Synthesis, Characterization, Magnetic Properties, and DFT Investigations of Heterobimetallic Nickel–Lanthanide LNiIILnIII (Ln = Ce, Gd, Tb, Dy) Complexes Supported by Schiff Base Ligands

Four Schiff base complexes LNiLn (Ln = Ce (2), Gd (3), Tb (4), and Dy (5), H₂L= N,N′-bis(3-methoxysalicylaldiimine)-1,3-propylene-2-ol)) are synthesized from the precursor LNi (1) moieties. However, compound 2, which crystallizes in the tetragonal system, differs from the other isostructural three 3, 4, and 5 congeners. The dc magnetic studies reveal ferromagnetic interaction between the Ni(II) (S = 1) and the trivalent lanthanide (Ln(III) = Gd, Tb, and Dy) but not for Ce(III) in agreement with the computational results. The dynamic magnetic investigations highlight field-induced single-molecule magnet behaviors at 2 K for Ln(III) = Ce, Tb, and Dy. In case of compound 4, it is determined that the slow magnetic relaxation occurs through an Orbach process only with Δ = 19.1(3) K and τ₀ = 3.99(4) × 10⁻⁷ s (H = 1200 Oe). Electronic structures and magnetic properties have been investigated theoretically using relativistic density functional theory calculations combined with the broken symmetry approach for the magnetic properties. The results indicate a Ferro character for 3 (+1.03 cm⁻¹), 4 (+5.44 cm⁻¹), and 5 (+1.35 cm⁻¹), and an antiferromagnetic (AF) behavior for complex 2 (−2.82 cm⁻¹), in agreement with experimental magnetic susceptibility measurements. Moreover, the computed Mayer and Nalewajski–Mrozek Ni(II)–O_b and O_b–Ln(III) bond orders are found to be higher for 2 than for 3, 4, and 5, correlating well with the AF and Ferro character of each species.