A Bimodal Oxobenzene-bridged Bisdithiazolyl Radical Conductor

The preparation and structural characterization of the
methyl-substituted
oxobenzene-bridged bisdithiazolyl radical 3b is described.
Crystals of 3b belong to the monoclinic space group C2/c and contain two distinct radical environments, A and B. There are eight A radicals
in the unit cell, which occupy general positions and form alternating
twisted π-stacks running parallel to the c-axis.
The four B radicals also adopt an alternating π-stack
pattern, but each molecule lies on a crystallographic 2-fold rotation
axis, and the overlay of neighboring radicals is centrosymmetric.
Stacks of A radicals are linked by close intermolecular
S···O′ and S···N′ contacts
into ribbon-like arrays that weave along the y-direction,
and the B radical stacks are located in columnar cavities
generated by the out-of-register alignment of the ribbons of A radicals. Variable temperature magnetic susceptibility measurements
indicate a strongly antiferromagnetically coupled system, a result
in accord with DFT estimated exchange energies for intrastack radical–radical
interactions. Four-probe conductivity measurements indicate a conductivity
σ­(300 K) = 9.0 × 10–4 S cm–1, with a thermal activation energy Eact = 0.13 eV.

本文报道了甲基取代氧苯桥联双二噻唑基自由基3b的制备与结构表征。3b的晶体属于单斜晶系空间群C2/c，晶胞内存在两种截然不同的自由基环境，分别标记为A与B。晶胞中包含八个A型自由基，它们占据一般晶位，并形成沿c轴方向平行排布的交替扭转π堆叠结构。四个B型自由基同样呈现交替π堆叠模式，但每个分子均位于晶体学二重旋转轴上，相邻自由基的重叠具有中心对称性。A型自由基堆叠通过分子间近距离的S···O′与S···N′接触相互作用连接成沿y方向蜿蜒分布的带状阵列，而B型自由基堆叠则位于由A型自由基带状阵列错位排列所形成的柱状空腔中。变温磁化率测试结果表明该体系为强反铁磁耦合体系，这一结果与密度泛函理论(Density Functional Theory)估算得到的堆叠内自由基-自由基相互作用交换能相符。四探针电导率测试结果显示，其300 K下的电导率σ(300 K)=9.0×10⁻⁴ S·cm⁻¹，热活化能Eact=0.13 eV。