Synthesis, structure, spectroscopy, and magnetism of two new dinuclear carbonato-bridged Cu(II) complexes

Two new dinuclear μ-CO3 2− Cu(II) complexes with different coordination modes for the carbonato bridge have been obtained by fixation of atmospheric CO2 and also directly prepared from the carbonate salt. The compounds comprise: [Cu2(μ-CO3)(dpyam)4](ClO4)2(H2O)4 (1), and [Cu2(μ-CO3)2(dpyam)2](H2O) (2), (in which dpyam=di-2-pyridylamine). For 1, the carbonate ligand acts as a bridge between two Cu(II) centres showing an anti–anti (μ-η1-η1-CO3 2−) coordination mode with a distorted square-based pyramidal geometry for each Cu(II) environment. Complex 2 involves the di-μ-CO3 2− bridge with a novel tridentate μ-η1-η2-CO3 2− coordination mode. The geometry around each copper atom is distorted square-based pyramidal. Susceptibility measurements for both complexes show a weak to moderately strong antiferromagnetic coupling with J values of −90.4 and −9.9 cm−1 for 1 and 2, respectively. The tridentate co-ordination mode of the carbonate bridge in 2 has not previously been reported for dinuclear Cu(II) complexes. Also its magnetic behaviour and superexchange pathway are discussed.