Radical Cation Layers Research Articles

Layered Organic Conductors Based on BEDT-TTF and Ho, Dy, Tb Chlorides

Molecular semiconductors with lanthanide ions have been synthesized based on BEDT-TTF and lanthanide chlorides: (BEDT-TTF)2[HoCl2(H2O)6]Cl2(H2O)2 (1, which contains a 4f holmium cation), and (BEDT-TTF)2LnCl4(H2O)n (Ln = Dy, Tb, Ho (2–4), which contain 4f anions of lanthanides). Conductivity and EPR measurements have been carried out along with the SQUID magnetometry, and the crystal structure has been established for 1. The structure of 1 is characterized by an alternation of organic radical cation layers composed of BEDT-TTF chains and inorganic layers consisting of chains of the [HoCl2(H2O)6]+ cations interlinked by chlorine anions and crystallization water molecules. The magnetic susceptibility of 1–3 determined mainly by lanthanide ions follows the Curie–Weiss law with the Weiss temperatures of −3, −3, −2 K for 1–3, respectively, indicating weak antiferromagnetic coupling between paramagnetic lanthanide ions. The signals attributed to the BEDT-TTF+· radical cations only are observed in the EPR spectra of 1–3, which makes it possible to study their magnetic behavior. There are two types of chains in the organic layers of 1: the chains composed of neutral molecules and those formed by BEDT-TTF+· radical cations. As a result, uniform 1D antiferromagnetic coupling of spins is observed in the BEDT-TTF+· chains with estimated exchange interaction J = −10 K. The study of dynamic magnetic properties of 1–3 shows that these compounds are not SMMs.

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.

Radical cation salts of BETS and ET with dicyanamidocuprate anions demonstrating metal-insulator and semiconductor–semiconductor transitions

Electrocrystallization of bis(ethylenedithio)tetraselenafulvalene (BETS) and bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of an electrolyte (Ph4P)[Cu(dca)]3⋅H2O [(dca) = N(CN)2] has been studied using different solvents. A new organic metal (BETS)2Cu(dca)3 (1), and the first radical cation salt with 3D dicyanamidocuprate anion, incorporating both diamagnetic Cu1+ and paramagnetic Cu2+atoms, (ET)2Cu1.8(dca)4 (2) have been obtained. Crystal structure, conducting properties of both salts, as well as the electronic structure of 2 and its structural analog (ET)2CuMn(dca)4 (3) were analysed. The salts 1 and 2 have layered structures. In contrast to the BETS radical cation salt 1, complex 2 is characterized by the presence of a 3D polymeric anion built into the ET radical cation layers. At ambient pressure, the resistance of the crystals 1 shows semimetal behaviour down to 30 K. Below 30 K, the resistance sharply increases and the sample becomes insulating. The application of a pressure of about 3 kbar suppresses the metal-insulator transition. The salt 2 undergoes a semiconductor I - semiconductor II phase transition, which is manifested by a jump in the resistance and a hysteresis in the R(T) curves in a very large temperature range (185 – 250 K). The phase transition is accompanied by changes in the charge state of the ET molecules, and notable structure changes in the anion layer, especially in the environment of Cu2+. For the salt 3 the calculated selfconsistent charges show upon cooling a sharp increase of charge order between 291 K and 285 K.

Organic conductors with BiIII and SbIII chloride-based anions

New layered organic conductors, (BEDT-TTF)4(BiCl5)1 7 (1), δ-(BEDT-TTF)2BiCl5 (2), and δ-(BEDT-TTF)6Sb3Cl12 (3), were obtained (BEDT-TTF is bis(ethylenedithio)tetrathia-fulvalene). In the crystal structures of 1—3, organic radical cation layers are composed of di-merized stacks. The dimers are formed by BEDT-TTF radical cations rotated through angle ω relative to each other, which results in twisted stacks, giving rise to so-called twisted overlap mode in the layers. These layers alternate with non-conductive inorganic layers consisting of chains in which the Cl, Bi, and Sb sites are partially occupied. This indicates discontinuities in the chains of anions, and, apparently, the absence of continuous polymer chains in the crystal structure. According to measurements of the temperature dependence of the electrical resistance, the compounds are semiconductors.

Synthesis particularities, structure and properties of the radical cation salts ω-(BEDT-TTF)5M(SCN)6·C2H5OH, M = Mn, Ni

Electrochemical oxidation of donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) in 1,1,2-trichloroethane-ethanol in the presence of electrolytes including two type of ligands, namely, (Ph4P)2[M(dca)2(SCN)2], M=Mn, Ni; dca=[N(CN)2]−, has been performed and analyzed for the first time. It has been found that in the reaction of electrochemical oxidation of BEDT-TTF, [M(dca)2(SCN)2]2− anion decomposes to form new metal-complex anions, [Mn(dca)3(SCN)2·H2O]3− and [Mn(SCN)6]4− or [Ni(SCN)6]4−, respectively, as well as (dca) and SCN anions. New radical cation salts, (BEDT-TTF)4Mn[(dca)3(SCN)2·H2O](SCN)x, x<1, (I), ω-(BEDT-TTF)5M(SCN)6·C2H5OH, M=Mn (III), Ni (IV), and previously described α″-(BEDT-TTF)2(dca)·2H2O (II) have been synthesized. A solid-phase transformation of crystals I to crystals II have been found. Crystal structure and conducting of the salts, as well as the electronic structure and magnetic properties of III, were analyzed. Salts III and IV have layered structure in which ω-type radical cation layers alternate with insulating anion layers composed of [M(SCN)6]4− anions. Crystals I is a bad metal while two others exhibit a semiconducting behavior of conductivity. No exchange interactions for Mn2+ ions observed in the salt III.

Metallic Bi‐ and Monolayered Radical Cation Salts Based on Bis(ethylenedithio)­tetrathiafulvalene (BEDT‐TTF) with the Tris(oxalato)gallate Anion

AbstractNew metallic triclinic (1) and monoclinic (2) crystals of the (BEDT‐TTF)4AI[MIII(C2O4)3]G family of organic molecular conductors have been prepared: α‐“pseudo‐κ”‐(BEDT‐TTF)4Kx(H3O)1–x[GaIII(C2O4)3]·1,2‐C6H4Br2 (x ≈ 0.45) (1) and β″‐(BEDT‐TTF)4Kx(H3O)1–x[GaIII(C2O4)3]·PhBr (x ≈ 0.33) (2). The triclinic crystals belong to a quite rare type of bilayered radical ion salts and contain alternating BEDT‐TTF layers with two distinct packing motifs (α‐ and “pseudo‐κ”). The monoclinic crystals contain one kind of BEDT‐TTF radical cation layers. The crystal structure, transport, and magnetotransport properties of 1 and 2 have been studied. The Shubnikov–de Haas (SdH) oscillations were found in both phases. The structure and properties of 1 and 2 are compared with another similar phase with M = FeIII.

The first BETS radical cation salts with dicyanamide anion: Crystal growth, structure and conductivity study

Electrochemical oxidation of bis(ethylenedithio)tetraselenafulvalene (BETS) has been investigated. Simple and complex dicyanamides of transition metals (Mn 2+, Ni 2+ and Fe 2+) were used as electrolytes. The correlation between composition of prepared radical cation salts and metal nature in electrolytes was established. Manganese dicyanamides provide the formation of BETS salts with the {Mn[N(CN) 2] 3}- and [N(CN) 2]-XH 2O anions. When Ni- or Fe-containing electrolytes were used only metalless BETS salts, α″-BETS 2[N(CN) 2]·2H 2O ( I) and θ-BETS 2[N(CN) 2]·3.6H 2O ( II), formed. Structures and conducting properties of these salts were analyzed. Both salts exhibit layered structure. Conducting radical cation layers have α″ (I)- or θ -type ( II). Anion sheets appear as two-dimensional polymer networks of different types. These networks are formed by [N(CN)] 2 − anions and water molecules interlinked by hydrogen bonds. Salt I is a semiconductor and II demonstrates resistance drop down to150 K at normal pressure and down to 72 K at ∼0.4 kbar pressure.

ET based conductors with different behavior of resistivity along and across conducting layers

A series of novel bis(ethylenedithio)tetrathiafulvalene (ET) based radical cation salts with tetrahedral [HgBr 4] 2− and [CdBr 4] 2− dianions of (ET) 4MBr 4(solvent) stoichiometry (M = Hg, Cd; solvent = C 6H 5X or 1,2-C 6H 4X 2, X = Cl, Br) has been prepared. Crystal structures of θ-(ET) 4HgBr 4(1,2-C 6H 4X 2) (X = Cl, Br) were found to involve conducting ET radical cation layers of the θ-type packing and insulating layers consisting of [HgBr 4] 2− anions and solvent molecules. The donor stacking directions of the neighboring conducting layers are perpendicular to each other. Depending on salt composition, intralayer electrical resistivity of θ-(ET) 4MBr 4(solvent) showed metal-like behavior down to temperatures varying within 4.3–100 K range. Electrical resistivity perpendicular to the layers revealed nonmetallic behavior. The study of magnetoresistance of θ-(ET) 4HgBr 4(1,2-C 6H 4Cl 2) revealed Shubnikov-de Haas oscillations in fields up to 15 T with the only frequency F = 900 T. The θ-(ET) 4MBr 4(C 6H 4Cl 2) M = Hg, Cd compounds are the first ET-based conductors which show metallic behavior of conductivity in layers and semiconducting behavior across layers down to 4.3 K.

Phase transition at 320 K in a new layered organic metal conductor (BEDT-TTF)4CoBr4(C6H4Cl2)

A new layered organic conductor θ-(BEDT-TTF)4CoBr4(1,2-C6H4Cl2) with different resistivity behaviour that has metallic conducting layers and is semiconducting perpendicular to the layers has been prepared. A phase transition near 320 K was found in this salt by temperature variable resistivity and X-ray diffraction measurements. Precise crystal structure data, below transition (triclinic phase) and above transition (tetragonal phase), was determined. The crystal structures of both phases are composed of θ-type radical cation layers alternating with layers involving [CoBr4]2− anions and 1,2-dichlorobenzene molecules. The lower symmetry in the crystal structure of the triclinic phase is due to a non-symmetrical arrangement of the solvent molecules within the anion layers. In each structure, the neighbouring conducting layers of the unit cell differ in stacking directions. In the tetragonal phase, all conducting layers are similar in structure, and in the low-temperature triclinic phase, the neighbouring conducting layers differ in periods along the stacks (4.703 A and 4.993 A) and in dihedral angles θ between the BEDT-TTF radical cations of the adjacent stacks. The finding of compounds of the θ-(BEDT-TTF)4CoBr4(1,2-C6H4Cl2) type with phase transitions above room temperature provides a wide possibility of investigating magnetoresistance, quantum oscillations, and the mechanism of interlayer transport in layered conductors.

10.1007/s11176-008-1002-5

New multicomponent radical cation salts derived from bis(ethylenedithio)tetrathiafulvalene (ET) were prepared: bis(ethylenedithio)tetrathiafulvalene dicyanamide dihydrate α″-(ET)2N(CN)2·2H2O and bis-(ethylenedithio)tetrathiafulvalene nitrate α‴-(ET)6(NO3)3·2C2H5O2N3 containing two biuret molecules (C2H5O2N3). The crystal structures of the compounds were determined, and their conducting properties were examined. Both salts have layered structures in which radical cation layers alternate with nonconducting anionic layers. The radical cation layers in the salts α″-(ET)2N(CN)2·2H2O and α‴-(ET)6(NO3)3·2C2H5O2N3 are packed in the α″ and α‴ fashion, respectively. Anionic layers consist of polymeric chains formed by hydrogen bonding between [N(CN)2]− anions and water molecules in α″-(ET)2N(CN)2·2H2O or between NO−3 anions and biuret molecules in α‴-(ET)6(NO3)3·2C2H5O2N3. Both salts show semiconductor conductivity.

Two-dimensional organic metals θ-(BETS) 4MBr 4(PhBr), M = Cd, Hg with differently oriented conducting layers

New bis(ethylenedithio)tetraselenafulvalene (BETS) based radical cation salts with tetrahedral dianions [CdBr 4] 2− and [HgBr 4] 2− of the (BETS) 4MBr 4(PhBr) composition were prepared by electrochemical crystallization. Room-temperature crystal structure of (BETS) 4CdBr 4(PhBr) determined by single crystal X-ray diffraction involves BETS radical cation layers of the θ-type packing and insulating layers consisting of [CdBr 4] 2− anions and PhBr molecules. In the neighboring conducting layers, the stacks are arranged perpendicular to each other. A metal-to-metal transition within 225–230 K range was found in both (BETS) 4CdBr 4(PhBr) and (BETS) 4HgBr 4(PhBr). The behavior of electrical resistivity of these salts differs substantially along and across conducting layers. The study of magnetoresistance of (BETS) 4HgBr 4(PhBr) revealed weak Shubnikov-de Haas oscillations in fields higher than 6 T.

A new hybrid molecular metal assembling a BEDT-TTF conducting network and the magnetic chain anion [Mn2Cl5(H2O)5]−∞: α-(BEDT-TTF)2[Mn2Cl5(H2O)5

The synthesis, X-ray crystal and electronic band structures as well as magnetotransport and magnetic properties of the α-(BEDT-TTF)2[Mn2Cl5(H2O)5] radical cation salt with a new type of magnetic polymeric complex anion, [Mn2Cl5(H2O)5]−∞, are reported. The crystal structure is characterized by radical cation layers alternating with layers of the polymeric 1-D chain anions constructed from MnCl3(H2O)3 and MnCl4(H2O)2 octahedra connected to each other via the apical Cl atoms. The calculated electronic band structure suggests that the salt should be a stable 2-D metal and the conductivity measurements show that it exhibits metallic behavior down to 0.4 K. Shubnikov-de Haas oscillations, observed at B > 10 T, are characterized by two fundamental frequencies, corresponding to cross-sections of the Fermi surface, in agreement with the electronic band structure calculations. Magnetic measurements reveal antiferromagnetic correlations in the anion network.

New multicomponent organic semiconductors based on ET with polymeric Anions: α″-(ET)2N(CN)2·2H2O and α‴-(ET)6(NO3)3·2C2H5O2N3

New multicomponent radical cation salts derived from bis(ethylenedithio)tetrathiafulvalene (ET) were prepared: bis(ethylenedithio)tetrathiafulvalene dicyanamide dihydrate α″-(ET)2N(CN)2·2H2O and bis-(ethylenedithio)tetrathiafulvalene nitrate α‴-(ET)6(NO3)3·2C2H5O2N3 containing two biuret molecules (C2H5O2N3). The crystal structures of the compounds were determined, and their conducting properties were examined. Both salts have layered structures in which radical cation layers alternate with nonconducting anionic layers. The radical cation layers in the salts α″-(ET)2N(CN)2·2H2O and α‴-(ET)6(NO3)3·2C2H5O2N3 are packed in the α″ and α‴ fashion, respectively. Anionic layers consist of polymeric chains formed by hydrogen bonding between [N(CN)2]− anions and water molecules in α″-(ET)2N(CN)2·2H2O or between NO−3 anions and biuret molecules in α‴-(ET)6(NO3)3·2C2H5O2N3. Both salts show semiconductor conductivity.

Molecular magnetic semiconductors formed by cationic and anionic networks: (ET)2Mn[N(CN)2]3 and (ET)2CuMn[N(CN)2

Crystals of (ET)2Mn[N(CN)2]3 (1) and (ET)2CuMn[N(CN)2]4 (2) with mono- and first bimetal dicyanamide anions were obtained and their structure, conducting and magnetic properties were investigated. The structure of 2 is not typical for ET radical cation salts and is characterized by the presence of a 3D polymeric anion built into the ET radical cation layers. The crystals of 1 exhibit a semiconducting behavior of conductivity and 2 undergoes a semiconductor I–semiconductor II phase transition at 295–291 K, which is specified by a jump of resistivity and the appearance of a hysteresis in the R(T) curves. The phase transition is accompanied by changes in the charge state of the ET molecules and intermolecular interactions in the crystal. Antiferromagnetic correlations of spins associated with anionic subsystems were found in both salts at temperatures lower than 25 K. Antiferromagnetic ordering in 1 has a long-range character. The effect of the spin frustrated state of localized spins on conducting electrons of ET subsystem was found in 1.

Synthesis, conductivity, and the crystal structure of a new stable metal, β″-(DOEO)2HSeO4 · H2O

The stable metal β″-(DOEO)2HSeO4 · H2O I) based on a new donor compound, 3,4-(1,4-dioxanediyl-2,3-dithio)-3′,4′-ethylenedioxo-2,5,2′,5′-tetrathiafulvalene] (DOEO), is synthesized and structurally characterized for the first time. The synthesis is performed by the electrocrystallization technique (direct current density j = 2 × 10−6 A/cm2). The crystals are triclinic, and the unit cell parameters are as follows: a = 5.495(1) A, b = 9.715(2) A, c = 16.878(3) A, α = 83.52(3)°, β = 82.54(3)°, γ = 73.51(3)°, Z = 1, and space group \(P\bar 1\). The salt has a layered structure. The DOEO1/2+ radical cation layers are aligned parallel to the ab planes. The HSeO 4 − · H2O solvated anions are located in channels along the a axis and are disordered over two positions near the center of symmetry (1/2 0 0) with a probability of 50%. The conductivity of the salt is equal to 300–400 Ω−1 cm−1 at room temperature and increases upon cooling to the boiling point of liquid helium (4.2 K) by a factor of 100–200 depending on the sample.

New organic metal β-(DOET)2FSO3 · H2O: Synthesis and crystal structure

An organic metal β-(DOET)2FSO3 · H2O based on a novel donor DOET (DOET is (1,4-dioxane-2,3-diyldithio)ethylenedithiotetrathiafulvalene) was synthesized and structurally characterized. Single crystals were prepared by electrochemical oxidation of DOET in the d.c. mode. The salt has a layered structure with the DOET1/2+ radical cation layers parallel to the ab plane. The FSO3− anion is equiprobably disordered over two positions relative to the center of symmetry (1/2, 0, 0). The temperature behavior of conductivity is characteristic of metals in the temperature range from 293 down to 96 K; below 96 K, an increase in resistance is observed.

Multi-component molecular conductors with supramolecular assembly based on ET radical cation salts with (NO 3) − anion

Synthesis, structure and conducting properties of two new multi-component radical cation ET salts with the (NO 3) − counterion: (ET) 2(NO 3)·C 2H 4(OH) 2 ( I) and (ET) 2(NO 3)·0.5[C 2H 4(OH) 2]·H 2O ( II) are described. Both salts have layered structures with the distinguishing feature of hydrogen bonds being present between the radical cation layers and anion sheets. It was found that introduction of glycol molecules to compositions of I and II significantly affects the structure of their cation and anion layers and, as a result, their conducting properties. I is a semiconductor, while II demonstrates metallic conductivity down to 4.2 K.

Crystal structure of the new radical cation salt (DOET)4[Fe(CN)5NO]1.25(C6H5Cl)0.75

A new radical cation salt based on 4,5-(1,4-dioxanediyl-2,3-dithio)-4{sup '},5{sup '}-ethylenedithiotetrathiafulvalene (DOET) with the photochromic anion [Fe(CN){sub 5}NO]{sup 2-}, namely, (DOET){sub 4}[Fe(CN){sub 5}NO]{sub 1.25}(C{sub 6}H{sub 5}Cl){sub 0.75} , is synthesized. Single crystals of this salt are studied using X-ray diffraction [a = 10.398(2) A, b = 11.168(2) A, c = 18.499(4) A, {alpha} = 103.14(3) deg., {beta} = 92.80(3) deg., {gamma} = 106.02(3) deg., V = 1996.3(7) A{sup 3} , space group P1-bar, and Z = 1]. In the structure, radical cation layers alternate with anion layers along the c axis. The centrosymmetric dimers are formed by DOET radical cations in the donor layer with packing of the {beta} type. Like the vast majority of DOET-based salts, the new salt possesses semiconductor properties.

BETS]2. C60complex and BETS salts with square-planar platinate (II), nickelate (II) anions: (BETS)4. Pt(CN)4, (BETS)4. Ni(CN)4

The (BETS) 2 .C 60 complex (1) and new radical cation salts based on bis(ethylenedithio)tetraselenafulvalene (BETS) with the square-planar [Ni(CN) 4 ] 2- , [Pt(CN) 4 ] 2- anions were synthesized: (BETS) 4 .Ni(CN) 4 (2), (BETS) 4 .Pt(CN) 4 (3). The crystal structure of 1 - 3 is layered. The layers consisting of C 60 molecules are alternated with the layers composed of BETS molecules in 1. The obtained complex is classified as molecular adduct in which the van der Waals interactions are predominant. The radical cation layers in the salt 2 are alternated with the anion layers along the c-direction of the unit cell. The salts retain metallic state down to 4.2 K. The band structure calculation of 2 shows 2-dimensional cylindrical Fermi surface, which is consistent with the θ- type structure and its conductivity.

Synthesis, crystal structure and properties of the new semiconductor (EVT) 4·[Pt(CN) 4

A novel radical cation salt based on of the donor (4,5-ethylenedithio-4′,5′-vinylenedithio)tetrathiafulvalene (EVT) with the square planar anion Pt(CN) 4 2− has been synthesized: (EVT) 4·[Pt(CN) 4] ( 1). According to the X-ray analysis its crystal structure includes EVT cation layers alternating with anion layers along the a-axis of the unit cell. The radical cation layer is formed by EVT stacks with β-packing type, the donors in stacks are tetramerized. The EPR spectra of a plate-like crystal of (EVT) 4·[Pt(CN) 4] salt shows a very weak signal with typical parameters of TTF derivative. The room temperature conductivity of salt 1 is 8×10 −2 Ω −1 cm −1 and the temperature dependence of the conductivity exhibits semiconducting character.