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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 CoII complexes, namely [Co(hfac)2(MeCN)2] (1), [Co(hfac)2(Spy)2] (2), [Co(hfac)2(MBIm)2] (3), and [Co(hfac)2(DMF)2] (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. [ABSTRACT FROM AUTHOR]

Using dicyanamides, three two-dimensional coordination polymers (CPs) [CuII(valdmpn)LnIII(μ-1,5-dca)3]n (LnIII = Gd (1), Tb (2) and Dy (3)) were synthesized and characterized. Compounds 1–3 are two-dimensional coordination polymers bridged with μ-1,5-dca connecting the [CuII(valdmpn)LnIII]3+ units. In compounds 1–3, the Cu atom was pentacoordinated with an elongated square pyramidal (C4v) geometry, while the Ln (Gd, Tb and Dy) atom was nine-coordinated with a muffin (Cs) geometry. Detailed direct current (dc) magnetic measurements and simulated data demonstrated the existence of a ferromagnetic CuII–GdIII interaction for compound 1. Alternating current (ac) magnetic measurements revealed that compound 2 exhibited a slow magnetic relaxation behavior under a zero dc field. A hysteresis loop at 1.8 K was observed in compound 2, characteristic of typical single-molecule magnets (SMMs). However, compound 3 showed a slow magnetic relaxation behavior under a dc field. This system provides a good opportunity to determine the character of the Ln(III) ions incorporated and/or the origin of the slow magnetic relaxation behavior. [ABSTRACT FROM AUTHOR]