EPR of mixed valence complexes: Frequency and concentration dependent linewidths in hexaminechromium (III) chlorocuprates (I, II)

Abstract

Nine compounds in the mixed valence series of hexaminechromium (III) chlorocuprate (I,III), which may be formulated as [Cr(NH3)6] [CuCl4]1−x [CuCl5]x over a substantial range of x, have been investigated by a room temperature EPR study employing four microwave frequencies. The data indicate a variation of linewidth with concentration and frequency for each compound. The linewidth variation with concentration is largely associated with a concentration dependence of the internal dipolar and exchange fields while the frequency dependence is mainly associated with the ``10/3 effect.'' A simple model is employed to account for these variations and to evaluate the appropriate exchange fields. This is the first example of EPR study incorporating two different paramagnetic ions in which the concentration of one of the ions can be variated over a large range with little variation in other parameters.