Crystals doped with Cu2+, and grown from solution, were studied at 4.2 to 300K by means of Q-band electron paramagnetic resonance. The crystals grown under these conditions contained CuBr4(NH3)22− paramagnetic centers which exhibited a sensitivity to NH4Br phase transitions. An electron paramagnetic resonance study of this center was performed in order to determine spin Hamiltonian parameters as the crystals underwent phase transitions below room temperature. The results showed that the paramagnetic center had tetragonal symmetry at room temperature and below 78K, with some orthorhombic symmetry remaining  in this region. At 78 to 235K, the tetragonal and orthorhombic symmetries coexisted.

EPR of the CuBr4(NH3)22− Paramagnetic Center in Ammonium Bromide. E.Di Mauro, S.M.Domiciano: Physica B, 2001, 304[1-4], 398-403