Emiko Fujiwara

Crystal structures and physical properties of single-component molecular conductors consisting of nickel and gold complexes with bis(trifluoromethyl)tetrathiafulvalenedithiolate ligands

The neutral nickel and gold complexes with bis(trifluoromethyl)tetrathiafulvalenedithiolate ligands, [M(hfdt)2] (M = Ni, Au) were prepared in order to examine the possibility of the development of single-component molecular conductors soluble in organic solvents. However, in contrast to the previous report, the crystals did not show any solubility in the usual organic solvents. On the other hand, the crystal structure analyses showed unique two-dimensional layered structures, despite that the single-component molecular conductors usually tend to take a compact three-dimensional molecular arrangement. Each layer is separated by the terminal CF3 groups to form the “CF3 bilayer structure”. The shortest intermolecular F⋯F distance (3.018 A for [Ni(hfdt)2] and 2.862 A for [Au(hfdt)2]) is significantly longer than the van der Waals F⋯F distance (2.70 A) and the distribution of the frontier electrons is almost zero around the CF3 bilayer region. This is due to the strong F⋯F segregation effect, which will provide a useful way to control the molecular aggregation in the single-component molecular conductors. Extended-Huckel tight-binding band structure calculations and the ab initio local density approximation (LDA) band structure calculations were made for [Ni(hfdt)2], which explains the semiconducting and non-magnetic properties of the system. Extended-Huckel tight-binding band structure calculations were also made for [Au(hfdt)2]. The calculated band structure is consistent with the semiconducting and almost non-magnetic properties of [Au(hfdt)2].

Conducting Dimerized Cobalt Complexes with Tetrathiafulvalene Dithiolate Ligands

To obtain novel single-component molecular metals, we attempted to synthesize several cobalt complexes coordinated by TTF (tetrathiafulvalene)-type dithiolate ligands. We succeeded in the syntheses and structure determinations of ((n)Bu(4)N)(2)[Co(chdt)(2)](2) (1), ((n)Bu(4)N)(2)[Co(dmdt)(2)](2) (2), [Co(dmdt)(2)](2) (3), and [Co(dt)(2)](2) (4) (chdt = cyclohexeno-TTF-dithiolate, dmdt = dimethyl-TTF-dithiolate, and dt = TTF-dithiolate). Structure analyses of complexes 1-4 revealed that two monomeric [Co(ligand)2]- or [Co(ligand)(2)](0) units are connected by two Co-S bonds resulting in dimeric [Co(ligand)(2)](2)(2-) or [Co(ligand)(2)](2) molecules. Complex 1 has a cation-anion-intermingled structure and exhibited Curie-Weiss magnetic behavior with a large Curie constant (C = 2.02 K x emu x mol(-1)) and weak antiferromagnetic interactions (theta = -8.3 K). Complex 2 also has a cation-anion-intermingled structure. However, the dimeric molecules are completely isolated by cations. Complexes 3 and 4 are single-component molecular crystals. The molecules of complex 3 form two-dimensional molecular stacking layers and exhibit a room-temperature conductivity of sigmart = 1.2 x 10(-2) S.cm(-1) and an activation energy of E(a) = 85 meV. The magnetic behavior is almost consistent with Curie-Weiss law, where the Curie constant and Weiss temperature are 8.7 x 10(-2) K x emu x mol(-1) and -0.85 K, respectively. Complex 4 has a rare chair form of the dimeric structure. The electrical conductivity was fairly large (sigmart = 19 S.cm(-1)), and its temperature dependence was very small (sigma(0.55K)/sigma(rt) = ca. 1:10), although the measurements were performed on the compressed pellet sample. Complex 4 showed an almost constant paramagnetic susceptibility (chi(300) (K) = 3.5 x 10(-4) emu x mol(-1)) from 300 to 50 K. The band structure calculation of complex 4 suggested the metallic nature of the system. Complex 4 is a novel single-component molecular conductor with a dimeric molecular structure and essentially metallic properties down to very low temperatures.

The pressure effect on the antiferromagnetic and superconducting transitions of κ-(BETS)2FeBr4

The temperature–pressure phase diagram of the first antiferromagnetic organic superconductor κ-(BETS)2FeBr4 shows that the Neel temperature increases with pressure, while the superconducting transition temperature decreases rapidly around 3 kbar.

Synthesis, structures and properties of new organic donors connecting to a TEMPO radical through a pyrrolidine ring

We report the synthesis, structures and physical properties of new TEMPO-containing electron donors in which a TEMPO radical part connects to the EDT-TTF (1) or EDO-TTF (2) skeletons through a pyrrolidine ring. The donors are paramagnetic and showed a slight antiferromagnetic interaction at low temperature region. The CV measurement showed two pairs of reversible redox waves originated from the TTF part and one oxidation wave from the TEMPO radical part. Physical properties of the iodine complex of 1 are also presented.

Synthesis, structures and physical properties of the cation radical salts based on TEMPO radical containing electron donors

We have synthesized new electron donors in which one or two TEMPO radical parts connect to the TTF skeleton through a 1,3-dithiol-2-ylidene ring to prevent the steric hindrance of the bulky TEMPO radical for the purpose of the realization of metallic conductivity. Furthermore crystal structure and physical properties of the donors and the cation radical salt have been clarified.

Synthesis, structure and physical properties of donors containing a PROXYL radical

We succeeded in the synthesis of several new donors containing a TTF moiety and a PROXYL radical within a single molecule for the development of magnetic conductors. We clarified the crystal structure and physical properties of these donors. The CV measurements revealed that both the donors showed one pair of one-electron reversible redox waves (E 1 1/2: +0.49 and +0.57 V vs. Ag/AgCl. respectively) and one pair of broad two-electron reversible redox waves (E 2 1/2: +0.89 and +0.92 V. respectively). ESR spectra of the donors indicated three absorption lines (g =2.0059, a N = 14.2 G) characteristic of the PROXYL radical. The donors 1 and 2 are paramagnetic and showed antiferromagnetic interaction (θ = -2.1 and -8.7 K, respectively).

Electronic properties of BETS superconductors with magnetic anions (BETS=bis(ethylenedithio)tetraselenafulvalene)☆

The physical properties of BETS (=bis(ethylenedithio)tetraselenafulvalene) conductors with tetrahalide magnetic anions and related systems were investigated. We have recently succeeded to find the superconducting transition of the crystal of K-type T1C1 4 - salt coated with epoxy resin (T c (onset) = 2.5 K). The specific heat measurements on the antiferromagnetic organic superconductor, k(BETS) 2 FeCl 4 was performed down to 60 mK, which gave sharp peak at 0.45 K (T N ). The peak trails a tail at T > T N , suggesting low-dimensionality of the spin system. Resistivity measurements under magnetic field of λ-(BETS) 2 Fe x Ga 1-x Cl 4 x 0.4) exhibiting superconductor-to-insulating (SC-I) transition, I-SC phase transition was observed around 4 T at T < 3 K. The low-field superconducting region between metallic and insulating phases around zero magnetic field is connected with the high-field superconducting region.

Interplay of magnetism and superconductivity in BETS conductors (BETS= bis(ethylenedithio)tetraselenafulvalene)

Electromagnetic properties of organic superconductors based on BETS [=bis(ethylenedithio)tetraselenafulvalene)] and MX 4 -(M= Fe, Ga; X= Cl, Br) were examined. Based on the results of resistivity measurements, the temperature-pressure-composition phase diagram of λ-(BETS) 2 Fe x Ga 1-x Br y Cl 4-y was determined. Due to the existence of Fe 3+ ions, the crystal of λ-(BETS) 2 Fe x Ga 1-x Cl 4 (x=0.4) exhibiting a superconductor-to-insulator transition showed an unprecedented resistivity behavior under magnetic field. λ-(BETS) 2 Fe 0.4 Ga 0.6 Cl 4 exhibited the successive insulator→superconductor→metal→(field-induced) superconducting transitions with increasing the magnetic field parallel to the conduction plane up to 15 T and the insulator→superconductor→metal transitions for the field Perpendicular to the conduction plane. The magnetoresistance experiments on the first antiferromagnetic organic superconductor, κ-(BFTS) 2 FeBr 4 down to 0.58 K disclosed an onset of field-induced superconducting transition around 12.5 T.

Magnetic Organic Superconductors Based on BETS Molecules--Interplay of Conductivity and Magnetism

Among six BETS (=bis(ethylenedithio)tetraselenafulvalene) superconductors, the systems with FeX 4 m (X=Cl, Br) anions exhibit salient electronic properties due to the coupling between ~ and d electron systems. u -BETS 2 FeCl 4 undergoes successive transitions as, antiferromagnetic insulating phase M metallic phase with ferromagnetically oriented Fe 3+ spins M superconducting phase ( H //conduction plane) M metallic phase, with increasing magnetic field. s -BETS 2 FeX 4 exhibits successive antiferromagnetic and superconducting transitions with decreasing temperature. Resistivity anomaly observed at antiferromagnetic transition temperature indicates an evidence for the coupling between ~ and d electron systems. antiferromagnetic organic superconductor BETS magnetic organic superconductor organic superconductor

Development of single-component molecular metals based on extended-TTF dithiolate ligands

The novel nickel complex with the extended-TTF dithiolate ligand [Ni(tmdt) 2 ] (tmdt 2- =trimethylenedithiotetrathiafulvalenedithiolate) is the first three-dimensional single-component molecular metal. Structures and physical properties of analogous single-component molecular conductors [Ni(dmdt) 2 ] (dmdt 2- =dimethyltetrathiafulvalenedithiolate), [Ni(eodt) 2 ] (eodt 2- =ethylenedioxytetrathiafulvalenedithiolate) and [Pd(C3-tdt) 2 ] [(C3-tdt) 2- =dipropylthiotetrathiafulvalenedithiolate] were examined. The structure of [Au(tmdt) 2 ] was determined by synchrotron radiation powder diffraction experiments and the MEM/Rietveld analysis. The single-component paramagnetic molecule [Cu(dmdt) 2 ] was also studied to clarify the possibility of single-component magnetic molecular conductors.