New Trends in the Synthesis of π-Electron Donors for Molecular Conductors and Superconductors

Chemical Modifications of BDH-TTP [2,5-Bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene]: Control of Electron Correlation

“…It is well known that BEDT-TTF gives CT materials with a wide variety of electrical conducting properties, including insulators, semiconductors, metals and superconductors [3][4][5][6], whereas BDH-TTP shows the tendency to produce metallic CT salts with many anions [14,15,[31][32][33][34][35][36]. The metallic conductivity observed in the BDH-TTP salts stems from a 2D (two-dimensional) interaction with a strong network of side-by-side, as well as face-to-face, S· · · S contacts shorter than the van der Waals distance (3.70 Å).…”

“…In addition, the Au(CN) 2 salt of DHOT-TTP exhibited semiconducting behavior with E a = 36 meV and σ rt (room-temperature conductivity) = 2.4 S cm −1 [43]. The Au(CN) 2 -anion with BDH-TTP also gave a semiconducting salt with E a = 7 meV and σ rt = 11 S cm −1 [43]; therefore, the Au(CN) 2 salt of BDH-TTP is an exception to the tendency that BDH-TTP forms metallic salts with linear, tetrahedral and octahedral anions [14]. On the other hand, as shown in Figure 15a, the resistivities of the AuI 2 , PF 6 and AsF 6 salts of DHOT-TTP monotonically decreased with decreasing temperatures to 1.4 K: Similarities can be seen in the BDH-TTP salts with the same anions [15].…”

“…Therefore, organic molecular conductors with the strongly correlated electron system have a great potential for leading to superconductivity as well as exotic physical properties induced by the application of external stimuli such as pressure, light, voltage and current. On the other hand, we have been studying the synthesis of donor molecules containing the BDY [bis(1,3-dithiol-2-ylidene), Figure 2a] unit as a π-electron system and the physical and structural properties of their CT materials [12][13][14]. Analogous to the TTF unit, the BDY unit consists of two DT (1,3-dithiol-2-ylidene) units; however, the linkage pattern of the two DT units in the BDY unit is different from that in the TTF unit.…”

“…Accordingly, by comparing the physical and structural aspects of CT materials derived from the BDY donor family and the TTF donor family, a wider understanding of physical phenomena particular to organic molecular conductors would be gained. Among the BDY donors we synthesized, BDH-TTP [2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene] (Figure 2b) with various anions was found to form metallic salts stable down to low temperatures (4.2-1.5 K) [14,15], whereas BDA-TTP (Figure 2c) was found to produce ambient-pressure and pressure-induced superconductors [16][17][18]. Compared to the outer dithiolane rings of BDH-TTP, BDA-TTP has more expanded outer dithiane rings, so that the molecular structure of BDA-TTP is nonplanar in comparison with that of BDH-TTP.…”

New aspects of π–d interactions in magnetic molecular conductors

“…At the interface between each pair of alternate layers, a direct d-d interaction between the neighboring d electrons (spins) of magnetic anions and an indirect π-d interaction between the conduction π electron and the d electron (spin) are formed ( figure 2(a)). The π-d interaction has a strong effect on the electron transport on the π conduction layer [5][6][7][8][9]. Upon increasing the π-d interaction, the scattering time τ of the conduction π electron shortens; accordingly, the electron mobility should be reduced.…”