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 d_x²–y² ground state with a dodecahedral (D_2d) structure. Electrochemical studies of 1a–1d show a quasi-reversible one-electron V^IV–V^III reduction at ≈–0.7 V vs. saturated calomel electrode (SCE). The manganese(III) complexes [Mn(aacda)₃]2a–2c are all high-spin species (µ_eff 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: E_½(ox)= 0.1 V and E_½(red)=–0.33 V vs. SCE due to Mn^IV–Mn^III and Mn^III–Mn^II electron transfers respectively.