Reversible CO Fixation and Release by a Trinuclear Zn(II) Cryptate Complex and Operando Analysis of the Complex Structure.

Metal complexes inspired by carbonic anhydrase (CA), which is a metalloenzyme containing Zn(II), have been investigated as alternatives for CO fixation systems operating under ambient temperature and pressure conditions. In this study, we designed a trinuclear Zn(II) cryptate complex (Zn L) and demonstrated rapid CO fixation with carbonation of CO using Zn L. The CO fixation performance of Zn L surpassed that of a standard CO absorbent, KOH(aq) solution, under conditions of the same solute concentration. In addition, the reaction achieved operation without support addition of base, which has been often required in systems of CA-inspired complexes. Fixed CO was released by protonating polyazacryptate ligand (L) and breaking the complex structure, and deprotonation of L induced the reconstruction of Zn L, allowing it to refix CO . This reaction mechanism was proposed based on the analysis of operando extended X-ray absorption fine structure spectroscopy. Zn L also demonstrated the ability to capture dilute CO from air, and the volume of CO captured by Zn L was approximately 2.6 times that captured by the KOH(aq) solution. Our Zn L exhibited three valuable properties: rapid CO fixation without a base, reversibility, and ability to capture dilute CO ; thus Zn L is a promising candidate as CO fixatives.