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We have investigated the infrared spectra of the quarter-filled charge-ordered insulators δ-(EDTTTF- CONMe2)2X (X= AsF6, Br) along all three crystallographic directions in the temperature range from 300 to 10 K. DFT-assisted normal mode analysis of the neutral and ionic EDT-TTF-CONMe2 molecule allows us to assign the experimentally observed intramolecular modes and to obtain relevant information on the charge ordering and intramolecular interactions. From frequencies of chargesensitive vibrations we deduce that the charge-ordered state is already present at room temperature and does not change on cooling, in agreement with previous NMR measurements. The spectra taken along the stacking direction clearly show features of vibrational overtones excited due to the anharmonic electronic molecule potential caused by the large charge disproportionation between the molecular sites. The shift of certain vibrational modes indicates the onset of the structural transition below 200 K. [ABSTRACT FROM AUTHOR]

Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-Tc cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above Tc. By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)2X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all. [ABSTRACT FROM AUTHOR]

(EDT-TTF-CONH2)6[Re6Se8(CN)6], space group R..., was prepared by electrocrystallization from the primary amide-functionalized ethylenedithiotetrathiafulvalene, EDT-TTF-CONH2 (E½1 = 0.49 V vs SCE in CH3CN), and the molecular cluster tetraanion, [Re6Se8(CN)6]4- (E½ = 0.33 V vs SCE in CH3CN), equipped with hydrogen bond donor and hydrogen bond acceptor functionalities, respectively. Its Kagome topology is unprecedented for any TTF-based materials. The metallic state observed at room temperature has a strong two-dimensional character, in coherence with the Kagome lattice symmetry, and the presence of minute amounts of [Re6Se8(CN)6](3-)· identified by electron spin spectroscopy. A structural instability toward a distorted form of the Kagome topology of lesser symmetry is observed at ca. 180 K. The low-temperature structure is associated with a localized, electrically insulating electronic ground state and its magnetic susceptibility accounted for by a model of uniform chains of localized S = ½ spins in agreement with the 100 K triclinic crystal structure and band structure calculations. A sliding motion, within one out of the three (EDT-TTF-CONH2)2 dimers coupled to the [Re6Se8(CN6)(3-)·]/[Re6Se8(CN6)4-] proportion at any temperature, and the electronic ground state of the organic-inorganic hybrid material are analyzed on the basis of ESR, dc conductivity, ¹H spin-lattice relaxation, and static susceptibility data which qualify a Mon localization in [EDT-TTF-CONH2]6[Re6Se8(CN)6]. The coupling between the metal-insulator transition and a structural transition allows for the lifting of a degeneracy due to the ternary axis in the high temperature, strongly correlated metallic phase which, in turn, leads to Heisenberg chains at low temperature. [ABSTRACT FROM AUTHOR]

Optical investigations of quarter-filled charge ordered insulators δ-(EDT-TTF-CONMe2)2-X,X = AsF6, Br are reported. The spectra evidence the one-dimensional nature of the systems at all temperatures. The charge order exists already at room temperature, the optical gap is estimated to be of the order of 550 cm-1 for the X = Br compound and about 700 cm-1 for the X = AsF6 material. The optical response in the direction of the stacks is discussed in terms of domain-wall excitations of one-dimensional quarter-filled Wigner lattice at moderate values of nearest-neighbor electronic repulsion. A similarity between the effects of temperature contraction and chemical pressure is found. [ABSTRACT FROM AUTHOR]

As a point of entry to investigate the potential of halogen-bonding interactions in the construction of functional materials and crystalline molecular machines, samples of 1,4-bis- (iodoethynyl)bicyclo[2.2.2]octane (BIBCO) were synthesized and crystallized. Knowing that halogen-bonding interactions are common between electron-rich acetylenic carbons and electron-deficient iodines, it was expected that the BIBCO rotors would be an ideal platform to investigate the formation of a crystalline array of molecular rotors. Variable temperature single crystal X-ray crystallography established the presence of a halogen-bonded network, characterized by lamellarly ordered layers of crystallographically unique BIBCO rotors, which undergo a reversible monoclinic-to- triclinic phase transition at 110 K. In order to elucidate the rotational frequencies and the activation parameters of the BIBCO molecular rotors, variable-temperature `H wide-line and 13C cross-polarization/magic-angle spinning solid-state NMR experiments were performed at temperatures between 27 and 290 K. Analysis of the 1H spin-lattice relaxation and second moment as a function of temperature revealed two dynamic processes simultaneously present over the entire temperature range studied, with 10 -1 / -I 10 -I temperature-dependent rotational rates of krot = 5.21 x 10 s exp-1.48 kcal mol /RT) and krot = 8.00 x 10 s exp- (-2.75 kcalmoF'/RT). Impressively, these correspond to room temperature rotational rates of 4.3 and 0.8 GHz, respectively. Notably, the high-temperature plastic crystalline phase I of bicyclo[2.2.2]octane has a reported activation energy of 1.84 kcal mol' for rotation about the 1,4 axis, which is 24% larger than E, = 1.48 kcal mol' for the same rotational motion of the fastest BIBCO rotor; yet, the BIBCO rotor has three fewer degrees of translational freedom and two fewer degrees of rotational freedom! Even more so, these rates represent some of the fastest engineered molecular machines, to date. The results of this study highlight the potential of halogen bonding as a valuable construction tool for the design and the synthesis of amphidynamic artificial molecular machines and suggest the potential of modulating properties that depend on the dielectric behavior of crystalline media. [ABSTRACT FROM AUTHOR]