Tuning the Origin of Magnetic Relaxation by Substituting the 3d or Rare-Earth Ions into Three Isostructural Cyano-Bridged 3d–4f Heterodinuclear Compounds

Three isostructural cyano-bridged 3d–4f compounds, [YFe­(CN)6(hep)2(H2O)4] (1), [DyFe­(CN)6(hep)2(H2O)4] (2), and [DyCo­(CN)6(hep)2(H2O)4] (3), were successfully assembled by site-targeted substitution of the 3d or rare-earth ions. All compounds have been structurally characterized to display slightly distorted pentagonal-bipyramidal local coordination geometry around the rare-earth ions. Magnetic analyses revealed negligible magnetic coupling in compound 1, antiferromagnetic intradimer interaction in 2, and weak ferromagnetic coupling through dipolar–dipolar interaction in 3. Under an applied direct-current (dc) field, 1 (Hdc = 2.5 kOe, τ0 = 1.3 × 10–7 s, and Ueff/kB = 23 K) and 3 (Hdc = 2.0 kOe, τ0 = 7.1 × 10–11 s, and Ueff/kB = 63 K) respectively indicated magnetic relaxation behavior based on a single [FeIII]LS ion and a DyIII ion; nevertheless, 2 (Hdc = 2.0 kOe, τ0 = 9.7 × 10–8 s, and Ueff/kB = 23 K) appeared to be a single-molecule magnet based on a cyano-bridged DyFe dimer. Compound 1, which can be regarded as a single-ion magnet of the [FeIII]LS ion linked to a diamagnetic YIII ion in a cyano-bridged heterodimer, represents one of the rarely investigated examples based on a single FeIII ion explored in magnetic relaxation behavior. It demonstrated that the introduction of intradimer magnetic interaction of 2 through a cyano bridge between DyIII and [FeIII]LS ions negatively affects the energy barrier and χ″(T) peak temperature compared to 3.