离子占比下降，但被交换的中心镉离子占比与吸附铜离子总量均呈上升趋势。在稀溶液中，吸附过程主要以金属离子吸附为主；而在浓溶液中，离子吸附与离子交换共同主导整个过程。与此同时，这类材料可作为针对Pb²⁺、Zn²⁺、Mn²⁺、Co²⁺、Ni²⁺等多种金属阳离子的理想吸附剂。但当上述金属离子共存于混合溶液中时，这两种二茂铁基配合物仅会选择性大量吸附Pb²⁺（配合物1吸附率为88.54%，配合物2为75.80%）与Cu²⁺（配合物1吸附率为90.94%，配合物2为79.45%）。离子吸附与中心镉离子交换的过程，主要受金属离子对自由官能团的配位能力、吸附金属离子的离子半径以及吸附金属盐的溶液浓度所调控。基于对离子交换过程的认知，通过离子交换诱导的单晶到单晶转变，可得到配合物2的中心金属离子交换产物{[Cd₀.₅Cu₀.₅(bpy)₂(O₃SFcSO₃)]·(CH₃OH)₄}ₙ 3。