Utilization of radical ligands to bridge lanthanide ions has recently gained traction as a method for improving the magnetic properties of polylanthanide complexes. Unlike their transition metal counterparts, polylanthanide complexes bridged by closed-shell ligands (e.g. CH3COO-, OH-) typically display very weak magnetic superexchange interactions between lanthanide ions. As a result, the magnetism in such complexes primarily arises from lanthanide single-ion effects, rather than from the metals acting as a coupled unit. In contrast, radical bridging ligands engender direct exchange interactions with the lanthanide ions, leading to higher degrees of magnetic coupling and improving molecular magnetic properties, such as single molecule magnetism (SMM). Herein, the synthesis of a series of dilanthanide complexes bridged by radical-bearing 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) and 2,2’-azobipyridine (abpy) ligands is described. The magnetic properties of these radical-bridged complexes are compared with their neutral-bridged counterparts in order to precisely determine the role that the radical plays in the magnetism of these compounds. In each case, the presence of a radical on the bridging ligand increases magnetic coupling within the complex, and in several cases, the radical improves SMM behavior by limiting quantum tunneling of magnetization. We also describe the synthesis and magnetism of the first radical-bridged trilanthanide metallacycles (Ln3(hfac)6(bptz)3 and Ln3(dbm)6(bptz)3; hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, dbm = 1,3-diphenyl-1,3-propanedionate). The ease of synthesis and the magnetic properties of these compounds informs our future work to synthesize higher nuclearity radical-bridged lanthanide systems.

Radical-bridged dinuclear and metallacyclic trinuclear lanthanide complexes

255th National Meeting (2018)

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