Field-induced slow magnetic relaxation from linear trinuclear CoIII–CoII–CoIII to grid [2 × 2] tetranuclear mixed-valence cobalt complexes

Abstract

By employing the ligand azotetrazolyl-2,7-dihydroxynaphthalene (H₃ATD), two linear trinuclear mixed-valence cobalt complexes [Co^IICo^III₂(HATD)₄(H₂O)₄]·4DMA·3H₂O (1, DMA = N,N-dimethylacetamide) and [Co^IICo^III₂(HATD)₄(DMF)₂(H₂O)₂]·2DMF·2H₂O (2, DMF = N,N-dimethylformamide) were synthesized. Two [2 × 2] grid-like tetranuclear ion-pair complexes [Co^II₂Co^III₂(HATD)₄(bpp)₂(H₂O)₂][Co^III(HATD)₂]₂·8DMF·6H₂O (3, bpp = 2,6-di(pyrazol-1-yl)pyridine) and [Co^II₂Co^III₂(HATD)₄(bpp)₂(H₂O)₂][Co^III(HATD)₂]₂·8DMSO·4MeOH (4, DMSO = dimethyl sulphoxide) were obtained by the reaction of complex 1/2 with tridentate-chelating bpp in DMF and DMSO, respectively. The single-crystal X-ray diffraction analysis indicated that complexes 1 and 2 have a similar core, in which the DMA in 1 acts as a guest molecule, and the DMF in 2 acts as a coordinated molecule and guest molecule. Complexes 3 and 4 are isostructural. All the Co(II) ions in 1–4 are present in a distorted octahedral geometry. The ac susceptibility measurements show that all complexes display frequency-dependent peaks in the out-of-phase (χ_m′′) component of the alternating-current (ac) magnetic susceptibility data, which is the characteristic behavior of single molecule magnets (SMMs).