A Cationic Metal–Organic Solid Solution Based on Co(II) and Zn(II) for Chromate Trapping

We report the synthesis and characterization
of a solid solution
series of cationic metal–organic materials with full compositional
range from pure Co­(II) to Zn­(II) end-members. The materials consist
of [Znx­Co1–x­(H2O)4­(4,4′-bipy)2]2+ metal–organic clusters that π–π
stack into 2-D positively charged layers, with the metal ratio tunable
by molar ratio under hydrothermal conditions. The interlamellar α,ω-alkane­disulfonate
serves as an anionic template and noncovalently interacts with the
cationic layers. The weak interaction allows anion exchange for toxic
oxometal anions, such as chromate, CrO42–. The highest chromate adsorption capacity was 68.5 mg/g (0.43 mol/mol)
for the as-synthesized 50 mol % Co­(II)-incorporated material. Our
cationic material can also selectively trap these toxic oxo-anions
when nontoxic anions (e.g., nitrate, sulfate) were present in an over
50-fold excess concentration.