Synergy of Magnetic Anisotropy and Ferromagnetic Interaction Triggering a Dimeric Cr(II) Zero-Field Single-Molecule Magnet.

A novel Cr II -dimeric complex, [Cr II N(Si i Pr 3 ) 2 (μ-Cl)(THF)] 2 ( 1 ), has been successfully constructed using a bulky silyl-amide ligand. Single-crystal structure analysis reveals that complex 1 exhibits a binuclear motif, with a Cr 2 Cl 2 rhombus core, where two equivalent tetra-coordinate Cr II centers in the centrosymmetric unit display quasi-square planar geometry. The crystal structure has been well simulated and explored by density functional theory calculations. The axial zero-field splitting parameter ( D < 0) with a small rhombic ( E ) value is unambiguously determined by systematic investigations of magnetic measurements, high-frequency electron paramagnetic resonance spectroscopy, and ab initio calculations. Remarkably, ac magnetic susceptibility data unveil that 1 features slow dynamic magnetic relaxation typical of single-molecule magnet behavior with U eff = 22 K in the absence of a dc field. This increases up to 35 K under a corresponding static field. Moreover, magnetic studies and theoretical calculations point out that a non-negligible ferromagnetic coupling (FMC) exists in the dimeric Cr-Cr units of 1 . The coexistence of magnetic anisotropy and FMC contributes to the first case of Cr II -based single-molecule magnets (SMMs) under zero dc field.