Molecular Paramagnetic Semiconductor: Crystal Structures and Magnetic and Conducting Properties of the Ni(dmit)₂ Salts of 6-Oxoverdazyl Radical Cations (dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)

Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation ([1]+) and its mono- and dimethyl derivatives ([2]+ and [3]+) with Ni(dmit)2 anions (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([1]+[Ni(dmit)2]- (4), [2]+[Ni(dmit)2]- (5), [3]+[Ni(dmit)2]- (6), and [1]+[Ni(dmit)2]3- (7)) have been prepared, and the magnetic susceptibilities (χM) have been measured between 1.8 and 300 K. The χM values of salts 5 and 7 can be well reproduced by the sum of the contributions from (i) a Curie−Weiss system with a Curie constant of 0.376 (K emu)/mol and negative Weiss constants (ϑ) of −0.4 and −1.7 K and (ii) a dimer system with strong negative exchange interactions of 2J/kB = −354 and −258 K, respectively. The dimer formations in Ni(dmit)2 anions have been ascertained by the crystal structure analyses of salts 4−6. In salts 4 and 6, Ni(dmit)2 dimer molecules are sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction of 2J1/kB = −600 K and a central interaction of 2J2/kB = −280 K for 4 and 2J1/kB = −30 K and 2J2/kB = −580 K for 6, respectively. The results of the temperature dependence of the g(T) value in salts 4−6 obtained by ESR measurement also support the above analyses. The 1:1 salts 4−6 are insulators. On the other hand, the conductivity of the 1:3 salt 7 at 20 °C was σ = 0.10 S cm-1 with an activation energy EA = 0.099 eV, showing the semiconductor property. Salt 7 is a new molecular paramagnetic semiconductor.本工作制备了3-[4-(三甲基铵基)苯基]-1,5-二苯基-6-氧代verdazyl自由基阳离子（[1]+，3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation）及其单甲基、二甲基衍生物（[2]+与[3]+）与Ni(dmit)₂阴离子（dmit = 1,3-二硫杂环戊烯-2-硫酮-4,5-二硫醇盐，1,3-dithiol-2-thione-4,5-dithiolate）形成的4种1:1型与1:3型盐：[1]+[Ni(dmit)₂]⁻（4）、[2]+[Ni(dmit)₂]⁻（5）、[3]+[Ni(dmit)₂]⁻（6）以及[1]+[Ni(dmit)₂]₃⁻（7），并在1.8~300 K温度区间内测试了其磁磁化率（χ_M，magnetic susceptibilities）。盐5与7的χ_M值可通过两项贡献的加和得到精准拟合：(i) 居里-外斯（Curie-Weiss）系统，其居里常数为0.376 (K·emu)/mol，外斯常数（ϑ）分别为-0.4 K与-1.7 K的负值；(ii) 二聚体系统，其强负交换相互作用分别为2J/k_B = -354 K与-258 K。通过对盐4~6的晶体结构分析，证实了Ni(dmit)₂阴离子中存在二聚体结构。在盐4与6中，Ni(dmit)₂二聚体分子被夹于两个verdazyl自由基阳离子之间，表明盐4与6中形成了线性四聚体结构。针对盐4与6的磁磁化率数据，采用线性四聚体模型进行拟合：盐4的端基交换相互作用为2J₁/k_B = -600 K，中心相互作用为2J₂/k_B = -280 K；盐6的端基交换相互作用为2J₁/k_B = -30 K，中心相互作用为2J₂/k_B = -580 K。通过电子顺磁共振（ESR，electron spin resonance）测量得到的盐4~6的g(T)值随温度变化的结果，进一步佐证了上述分析。1:1型盐4~6均为绝缘体。与之相对，1:3型盐7在20℃下的电导率σ=0.10 S·cm⁻¹，活化能E_A=0.099 eV，表现出半导体特性。盐7是一种新型分子基顺磁半导体。