Ogura Satomi, Idobata Yuki, Zhou Biao, Kobayashi Akiko, Takagi Rina, Miyagawa Kazuya, Kanoda Kazushi, Kasai Hidetaka, Nishibori Eiji, Satoko Chikatoshi, Delley Bernard
Department of Chemistry, College of Humanities and Sciences, Nihon University , Setagaya-ku, Tokyo 156-8550, Japan.
Department of Applied Physics, University of Tokyo , Bunkyo-ku, Tokyo 113-8656, Japan.
Inorg Chem. 2016 Aug 1;55(15):7709-16. doi: 10.1021/acs.inorgchem.6b01166. Epub 2016 Jul 15.
Crystals of [Pd(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate) were prepared in order to investigate their physical properties. The electrical resistivity of [Pd(tmdt)2] was measured on single crystals using two-probe methods and showed that the room-temperature conductivity was 100 S·cm(-1). The resistivity behaviors implied that [Pd(tmdt)2] was a semimetal at approximately room temperature and became narrow-gap semiconducting as the temperature was decreased to the lowest temperature. X-ray structural studies on small single crystals of [Pd(tmdt)2] at temperatures of 20-300 K performed using synchrotron radiation at SPring-8 showed no distinct structural change over this temperature region. However, small anomalies were observed at approximately 100 K. Electron spin resonance (ESR) spectra were measured over the temperature range of 2.7-301 K. The ESR intensity increased as the temperature decreased to 100 K and then decreased linearly as the temperature was further decreased to 50 K, where an abrupt decrease in the intensity was observed. To investigate the magnetic state, (1)H nuclear magnetic resonance (NMR) measurements were performed in the temperature range of 2.5-271 K, revealing broadening below 100 K. The NMR relaxation rate gradually increased below 100 K and formed a broad peak at approximately 50 K, followed by a gradual decrease down to the lowest temperature. These results suggest that most of the sample undergoes the antiferromagnetic transition at approximately 50 K with the magnetic ordering temperatures distributed over a wide range up to 100 K. These electric and magnetic properties of [Pd(tmdt)2] are quite different from those of the single-component molecular (semi)metals [Ni(tmdt)2] and [Pt(tmdt)2], which retain their stable metallic states down to extremely low temperatures. The experimental results and the band structure calculations at the density functional theory level showed that [Pd(tmdt)2] may be an antiferromagnetic Mott insulator with a strong electron correlation.
制备了[Pd(tmdt)₂]（tmdt = 三亚甲基四硫富瓦烯二硫醇盐）晶体，以研究其物理性质。使用两探针法在单晶上测量了[Pd(tmdt)₂]的电阻率，结果表明室温电导率为100 S·cm⁻¹。电阻率行为表明，[Pd(tmdt)₂]在大约室温下是半金属，随着温度降低到最低温度，它会变成窄带隙半导体。利用SPring-8的同步辐射在20 - 300 K温度下对[Pd(tmdt)₂]的小单晶进行X射线结构研究，结果表明在该温度范围内没有明显的结构变化。然而，在大约100 K处观察到小的异常。在2.7 - 301 K温度范围内测量了电子自旋共振（ESR）光谱。ESR强度随着温度降低到100 K而增加，然后随着温度进一步降低到50 K而线性下降，在50 K处观察到强度突然下降。为了研究磁态，在2.5 - 271 K温度范围内进行了¹H核磁共振（NMR）测量，结果表明在100 K以下谱线变宽。NMR弛豫率在100 K以下逐渐增加，并在大约50 K处形成一个宽峰，随后随着温度降低到最低温度而逐渐下降。这些结果表明，大部分样品在大约50 K时经历反铁磁转变，磁有序温度分布在高达100 K的很宽范围内。[Pd(tmdt)₂]的这些电学和磁学性质与单组分分子（半）金属[Ni(tmdt)₂]和[Pt(tmdt)₂]有很大不同，后两者在极低温度下仍保持稳定的金属态。实验结果和密度泛函理论水平的能带结构计算表明，[Pd(tmdt)₂]可能是具有强电子关联的反铁磁莫特绝缘体。
