EPR examination of the class II (deeply trapped) mixed valence complexes [(bpy)2MnO2Mn(bpy)2]3+ (the bipyndyl(III,IV) dimer) and its phenanthroline analogue in acetonitrile solution verifies that these complexes possess inequivalent Mn ions at room temperature. Isotropic hyperfine structure for two Mn ions is resolved with A1 = 167 ± 3 G and A2 = 79 ± 3 G for both complexes. The hyperfine pattern with |A1| ≅ 2|A2| and the small g anisotropy are consistent with high-spin Mn(III) antiferromagnetically coupled to Mn(IV), producing an S = 1/2 ground state. At room temperature a rate of less than 108 s-1 is estimated for the thermally activated intramolecular electron transfer, consistent with an upper limit of 106 s-1 calculated from Hush's theory. The magnetic susceptibility of the (III,IV) complexes is characteristic of a strongly antiferromagnetically coupled S = (2, 3/2) pair. The temperature dependence of the data was in good agreement with the isotropic Heisenberg exchange Hamiltonian H = -2JS1S2, yielding J = -150 ± 7 cm-1 for the bipyridyl(III,IV) dimer and J = -134 ± 5 cm-1 for the phenanthroline analogue.
|Number of pages||5|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 1978|
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