(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) (NN2Az) and bis(iminonitroxide) (IN2Az) diradicals and their Cu(hfac)2 (hfac=hexafluoroacetylacetonate) complexes were investigated. NN2Az was shown to have an intramolecular ferromagnetic interaction with Jobs/kB=+10.0 K (H=−2JS1⋅S2) between (nitronyl nitroxide) spins, whereas IN2Az was estimated to have a much weaker intramolecular magnetic interaction. The reactions of NN2Az and IN2Az with Cu(hfac)2 gave a 1:2 [{Cu(hfac)2}2(NN2Az)] complex and a 1:1 [Cu(hfac)2(IN2Az)]⋅C6H12 complex, respectively. [{Cu(hfac)2}2(NN2Az)] showed strong intramolecular antiferromagnetic interactions (J1‐Cu‐R/kB≈−800 K, J2‐Cu‐R/kB≈−500 K) between the CuII spins and the coordinating NN spins, whereas [Cu(hfac)2(IN2Az)] exhibited a ferromagnetic exchange interaction (Jobs‐Cu‐R/kB=+114 K) between the CuII spin and the imino‐coordinated iminonitroxide spin. Nonalternant exchange: Bis(nitronyl nitroxide) and bis(iminonitroxide) diradicals linked by a nonalternant azulene‐1,3‐diyl coupler (i.e., NN2Az and IN2Az, respectively) and their Cu(hfac)2 (hfac=hexafluoroacetylacetonate) complexes, [{Cu(hfac)2}2(NN2Az)] and [Cu(hfac)2(IN2Az)], are synthesized and their magnetic properties are investigated.