New BDH-TTP/[MIII(C5O5)3]3– (M = Fe, Ga) Isostructural Molecular Metals

Two new isostructural molecular metals(BDH-TTP)6[MIII(C5O5)3]·CH2Cl2 (BDH-TTP = 2,5-bis­(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene, where M = Fe (1) and Ga (2))have been prepared and fully characterized. Compound 1 is a molecular conductor showing paramagnetic behavior, which is due to the presence of isolated [Fe­(C5O5)3]3– complexes with high-spin S = 5/2 Fe­(III) metal ions. The conductivity originates from the BDH-TTP organic donors arranged in a κ-type molecular packing. At 4 kbar, compound 1 behaves as a metal down to ∼100 K, showing high conductivity (∼10 S cm–1) at room temperature. When applying a pressure higher than 7 kbar, the metal–insulator (M-I) transition is suppressed and the compound retains the metallic state down to low temperatures (2 K). For 1, ESR signals have been interpreted as being caused by the fine structure splitting of the high-spin (S = 5/2) state of Fe­(III) in the distorted octahedral crystal field from the ligands. At 4 kbar, the isostructural compound 2 behaves as a metal down to ∼100 K, although it is noteworthy that the M-I transition is not suppressed, even at pressures of 15 kbar. For 2, only the signal assigned to delocalized π-electrons has been observed in the ESR measurements.本研究成功合成并全面表征了两种新型同构分子金属——(BDH-TTP)₆[MⅢ(C₅O₅)₃]·CH₂Cl₂（其中BDH-TTP为2,5-双(1,3-二硫杂环戊烷-2-亚基)-1,3,4,6-四硫杂戊搭烯，M分别为Fe（化合物1）与Ga（化合物2））。化合物1属于表现出顺磁行为的分子导体，其顺磁特性源于含高自旋S=5/2三价铁(Fe(Ⅲ))离子的孤立[Fe(C₅O₅)₃]³⁻配合物。该化合物的导电特性源于以κ型分子堆积方式排列的BDH-TTP有机给体单元。在4千巴压力下，化合物1降温至约100 K时仍保持金属态，室温电导率可达约10 S cm⁻¹。当施加高于7千巴的压力时，其金属-绝缘体(M-I)转变被抑制，可降温至低温(2 K)仍维持金属态。针对化合物1，其电子顺磁共振(Electron Spin Resonance, ESR)信号被归因于配体形成的畸变八面体晶体场中，三价铁(Ⅲ)高自旋(S=5/2)态的精细结构分裂。在4千巴压力下，同构化合物2同样可降温至约100 K保持金属态，但值得注意的是，即便在15千巴压力下，其金属-绝缘体转变也未被抑制。针对化合物2，在电子顺磁共振测试中仅观测到归属为离域π电子的信号。