The reactions of bicarbonate ion with a series of binuclear Cu(II) complexes in buffered aqueous solution have been studied, and effective binding constants for bicarbonate have been determined at pH 7.4 for the complexes [Cu 2(taec)] 4+ (taec = N,N′,N″,N‴- tetrakis(2-aminoethyl)-1,4,8,11-tetraazacyclotetradecane) and [Cu 2(tpmc)(OH)] 3+ (tpmc = N,N′,N″,N‴- tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane). [Cu 2(o-xyl-DMC 2)] 4+ (o-xyl-DMC 2 = α,α′-bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl) -o-xylene) did not react with bicarbonate ion in an aqueous solution buffered at this pH. The complexes were reduced by controlled-potential electrolysis, and the stability of the Cu(I) derivatives in aqueous solution and their affinity for bicarbonate/carbonate ion were investigated. On the basis of these fundamental studies, [Cu 2(tpmc)(μ-OH)] 3+ has been identified as an air-stable, water-soluble carrier for the capture and concentration of CO 2 by electrochemically modulated complexation. The carrier binds to the carbonate ion strongly in its oxidized, Cu(II) form and releases the ion rapidly when reduced to the Cu(I) complex. In small-scale electrochemical pumping experiments designed to demonstrate the feasibility of this approach, CO 2 has been pumped from an initial 10% CO 2/N 2 mixture up to a final concentration of 75%.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry