FERROMAGNETIC INTERACTION IN ORGANIC RADICAL-ION SALTS

The N-methylated and/or N-ethylated 1- and BF4- salts of 2-(3-pyridyl)- (2(m)) and 2-(4-pyridyl)-4,4,5,5-tetramethyl-nitronylnitroxides (2(p)), and 2-(4-pyridyl)-4,4,5,5-tetra-methylimidazolin-1-oxyl (3(p)), and also the radical cation/radical anion salts obtained by the exchange reaction of 1- and BF4- in the above radical cation salts with radical anions of TCNQ, TCNQF4 and HCBD were synthesized, and their paramagnetic susceptibilities (chi(para)'s) were measured in the temperature range of 2 (or 5) - 300 K. As shown from the chi(para).T vs. T plots, among the radical cation and radical cation/radical anion salts 2(m)-Me+.(TCNQ2)-, 2(m)-Me+.TCNQF4-.,3(p)-Me+.TCNQF4-. and 3(p)-Me+.HCBD-. exhibited ferromagnetic interaction. The X(para).T value almost equal to S=1/2 at r.t. and the production of the thermally-accessible triplet suggest that the ferromagnetic interaction comes from that between the radical cations as a result of dimer formation of the radical anions. Nevertheless, the radical anion also plays a crucial role as a partner in the tight contact and/or the ferromagnetic interaction between the radical cations.