Dinuclear cobalt(II) and cobalt(III) complexes of bis-bidentate napthoquinone ligands

The combination of bridging bis-bidentate redox-active ligands derived from 3,3-bis-2-hydroxy-1,4-naphthoquinone (bhnqH2), ancillary ligands based on tris(2-pyridylmethyl)amine (tpa) and cobalt salts has afforded a new family of dinuclear cobalt complexes. Compounds of the complexes [Co2(bhnq)(tpa)2](2+) (1), [Co2(bhnq)(Metpa)2](2+) (2), [Co2(bhnq)(Me2tpa)2](2+) (3) [Co2(bhnq)(Me3tpa)2](2+) (4), [Co2(bhnq)(tpa)2](4+) (5), [Co2(bhMenaph)(tpa)2](2+) (6) and [Co2(bhPronaph)(tpa)2](2+) (7) (Mentpa involves n = 0, 1, 2 and 3 methyl groups at the 6-position of the tpa pyridine rings; bhMenaphH4 = bis-3,4-dihydroxy-4-methoxynaphthalene-1-one; bhPronaphH4 = bis-3,4-dihydroxy-4-(2-oxopropyl)naphthalen-1(4H)-one) have been characterised by single crystal X-ray diffraction. While complexes 1-4 possess divalent cobalt centres, trivalent cobalt is evident in complexes 5-7. The bis-bidentate redox-active bridging ligand remains in the diamagnetic quinone bhnq(2-) redox state in complexes 1-5. Metal-catalysed reaction with methoxide or acetone enolate ions gives rise to the derivatised bridging ligands present in 6 and 7. The electronic properties of compounds of 1-7 have been explored in the solid state by infrared spectroscopy and variable temperature magnetic measurements and in solution by electronic absorption spectroscopy and cyclic voltammetry.