Thermally Induced Spin Transitions in Nitroxide−Copper(II)−Nitroxide Spin Triads Studied by EPR

Thermally induced spin transitions in a family of heterospin polymer chain complexes of Cu2+ hexafluoroacetylacetonate
with two pyrazole-substituted nitronyl nitroxides are studied using electron paramagnetic resonance (EPR)
spectroscopy. The structural rearrangements at low temperatures induce spin transitions in exchange-coupled spin
triads of nitroxide−copper(II)−nitroxide. The values of exchange interactions in spin triads of studied systems are
typically on the order of tens to hundreds of inverse centimeters. The large magnitude of exchange interaction
determines the specific and very informative peculiarities in EPR spectra due to the predominant population of the
ground state of a spin triad and spin exchange processes. The variety of these manifestations depending on
structure and magnetic properties of spin triads are described. EPR is demonstrated as an efficient tool for the
characterization of spin transitions and for obtaining information on the temperature-dependent sign and value of
the exchange interaction in strongly coupled spin triads.