Robust Dirac-Cone Band Structure in the Molecular Kagome Compound (EDT-TTF-CONH₂)₆[Re₆Se₈(CN)₆]

Abstract

(EDT-TTF-CONH2)6[Re6Se8(CN)6] is a molecular solid with R3 space group symmetry and has the remarkable feature of exhibiting hybrid donor layers with a kagome topology which sustain metallic conductivity. We report a detailed study of the structural evolution of the system as a function of temperature and pressure. This rhombohedral phase is maintained on cooling down to 220 K or up to 0.7 GPa pressure, beyond which a symmetry-breaking transition to a triclinic P1 phase drives a metal to insulator transition. Band structures calculated from the structural data lead to a clear description of the effects of temperature and pressure on the structural and electronic properties of this system. Linear energy dispersion is calculated at the zero-gap Fermi level where valence and conduction bands touch for the rhombohedral phase. (EDT-TTF-CONH2)6[Re6Se8(CN)6] thus exhibits a regular (right circular) Dirac-cone like that of graphene at the Fermi level, which has not been reported previously in a molecular solid. The Dirac-cone is robust over the stability region of the rhombohedral phase, and may result in exotic electronic transport and optical properties.

Size-Exclusion Mechanism Driving Host–Guest Interactions between Octahedral Rhenium Clusters and Cyclodextrins

“…Octahedral rhenium cluster complexes due to their antitumoral, antibacterial, photoluminescent, redox, and X-ray contrast properties are appealing inorganic species for applications in biology and medicine. − Their encapsulation within biocompatible drug carrier, such as cyclodextrins, represents a promising way to develop biological applications. In context, we demonstrated that clusters [Re 6 Q 8 (CN) 6 ] 4– (with Q = S, Se, and Te; see Figure a–c) interact with γ-CD, forming strong host–guest complexes built on cluster embedded within two tori hosts …”

Reversible Electrochemical Lithium-Ion Insertion into the Rhenium Cluster Chalcogenide–Halide Re6Se8Cl2

“…Previous studies focused on the luminescent and electrochemical properties of the molecular [Re 6 Se 8 ] 2+ unit, − as well as using the cluster core as a building block to prepare materials for a variety of applications. − This investigation focuses on Re 6 Se 8 Cl 2 with the [Re 6 Se 8 ] 2+ cluster unit isostructural to that found in the superconducting Mo 6 Q 8 Chevrel-phase core . Theoretical and experimental studies have explored the ability of Chevrel-phase materials (Mo 6 S 8 ) to reversibly transfer four electron equivalents (ee) per formula unit. − Unlike the molybdenum analogue, the hexarhenium core has been studied as a “building unit” in extended solid frameworks, where motifs of three, two, and one dimensionality are possible. , These frameworks consist of rigid cluster–cluster linkages, some of which can undergo dimensional reduction in the presence of Cs + or Tl + halides.…”

Unusual stoichiometry, band structure and band filling in conducting enantiopure radical cation salts of TM-BEDT-TTF showing helical packing of the donors

“…Consequently, if the coupling through donors B could be reinforced, for instance through applied pressure, and the metallic state could be stabilized, the Fermi level would occur at the K point and thus would coincide with a Dirac cone which could lead to the exotic transport properties predicted for this situation. 35 Among molecular conductors, only (EDT-TTF-CONH 2 ) 6 [Re 6 Se 8 (CN) 6 ], 36,37 a-(BEDT-TTF) 2 I 3 under pressure, 38 [Pd(dddt) 2 ] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) under pressure, 39 [Pt(dmdt) 2 ] (dmdt = dimethyl-tetrathiafulvalenedithiolate) 40 and, very recently, a-(BETS) 2 I 3 (BETS = bis (ethylenedithio)-tetraselenafulvalene) 41 have been previously shown to exhibit such an uncommon electronic feature. Unfortunately, our measurements suggest that in the present salts the electrons remain localized at the pressures we could reach.…”