Synthesis, magnetic properties and dynamic behavior of cobalt complexes with an anthracene-containing dioxolene ligand

Abstract

The anthracene-functionalized cobalt complexes [Co(L)(TPA)]PF₆ (1) and [Co(L)(Me_nTPA)]PF₆ (2, n = 1; 3, n = 2; 4, n = 3) were synthesized by the combination of 9-(3,4-dihydroxyphenyl)anthracene (H₂L) and tris(2-pyridylmethyl)amine (TPA) or its derivatives (Me_nTPA, n = 1, 2, 3). Characterization of complexes 1–4 was performed by UV-vis absorption, IR, ¹H NMR, and magnetic susceptibility measurements. In the solid state, the variable-temperature magnetic susceptibility data showed that complex 1 is low-spin cobalt(III) catecholate (Co^III(LS)-Cat), while complex 4 is high-spin cobalt(II) semiquinonate (Co^II(HS)-SQ) in the range 4.5–400 K. The susceptibility data of complexes 2 and 3 suggested valence tautomerism between the Co^III(LS)-Cat and Co^II(HS)-SQ forms. Light-induced valence tautomerism was observed in complexes 2 and 3 at 5 K by photo-irradiation. In solution, the temperature dependence of ¹H NMR spectra of 1 and 2 showed an equilibrium between their geometrical isomers.