An anionic-MOF based on Co2+ and an alkane tetracarboxylate ligand exhibiting Ni2+ ion-exchange behavior

This study reports an anionic metal-organic framework (iMOF-A), {(H₂pa)₃[Co₃(BTCA)₃].6H₂O}_n, where H₂pa. is 1,3-propylenediamonium and BTCA is 1,2,3,4-butanetetracarboxylate. The compound, based on Co²⁺, crystallizes in a monoclinic system, (space group I2/a) with a non-interpenetrated three-dimensional pts topology. Its charge balancing is achieved by H₂pa cations located in the framework’s pores, which can be exchanged with Ni²⁺ ions. The compound was characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, and ultraviolet-visible absorption spectroscopy. The ion-exchange properties were evaluated by substituting the propanediammonium cations with Ni²⁺ from aqueous solution. Batch experiments assessed the framework’s effectiveness in selectively adsorbing Ni²⁺, considering variables like initial metal ion concentration and contact time. The results show a high affinity for Ni²⁺ ions, attributed to the unique polymer’s structural features. This work expands the library of anionic metal-organic frameworks and provides insights into the tunable ion-exchange properties of such frameworks.

Graphical abstract

A new metal-organic framework {(H₂pa)₃[Co₃(BTCA)₃].6H₂O}_n exhibits ion exchange between pore diammonium cations and hard metals in aqueous solution, supported by structural and spectroscopic studies.