Iwona Olejniczak

Chirality driven metallic versus semiconducting behavior in a complete series of radical cation salts based on dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF).

Enantiopure (S,S) and (R,R) dimethyl-ethylenedithio-tetrathiafulvalene (DM-EDT-TTF) 1 donors are synthesized by cross coupling followed by decarboxylation reactions. In the solid state the methyl groups are arranged in axial positions within sofa-type conformation for the six-membered rings. Crystalline radical cation salts formulated as [(S,S)-1]2PF6, [(R,R)-1]2PF6, and [(rac)-1]2PF6 are obtained by electrocrystallization. When the experiment is conducted with enantioenriched mixtures both enantiopure and racemic phases are obtained. The monoclinic enantiopure salts, containing four independent donors in the unit cell, show semiconducting behavior supported by band structure calculations of extended Hückel type. The racemic salt contains only one independent donor in the mixed valence oxidation state +0.5. Under ambient pressure the racemic material is metallic down to 120 K, while an applied pressure of 11.5 kbar completely suppresses the metal-insulator transition. Band structure calculations yield an open Fermi surface, typical for a pseudo-one-dimensional metal, with unperfected nesting, thus ruling out the possibility of charge or spin density modulations to be at the origin of the transition. Raman spectroscopy measurements, in agreement with structural analysis at 100 K, show no indication of low-temperature charge ordering in the racemic material at ambient pressure, thus suggesting Mott-type charge localization for the observed metal-insulator transition.

Charge‐Assisted Halogen Bonding: Donor–Acceptor Complexes with Variable Ionicity

Charge-assisted halogen bonding is unambiguously revealed from structural and electronic investigations of a series of isostructural charge-transfer complexes derived from iodinated tetrathiafulvalene and tetracyanoquinodimethane derivatives, (EDT-TTFI2)2(TCNQF(n)), n=0-2, which exhibit variable degrees of ionicity. The iodinated tetrathiafulvalene derivative, EDT-TTFI2, associates with tetracyanoquinodimethane (TCNQ) and its derivatives of increasing reduction potential (TCNQF, TCNQF2) through highly directional C-I⋅⋅⋅N≡C halogen-bond interactions. With the less oxidizing TCNQ acceptor, a neutral and insulating charge-transfer complex is isolated whereas with the more oxidizing TCNQF2 acceptor, an ionic, highly conducting charge-transfer salt is found, both of 2:1 stoichiometry and isostructural with the intermediate TCNQF complex, in which a neutral-ionic conversion takes place upon cooling. A correlation between the degree of charge transfer and the C-I⋅⋅⋅N≡C halogen-bond strength is established from the comparison of the structures of the three isostructural complexes at temperatures from 300 to 20 K, thus demonstrating the importance of electrostatics in the halogen-bonding interaction. The neutral-ionic conversion in (EDT-TTFI2)2(TCNQF) is further investigated through the temperature dependence of its magnetic susceptibility and the stretching modes of the C≡N groups.

Vibrational and electronic properties of [60]fullerene—tetrathiafulvalenes (TTFs) cyclohexene fused polyads

Abstract Extended spectral investigations of several new bis-linked tetrathiafulvalenes (TTFs) to [60]fullerene were performed. From UV–Vis–NIR–IR spectra, it was stated that charge distribution on the fullerene sphere and on the TTFs substituents is distinctly disturbed after the adduct formation. A particularly strong resonant effect was observed in the infrared spectra of the one of double-substituted fullerene molecules.

Structural and physical properties of τ-(P-S, S- DMEDT-TTF)2(AuBr2)1(AuBr2)0.75 and τ-(EDO-S, S-DMEDT-TTF)2(AuBr2)1 (AuBr2)0.75, 2D conductors

Abstract The structural and physical properties of the title compounds (where P- S,S -DMEDT-TTF is pyrazino- S,S -dimethylethylenedithio-tetrahiafulvalene and EDO- S,S -DMEDT-TTF is ethylenedioxy- S,S -dimethylethylenedithio-tetrathiafulvalene) show that these crystals are 2D metals with unusual behaviour for temperatures lower than that of metal-insulator transition (

Vibrational and Electronic Properties of Perylenediimide Linked to Fullerene and Tetrathiafulvalene

Solid-state electronic (UV-Vis) and vibrational (IR) spectra of the tetrathiafulvalene-perylenediimide (PDI-TTF) 1 and perylenediimide-fullerene (PDI-C60) 2 dyads as well as PDI 3 , TTF 8 and fullerene 9 derivatives used as references molecules were investigated in the frequency range between 400 and 45,500 cm−1. Electronic and vibrational features of the dyads were compared and analysed. Molecular geometry of the compounds and their IR and Raman theoretical spectra were calculated. It was stated, that small redistribution of the charges occurs in both moieties of these dyads. This effect is observed as shifts of both electronic and vibrational bands of the dyads in comparison with the respective bands of free components.

Structural Distortions upon Oxidation in Heteroleptic [Cp2W(dmit)] Tungsten Dithiolene Complex: Combined Structural, Spectroscopic, and Magnetic Studies

Four different cation radical salts are obtained upon electrocrystallization of [Cp(2)W(dmit)] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in the presence of the BF(4)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions. In these formally d(1) cations, the WS(2)C(2) metallacycle is folded along the S···S hinge to different extents in the four salts, an illustration of the noninnocent character of the dithiolate ligand. Structural characteristics and the charge distribution on atoms, for neutral and ionized complexes with various folding angles, were calculated using DFT methods, together with the normal vibrational modes and theoretical Raman spectra. Raman spectra of neutral complex [Cp(2)W(dmit)] and its salts formed with BF(4)(-), AsF(6)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions were measured using the red excitation (λ = 632.8 nm). A correlation between the folding angle of the metallacycle and the Raman spectroscopic properties is analyzed. The bands attributed to the C═C and C-S stretching modes shift toward higher and lower frequencies by about 0.3-0.4 cm(-1) deg(-1), respectively. The solid state structural and magnetic properties of the three salts are analyzed and compared with those of the corresponding molybdenum complexes. Temperature dependence of the magnetic susceptibility shows the presence of one-dimensional antiferromagnetic interactions in the BF(4)(-), PF(6)(-), and [Au(CN)(2)](-) salts, while an antiferromagnetic ground state is identified in the Br(-) salt below T(Néel) = 7 K. Interactions are systematically weaker in the tungsten salts than in the isostructural molybdenum analogs, a consequence of the decreased spin density on the dithiolene ligand in the tungsten complexes.

Spectral studies of the bis-linked tetrathiafulvalenes to [60]fullerene

Abstract Spectral properties of selected charge-transfer complexes of the fullerene C 60 with planar electron donor molecules as well as polyadducts of tetrathiafulvalenes (TTFs) linked to C 60 by a rigid bridge have been investigated. It was shown that charge distribution on the C 60 sphere and on the TTF-derived donor substituents is distinctly disturbed after the adduct formation. The most interesting feature of selected polyadducts is an appearance of very strong bands in the IR spectra. A resonance coupling between vibrations of appropriate parts of substituents is suggested as a reason of this effect.

Charge-sensitive vibrational modes in the (EDT-TTF-OX)2AsF6 chiral molecular conductors

Infrared and Raman spectra of three chiral molecular conductors (EDT-TTF-OX)2AsF6, comprising of two salts based on enantiopure EDT-TTF-OX donor molecules and one based on their racemic mixture, have been measured as a function of temperature. In the frequency range of the C=C stretching vibrations of EDT-TTF-OX, charge-sensitive modes are identified based on theoretical calculations for neutral and oxidized EDT-TTF-OX using density functional theory (DFT) methods. The positions of C=C stretching modes in both Raman and infrared spectra of the (EDT-TTF-OX)2AsF6 materials are analyzed assuming a linear relationship between the frequency and charge of the molecule. The charge density on the EDTTTF-OX donor molecule is estimated to be +0.5 in all investigated materials and does not change with temperature. Therefore we suggest, that M-I transition observed in (EDT-TTF-OX)2AsF6 chiral molecular conductors at low temperature is not related to the charge ordering mechanism.

Supramolecular Structure and Spectral Properties of Selected Fullerene–Organic Chromophore Systems

The goal of the article is to collect and discuss spectral data for the dyads and reference molecules in the large spectral range, using various methods of investigations. We present information on change of configurations, electronic and vibrational properties of both parts of the dyads after their formation, and their possible relationship with electron transfer mechanism. From the conformational and spectral investigations, a strong correlation between the molecular structure of investigated species and their electronic as well as vibrational spectra arises. It testifies a significant redistribution of the charges upon the covalent linkage of a dyad.

Magnetic field dependent vibrational modes in κ − ( ET ) 2 Cu ( SCN ) 2

Max Planck Insitute for the Physics of Complex Systems, Nothnitzer Str. 38, 01187 Dresden, Germany (Received 11 October 2002; revised manuscript received 20 December 2002; published I May 2003) We report the infrared reflectance of the 10.4 K organic superconductor κ-(ET) 2 Cu(SCN) 2 as a function of applied magnetic field at 4.2 K, allowing us to explore changes in intramolecular vibrational modes between the superconducting (low field) and normal (high field) states. Several vibrational modes display field dependence, including v 3 (A g ), v 6 0 (B 3 g ), and v 2 1 (B 1 g ). Changes in v 3 , which involve the central C=C bond of the ET building block molecule, are especially complex, and include frequency, linewidth, and intensity modifications. These results show that intramolecular vibrational modes are involved in the superconducting to normal state transition in κ-(ET) 2 Cu(SCN) 2 below T c .