Single and double quantum transitions in the multi-frequency continuous wave electron paramagnetic resonance (cwEPR) of three six co-ordinate nickel(II) complexes: [Ni(EtL)2(Me5dien)] and [Ni(5-methylpyrazole)6]X2, X=(ClO4)- or (BF4)-. The single crystal X-ray structure at room temperature of [Ni(5-methylpyrazole)6](ClO4)2

Abstract

Multi-frequency, variable temperature cw EPR powder spectra of [Ni(EtL)2(Me5dien)] (3) and [Ni(5-methylpyrazole)6]X2, X = (ClO4)− (1) or (BF4)− (2) are reported. The spectra of 1 and 2 show a temperature variation which is consistent with an increase in ∣D∣ as the temperature decreases. The changes in the spectra of 1 are irreversible. The 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 simulations of the whole spectra at various frequencies, is discussed. The single crystal X-ray structure of 1 at room temperature is reported, whilst it was found that these crystals disintegrated on cooling. This behaviour is consistent with the change in the EPR behaviour of this compound on cooling.