Magneto-Structural Correlations in a Family of FeIIReIV(CN)2 Single-Chain Magnets: Density Functional Theory and Ab Initio Calculations.

Until now, the expressions of the anisotropic energy barriers Δξ and ΔA, using the uniaxial magnetic anisotropy D, the intrachain coupling strength J, and the high-spin ground state S for single-chain magnets (SCMs) in the intermediate region between the Ising and the Heisenberg limits, were unknown. To explore this relationship, we used density functional theory and ab initio methods to obtain expressions of Δξ and ΔA in terms of D, J, and S of six R4FeII-ReIVCl4(CN)2 (R = diethylformamide (1), dibutylformamide (2), dimethylformamide (3), dimethylbutyramide (4), dimethylpropionamide (5), and diethylacetamide (6)) SCMs in the intermediate region. The ΔA value for compounds 1-3 was very similar to the magnetic anisotropic energy of a single Fe'', while the value of Δξ was predicted using the exchange interaction of FeII with the neighboring ReIV, which could be expressed as 2JSReSFe. Similar to compounds 1-3, the anisotropy energy barrier ΔA of compounds 4 and 5 was also equal to (Di - Ei)SFe², but the correlation energy Δξ was closely equal to 2JSReSFe(cos 98.4 - cos 180) due to the reversal of the spins on the opposite FeII. For compound 6, one unit cell of ReIVFeII was regarded as a domain wall since it had two different ReIV-FeII couplings. Thus, the Δξ of compound 6 was expressed as 4JnSRe1Fe1SRe2Fe2, where Jn was the coupling constant of the neighboring unit cells of Re1Fe1 and Re2Fe2, and ΔA was equal to the anisotropic energy barrier of one domain wall given by DRe1Fe1(S²Re1Fe1 - 1/4). [ABSTRACT FROM AUTHOR]