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-di phenylverdazyl radical cations with tetra-cyanoquinodinlethanide (TCNQ) ani on ([p-EtPyDV](+)[TCNQ](-) (1), [m-EtPyDV](+)[TCNQ](-) (2), [p-EtPyDV](+)[T CNQ](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 lower ing the temperature. The chi (M) of the salt (2) follows the Curie-Weiss la w with a Curie constant of 0.374 K emu mol(-1) and a negative Weiss constan t of - 2.4 +/- 0.2 K in the temperature region 1.8-300 K, indicating disapp earance 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 equi librium model with 2J/k(B) = - 190 K. The chi (M) of the salt (4) shows a b road maximum at T-max = 9.3 +/- 0.5 K. The chi (M) can be well reproduced b y the sum of the contributions from: (i) a one-dimensional (1D) Heisenberg antiferromagnetic alternating-chain system with 2J/k(B) = - 15.2 K (alterna tion 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 res ults obtained by crystal structure analysis of (4). On the other hand, the susceptibility of the salt (!) showed anomalous magnetic behavior that cann ot be explained by a simple model. The (1:1) salts (1) and (2) are insulato rs. 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, sho wing the property as semiconductor. The two (1:2) salts (3) and (4) are new , genuine organic magnetic semiconductors. (C) 2001 Elsevier Science Ltd. A ll rights reserved.