Syntheses and properties of genuine organic magnetic conductors:: (1:1) and (1:2) salts of ethyl-pyridinium-substituted verdazyl radicals with TCNQ

Four kinds of (1:1) and (1:2) salts of 3-(4- and 3-ethyl-pyridinium)-1,5-diphenylverdazyl radical cations with tetra-cyanoquinodinlethanide (TCNQ) anion ([p-EtPyDV](+)[TCNQ](-) (1), [m-EtPyDV](+)[TCNQ](-) (2), [p-EtPyDV](+)[TCNQ](2)(-) (3), and [m-EtPyDV](+)[TCNQ](2)(-) (4)) have been prepared, and the magnetic susceptibilities (chi (M)) measured between 1.8 and 300 K. The values of chi T-M at 300 K are 0.437, 0.383, 0.620, and 0.482 K emu mol(-1) for the salts (1), (2), (3), and (4), respectively, and decrease by lowering the temperature. The chi (M) of the salt (2) follows the Curie-Weiss law with a Curie constant of 0.374 K emu mol(-1) and a negative Weiss constant of - 2.4 +/- 0.2 K in the temperature region 1.8-300 K, indicating disappearance of a net magnetic moment due to the formation of strong spin pairs in TCNQ anion molecules. The chi (M) of the salt (3) shows a broad maximum at T-max = 118 +/- 2 K, and can be well explained by a singlet-triplet equilibrium model with 2J/k(B) = - 190 K. The chi (M) of the salt (4) shows a broad maximum at T-max = 9.3 +/- 0.5 K. The chi (M) can be well reproduced by the sum of the contributions from: (i) a one-dimensional (1D) Heisenberg antiferromagnetic alternating-chain system with 2J/k(B) = - 15.2 K (alternation parameter alpha = J(2)/J(1) = 0.4); and (ii) the dimer system with 2J/k(B) = - 741 K. The magnetic property of (4) was discussed based on the results obtained by crystal structure analysis of (4). On the other hand, the susceptibility of the salt (!) showed anomalous magnetic behavior that cannot be explained by a simple model. The (1:1) salts (1) and (2) are insulators. On the other hand, the pressed pellet conductivity (sigma) of the (1:2) salts (3) and (4) at 20 degreesC was sigma = 6.9 x 10(-2) and 1.5 x 10(-3) S cm(-1) with activation energy E-A= 0.072 acid 0.25 eV, respectively, showing the property as semiconductor. The two (1:2) salts (3) and (4) are new, genuine organic magnetic semiconductors. (C) 2001 Elsevier Science Ltd. All rights reserved.