Heisenberg spin exchange takes place when two or more unpaired spins in close proximity interact, so that their relative orientations are no longer independent of one another. Previous studies on dimeric complexes of [MM’(tren)2(CAn-)]m+ (Figure 1) provide experimental evidence that the presence of spin exchange can affect optical and magnetic properties. The bridging ligand is redox active, which can be changed to have various combinations of semiquinone, catecholate, or quione via redox reactions. The Heisenberg model predicts that the introduction of spin exchange results in a net thermodynamic stabilization of the system. The results seen in cyclic voltammetry (CV) previously studied (Figure 2) suggest that the larger peak separation (Eechem) of [Cr2(tren)2(CA)]m+ may be a thermodynamic consequence of spin exchange comparing with the ones of [Ga2(tren)2(CA)]m+. In order to further examine the effects of the thermodynamic stabilization by the spin exchange interaction, and establish the thermodynamic correlation seen in both electrochemical and magnetic behaviors, CrIII and GaIII analogues with various substituents on the tetraoxolene bridge are synthesized. R= H, F, Cl, Br, I, phenyl, piperidino, N,N-dimethylaminophenyl, and cyanophenyl make excellent choices of substituents. Additionally, a horizontally-elongated bridging ligand, because this ligand may be able to delocalize the spin density further away from the metal ions. The CV and magnetic data of these [Cr2(tren)2(L)]n+ and [Ga2(tren)2(L)]n+ systems were collected and compared. Among all, Eechem of the Me2AnT complexes are the smallest. This result matches the prediction of both our hypothesis and our density functional theory calculations. This also suggests that electrochemical and magnetic measurement will become advantageous tools for the further study of spin polarization of spin-coupled systems.

Effects of intramolecular spin polarization on the thermodynamic properties of tetraoxolene exchange-coupled systems

256th National Meeting (2018)

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