Charge fluctuations and ethylene-group-ordering transition in β''-(BEDT-TTF)4[(H3O)Fe(C2O4)3]⋅Y molecular charge-transfer salts

The polarized infrared reflectance and Raman spectra of the three quasi-two-dimensional β''-(BEDT-TTF)4[(H3O)Fe(C2O4)3]⋅Y bifunctional charge-transfer salts, where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene and Y = C6H5Br, (C6H5CN)0.17(C6H5Br)0.83, (C6H5CN)0.4(C6H5F)0.6, have been measured as a function of the temperature. Signatures of charge inhomogenity have been found in both Raman and infrared spectra of the β''-(BEDT-TTF)4[(H3O)Fe(C2O4)3]⋅Y superconductors. A 100 K transition to a mixed insulating/metallic state is clearly seen for the first time in the temperature dependence of the electronic spectra of superconducting β''-(BEDT-TTF)4[(H3O)Fe(C2O4)3]⋅C6H5Br. We suggest that this phase transition is due to subtle changes in the ethylene groups ordering, which are related to a structural phase transition in the anionic layer. The infrared and Raman spectra of quasi-two-dimensional metal α-'pseudo-κ'-(BEDT-TTF)4[(H3O)Fe(C2O4)3]C6H4Br2 are also investigated.

Two alternating BEDT-TTF packing motifs in α-κ-(BEDT-TTF)2Hg(SCN)3

The first BEDT-TTF charge transfer salt in which alternating electron-donor layers possess alpha- and kappa-type packing motifs has been synthesized. The crystal structure and physical properties of the organic conductor alpha-kappa-(BEDT-TTF)2Hg(SCN)3 are described, including a detailed description of its optical properties. The electronic behavior is dominated by a sharp metal-to-insulator transition at T = 176 K which is due to a first-order structural phase transition. The optical properties in the metallic regime are a superposition of those of the alpha- and kappa-phases, while in the insulating state the spectra become more anisotropic in the conducting plane, and the features of the two layers cannot be distinguished.

Assignment of the Raman spectra of some deuterated-BEDT-TTF superconductors

We present the room-temperature Raman spectra of both the protonated and deuterated forms of kappa-(BEDT-TTF)2Cu[N(CN)2]Br, kappa-(BEDT-TTF)2Cu(NCS)2 and beta-(BEDT-TTF)2I3. Along with data for the neutral BEDT-TTF molecule these spectra are used to assign the many features in the spectra of the deuterated compounds.

New tetrathiapentalene-derived charge transfer salts with paramagnetic transition metal complex anion: kappa-(EDDH-TTP)(3)[Cr(phen)(NCS)(4)] x 2CH(2)Cl(2) and kappa(21)-(BDH-TTP)(5)[Cr(phen)(NCS)(4)](2) x 2CH(2)Cl(2)

The preparation, crystal structures, and optical and magnetic properties of two new charge-transfer salts kappa-(EDDH-TTP)(3)[Cr(phen)(NCS)(4)] x 2CH(2)Cl(2) (1) and kappa(21)-(BDH-TTP)(5)[Cr(phen)(NCS)(4)](2) x 2CH(2)Cl(2) (2), where phen = 1,10- phenanthroline, EDDH-TTP = 2-(4,5-ethylenedithio-1,3-dithiol-2-ylidene)-5-(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene, and BDH-TTP = 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene, are reported. Crystal data: (1) monoclinic P2(1)/a, a = 25.0752(5) A, b = 10.6732(3) A, c = 28.1601(6) A, beta = 95.195(2) degrees, Z = 4, R = 0.0585 for 6741 independent reflections with I > 3 sigma(I); (2) monoclinic P2(1)/a, a = 23.8275(4) A, b = 9.1015 (2) A, c = 27.0420(1) A, beta = 99.9297(8) degrees, Z = 4, R = 0.0530 for 4565 independent reflections with I > 2 sigma(I). The crystal structures for both compounds consist of alternating organic and inorganic layers. The organic layer in compound 1 is characterized as kappa-type, while the organic layer in 2 resembles the kappa-type but it contains orthogonal dimers and monomers, and it is therefore called kappa(21). Compound 1 shows metallic behavior down to low temperature. Salt 2 shows semiconductive behavior, which is explained as the result of either charge ordering owing to the kappa(21)-type structure or Peierls distortion due to the one-dimensional electronic nature. However, weak metallic behavior could be observed at 10 kbar above ca. 150 K and at 15 kbar above 170 K. The magnetic susceptibilities for both compounds show Curie-Weiss behavior, showing that the exchange interactions between the magnetic anions are weak. Polarized reflectance spectra of single crystals were measured over the spectral range from 650 to 7000 cm(-1). Moreover, absorption and diffusion reflectance spectra of powdered crystals dispersed in KBr (from 400 to 7000 cm(-1)) were recorded. Vibrational and electronic features are discussed.