Novel cobalt(II) complexes with pyridyl/ether or pyridyl/thioether ligands. The conversion of pyridyl/thioether cobalt(II) complex to pyridyl/sulfinato cobalt(III) compound

Abstract

Two new cobalt(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesized as perchlorate salts. The crystal structures show that [Co(pydado)](ClO 4) 2 · H 2O ( 1) crystallizes in the triclinic space group P 1 ¯ and [Co(pydadt)](ClO 4) 2 ( 2) crystallizes in the monoclinic space group P2 1/ c . The cation [Co(pydado)] 2+ is pseudo-octahedral with the two pyridyl groups in trans position. However, in [Co(pydadt)] 2+ complex, the size of thioether sulfur atoms imposes a distorted octahedral geometry; the pyridyl groups and the sulfur atoms are in trans position. The reaction of the complex 2 and hydrogen peroxide resulted to the oxidation of Co II into Co III and the thioether groups of the ligand to sulfinate groups with elimination of the central ethylenic group of pydadt. Thus, complex 2 was converted to bis[3-(2-pyridylmethylamino)ethanesulfinate] cobalt(III) complex ( 3) {[Co(pynso) 2](ClO 4) · 0.5H 2O}. The X-ray crystal structure reveals that the compound 3 crystallizes in the triclinic space group P 1 ¯ with the same donor atoms (N pyridyl, N amine and S) belonging to the two ligands in cis-position. In aqueous solution, the stability constants of the Co(II) chelates with these two ligands, determined by potentiometry, show the formation of [Co(LH)] 3+ and [CoL] 2+ species in all cases. The chelating power of pydadt ligand is slightly greater than that of pydado.