(Azulene-1,3-diyl)-bis(nitronyl nitroxide) and (Azulene-1,3-diyl)-bis(iminonitroxide) and Their Copper Complexes

In contrast to diradicals connected by alternant hydrocarbons, only a few studies on those connected by nonalternant hydrocarbons have been reported. The syntheses, structures, and magnetic properties of azulene-1,3-diyl linked bis(nitronyl nitroxide) (NN(2)Az) and bis(iminonitroxide) (IN(2)Az) diradicals and their Cu(hfac)(2) (hfac=hexafluoroacetylacetonate) complexes were investigated. NN(2)Az was shown to have an intramolecular ferromagnetic interaction with J(obs)/k(B)=+10.0K (H=-2JS(1)S(2)) between (nitronyl nitroxide) spins, whereas IN(2)Az was estimated to have a much weaker intramolecular magnetic interaction. The reactions of NN(2)Az and IN(2)Az with Cu(hfac)(2) gave a 1:2 [{Cu(hfac)(2)}(2)(NN(2)Az)] complex and a 1:1 [Cu(hfac)(2)(IN(2)Az)]C6H12 complex, respectively. [{Cu(hfac)(2)}(2)(NN(2)Az)] showed strong intramolecular antiferromagnetic interactions (J(1-Cu-R)/k(B)approximate to-800K, J(2-Cu-R)/k(B)approximate to-500K) between the Cu-II spins and the coordinating NN spins, whereas [Cu(hfac)(2)(IN(2)Az)] exhibited a ferromagnetic exchange interaction (J(obs-Cu-R)/k(B)=+114K) between the Cu-II spin and the imino-coordinated iminonitroxide spin.