Anion−π Interaction Powered Perrhenate Recognition and Extraction in Aqueous Media
Hongmei Qin, Jing Jiang, Xiaoxu Sun, Na Lin, Pengfei Yang, Yin Chen
Abstract
Selective anion recognition and extraction in aqueous media is a challenging research topic, and the anion−π interaction is an undetermined solution for the development of anion sorbent materials with better affinity and selectivity. Here, noncovalent anion−π interaction was introduced as the driving force for this purpose. A cage-based 2D cationic metal–organic framework, IPM-21, is featured with porous channels formed by complementary V-shape electron-deficient cavities. This 3D rhombic electron-deficient cavity can bind two anions with the clipped π-acidic surfaces, exhibiting much higher affinity toward ReO 4 – due to the strong complementary effect. This cavity was forced to expand its opening size to seamlessly adopt the ReO 4 – anion with a large volume. Experimental results found that the binding energy of IPM-21 with ReO 4 – is around 2.3 kJ/mol higher than that with ClO 4 – . Parts per million levels of the ReO 4 – anion in aqueous media can be effectively extracted by IPM-21 with a removal up to 99%, even with mixed competing anions. IPM-21 can be easily recycled and reused by treatment with high concentration aqueous NaClO 4 . Due to the extremely low interlamellar interaction, the IPM-21 crystal exhibited enhanced ReO 4 – extraction performance with the recycling times due to self-exfoliation; as a result, ultrathin IPM-21 nanosheets with large lateral sizes were produced in this process.