Ken-ichi Sakaguchi

Preparation and ionicity of C60 charge transfer complexes

Abstract The electron-accepting ability of a C 60 molecule in solution was evaluated by the measurements of the charge transfer (CT) absorption energy and the redox potential. It was concluded that C 60 is a weak electron acceptor comparable to 2,5-dibromo- p -xyloquinone, s -tetracyanobenzene or 2,3-dichloro-1,4-naphthoquinone. The adibatic electron affinity of a C 60 molecule was estimated as (2.10–2.21)±0.1 eV. Several black solid CT complexes of C 60 were prepared with mainly TTF derivatives and the ionicity of the ground state was examined by their CT band energies and vibrational spectra. These CT complexes were found to be neutral. A crystal structure of the OMTTF complex from benzene was determined.

New ambient-pressure organic superconductors based on BEDT-TTF, Cu, N(CN)2 and CN with Tc=10.7K and 3.8K

Abstract Syntheses and superconductivities of two new ambient-pressure organic superconductors of BEDT-TTF with Cu, N(CN)2 and CN are described. The resistivity measurements showed Tc (midpoint of resistive transition) of 10.7K (high Tc salt) and 3.8K (low Tc salt) while the SQUID measurements showed the onset of superconductivity at 10.5–11.0K and >3.5K, respectively. They have almost the same lattice parameters but slightly different diffraction patterns and crystal densities.

Crystal and electronic structures of the organic superconductors, ϰ-(BEDT-TTF)2Cu(CN)[N(CN)2] and ϰ'-(BEDT-TTF)2Cu2(CN)3

Abstract The crystal structures of the newly obtained two BEDT-TTF superconductors prepared by the electrocrystallization in the presence of Cu, CN, and N(CN) 2 were analyzed. The compositions of the “high Tc salt ( Tc = 11.2 K )” and the “low Tc salt ( Tc = 3.8 K )” are (BEDT-TTF) 2 Cu(CN)[N(CN) 2 ] and (BEDT-TTF) 2 Cu 2 (CN) 3 , respectively. The donor packing patterns of them are classified into the ϰ-type salt. The band electronic calculations show the two-dimensional Fermi surfaces in both salts. The crystal structure of the “low Tc salt” is essentially identical to that of the reported ϰ-(BEDT-TTF) 2 Cu 2 (CN) 3 salt, however, the conducting properties are completely different. The differences may arise from the slight differences of the crystal structures.

Multi electron and proton-transfer system based on 2,2'-biimidazole derivatives

Abstract A systematical study of 2,2′-biimidazole (H2BIM) derivatives proved that these compounds form a new proton-transfer(PT) and electron (charge)-transfer(CT) system. The study of their acidity, redox property and complex formation with TCNQs confirmed seven new states in the speculated 25-independent species. Corresponding to the protonated states of H2BIM system, the formal charges of TCNQs in the complexes vary from completely ionic, partial CT, to neutral. Also, we developed a new method of electrocrystallization using the pH-controlled electrolytic solution. By applying this novel technique, dibenzobiimidazole system gave metallic to semiconductive TCNQ complexes.

Conductive Radical Cation Salts with Organic Anions of {RO-C[C(CN)2]2}

Abstract 2-alkyloxy substituted tetracyanoallyl anions (RO-TCA−, R = Me, Et, Pr, Bu) were examined in the formation of the radical cation salts of organic donor molecules systematically. 14 kinds of salts have been obtained so far. Among them, (BEDO-TTF)2(EtO-TCA)(H2O)0.75 showed weak metallic temperature dependence of the conductivity down to ca. 180 K ([sgrave]rt = 30 S cm−1). The crystal structure analyses of (BEDT-TTF)2(PrO-TCA) (needle form) and (TTT)(MeO-TCA) revealed the layered structure in both cases. The two C(CN)2 groups in an anion are twisted to each other in either salts. The structures of the anion layers showed the existence of various packing patterns for this anion series.

Strong tendency of BEDO-TTF to produce organic metals

Abstract Combining BEDO-TTF with 24 kinds of organic acceptors, 19 kinds of metallic complexes were obtained. The first redox potentials of the the acceptors which give the metallic complexes range over 0.82 V that is anomalously big among the organic metals of conventional 1:1 TTF-TCNQ system. The crystal structure of the (BEDO-TTF) 5 (HCTMM)(PhCN) 2 salt is regarded as one of the self-aggregated packing motif of the partially charged BEDO-TTF in which the donor interacts to each other through the side-by-side heteroatom network and through the face-to-face stacking. The semiconducting (BEDO-TTF) 5 (HCP)(PhCN) 0.2 salt preserves the common structural features to the metallic BEDO-TTF salts. The strong tendency of BEDO-TTF to produce organic metals is attributed both to its low ionization energy and to the ability of its self-aggregation.

1,5-Benzodithiepan-3-one 1,5-dioxide: A novel chiral auxiliary for asymmetric desymmetrization of meso-1,2-diols

Abstract A novel C 2 -symmetric bis-sulfoxide 1 was synthesized as a chiral auxiliary for asymmetric desymmetrization of meso -1,2-diols. cis -Cyclohexane-1,2-diol and cis -cyclopentane-1,2-diol were desymmetrized via acetalization with 1 followed by base-promoted acetal cleavage with high diastereoselectivity (>96% d.e. ).

Structural and physical properties of two new ambient pressure κ-type BEDT-TTF superconductors and their related salts

Abstract The electrooxidation of BEDT-TTF (ET) in the presence of Cu+, N(CN)2− and CN− gave three kinds of salts, two of which are ambient pressure superconductors; 1 κ-(ET)2Cu(CN)[N(CN)2]+ (Tc=11.2K) and 2 κ′-(ET)2Cu2(CN)3 (Tc=3.8K), and the other is a semiconductor; 3 θ-(ET)2Cu2(CN)[N(CN)2]2. In 1 , CN− bridges Cu+ to form a zigzag infinite chain and N(CN)2− coordinates to Cu+ as a pendant. In 2 , six CN− and six Cu+ form a hexagonal ring which constructs honeycomb network. In 1 and 2 the donor dimers fit into the openings of the anion layer. The polymerized anion structure of 3 is unique. Both 1 and 2 show no semiconductive behavior above 100K which has been observed in the 10K ambient pressure superconductors; κ-Cu(NCS)2 and κ-Cu[N(CN)2]Br. Tc decreases with pressure ( dTc/dP =−2.47 for 1 , −1.25 K/kbar for 2 ). A large inverse isotope effect on Tc is observed in 1 (Tc=12.3K for the deuterated salt, this is the highest Tc at ambient pressure among the ET superconductors). Hc2 values of 1 are almost comparable to those of κ-Cu(NCS)2 and κ-Cu[N(CN)2]Br [Hc2=21.5T(//), 7.0T(⊥) at 1.4K]. Shubnikov-de Haas oscillations are not observed up to ca.30T in 1 though the calculated Fermi surface indicates the presence of a closed orbit. The thermopower of 1 shows anisotropic temperature dependence which coincides with the calculated Fermi surface qualitatively.

Molecular and Crystal Structures of 2-Dicyanomethylene-1,1,3,4,5,5-Hexacyanopentenediide (DHCP) and its Tetrathiafulvalene (TTF) Complex

Abstract Although the molecular structure of the cyanocarbon anion of (C14N8)2- had been expected as 2,3-bis(dicyanomethylene)-1,1,4,4-tetracyanobutandiide, the crystal structure analyses revealed that it has the atomic connectivity corresponding to 2-Dicyanomethylene-1,1,3,4,5,5-hexacyanopentenediide (DHCP). This stable dianion is regarded as being consisted of two dicyanomethylene groups and a planar tetracyanobutandiide. Comparing the dihedral angles between these planar parts among the different kinds of the salts, it is concluded that DHCP shows the structural flexibility. This peculiar nature is regarded as the origin to afford the characteristic molecular packing of (TTF)2(DHCP)(CH3CN) in which the segragated stack of TTF and the donor-anion alternating stack co-exist. The salts with BEDT-TTF (ET) and BEDO-TTF (BO) showed the metallic conducting behavior down to liquid helium temperature or below.

Structural and physical properties of charge transfer complexes with [M(dto)/sub 2/ anions (M:Ni,Pt,Cu,Pd; dto:DITHIOOXALATE)

Summary form only given. We report the structural, electrical and magnetic properties of the charge transfer complexes of [M(dto)/sub 2/](M=transition metals) as electron acceptors and TTF derivatives. Three dimensional alternating stacks of donor dimer and anion molecule are observed in the 2:1 complexes of BEDT-TTF and BEDO-TTF with M (dto)/sub 2/(M=Ni, Pd). While BEDT-TTF complex with Pt(dto)/sub2/ is 2:1 with DDADDA stacking. They are insulators (10/sup -4/-10/sup -5/Scm/sup -1/) and singlet-triplet type magnetic behaviors were detected in BEDT-TTF-Pt(dto)/sub 2/ and BEDO-TTF-Ni(dto)/sub 2/ complexes. BEDT-TTF and Pd(dto)/sub 2/ gave a metallic (ca.1Scm/sup -1/ at RT) 4:1 complex, whose crystal structure is similar to the oxalate analogues. BEDO-TTF and Cu(dto)/sub 2/ form a metallic complex (20OScm/sup -1/ at RT).