Unusual N-oxide formation in the peroxidation of cobalt(ii) ethylenediaminetetraacetates

Abstract

Unlike the usual formations of peroxo and superoxo cobalt products as oxygen carriers, N-oxido cobalt(II) ethylenediaminetetraacetates K₄[Co₂(edtaO₂)₂]·nH₂O [n = 6.5 (1), 10 (2), H₄edta = ethylenediaminetetraacetic acid, C₁₀H₁₆O₈N₂] and their aggregate [Co₂(edtaO₂)(H₂O)₆]_n·2nH₂O (3) were obtained as dioxygen insertion products. The cobalt ions in dimers 1 and 2 are hexa-coordinated by two edtaO₂ ligands in different configurations respectively, which is attributed to the packing of an interesting (H₂O)₁₂ water cluster in 2. Further reaction of K₄[Co₂(edtaO₂)₂]·nH₂O with hydrogen peroxide results in the final trivalent cobalt ethylenediaminetetraacetate K[Co(edta)]·2H₂O (4). A water-soluble coordination polymer Na_2n[Co(edta)]_n·4nH₂O (5) was also obtained with a one dimensional zigzag structure. Bond valence calculation is consistent with the products 1–5.