We have a longstanding interest in using organic radical ligands to bridge metal spins with the goal of engendering strong magnetic exchange coupling. Recently we targeted dinuclear complexes in which two metal centers are bridged by the radical anion form of the tetrazine-based ligand bmtz (bmtz = 3,6-bis(2’-pyrimidyl)-1,2,4,5-tetrazine). Several new transition metal compounds of the type [{M(TPMA)}2-μ-bmtz�-](X)3 (M = first-row transition metal, TPMA = tris(2-pyridylmethyl)amine, X = counter-anion) have been prepared and their magnetic properties evaluated. These complexes exhibit strong magnetic exchange coupling, with the nickel complex exhibiting ferromagnetic metal-radical coupling. Our interest in radical bridging ligands also involves lanthanide complexes. Due to the contracted nature of the f orbitals of lanthanide ions, exchange coupling between them is generally quite weak which prevents the rare earth ions from realizing their full potential as magnetic molecules. It has recently been shown that the use of an additional spin carrier as a bridge, e.g. an organic radical, can greatly increase the magnitude of the interaction between lanthanide ions. We believe the strong coupling already observed in transition metal – bmtz complexes makes this ligand a promising candidate for improving the magnetic properties of lanthanide complexes as well. This presentation will discuss our efforts at expanding the family of transition metal – bmtz complexes to the rest of the 3d metals, our foray into lanthanide – bmtz chemistry, as well as efforts at using other radical bridging ligands and capping ligands in order to understand the effects of the radical as well as the electronic environment provided by the capping ligand on the observed magnetic properties.

Paramagnetic dinuclear complexes with radical diimine ligands

251st National Meeting (2016)

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