(Nitronyl Nitroxide)-Substituted Trioxytriphenylamine Radical Cation Tetrachlorogallate Salt: A 2p-Electron-Based Weak Ferromagnet Composed of a Triplet Diradical Cation

The synthesis and the solid state magnetic properties of (nitronyl nitroxide)‐substituted trioxytriphenylamine radical cation tetrachlorogallate, NNTOT+·GaCl4−, are reported. In the temperature region between 300 and 3 K, the magnetic behavior is characterized by the strong intramolecular ferromagnetic interaction (J/kB=+400 K) between the radical (NN) and the radical cation (TOT+) and the weak intermolecular antiferromagnetic interaction (J/kB=−1.9 K) between NNTOT+ ions. Below 3 K, a 3D‐type long‐range magnetic ordering into a weak ferromagnet was observed (TN=2.65 K). The magnetic entropy (Smag=8.97 J K−1 mol−1) obtained by the heat capacity measurement is in good agreement with the theoretical value of R ln3=9.13 J K−1 mol−1 based on the S=1 state. A light magnet: An organic stable triplet diradical cation with a diamagnetic tetrachlorogallate anion (NNTOT+⋅GaCl4−, see picture) was prepared and its magnetic properties were investigated by the measurements of magnetic susceptibilities and heat capacity. The compound exhibited a magnetic phase transition at TN=2.65 K from a short‐range‐ordered antiferromagnetic chain to a 3D weak ferromagnet.