Slow Magnetic Relaxation in a Palladium–Gadolinium Complex Induced by Electron Density Donation from the Palladium Ion

Incorporating palladium in the first coordination sphere of acetato-bridged lanthanoid complexes, [Pd₂Ln₂(H₂O)₂(AcO)₁₀]⋅2 AcOH (Ln=Gd (1), Y (2), Gd_0.4Y_1.6 (3), Eu (4)), led to significant bonding interactions between the palladium and the lanthanoid ions, which were demonstrated by experimental and theoretical methods. We found that electron density was donated from the d⁸ Pd²⁺ ion to Gd³⁺ ion in 1 and 3, leading to the observed slow magnetic relaxation by using local orbital locator (LOL) and X-ray absorption near-edge structure (XANES) analysis. Field-induced dual slow magnetic relaxation was observed for 1 up to 20 K. Complex 3 and frozen aqueous and acetonitrile solutions of 1 showed only one relaxation peak, which confirms the role of intermolecular dipolar interactions in slowing the magnetic relaxation of 1. The slow magnetic relaxation occurred through a combination of Orbach and Direct processes with the highest pre-exponential factor (τ_o=0.06 s) reported so far for a gadolinium complex exhibiting slow magnetic relaxation. The results revealed that transition metal–lanthanoid (TM–Ln) axial interactions indeed could lead to new physical properties by affecting both the electronic and magnetic states of the compounds.