Design, synthesis and physical properties of the metal complexes using π-radical with photo-excited high-spin state as a ligand

Abstract

Two π-radicals, 3-pyridinyl-phenylanthracene(iminonitroxide) (3) and 3-pyridinyl-phenylanthracene-(nitronylnitroxide) (4) were designed as candidates of the ligand for the metal complexes to clarify the exchange interactions between the paramagnetic centers of the metal ions and the photo-excited high-spin states of the purely organic π-radical. Compounds 3 and 4 were synthesized and their magnetic properties were examined, showing weak antiferromagnetic interactions, θ = -1.5 K for 3 and -0.7 K for 4. The photo-excited states of 3 and 4 were investigated by time-resolved ESR and clarified that both π-radicals have the quartet (S = 3/2) high-spin states as their lowest photo-excited states. Two metal complexes [Fe(III)(L)(4)] · (BPh4) (Low spin) (LH2 = N,N′-bis(1-hydroxy-2-benzyliden)-1,7-diamino-4-azaheptane) and [Cu(II)(hfac)2(4)2] using 4 were prepared. Their magnetic behaviors are well analyzed with the Bleaney-Bowers model with J/kB = - 0.86 K and three S = 1/2 spin cluster model with J/kB = -1.0 K, respectively, showing weak antiferromagnetic interactions between the paramagnetic centers of the metal ions and the π-radical in the ground state. © 2006 Elsevier Ltd. All rights reserved.