| Abstract
| - A study of the reversible CO2 fixation by a series of macrocyclic dicopper complexes is described. The dicoppermacrocyclic complexes [Cu2(OH)2(Me2p)](CF3SO3)2, 1(CF3SO3)2, and [Cu2(μ-OH)2(Me2m)](CF3SO3)2, 2(CF3SO3)2,(Scheme 1) containing terminally bound and bridging hydroxide ligands, respectively, promote reversible inter- andintramolecular CO2 fixation that results in the formation of the carbonate complexes [{Cu2(Me2p)}2(μ-CO3)2](CF3SO3)4, 4(CF3SO3)4, and [Cu2(μ-CO3)(Me2m)](CF3SO3)2, 5(CF3SO3)2. Under a N2 atmosphere the complexes evolveCO2 and revert to the starting hydroxo complexes 1(CF3SO3)2 and 2(CF3SO3)2, a reaction the rate of which linearlydepends on [H2O]. In the presence of water, attempts to crystallize 5(CF3SO3)2 afford [{Cu2(Me2m)(H2O)}2(μ-CO3)2](CF3SO3)4, 6(CF3SO3)4, which appears to rapidly convert to 5(CF3SO3)2 in acetonitrile solution. [Cu2(OH)2(H3m)]2+, 7, which contains a larger macrocyclic ligand, irreversibly reacts with atmospheric CO2 to generate cagelike[{Cu2(H3m)}2(μ-CO3)2](ClO4)4, 8(ClO4)4. However, addition of 1 equiv of HClO4 per Cu generates [Cu2(H3m)(CH3CN)4]4+ (3), and subsequent addition of Et3N under air reassembles 8. The carbonate complexes 4(CF3SO3)4,5(CF3SO3)2, 6(CF3SO3)4, and 8(ClO4)4 have been characterized in the solid state by X-ray crystallography. Thisanalysis reveals that 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 consist of self-assembled molecular boxes containingtwo macrocyclic dicopper complexes, bridged by CO32- ligands. The bridging mode of the carbonate ligand isanti-anti-μ-η1:η1 in 4(CF3SO3)4, anti-anti-μ-η2:η1 in 6(CF3SO3)4 and anti-anti-μ-η2:η2 in 5(CF3SO3)2 and 8(ClO4)4.Magnetic susceptibility measurements on 4(CF3SO3)4, 6(CF3SO3)4, and 8(ClO4)4 indicate that the carbonate ligandsmediate antiferromagnetic coupling between each pair of bridged CuII ions (J = −23.1, −108.3, and −163.4 cm-1,respectively, H = −JS1S2). Detailed kinetic analyses of the reaction between carbon dioxide and the macrocycliccomplexes 1(CF3SO3)2 and 2(CF3SO3)2 suggest that it is actually hydrogen carbonate formed in aqueous solutionon dissolving CO2 that is responsible for the observed formation of the different carbonate complexes controlled bythe binding mode of the hydroxy ligands. This study shows that CO2 fixation can be used as an on/off switch forthe reversible self-assembly of supramolecular structures based on macrocyclic dicopper complexes.
- Reversible self-assembly of cagelike tetracopper carbonate complexes with potential use as supramolecular containers is described. Assembly−disassembly is triggered by CO2 fixation−release by the macrocyclic hydroxo complexes. Kinetic studies unexpectedly reveal that CO2 fixation occurs via reaction of the hydroxo complexes with HCO3-, previously generated by reaction of CO2 with H2O.
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