Origin of the relaxation barriers in a family of MReIV(CN)2 single-chain magnets (M = MnII, NiII, and CoII): a theoretical investigation

Abstract

Through investigation of the origin of the relaxation barriers and the magneto-structural correlations in three (DMF)₄MRe^IVCl₄(CN)₂ (DMF = dimethylformamide; M = Mn^II (1), Ni^II (2), and Co^II (3)) single-chain magnets (SCMs) in the intermediate regime between the Ising and the Heisenberg limits using hybrid functional theory (B3LYP) and complete active space second-order perturbation theory (CASPT2) methods, we succeeded in obtaining the magnetic anisotropy and correlation energy barriers Δ_A and Δ_ξ in terms of D (magnetic anisotropy parameter), J (magnetic exchange coupling constant), and S (spin value). B3LYP calculations show that the antiferromagnetic Re^IV–Mn^II coupling interactions decrease with the increase of the Mn–N–C angle, while the ferromagnetic Re^IV–Ni^II coupling interactions increase with the increase of the Ni–N–C angle. But, the Re^IV–Co^II exchange interactions with the variation of the Co–N–C angle are almost the same. The total energy barriers Δ_τ of 1 and 2 mainly come from the contribution of the transverse anisotropy of Re^IV, while the Mn^II and Ni^II ions only transmit the exchange coupling between Re^IV and almost have no contributions. For 3, however, both of the Re^IV and Co^II ions have contributions to the total energy barrier.