Synthesis, structure and fluxionality of Co(III) complexes containing chelated sulfate

Abstract The syntheses and characterisation of the complexes [Co(pmea)(O2SO2)]ClO4 and [Co(pmap)(O2SO2)]ClO4 (pmea = bis((2-pyridyl)methyl)-2-((2-pyridyl)ethyl)amine; pmap = bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine), containing chelating sulfato ligands, are reported. These were prepared by oxidation of a solution containing CoSO4·7H2O and the tripodal tetraamine ligand with either (NH4)2[Ce(O2NO)6] (pmea) or Oxone (2KHSO5·KHSO4·K2SO4; pmap), and their structures were confirmed by X-ray crystallography. [Co(pmap)(O2SO2)]ClO4 crystallised as the 6-isomer from aqueous NaClO4 solution, while [Co(pmea)(O2SO2)]ClO4 was obtained as a mixture of the 5- and 6-isomers, with both isomers being able to be resolved in the X-ray structure. Comparison of the IR spectra of [Co(pmap)(O2SO2]ClO4 and [Co(pmap)(O2CO)]ClO4 allowed assignment of IR bands due to the chelated sulfato ligand. Fluxionality in [Co(pmea)(O2SO2)]ClO4 was resolved using 1H VT-NMR, and was found to result from ‘flapping’ of the pyridylethyl arm of the pmea ligand between two possible conformations.