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

By employing the ligand azotetrazolyl-2,7-dihydroxynaphthalene (H 3 ATD), two linear trinuclear mixed-valence cobalt complexes [Co II CoIII2(HATD) 4 (H 2 O) 4 ]·4DMA·3H 2 O ( 1 , DMA = N , N -dimethylacetamide) and [Co II CoIII2(HATD) 4 (DMF) 2 (H 2 O) 2 ]·2DMF·2H 2 O ( 2 , DMF = N , N -dimethylformamide) were synthesized. Two [2 × 2] grid-like tetranuclear ion-pair complexes [CoII2CoIII2(HATD) 4 (bpp) 2 (H 2 O) 2 ][Co III (HATD) 2 ] 2 ·8DMF·6H 2 O ( 3 , bpp = 2,6-di(pyrazol-1-yl)pyridine) and [CoII2CoIII2(HATD) 4 (bpp) 2 (H 2 O) 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).