Strong Ferromagnetic Exchange Coupling and Single-Molecule Magnetism in MoS43--Bridged Dilanthanide Complexes

• Published in: Journal of the American Chemical Society Vol. 143; no. 22
• Main Authors: Darago, Lucy E, Boshart, Monica D, Nguyen, Brian D, Perlt, Eva, Ziller, Joseph W, Lukens, Wayne W, Furche, Filipp, Evans, William J, Long, Jeffrey R
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society (ACS) 24.05.2021
• Subjects: Charge transfer; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Lanthanides; Ligands; Magnetic properties; Quantum mechanics
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.1c03098

We report the synthesis and characterization of the trinuclear 4d-4f compounds [Co(C5Me5)2][(C5Me5)2Ln(μ-S)2Mo(μ-S)2Ln(C5Me5)2], 1-Ln (Ln = Y, Gd, Tb, Dy), containing the highly polarizable MoS43- bridging unit. UV-Vis-NIR diffuse reflectance spectra and DFT calculations of 1-Ln reveal a low-energy metal-to-metal charge transfer transition assigned to charge transfer from the singly occupied 4dz2 orbital of MoV to the empty 5d orbitals of the lanthanides (4d in the case of 1-Y), mediated by sulfur-based 3p orbitals. Electron paramagnetic resonance spectra collected for 1-Y in a tetrahydrofuran solution show large 89Y hyperfine coupling constants of A⊥ = 23 MHz and A|| = 26 MHz, indicating the presence of significant yttrium-localized unpaired electron density. Magnetic susceptibility data support similar electron delocalization and ferromagnetic Ln-Mo exchange for 1-Gd, 1-Tb, and 1-Dy. This ferromagnetic exchange gives rise to an S = 15/2 ground state for 1-Gd and one of the largest magnetic exchange constants involving GdIII observed to date, with JGd-Mo = +16.1(2) cm-1. Additional characterization of 1-Tb and 1-Dy by ac magnetic susceptibility measurements reveals that both compounds exhibit slow magnetic relaxation. Although a Raman magnetic relaxation process is dominant for both 1-Tb and 1-Dy, an extracted thermal relaxation barrier of Ueff = 68 cm-1 for 1-Dy is the largest yet reported for a complex containing a paramagnetic 4d metal center. Furthermore, these results provide a potentially generalizable route to enhanced nd-4f magnetic exchange, revealing opportunities for the design of new nd-4f single-molecule magnets and bulk magnetic materials.