N(CH3)4.

The successive phase transitions of left bracket N(CH//3)//4 right bracket //2ZnCl//4 have been investigated by means of EPR and DSC of Mn**2** plus doped samples. Changes in the EPR spectrum with varying temperature show the presence of six phases (I, II, . . . , VI) between 27 and minus 140 degree C. The spin Hamiltonian parameters and the orientations of the D tensor were determined in phases I and V. In phase II, the broadening and splitting of the spectrum are attributed to incommensuration. A discommensurate phenomenon is also detected. The spectra in phases III, IV and VI, are characteristic of modulated superstructures. The modulation amplitude and orientation angle for ZnCl//4**2** minus ion are related to the phase angle. The effect of changing temperature on the modulation amplitude and initial phase are shown.