Synthesis and characterisation of sulfur-rich manganese(III) and vanadium(IV) complexes containing dithioacid ligands
Abstract
The chemistry of the bidentate (S,S′)– donor ligand 2-aminocyclopent-1-ene-1-carbodithioic acid (Hacda) and its N-alkylated derivatives [R = Et (Heacda), Prn(Hpacda), or Bun(Hbacda)] with vanadium(IV) and manganese(III) has been studied. The vanadium(IV) complexes [V(aacda)4]1a–1d are all eight-co-ordinated non-oxo species containing a VS8 chromophore. Their ESR spectra in frozen solution (140 K) exhibit axial anisotropy with a 16-line 51V hyperfine pattern. The observed order in spin-Hamiltonian parameters (g‖≈ 1.932, g⊥≈ 1.985, A‖≈ 175 × 10–4 cm–1 and A⊥≈ 74 × 10–4 cm–1) indicates a dx2–y2 ground state with a dodecahedral (D2d) structure. Electrochemical studies of 1a–1d show a quasi-reversible one-electron VIV–VIII reduction at ≈–0.7 V vs. saturated calomel electrode (SCE). The manganese(III) complexes [Mn(aacda)3]2a–2c are all high-spin species (µeff 5.01–5.10) and exhibit two ligand-to-metal charge-transfer bands at ≈ 610 and 530 nm. Their cyclic voltammograms reveal the presence of two quasi-Nernstian couples: E½(ox)= 0.1 V and E½(red)=–0.33 V vs. SCE due to MnIV–MnIII and MnIII–MnII electron transfers respectively.