Until now, the expressions of the anisotropic energy barriers Delta(xi) and Delta(A), 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 Delta(xi) and Delta(A) in terms of D, J, and S of six R4FeII-(ReCl4)-Cl-IV(CN)(2) (R = diethylformamide (1), dibutylformamide (2), dimethylformamide (3), dimethylbutyramide (4), dimethylpropionamide (5), and diethylacetamide (6)) SCMs in the intermediate region. The Delta(A) value for compounds 1-3 was very similar to the magnetic anisotropic energy of a single Fe-II, while the value of Delta(xi) was predicted using the exchange interaction of Fe-II with the neighboring Re-IV, which could be expressed as 2JS(Re)S(Fe). Similar to compounds 1-3, the anisotropy energy barrier Delta(A) of compounds 4 and 5 was also equal to (D-i - E-i)S-Fe(2), but the correlation energy Delta(xi) was closely equal to 2JS(Re)S(Fe)(cos 98.4 - cos 180) due to the reversal of the spins on the opposite Fe-II. For compound 6, one unit cell of (ReFeII)-Fe-IV was regarded as a domain wall since it had two different Re-IV-Fe-II couplings. Thus, the Delta(xi) of compound 6 was expressed as 4J '' SRe1Fe1SRe2Fe2, where J '' was the coupling constant of the neighboring unit cells of Re1Fe1 and Re2Fe2, and Delta(A) was equal to the anisotropic energy barrier of one domain wall given by D-Re1Fe1 (S-Re1Fe1(2) - 1/4).