(EDT-TTF-CONH2)6[Re6Se8(CN)6], a metallic Kagome-type organic-inorganic hybrid compound:: Electronic instability, molecular motion, and charge localization

(EDT-TTF-CONH2)(6)[Re6Se8(CN)(6)], space group M, 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-)center dot) 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-)center dot)]/[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, H-1 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.