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Magnetic Semiconductor:  Structural, Magnetic, and Conducting Properties of the Salts of the 6-Oxoverdazyl Radical Cation with M(dmit)2 Anions (M = Ni, Zn, Pd, and Pt, dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

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posted on 29.08.2002, 00:00 by K. Mukai, T. Hatanaka, N. Senba, T. Nakayashiki, Y. Misaki, K. Tanaka, K. Ueda, T. Sugimoto, N. Azuma
Five kinds of (1:1), (1:3), and (2:1) salts of 3-[4-(diethylmethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation [V]+ with M(dmit)2 anions (M = Ni, Zn, Pd, and Pt, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([V]+[Ni(dmit)2]- (1), [V]+[Ni(dmit)2]3- (2), [V]+2[Zn(dmit)2]2- (3), [V]+2[Pd(dmit)2]2- (4), and [V]+2[Pt(dmit)2]2- (5)) and an iodide salt of [V]+ ([V]+[I]- (6)) have been prepared, and the magnetic susceptibilities (χM values) have been measured between 1.8 and 300 K. The χM of the (1:1) Ni salt (1) can be well reproduced by the sum of the contributions from (i) a Curie−Weiss system with a Curie constant (C) of 0.376 K emu/mol and a negative Weiss constant (θ) of −1.5 K and (ii) the one-dimensional Heisenberg antiferromagnetic alternating chain system with 2JA-B/kB = −274 K (alternation parameter α = JA-C/JA-B = 0.2). The χM of the (1:3) Ni salt (2) can be well explained by the two-term contributions from (i) the Curie−Weiss system with C = 0.376 K emu/mol and θ = −5.0 K and (ii) the dimer system with 2J/kB = −258 K. The magnetic properties of 1 and 2 were discussed based on the results obtained by crystal structure analysis and ESR measurements of 1 and 2. The χM values of the (2:1) Zn, Pd, Pt salts 3, 4, and 5 and [V]+[I]- salt 6 follow the Curie−Weiss law with C = 0.723, 0.713, 0.712, and 0.342 K emu/mol and θ = −2.8, −3.1, −2.6, and +0.02 K, respectively, indicating that only the spins of the verdazyl radical cation contribute to the magnetic property of these salts. The salts 1, 3, and 5 are insulators. On the other hand, the conductivity (σ) of the Ni salt 2 and Pd salt 4 at 20 °C was σ = 8.9 × 10-2 and 1.3 × 10-4 S cm-1 with an activation energy EA = 0.11 and 0.40 eV, respectively. The salts 2 and 4 are new molecular magnetic semiconductors.