P. Berges

Structure and electrical conductivity of TCNQ-2,3,7,8-tetramethoxychalcogenanthrene complexes

Abstract Charge-transfer complexes formed by reaction of 2,3,7,8-tetramethoxychalcogenanthrenes(5,10-dichalcogenacyclo-diveratrylenes, ‘Vn 2 E 2 ’) with 7,7,8,8-tetracyanoquinodimethane (TCNQ) are prepared and their structures determined. Spin concentration, mobilities and gap energies of the polycrystalline samples are evaluated from e.s.r. intensities and electrical conductivity measurements. The influence of the different chalcogen atoms on physical properties is discussed.

Structure, electrical conductivity and dielectric relaxation of the phenothiazine-tetracyanoethene 1:1 complex

Abstract Phenothiazine (PTZ) as a donor and tetracyanoethene (TCNE) as an acceptor form the dark blue charge-transfer complex PTZ-TCNE. In the solid state stacks are found in which the donor (D) and acceptor (A) molecules alternate according to the sequence –D—A– –D—A– –D—A–. Within the stacks the donor and acceptor molecules are arranged coplanarly to each other in such a way that an optimum overlap of the corresponding HOMOs and LUMOs is guaranteed, as is shown by MNDO calculations. PTZ-TCNE is a semiconductor with a gap energy of E g = 1.69 eV and a pre-exponential factor of σ o = 575 S cm −1 . Its dielectric relaxation is of the non-Debye type (non-symmetrical Cole-Cole plot, described by a Havriliak-Negami equation) showing a temperature dependence characterized by an Erying equation with an activation enthalpy of ΔH ν = 0.99 eV and entropy ΔS ν ≈ 10 −3 eV K −1 . The temperature dependence was also analysed in terms of an Arrhenius equation leading to E a = 1.05 eV.

Structure and dielectric relaxation of 2,3,7,8-tetramethoxychalcogenanthrene-TCNQ complexes

Abstract 2,3,7,8-Tetramethoxychalcogenanthrenes (5,10-dichalcogena- cyclo -diveratrylenes, Vn 2 EE′) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) form charge-transfer (CT) complexes of composition Vn 2 EE′·TCNQ (E = E′ = S, Se; E = S, E′ = Se, Te). The structure of the hitherto unknown compound Vn 2 STe·TCNQ is described. The dielectric relaxation of the whole series of CT complexes is determined and the results are correlated with the structural data.

Structure, electrical conductivity and dielectric relaxation of a 1,2-dimethoxybenzene-tetracyanoethene 1:1 complex

Abstract 1,2-Dimethoxybenzene (Ver) as a donor and tetracyanoethene (TCNE) as an acceptor from the dark blue charge-transfer complex Ver·TCNE. In the crystal stacks, in which the donor (D) and acceptor (A) molecules alternate according to the sequence …DAD…A…DAD…A…, centro-symmetric DAD units can be distinguished. In these units the molecules are arranged in such a way that an optimum overlap of the corresponding HOMOs and LUMOs is guaranteed, as is shown by MNDO and HAM 3 calculations. Ver·TCNE is a semiconductor with a gap energy of Eg = 0.85 eV and a pre-exponential factor of σo = 0.91 S/cm. The temperature dependence of dielectric relaxation is characterized by an Eyring equation and gives an activation enthalpy of ΔH ‡ = 0.76 eV and entropy ΔS ‡ = 0.95 × 10 −4 eV/K .

Cyclic ligands with fixed co-ordination geometry. Part 6(1). Chalcogenanthrenes as bridging ligands in dinuclear complexes of rhenium(I) and platinum(IV)-X-ray crystal structure of di(μ-chloro) (μ-2, 3, 7, 8-tetramethoxyselenanthrene) hexamethyl diplatinum(IV)

SummaryThe chalcogenanthrenes Vn2EE′; 2, 3, 7, 8-tetramethoxythianthrene (E=E′=S), 2, 3, 7, 8-tetramethoxydibenzothiaselenin (E=S, E′=Se), and 2, 3, 7, 8-tetramethoxyselenanthrene (E=E′=Se), react with [{ReBr(CO)3(THF)}2] and [{PtXMe3}4] (X=Cl or Br) to give the dinuclear complexes [(fac-L3M)2(μ-X)2 (μ-Vn2EE′)] (M=Re, L=CO, X=Br; M=Pt, L=Me, X=Cl or Br) in which the chalcogenanthrenes reveal a hitherto unknown co-ordination mode as bridging ligands. Telluranthrene (Pn2 Te2), however, forms mononuclear complexes of compositionfac-[L3MX(Pn2Te2)] (M=Re, L=CO, X=Br; M=Pt, L=Me, X=Br) with a chelating chalcogenanthrene ligand. Whereas the rhenium compounds are not stable enough in solution to be studied by i.r. spectroscopy, the platinum compounds can be well characterised by their1H n.m.r. spectra. Furthermore, the results of a single-crystal structure determination of [Pt2Cl2Me6(Vn2Se2)] are reported. The Pt−Se distance of 259 pm indicates a relatively weak interaction between the chalcogenanthrene and the remaining dinuclear fragment of the molecule.

Selbststapelnde Systeme, IV 2,3,7,8-Tetramethoxythianthreniumsalze/Selfstacking Systems, Part IV 2.3.7.8-Tetramethoxythianthrenium Salts

Abstract By addition of solutions of nitrosyl hexachloroantimonate(V) in acetonitrile or of diiodine in n-hexane to a solution of 2.3.7.8-tetramethoxythianthrene (“Vn2S2”, 1) in toluene the oxidation products [Vn2S2][SbCl6] • CH3CN (2) and [Vn2S2]I3 (3), resp., are formed. Crystal structure determinations show both compounds to contain the [Vn2S2]+ ion. In contrast to the folded parent compound Vn2S2 its monocation [Vn2S2] T is planar, the short CS and CO distances (172-173 pm and 134-135 pm resp.) indicate an extended mesomeric system. Both compounds crystallize with segregated stacks of cations and anions. In 2 the coplanarly and equidistantly stacked [Vn2S2]+ ions have an A,B-sequence (distance between the planes of the ions 353 pm, intermolecular S···S distance 366 pm). In 3 the [Vn2S2]+ ions form dimers by SS contacts (S···S distance 316 pm); these dimers are arranged in a stair-like manner (distances between atoms of adjacent dimers 350-380 pm). The conductivities of 2 and 3 are 9.4 • 10-9 and 5.3 • 10-6 Sem-1 , resp.