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

Abstract

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 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 ⁵⁹Co magnetogyric ratio and β(ΔE)⁻¹ (β = the nephelauxetic ratio; ΔE the energy of the ¹A_1g → ¹T_1g transition) for a series of amine and mixed amine/thioether donor complexes.