Tuning Magnetic Anisotropy in a Class of Co(II) Bis(hexafluoroacetylacetonate) Complexes.

Tuning the magnetic anisotropy of metal ions remains highly interesting in the design of improved single-molecule magnets (SMMs). We herein report synthetic, structural, magnetic, and computational studies of four mononuclear Co complexes, namely [Co(hfac) (MeCN) ] (1), [Co(hfac) (Spy) ] (2), [Co(hfac) (MBIm) ] (3), and [Co(hfac) (DMF) ] (4) (MeCN=acetonitrile, hfac=hexafluoroacetylacetone, Spy=4-styrylpyridine, MbIm=5,6-dimethylbenzimidazole, DMF=N,N-dimethylformamide), with distorted octahedral geometry constructed from hexafluoroacetylacetone (hfac) and various axial ligands. By a building block approach, complexes 2-4 were synthesized by recrystallization of the starting material of 1 from various ligands containing solution. Magnetic and theoretical studies reveal that 1-4 possess large positive D values and relative small E parameters, indicating easy-plane magnetic anisotropy with significant rhombic anisotropy in 1-4. Dynamic alternative current (ac) magnetic susceptibility measurements indicate that these complexes exhibit slow magnetic relaxation under external fields, suggesting field-induced single-ion magnets (SIMs) of 1-4. These results provide a promising platform to achieve fine tuning of magnetic anisotropy through varying the axial ligands based on Co(II) bis(hexafluoroacetylacetonate) complexes.