Mononuclear complexes of FeII, CoII and CoIII containing imine-based ligands of 8-aminoquinoline and 7-aminoindazole: spin state tuning of FeII complexes in solution

Abstract

Five mononuclear metal complexes were synthesised, three complexes of iron(II), one complex of cobalt(III) and one complex of cobalt(II) containing imine ligands based on 8-aminoquinoline or 7-aminoindazole and 2-formylpyridine or 3-formylpyrazole, namely [Fe^II(L1)₂](BF₄)₂ (1), [Co^III(L1)(L1′)](BF₄)₂ (2), [Fe^II(HL2)₂](BF₄)₂ (3), [Fe^II(HL3)₂](BF₄)₂ (4) and [Co^II(HL3)₂](BF₄)₂ (5). Iron(II) complexes 1 and 3 derived from 8-aminoquinoline and 2-formylpyridine or 3-formylpyrazole, respectively, were stabilised in the LS-state (S = 0) as proven by NMR spectroscopy and X-ray crystallography, whereas complex 4, based on indazole and pyridine, shows a gradual and incomplete spin conversion in CD₃CN solution (the Evans method). According to NMR spectroscopy and X-ray crystallography, the cobalt complexes 2 and 5 were stabilised in different oxidation states.