1,1,2,2-Ethenetetrathiolate (ett⁴⁻) coordination polymers, such as poly[K_x(Ni-ett)], have been known for decades for their excellent thermoelectric properties. However in reality, ett⁴⁻ is neither a “true” comonomer which participates in the polymerization, nor represents a “true” repeat unit of the target polymer. Indeed, poly[K₂(Ni-ett)], which is formally the product of Ni-induced polymerization of ett⁴⁻, has a poor conductivity and needs to be oxidized to show attractive thermoelectric characteristics. The polymerization and oxidation processes are poorly controllable which causes irreproducibility of the polymer properties. To improve the synthesis reproducibility, we studied polymerization of potassium tetrathiooxalate (K₂tto), the convenient synthesis of which was developed in our recent work. Because K₂tto is the “true monomer”, and not its precursor, a high quality product is reproducibly formed simply by mixing K₂tto with NiCl₂ at room temperature. The procedure does not require additional components (bases), or special conditions (prolonged heating), which are usually needed for the preparation of this polymer from the monomer precursor 1,3,4,6-tetrathiapentalene-2,5-dione (TPD). Furthermore, as tto²⁻ is formally the product of two-electron oxidation of ett⁴⁻, the poorly controllable oxidation process is avoided and poly[Ni-tto] almost free from K is directly formed upon the complexation of Ni²⁺ and tto²⁻. Thus-obtained poly[Ni-tto] possesses conductivity in the range of 27–47 S cm⁻¹ and a Seebeck coefficient in the range of −38 to −55 μV K⁻¹, which are superior thermoelectric properties compared to poly[K_x(Ni-ett)] samples obtained by the previously reported methods. Redox and structural properties of poly[Ni-tto] were compared with those of poly[K_x(Ni-ett)] obtained by the reported methods. Furthermore, DFT calculations were performed to shed more light on generally promising properties of this class of materials. Particularly, possible packing models have been predicted for polymers, and the molecular dynamics simulations have been used to simulate the molecular arrangements under ambient conditions.

中文翻译：

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聚乙烯四硫代酯或聚四硫代草酸酯？改进的合成，对重要热电聚合物的比较分析及其对电荷传输机制的影响†

1,1,2,2-四硫代乙烯酯（ett ^4-）配位聚合物，例如聚[K _x（Ni-ett）]，几十年来因其出色的热电性能而闻名。然而，实际上，ett ^4-既不是参与聚合的“真”共聚单体，也不代表目标聚合物的“真”重复单元。实际上，poly [K ₂（Ni-ett）]是形式上由Ni诱导的ett ^4-的聚合产物，具有差的电导率，并且需要被氧化以显示出有吸引力的热电特性。聚合和氧化过程可控性差，这导致聚合物性能的不可再现性。为了提高合成的可重复性，我们研究了四硫代草酸钾（K ₂ tto）的聚合反应，该合成方法在我们最近的工作中得到了发展。由于K ₂ tto是“真正的单体”，而不是其前体，因此，只需将K ₂ tto与NiCl ₂混合即可形成高品质的产物。在室温下。该程序不需要其他成分（碱）或特殊条件（长时间加热），这通常是由单体前体1,3,4,6-四硫杂戊烯-2,5-二酮（TPD）制备该聚合物所需的）。此外，由于tto ²⁻形式上是ett ⁴⁻的两电子氧化的产物，因此避免了可控性较差的氧化过程，并且在Ni ²⁺和tto络合时几乎直接形成了几乎不含K的聚[Ni-tto] ²⁻。如此获得的聚[Ni-tto]的电导率范围为27–47 S cm ^-1和塞贝克系数在-38至-55μVK ^-1范围内，与通过先前报道的方法获得的poly [K _x（Ni-ett）]样品相比，具有优异的热电性能。将聚[Ni-tto]的氧化还原和结构性能与通过报道的方法获得的聚[K _x（Ni-ett）]的氧化还原和结构性能进行了比较。此外，进行了DFT计算以更加了解此类材料的普遍前景。特别地，已经针对聚合物预测了可能的堆积模型，并且已经使用分子动力学模拟来模拟环境条件下的分子排列。