Static magnetic-susceptibility measurements in the temperature range 1.4°—300°K are reported on powder samples of the stable aromatic free radicals N-picryl−9-aminocarbazyl (PAC), 2,2-diphenyl−1-picrylhydrazyl in the 106°C mp [DPPH(I)] and 137°C mp [DPPH(II)] crystal modifications, 2-phenyl−2-p-nitrophenyl−1-picrylhydrazyl (DHNO2·) and 2,2-bis(p-nitrophenyl)−1-picrylhydrazyl [D(NO2)2·]. Radical concentrations in the range from 0.81 to 0.99 and Weiss constants in the range −36° to −5.2°K are determined. The measurements are interpreted assuming that the magnetic behavior is due to alternating antiferromagnetic exchange-coupled linear chains. Exchange integrals are inferred from fitting theoretical curves to the susceptibility maxima. Evidence is presented for the presence of random dilution by diamagnetic sites in PAC.
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Duffy et al. (1967) studied this question.