Heisenberg exchange coupling is a phenomenon that occurs
when two or more unpaired spins are in energetic proximity and interact via an
orbital mechanism. This phenomenon is exhibited in many molecules, compounds
and complexes; however, I am interested in studying paramagnetic transition
metals bonded to a single semiquinone moiety.
Semiquinones are bidentate, radical containing ligands. Transition metal
cations of interest are NiII and CrIII; these cations
were chosen because when interacting with a semiquinone ligand, they produce
ferromagnetic (parallel spin alignment) and antiferromagnetic (antiparallel
spin alignment) exchange coupling, respectively. If substituents are placed on the semiquinone
ligand, then the unpaired spin density will be polarized either towards or away
from the paramagnetic transition metal.
Locating the spin density in these transition metal-semiquinone
complexes will aid in determining their chemical reactivity and the rational
design of molecular magnetic materials.
A variety of techniques are employed to study these ligand-metal
interactions including EPR spectroscopy, crystallography, theoretical
calculations and magnetometry.