Embracing ligands. Synthesis, characterisation and the correlation between ~(59)Co NMR and ligand field parameters of Co(III) complexes with a new class of nitrogen–thioether multidentate ligand

摘要

The syntheses of the hexadentate ligands 2,2,10,10-tetra(methyleneamine)-4,8-dithiaundecane (PrN_4S_2amp), 2,2,11,11-tetra(methyleneamine)-4,9-dithiadodecane (BuN_4S_2amp), and 1,2-bis(4,4-methyleneamine)-2-thiapentyl)benzene (XyN_4S_2amp) are reported and the complexes [Co(RN_4S_2amp)]~(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 ~1A_(1g) → ~1T_(1g) and ~1A_(1g) → ~1T_(2g) and spin forbidden ~1A_(1g) → ~3T_(1g) and ~1A_(1g) → ~3T_(2g) bands, octahedral ligand-field parameters (10D_q, 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 ~(59)Co magnetogyric ratio and (E)–1 ( = the nephelauxetic ratio; E the energy of the ~1A_(1g) → ~1T_(1g) transition) for a series of amine and mixed amine/thioether donor complexes.