Chemical Fixation of Atmospheric CO 2 by Copper(II) Complexes of a Tridentate N ‐donor Ligand

Using an unsymmetrical tridentate N‐donor ligand (2‐pyridylethyl){2‐(1‐methylimidazolyl)methyl}methylamine (L 3 ), synthesis, spectral (IR, UV/Vis, ESI‐MS, and EPR), magnetic (as solid/in solution) and redox properties of a monomeric green [(L 3 )Cu II Cl 2 ] · MeOH ( 1 ), a dimeric light‐blue [{(L 3 )Cu II (μ‐OH)} 2 ](ClO 4 ) 2 ( 2 ), a dimeric blue [{(L 3 )Cu II (μ‐OMe)} 2 ](ClO 4 ) 2 ( 3 ), and a trimeric ink‐blue [{(L 3 )Cu II (OClO 3 )} 3 (μ 3 ‐OCO 2 )](ClO 4 ) ( 4 ) complexes were achieved. Complexes 1 , 3 , and 4 were structurally characterized. Isolation of 4 was achieved by the reaction between {(L 3 ) 2 Cu II 2 (μ‐OH) 2 } 2+ species (formed from the reaction between (i) solution‐generated yellow [(L 3 )Cu I (MeCN)] 1+ species and O 2 , followed by reaction with moisture and (ii) 1 and NaOH in water and CO 2 in open air, under ambient conditions. Reactivity of 2 with MeOH results in the formation of 3 . The observed CO 2 fixation by reactive complex 2 to afford 4 was rationalized, through designed experiments including kinetic measurements. Thermodynamic parameters of HCO 3 – /CO 2 binding were also derived. Temperature‐dependent magnetic measurements of 4 indicated a ferromagnetic exchange‐coupling ( J = 48 cm –1 ). Notably, 4 exhibits largest ferromagnetic coupling ( J = 48 cm –1 ) amongst all complexes reported so far with similar mode of carbonate‐bridging.