Electron paramagnetic resonance of Ni(II) doped tris(ethylenediamine)zinc(II) dinitrate Original Research Article

Variable temperature electron paramagnetic resonance spectra of tris(ehtylenediamine)zinc(II) dinitrate single crystals doped with Ni(II) have been measured. The host crystal undergoes a trigonal to monoclinic phase transition at 146 K. Above the transition temperature the zero field splitting tensor is axially symmetric with D = −0.831 cm−1 and below it becomes rhombic with D = −0.785 cm−1, E = −0.088 cm−1. The low temperature spectrum is characterised by the pattern repeating every 60° when the crystal is rotated about the high temperature c axis. The analysis shows that the Zn(II) site retains a C2 symmetry axis and that the distortion away from the D3 site symmetry observed for high temperatures is small, the principal axes being tilted by 2.6°. This implies that the phase transition involves the flipping of the CC backbone in one of the ethylenediamine ligands of the complex, resulting in a Λδδδ to Λδδλ type conformational change.