Triplet Diradical-Cation Salts Consisting of the Phenothiazine Radical Cation and a Nitronyl Nitroxide

The spin-spin and magnetic properties of two (nitronyl nitroxide)-(di-p-anisylamine-phenothiazine) diradical cation salts, (DAA-PTZ)⁺ -NN⋅MBr₄ ^- (M=Ga, Fe), have been investigated. These diradical-cation species were prepared by the cross-coupling of iodophenothiazine DAA-PTZ-I with NN-AuPPh₃ followed by oxidation with the thianthrenium radical cation (TA⁺ ⋅MBr₄ ^- ). These salts were found to be highly stable under aerobic conditions. For the GaBr₄ salt, large ferromagnetic intramolecular and small antiferromagnetic intermolecular interactions (J₁ /k_B =+320 K and J₂ /k_B =-2 K, respectively) were observed. The magnetic property of the Fe³⁺ salt was analyzed by using a six-spin model assuming identical intramolecular exchange interaction (J₃ /k_B =+320 K) and the other exchange interactions (J₄ /k_B =-7 K and J₅ /k_B =-4 K). A significant color change was observed in the UV/Vis/NIR absorption spectra upon electrochemical oxidation of the doublet DAA-PTZ-NN to the triplet (DAA-PTZ)⁺ -NN.