(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(+)⋅GaCl(4)(-), are reported. In the temperature region between 300 and 3 K, the magnetic behavior is characterized by the strong intramolecular ferromagnetic interaction (J/k(B)=+400 K) between the radical (NN) and the radical cation (TOT(+)) and the weak intermolecular antiferromagnetic interaction (J/k(B)=-1.9 K) between NNTOT(+) ions. Below 3 K, a 3D-type long-range magnetic ordering into a weak ferromagnet was observed (T(N)=2.65 K). The magnetic entropy (S(mag)=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.