Browsing by Author "Endres, Helmut"

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Open Access
α- and β-(BEDT-TTF)2+I3-: two dimensional organic metals
(1985) Hennig, Ingolf; Bender, Klaus; Schweitzer, Dieter; Dietz, Klaus; Endres, Helmut; Keller, Heimo J.; Gleitz, Arno; Helberg, Hans W.
Electronic properties of α- and β-(BEDT-TTF)2I3 crystals are reported.
Open Access
(BEDT-TTF)2+J3- : a two-dimensional organic metal
(1984) Bender, Klaus; Dietz, Klaus; Endres, Helmut; Helberg, Hans W.; Hennig, Ingolf; Keller, Heimo J.; Schäfer, Herbert; Schweitzer, Dieter
Temperature-dependent thermopower-, dc- and microwave-conductivity measurements on the two-dimensional organic metal (BEDT-TTF)2+J3- are reported.
Open Access
The double-stack structure of di(3,4-ethylenedithio-3',4'-dimethyl-2,2',5,5'-tetrathiafulvalenium)perchlorate, (DIMET)2ClO4
(1987) Endres, Helmut; Heid, Rolf; Keller, Heimo J.; Heinen, Ilsabe; Schweitzer, Dieter
2C10H10S6 1/2+.ClO-4 , M r= 744·62, triclinic, PI, α=7·000 (2), b =7·824 (3), c = 27·010 (14) A, α = 88· 10 (4), β= 89·02 (4), Y = 74· 58 (3)°, V = 1425 A 3, Z=2, Dx=1·73gcm-3, λ( MoKa) = 0·7107 A, μ= 10·1 cm-1, F(000) = 762, room temperature, final R = 0.063 for 3076 observed independent reflections. Two crystallographically independent DIMET molecules each with an average charge of ½+ form stacks, which run nearly perpendicularly to one another. Within each stack, two different interplanar spacings between adjacent parallel molecules are found. These overlap patterns are similar to those found in tetrahydrofuran solvate. The stacks are arranged side by side perpendicular to the long molecular axis to give a sheet-like arrangement.
Open Access
Electrocrystallization and structures of perylene radical salts: hexaperylene perchlorate, (C20H12)6+ClO4-, triperylene perchlorate, (C20H12)3+ClO4-, and diperylene hexafluorophosphate-tetrahydrofuran (3/2), (C20H12)2+PF6-.2/3C4H8O
(1985) Endres, Helmut; Keller, Heimo J.; Müller, Barbara; Schweitzer, Dieter
Crystals grown by electrocrystallization, species obtained depending on perylene concentration. Room-temperature data collect ions, Mo Kat λ = 0·71069 A. 6:1 salt: Mr= 1613·3, triclinic. pl, a = 12·57 1 (7), b = 13·699(5). c = 13.835(II)A, α = 110·43 (4), β= 107·13 (7), γ= 107·09 (4)°, V = 1913A3, Z = 1, Dx = 1.40gcm-3, μ= 1.1 cm- ', F(OOO) = 841, final R = 0·077 for 3171 observed reflections. The structure contains three independent perylene π dimers arranged nearly perpendicularly to each other. The anions are severely disordered or freely rotating. 3:1 salt: Mr = 856·4, triclinic, PI, a = 13·009(8), b= 13.821 (10), c= 13·850(15)A, α = 66·05(7), β = 83·36 (8). γ= 63·5 1 (6)°, V = 2030A3, Z = 2, Dx= 1.40gcm-3 , μ= 1·5cm-1 , F(OOO) = 890, final R = 0· 138 for 3523 observed reflections. Tetrameric perylene stacks are surrounded on four sides by single perylene species, having their planes nearly perpendicular to the molecular planes in the stacks. 2:1 salt: Mr = 697· 7, monoclinic, P2/m, a = 13·04(1), b = 14 · 12 (1), c = 13·75 (1)A, β=110·80 (2)°, V = 2367 A3, Z = 3, Dx = 1·47 g cm-3',μ= 1·5 cm- ', F(OOO) = 1079, final R =0· 121 for 1737 observed reflections. Nearly regular perylene stacks are surrounded by single perylene species in a way similar to the 3:1 salt. The thf solvent and one of the perylene molecules are disordered over two orientations.
Open Access
A novel molecular metal: (oxamide oximato)(oxamide oxime)nickel(II) tetracyanoquinodimethanide, [Ni(oaoH)(oaoH2)]tcnq, and physical properties of its semiconducting Pt analogue
(1985) Endres, Helmut; Bongart, August; Nöthe, Dietrich; Hennig, Ingolf; Schweitzer, Dieter; Schäfer, Herbert; Helberg, Hans W.; Flandrois, Serge
(C4H11N8NiO4)+(C12H4N4)-, Mr = 498.09 is triclinic, p1, a -=3.7718(6), b = 7.436(2), c =17.511(4) A, a=88.67(2), β=86.93(2), γ=85.05(2), γ= 488.51 A 3, Z = 1, d c=1.69 gcm -3, final R w= 0.035 for 1454 observed independent reflections. The crystals consist of segregated regular parallel stacks of planar metal complex cations and tcnq - counterions with intermolecular H bonds stabilizing the structure. The compound is metallic at room temperature. A metal to semiconductor transition around 230 K shows up in thermopower data, in the microwave conductivity and epr around 170 K. It is not visible in the static magnetic susceptibility.
Open Access
Organic metals from simple aromatic hydrocarbons: perylene radical salts
(1985) Schweitzer, Dieter; Hennig, Ingolf; Bender, Klaus; Endres, Helmut; Keller, Heimo J.
Crystal structures, temperature dependent thermopower and conductivity measurements of several metallic perylene radical salt phases are discussed.
Open Access
The preparation of new metallic charge-transfer complexes: anthra [9.1-cd:10.5-c'd'] bis [1.2] dithiol (TTA), -diselenol (TSA) and their polyiodides
(1982) Endres, Helmut; Keller, Heimo J.; Queckbörner, Jobst G.; Veigel, Jürgen; Schweitzer, Dieter
The donors TTA and TSA were prepared starting from 1.5-dichloro-9.10-anthracenedione which was converted into 1.5.9.10-tetrachloroan-thracene (TCA) by two alternating chlorination and elimination steps. TCA was reacted under a dry argon atmosphere with suspensions of Na2S2 and Na2Se2 to yield TTA and TSA, respectively. Action of elemental iodine gives highly conductive polyiodides of both donors. Single crystals of TSA·I1.2 actually behave metallic between 220 and 300 K. The X-ray structure of TSA and TSA·I1.2 allows a comparison of intermolecular distances in the neutral and the partially oxidized, ionic stacks of the donor.
Open Access
Preparation, structure and investigations of BEDT-TTF trihalides
(1985) Endres, Helmut; Hiller, M.; Keller, Heimo J.; Bender, Klaus; Gogu, Emil; Heinen, Ilsabe; Schweitzer, Dieter
Crystals of the β-phases of (BEDT-TTF)2Br-I-Br (1) and (BEDT-TTF)2I-I-Br (2) have been isolated by electrocrystallization. The solids can be obtained using different tetrabutylammonium trihalides containing iodine and bromine as supponing electrolytes. Cyclovoltammetric results show clearly that the trihalide anions are involved in the oxidation reactions near the anode which finally lead to the crystals.
Open Access
Preparation, structure and physical properties of BEDT-TTF nitrates
(1985) Weber, Angelika; Endres, Helmut; Keller, Heimo J.; Gogu, Emil; Heinen, Ilsabe; Bender, Klaus; Schweitzer, Dieter
Electrocrystallization of BEDT-TIF in THF with tetrabutylammonium nitrate as supporting electrolyte leads to the deposition of at least three different phases. Sheets of BEDT-TTF radical cations with short intermolecular S···S contacts (>3.315(4) A) are separated by anion layers. Two more BEDT-TrF nitrates have been characterized by their unit cell data. Resuhs of temperature dependent electrical conductivity and thermopower measurements on crystals of the a-phase are presented. They are metallic down to about 30 K.
Open Access
Radical cation salts of an unsymmetrical BEDT-TTF derivative: DIMET
(1987) Bender, Klaus; Endres, Helmut; Gärtner, Stephan; Gogu, Emil; Heid, Rolf; Heinen, Ilsabe; Keller, Heimo J.; Kraatz, Andrea; Schweitzer, Dieter
A surprising fact in the structures of the organic superconductors (TMTSF)2 Cl04 and -β-(BEDT-TTF)2X (X=I3-, IBr2- and AuI2-) is that there exists a slight dimerisation of the donor molecules within the stacks of these radical cation salts. Therefore, the question arises whether a more pronounced dimerisation in organic radical salts of this type leads to stronger intra- and interstack interactions and to stronger couplings between the unpaired electrons. This might result in an increase of the transition temperature to superconductivity. A step in this direction is the preparation of "unsymmetrical" donors like DIMET, which was synthesized recently. This new donor was electrocrystallized by us in different solvents using tetrabutylammonium salts of various anions like ClO4-, ReO4-, NO3-, I3-, (AuI2)-, PF6-, ASF6- and SbF6- as electrolytes. With all these anions radical salts were obtained and in some cases even several crystallographic different phases.
Open Access
Radical cation salts of an unsymmetrical BEDT-TTF derivative: molecular structure and physical properties of (DIMET)2ClO4xTHF
(1985) Heid, Rolf; Endres, Helmut; Keller, Heimo J.; Gogu, Emil; Heinen, Ilsabe; Bender, Klaus; Schweitzer, Dieter
Sheets of cations with an average charge of 1/2+ are separated by sheets of anions and THF solvent molecules. Intermolecular S···S contacts result in two-dimensional physical properties. Electrical conductivity and thermopower measurements indicate two broad phase transitions at around 200 K and 80 K.
Open Access
Radical cation salts of BEDT-TTF and an unsymmetrical BEDT-TTF derivative
(1986) Schweitzer, Dieter; Bender, Klaus; Endres, Helmut; Gärtner, Stephan; Heid, Rolf; Heinen, Ilsabe; Keller, Heimo J.; Weber, Angelika; Weger, Meir
Investigations of several BEDT-TTF and DIMET radical salts are presented. Measurements on β-(BEDT-TTF)2IAuI crystals show that their conducting and superconducting properties might vary strongly depending on the decomposition of (IAuI)− anions during the electrochemical process.
Unknown
Structure of anthra[9,1-cd:10,5-d'd']bis[1,2]-diselenole (TSA) and of its partially oxidized, metallic polyiodide TSA I1.2
(1982) Endres, Helmut; Keller, Heimo J.; Queckbörner, Jobst G.; Schweitzer, Dieter; Veigel, Jürgen
Tetraselenaanthracene' (TSA), C 14H6Se4' M r = 490·04, crystallizes in the monoclinic space group P2 1/n with a = 9·318 (3), b = 4·111 (1), c = 16·035 (4) A,β = 90·43 (2)°, V = 614·3 A3, Z = 2, d c = 2·65 Mg m-3• R = 0·030 for 1039 observed reflections. The planar molecules form stacks along b with an interplanar separation of 3·59 A. The normals to the molecular planes are inclined at 29° to the stacking axis. Short intermolecular Se-Se contacts exist between adjacent stacks, the shortest one being 3·467 (1) A. 'Tetraselenaanthracenium iodide' (TSA I 1.2), C14H6I 1.20Se4' Mr = 642·32, is monoclinic, P2 1/c, with a = 18·644 (12), b = 3·856 (2), c = 19·746(12)A,β= 93.36 (5)0,.V= 1417·1A3, dc = 3·01 Mg m-3• R = 0·118 for 1080 observed reflections.
Open Access
Synthesis, structure and physical properties of a two-dimensional organic metal, di[bis(ethylenedithiolo)tetrathiofulvalene] triiodide, (BEDT-TTF)2+I3-
(1984) Bender, Klaus; Hennig, Ingolf; Schweitzer, Dieter; Dietz, Klaus; Endres, Helmut; Keller, Heimo J.
Electrical oxidation of bis(ethylenedithiolo)tetrathiofulvalene (BEDT-TTF) 1 in a nitrogen saturated tetrahydrofurane solution containing (n-C4H10)4N+I3 as electrolyte results in the deposition of crystal plates of (BEDT-TTF)+2I3 (C10H8S8)2I3. These two dimensional crystals are triclinic, space group P1, a = 9.211(2), b=10.850(4), c = 17.488(5) Aring, agr=96.95(2), β = 97.97(2), γ = 90.75(2)°, V = 1717 Aring3, Mr = 1150.01, Z=2, Dx =2.22 g cm-3. Rw = 0.037 for 2462 observed reflections. Sheets of alternating cations and anions occur in the compound. The most prominent intermolecular S-S contacts (∼3.5Aring) are found between the stacks of BEDT-TTF. The stacking of the molecules and the interstack contacts give the compound a two-dimensional character which influences the physical properties.
Open Access
TCNQ salts of planar metal complex cations: novel molecular conductors and semiconductors
(1985) Endres, Helmut; Bongart, August; Nöthe, Dietrich; Hennig, Ingolf; Schweitzer, Dieter; Helberg, Hans W.; Schäfer, Herbert
The facile variation of positive charge of oxamide oxime metal complexes, caused by acid-base equilibrium, allows the growth of single crystals of their TCNQ salts. 1:1 salts consist of reqular segregated stacks of the components, with metallic room temperature behaviour of the Ni compound, the Pt compound being a semiconductor. Room temperature conductivities are of the order of 10 Siemens per cm. A 2:3 Pt complex TCNQ salt contains segregated acceptor stacks with half a negative charge per molecule. These stacks run perpendicular to mixed stacks -D-D-A-D-D-A-, with integral charges on donors D and acceptors A.
Open Access
X-ray investigations of the low-temperature phases of the organic metals α- and β-(BEDT-TTF)2I3
(1986) Endres, Helmut; Keller, Heimo J.; Swietlik, Roman; Schweitzer, Dieter; Angermund, Klaus; Krüger, Carl
The structure of single crystals of the organic metals α- and β-(BEDT-TTF) was determined at 100 K, well below the phase transitions indicated by resistivity and thermopower measurements as well as by differential thermal analysis. In the α-phase no unusual change of the room temperature unit cell but a slight variation in the triiodide network and especially a more pronounced dimerization in one of the two donor stacks have been found. The β-phase develops a superstructure with a unit cell volume three times as large as that at room temperature and with pronounced distortions of the I3--ions.