Metal-insulator interplays rendered by lattice transformations and structural disorder in DOEO salts

Three salts, β-DOEONO(HO) (I), β″-DOEONO(HO) (II), and β″-DOEOHSO(HO) (III), have been synthesized and characterized by means of four-probe conductivity measurements from room temperature down to 4.2 K and X-ray single crystal analysis at room temperature and 100 K. Salt I shows dielectric properties below room temperature, and salts II and III are stable metals. The DOEO molecules in I-III are packed into organic (conductive) layers expanding along the ab plane. The layer packing in II and III is the same in the projection along the long molecular axis and is of the β″ type, but differs noticeably in the perpendicular direction. Salts I and II are not isostructural, but their structures are very similar. However, the electronic structures of II and III are very similar, which leads to quantitatively comparable conductivities for II and III. The upper bands of II and III are 1/4-filled, whereas strong dimerization and band splitting leads to effective 1/2-filling of the upper band in I, which predetermines stable metallic properties for the former and renders strong electronic correlations in the latter. A superstructure of I is formed at room temperature. The Fermi surface obtained by means of extended Hückel tight-binding (EHTB) calculations is essentially altered by the superstructure: Two parallel 1D chains instead of a set of 1D chains and closed 2D pockets visible on the substructure are realized. The Fermi surface of I consists of flattened sections that could be a source of nesting instability. In contrast, the appearance of a superstructure of II at 100 K does not alter the Fermi surface that significantly, leaving the 2D conduction system intact and the Fermi surface with enough curvature to be stable against nesting effects. The DOEO terminal ethylene groups are strongly disordered in I with position occupancies (PO) of 0.6/0.4, less disordered in III (PO: 0.8/0.2), and fully ordered in II at room temperature. All these factors together with the very large value of the dimensionless ratio U/W = 1.66, where U is an on-site Coulomb repulsion and W is a bandwidth, indicate that I most likely is a Mott insulator. Two polymorphs were observed for DOEONO(HO): β and β″.The β polymorph is a Mott insulator with U/W = 1.66, where U is an on-site Coulomb repulsion and W is a bandwidth, whereas β″ is a stable metal with a wide 1/4-filled (W = 1 eV) upper band. DOEOHSO(HO) also shows β″ packing. Electronic structures and conductivities of both β″ compounds are nearly the same. Their X-ray structures are similar, however not isostructural

New Radical Cation Salts Based on BDH-TTP Donor: Two Stable Molecular Metals with a Magnetic [ReF6]2− Anion and a Semiconductor with a [ReO4]− Anion

Three radical cation salts of BDH-TTP with the paramagnetic [ReF6]2− and diamagnetic [ReO4]− anions have been synthesized: κ-(BDH-TTP)4ReF6 (1), κ-(BDH-TTP)4ReF6·4.8H2O (2) and pseudo-κ″-(BDH-TTP)3(ReO4)2 (3). The crystal and band structures, as well as the conducting properties of the salts, have been studied. The structures of the three salts are layered and characterized by alternating κ-(1, 2) and κ″-(3) type organic radical cation layers with inorganic anion sheets. Similar to other κ-salts, the conducting layers in the crystals of 1 and 2 are formed by BDH-TTP dimers. The partial population of positions of Re atoms and disorder in the anionic layers of 1–3 are their distinctive features. Compounds 1 and 2 show the metallic character of conductivity down to low temperatures, while 3 is a semiconductor. The ac susceptibility of crystals 1 was investigated in order to test the possible slow relaxation of magnetization associated with the [ReF6]2− anion.This research was funded by the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2020-779). Work in Spain was supported by MICIU (through the Severo Ochoa FUNFUTURE (CEX2019-000917-S) Excellence Centre distinction and Grant PGC 2018-096955-B-C44), and by Generalitat de Catalunya (2017SGR1506).Peer reviewe

Specific Structural Disorder in an Anion Layer and Its Influence on Conducting Properties of New Crystals of the (BEDT-TTF)4A+[M3+(ox)3]G Family, Where G Is 2-Halopyridine; M Is Cr, Ga; A+ Is [K0.8(H3O)0.2]+

New crystals (1–4) of organic conductors based on the radical cation salts of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with paramagnetic and diamagnetic tris(oxalato)metallate anions {A+[M3+(ox)3]3−G}2−, where M is Cr, Ga; G is 2-chloropyridine, 2-bromopyridine; and A+ is [K0.8(H3O)0.2]+ have been prepared and their crystal structure and transport properties were studied. All crystals belong to the monoclinic group of the (BEDT-TTF)4A+[M3+(ox)3]G family with β″-packing type of conducting BEDT-TTF layers. In contrast to the known superconducting crystals with M3+ = Fe3+ and G = 2-chloro- or 2-bromopyridine (Tc = 4.0–4.3 K), crystals with Cr3+ and Ga3+ ions exhibit metallic properties down to 0.5 K without superconducting transition. Upon cooling these crystals, the incommensurate superstructure appears, which has never been observed before in the numerous β″-salts of the family. In addition, orthorhombic (sp. group Pbca) semiconducting crystals α″-(BEDT-TTF)5[Ga(ox)3]·3.4·H2O·0.6 EtOH (5) were obtained. It is a new compound in the family of BEDT-TTF crystals with tris(oxalato)metallate anions

New radical cation salt κ-(BETS)2Co0.13Mn0.87[N(CN)2]3 with two magnetic metals: Synthesis, structure, conductivity and magnetic peculiarities

A new metallic radical cation salt κ-(BETS)2Co0.13Mn0.87[N(CN)2]3, where BETS is bis(ethylenedithio)tetraselenafulvalene, C10S4Se4H8, has been synthesized. In this salt, a part of Mn2+ ions are replaced by Co2+ which acts as a magnetic dopant with a different effective magnetic moment. Crystal structure, band structure, conducting and magnetic properties of the salt have been studied. Below 30 K the material undergoes a metal-insulator transition, which is suppressed by applying a pressure of ~ 0.5 kbar, leading to a superconducting ground state. While the structural and conducting properties are very similar to those of the parent salt κ-(BETS)2Mn[N(CN)2]3, magnetic properties associated with localized moments in the anion layer are found to be surprisingly different.We thank Prof. A. Kobayashi for providing BETS used in the work. N.D.K. and E.B.Y. were supported by the RFBR grant No. 14-0300119 and by Program No. 2 of the Presidium of the Russian Academy of Sciences. N.D.K., O.M.V, W.B., and M.V.K. acknowledge support by the German Research Foundation (DFG) via the grant KA 1652/4-1. E.C. acknowledges support by MINECO (Spain) through Grant FIS2015-64886-C5-4-P, Generalitat de Catalunya (2014SGR301), and by the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2015-0496.Peer reviewe

New Fulvalenium Salts of Cobalt Bis(dicarbollide): Crystal Structures and Electrical Conductivities

New radical cation salts (BEDT-TTF)[8,8',(7)-Cl2(Cl0.09)-3,3'-Co(1,2-C2B9H9.91)(1',2'-C2B9H10)] (1), (BEDT-TTF)[8,8'-Br0.75Cl1.25-3,3'-Co(1,2-C2B9H10)2] (2), and (BMDT-TTF)4[8,8'-Br1.16(OH)0.72-3,3'-Co(1,2-C2B9H10.06)2] (3) were synthesized, and their crystal structures and electrical conductivities were determined. All the radical cation salts are semiconductors. Compounds 1 and 2 were found to be isostructural, however their electrical conductivities strongly differ (s293 = 2 Ω−1cm−1 and 10−5 Ω−1cm−1, respectively)

New Radical-Cation Salts Based on the TMTTF and TMTSF Donors with Iron and Chromium Bis(Dicarbollide) Complexes: Synthesis, Structure, Properties

New radical-cation salts based on tetramethyltetrathiafulvalene (TMTTF) and tetramethyltetraselenefulvalene (TMsTSF) with metallacarborane anions (TMTTF)[3,3′-Cr(1,2-C2B9H11)2], (TMTTF)[3,3′-Fe(1,2-C2B9H11)2], and (TMTSF)2[3,3′-Cr(1,2-C2B9H11)2] were synthesized by electrocrystallization. Their crystal structures were determined by single crystal X-ray diffraction, and their electrophysical properties in a wide temperature range were studied. The first two salts are dielectrics, while the third one is a narrow-gap semiconductor: σRT = 5 × 10−3 Ohm−1cm−1; Ea ≈ 0.04 eV (aprox. 320 cm−1)

First charge-transfer complexes between tetrathiafulvalene and 1,2,5-chalcogenadiazole derivatives : design, synthesis, crystal structures, electronic and electrical properties

The authors are grateful to the Royal Society (RS International Joint Project 2010/R3), Deutsche Forschungsgemeinschaft (project 436 RUS 113/967/0-1 R), the Russian Foundation for Basic Research (project 10-03-00735), the Presidium of the Russian Academy of Sciences (projects 7.17, 8.14 and P-8), and to the Siberian Branch of the Russian Academy of Sciences (project 105) for funding.The first charge-transfer complexes of tetrathiafulvalene (1) with 1,2,5-chalcogenadiazole derivatives, i.e. with [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (2) and 3,4-dicyano-1,2,5-telluradiazole (3), were designed, prepared in the form of air and thermally stable single crystals and structurally defined by X-ray diffraction as 1-2 and 1.3(2), respectively. Starting compound 2 (effective electron acceptor with potentially broad application in the field) was synthesized by a new efficient one-pot method from 3,4-diamino-1,2,5-oxadiazole and disulfur dichloride. The electronic structure of complexes 1.2 and 1.3(2) and thermodynamics of their formation were studied by means of DFT and QTAIM calculations and UV-Vis spectroscopy. The electrical properties of single crystals of the complexes were investigated revealing semiconductor properties with an activation energy of 0.34 eV for 1.2 and 0.40 eV for 1.3(2). Polycrystalline films of the complexes displayed photoconductive effects with increased conductivity under white-light illumination.PostprintPeer reviewe

The Conducting Spin-Crossover Compound Combining Fe(II) Cation Complex with TCNQ in a Fractional Reduction State

The radical anion salt [Fe­{HC­(pz)₃}₂]­(TCNQ)₃ demonstrates conductivity and spin-crossover (SCO) transition associated with Fe­(II) complex cation subsystem. It was synthesized and structurally characterized at temperatures 100, 300, 400, and 450 K. The compound demonstrates unusual for 7,7,8,8,-tetracyanoquinodimethane (TCNQ)-based salts quasi-two-dimensional conductivity. Pronounced changes of the in-plane direct-current resistivity and intensity of the electron paramagnetic resonance (EPR) signal, originated from TCNQ subsystem, precede the SCO transition at the midpoint <i>T</i>* = 445 K. The boltzmannian growth of the total magnetic response and structural changes in the vicinity of <i>T</i>* uniquely show that half [Fe­{HC­(pz)₃}₂] cations exist in high-spin state. Robust broadening of the EPR signal triggered by the SCO transition is interpreted in terms of cross relaxation between the TCNQ and Fe­(II) spin subsystems

Multifunctional Compound Combining Conductivity and Single-Molecule Magnetism in the Same Temperature Range

We report the first highly conducting single-molecule magnet, (BEDO)₄[ReF₆]·6H₂O [<b>1</b>; BEDO = bis­(ethylenedioxo)­tetrathiafulvalene], whose conductivity and single-molecule magnetism coexist in the same temperature range. The compound was synthesized by BEDO electrocrystallization in the presence of (Ph₄P)₂[ReF₆]·2H₂O and characterized by crystallography and measurements of the conductivity and alternating-current magnetic susceptibility