title: (EDT-TTF-CONH2)6[Re6Se8(CN)6], a metallic Kagome-type organic-inorganic hybrid compound: electronic instability, molecular motion, and charge localization.
abstract: (EDT-TTF-CONH2)6[Re6Se8(CN)6], space group R, was prepared by electrocrystallization from the primary amide-functionalized ethylenedithiotetrathiafulvalene, EDT-TTF-CONH2 (E(1/2)1 = 0.49 V vs SCE in CH3CN), and the molecular cluster tetraanion, [Re6Se8(CN)6]4- (E(1/2) = 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 = 1/2 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 Mott 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.
authors.affiliation: Laboratoire de Chimie, Ingénierie Moléculaire et Matériaux d'Angers, UMR 6200 CNRS-Université d'Angers, 2 Boulevard Lavoisier, 49045 Angers, France.
authors.forename: Stéphane A
authors.initials: SA
authors.lastname: Baudron
authors.forename: Patrick
authors.initials: P
authors.lastname: Batail
authors.forename: Claude
authors.initials: C
authors.lastname: Coulon
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Clérac
authors.forename: Enric
authors.initials: E
authors.lastname: Canadell
authors.forename: Vladimir
authors.initials: V
authors.lastname: Laukhin
authors.forename: Roberto
authors.initials: R
authors.lastname: Melzi
authors.forename: Pawel
authors.initials: P
authors.lastname: Wzietek
authors.forename: Denis
authors.initials: D
authors.lastname: Jérome
authors.forename: Pascale
authors.initials: P
authors.lastname: Auban-Senzier
authors.forename: Sylvain
authors.initials: S
authors.lastname: Ravy
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004583:Electrons; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*; D012643:Selenium / Q000737:chemistry*; D013696:Temperature
chemical_list: D009942:Organometallic Compounds; D012211:Rhenium; D012643:Selenium