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# Very Strongly Ferromagnetically Coupled Diradicals from Mixed Radical Centers: Nitronyl Nitroxide Coupled to Oxoverdazyl via Polyene Spacers

journal contribution

posted on 2009-02-26, 00:00 authored by Iqbal A. Latif, Anirban Panda, Sambhu N. DattaWe predict extremely large and positive intramolecular magnetic exchange coupling constants (

*J*) for coupled diradicals constructed from nitronyl nitroxide (NN) and oxoverdazyl (o-VER). These radicals have the general formula o-VER(N)−*n*C−NN where*n*C represents an olefinic spacer with*n*= 0, 2, 4, 6, and 8. Species like o-VER(C)−*n*C−NN have negative coupling constants. The atoms in the parentheses show the point of attachment of the coupler to the verdazyl moiety. Both the N-linked series and C-linked series have comparable stability. The triplet molecular geometries were optimized by the density functional (UB3LYP) method using the 6-311 g(d,p) basis set. This was followed by single-point UB3LYP calculations using 6-311++g(3df,3pd) basis. To calculate*J*, single-point broken-symmetry computations were performed on the optimized triplet geometries and using the same basis set. The N-linked diradicals coupled through conjugated polyenes are topologically different. These are found to have coupling constants of the order of 1000 cm^{−1}, whereas the C-linked diradicals show coupling constants of the order of −100 cm^{−1}. In general, for both cases, the absolute magnitude of the coupling constant decreases with the increase in the length of the spacer.