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A total of five salicylaldoxime ligands, (HL1–5), analogues of commercial metal extractants were synthesised and characterised. The cobalt(II) complexes [CoL2] (L=L1–5) of these ligands were synthesised and characterised by microanalysis, atomic absorption, infra and mass spectroscopy. X-ray structure analysis was carried out on the adducts [Co(L)2(dmso)2] (L=L4,5). These are the only structurally characterised cobalt salicylaldoxime complexes apart from three five-coordinate nitroso complexes [CoL2(NO)] reported in the 1980s (J. Crystallogr. Spectrosc. Res. 13 (1983) 413; J. Crystallogr. Spectrosc. Res. 16 (1986) 6). The structures of the two adducts characterised show octahedral coordination with two dmso molecules occupying axial positions and two salicylaldoxime units in each molecule occupying equatorial positions. The introduction of nitro groups on the two ligands has been found to stabilise oxidation (II) in preference to (III) in both cobalt complexes. These groups were found to have what appears to be a significant contribution to intra-ligand hydrogen bonding resulting in three-centre H bonds on either side of the molecules, which in turn adopt unusual chair conformations. |
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