The syntheses of the hexadentate ligands 2,2,10,10-tetra(methyleneamine)-4,8-dithiaundecane (PrN4S2amp), 2,2,11,11-tetra(methyleneamine)-4,9-dithiadodecane (BuN4S2amp), and 1,2-bis(4,4-methyleneamine)-2-thiapentyl)benzene (XyN4S2amp) are reported and the complexes [Co(RN4S2amp)]3+ (R = Pr, Bu, Xy) characterised by single crystal X-ray study. The low-temperature (11 K) absorption spectra have been measured in Nafion films. From the observed positions of both spin-allowed 1A1g-->1T1g and 1A1g-->1T2g and spin forbidden 1A1g-->3T1g and 1A1g-->3T2g bands, octahedral ligand-field parameters (10Dq, B and C) have been determined. DFT calculations suggest that significant interaction between the d-d and CT excitations occurs for the complexes. The calculations offer an explanation for the observed deviations from linearity of the relationship between 59Co magnetogyric ratio and beta(DeltaE)(-1)(beta= the nephelauxetic ratio; DeltaE the energy of the 1A1g-->1T1g transition) for a series of amine and mixed amine/thioether donor complexes.