Syntheses, Structures, and Magnetic Properties of Acetato- and Diphenolato-Bridged 3d–4f Binuclear Complexes [M(3-MeOsaltn)(MeOH)_x(ac)­Ln(hfac)₂] (M = Zn^II, Cu^II, Ni^II, Co^II; Ln = La^III, Gd^III, Tb^III, Dy^III; 3‑MeOsaltn = N,N′‑Bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato; ac = Acetato; hfac = Hexafluoroacetylacetonato; x = 0 or 1)

A series of 3d–4f binuclear complexes, [M­(3-MeOsaltn)­(MeOH)_x(ac)­Ln­(hfac)₂] (x = 0 for M = Cu^II, Zn^II; x = 1 for M = Co^II, Ni^II; Ln = Gd^III, Tb^III, Dy^III, La^III), have been synthesized and characterized, where 3-MeOsaltn, ac, and hfac denote N,N′-bis­(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, acetato, and hexafluoroacetylacetonato, respectively. The X-ray analyses demonstrated that all the complexes have an acetato- and diphenolato-bridged M^II–Ln^III binuclear structure. The Cu^II–Ln^III and Zn^II–Ln^III complexes are crystallized in an isomorphous triclinic space group P1̅, where the Cu^II or Zn^II ion has square pyramidal coordination geometry with N₂O₂ donor atoms of 3-MeOsaltn at the equatorial coordination sites and one oxygen atom of the bridging acetato ion at the axial site. The Co^II–Ln^III and Ni^II–Ln^III complexes are crystallized in an isomorphous monoclinic space group P2₁/c, where the Co^II or Ni^II ion at the high-spin state has an octahedral coordination environment with N₂O₂ donor atoms of 3-MeOsaltn at the equatorial sites, and one oxygen atom of the bridged acetato and a methanol oxygen atom at the two axial sites. Each Ln^III ion for all the complexes is coordinated by four oxygen atoms of two phenolato and two methoxy oxygen atoms of “ligand-complex” M­(3-MeOsaltn), four oxygen atoms of two hfac^–, and one oxygen atom of the bridging acetato ion; thus, the coordination number is nine. The temperature dependent magnetic susceptibilities from 1.9 to 300 K and the field-dependent magnetization up to 5 T at 1.9 K were measured. Due to the important orbital contributions of the Ln^III (Tb^III, Dy^III) and to a lesser extent the M^II (Ni^II, Co^II) components, the magnetic interaction between M^II and Ln^III ions were investigated by an empirical approach based on a comparison of the magnetic properties of the M^II–Ln^III, Zn^II–Ln^III, and M^II–La^III complexes. The differences of χ_MT and M(H) values for the M^II–Ln^III, Zn^II–Ln^III and those for the M^II–La^III complexes, that is, Δ­(T) = (χ_MT)_MLn – (χ_MT)_ZnLn – (χ_MT)_MLa = J_MLn(T) and Δ­(H) = M_MLn(H) – M_ZnLn(H) – M_MLa(H) = J_MLn(H), give the information of 3d–4f magnetic interaction. The magnetic interactions are ferromagnetic if M^II = (Cu^II, Ni^II, and Co^II) and Ln = (Gd^III, Tb^III, and Dy^III). The magnitudes of the ferromagnetic interaction, J_MLn(T) and J_MLn(H), are in the order Cu^II–Gd^III > Cu^II–Dy^III > Cu^II–Tb^III, while those are in the order of M^II–Gd^III ≈ M^II–Tb^III > M^II–Dy^III for M^II = Ni^II and Co^II. Alternating current (ac) susceptibility measurements demonstrated that the Ni^II–Tb^III and Co^II–Tb^III complexes showed out-of-phase signal with frequency-dependence and the Ni^II–Dy^III and Co^II–Dy^III complexes showed small frequency-dependence. The energy barrier for the spin flipping was estimated from the Arrhenius plot to be 14.9(6) and 17.0(4) K for the Ni^II–Tb^III and Co^II–Tb^III complexes, respectively, under a dc bias field of 1000 Oe.