SINGLE AND DOUBLE-QUANTUM TRANSITIONS IN THE MULTIFREQUENCY CONTINUOUS-WAVE ELECTRON-PARAMAGNETIC-RESONANCE (CWEPR) OF 3 6 COORDINATE NICKEL(II) COMPLEXES - [NI(ETL)(2)(ME(5)DIEN)] AND [NI(5-METHYLPYRAZOLE)(6)]X-2, X = (CLO4)(-) OR (BF4)(-) - THE SINGLE-CRYSTAL X-RAY STRUCTURE AT ROOM-TEMPERATURE OF [NI(5-METHYLPYRAZOLE)(6)](CLO4)(2)

Multi-frequency, variable temperature cw EPR powder spectra of [Ni(EtL )(2)(Me(5)dien)] (3) and [Ni(5-methylpyrazole)(6)]X-2, X = (ClO4)(-) ( 1) or (BF4)(-) (2) are reported. The spectra of 1 and 2 show a tempera ture variation which is consistent with an increase in /D/ as the temp erature decreases. The changes in the spectra of 1 are irreversible. T he low temperature spectra for each compound exhibit a double quantum transition whose powder dependence is the same as that for the single quantum transitions. The reasons for this behaviour, as well as the si mulations of the whole spectra at various frequencies, is discussed. T he single crystal X-ray structure of 1 at room temperature is reported , whilst it was found that these crystals disintegrated on cooling. Th is behaviour is consistent with the change in the EPR behaviour of thi s compound on cooling.