Inclusion of Ln(III) in the Complexes of Co(II) with a Mannich Base Ligand: Development of Atmospheric CO2 Fixation and Enhancement of Catalytic Oxidase Activities

The reaction of the Mannich base ligand (H2L = N,N′-dimethyl-N,N′-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine) with Co(OAc)2·4H2O and Ln(III) nitrate salts (Ln = Gd, Tb, and Dy) under basic conditions afforded three carbonato-bridged isostructural tetranuclear heterometallic Co(II)–Ln(III) complexes (Co2Gd2L2(μ4-CO3)2(NO3)2] (1), [Co2Tb2L2(μ4-CO3)2(NO3)2] (2), and [Co2Dy2L2(μ4-CO3)2(NO3)2] (3)) by atmospheric CO2 fixation. In all structures, two dinuclear [(CoIIL)LnIII(NO3)] units are linked via two μ4-carbonato groups to form the tetranuclear CoII2LnIII2 core. The geometry around two penta-coordinated Co(II) ions is distorted square pyramid, and that around two nona-coordinated Ln(III) ions is intermediate between “spherical tricapped trigonal prism” and “spherical capped square antiprism” in all complexes. The complexes (1–3) showed catecholase-like and phenoxazinone-synthase-like catalytic activities. The kcat values calculated for the catecholase-like reaction were 254.5, 272.4, and 291.3 h...