Auke Meetsma

Influence of the solvent on the crystal structure of PCBM and the efficiency of MDMO-PPV:PCBM ‘plastic’ solar cells

Two crystal structures of PCBM, obtained from different crystallisation solvents, are presented; a proposed link with solvent dependence of the efficiency of MDMO-PPV:PCBM solar cells is described.

Identification of polymorphs of pentacene

Pentacene crystallizes in a layered structure with a herringbone arrangement within the layers. The electronic properties depend strongly on the stacking of the molecules within the layers [J. Phys. Chem. B. 106 (2002) 8288]. We have synthesized four different polymorphs of pentacene, identified by their layer periodicity, d(001): 14.1, 14.4, 15.0 and 15.4 Angstrom. Single crystals commonly adopt the 14.1 Angstrom structure, whereas all four polymorphs can be synthesized in thin film form, depending on growth conditions. We have identified part of the unit cell parameters of these polymorphs by X-ray and electron diffraction (ED). The 15.0 and 15.4 X polymorphs transform at elevated temperature to the 14.1 and 14.4 Angstrom polymorphs, respectively. Using SCLC measurements, we determined the mobility of the 14.1 Angstrom polymorph to be 0.2 cm(2)/V s at room temperature

Low-temperature structure of rubrene single crystals grown by vapor transport.

We report the crystal structure of rubrene, C42H28 (5,6,11,12-tetraphenyltetracene), in the temperature interval 100-300 K. The crystals are grown by physical vapor transport in an open system. The crystal structure is orthorhombic over the entire temperature range.

MHz unidirectional rotation of molecular rotary motors

A combination of cryogenic UV-vis and CD spectroscopy and transient absorption spectroscopy at ambient temperature is used to study a new class of unidirectional rotary molecular motors. Stabilization of unstable intermediates is achieved below 95 K in propane solution for the structure with the fastest rotation rate, and below this temperature measurements on the rate limiting step in the rotation cycle can be performed to obtain activation parameters. The results are compared to measurements at ambient temperature using transient absorption spectroscopy, which show that behavior of these motors is similar over the full temperature range investigated, thereby allowing a maximum rotation rate of 3 MHz at room temperature under suitable irradiation conditions.

Unexpected enhancement of enantioselectivity in copper(II) catalyzed conjugate addition of diethylzinc to cyclic enones with novel TADDOL phosphorus amidite ligands

Abstract The copper(II) catalyzed enantioselective 1,4-addition reactions of diethylzinc to cyclic enones in the presence of novel phosphorus amidite ligands, easily prepared from α,α,α′,α′-tetraphenyl-2,2′-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) derivatives, resulted in e.e.s up to 71% for cyclohexenone and up to 62% for cyclopentenone. A remarkable enhancement of enantioselectivity was observed upon the addition of powdered molecular sieves to the reaction mixture.

MISFIT LAYER COMPOUNDS (MS)NTS2 (M = SN, PB, BI, RARE-EARTH ELEMENTS - T = NB, TA - N = 1.08 - 1.19), A NEW CLASS OF LAYER COMPOUNDS

Abstract A study by X-ray diffraction and electron microscopy is reported of the type of compounds that is usually designated as ternary sulphides “MTS 3 ” ( M = Sn, Pb, Bi, rare earth metals; T = Nb, Ta). They are misfit layer compounds built of alternating double layers of MS with M in distorted square pyramidal coordination by sulphur and sandwiches TS 2 with T is distorted trigonal-prismatic coordination by sulphur. One intralayer lattice constant of MS is incommensurate with that of TS 2 . Recent progress in the understanding of the crystallographic description is discussed and a unifying view based on about ten compounds is presented. Results of electrical transport measurements are briefly summarized.

The crystal structure of some rhenium and technetium dichalcogenides

Abstract The crystal structures of ReSe., ReS., ReSSe and TeS2 are determined using single crystal X-ray diffraction. The compounds are triclinic with space groupPl. ReSe., ReS, and ReSSe have a distorted CdCl2-type structure: TeS2 has a distorted Cd(OH)-type structure. In the case of ReS, there are two sandwiches in the unit cell, related by symmetry centers. The other compounds have one sandwich per unit cell and the centers of symmetry are within the Re (Tc)-layer. In all compounds the Re (Te) atoms in each layer form parallelogram-shaped connected clusters with Re Re (Te Te) distances of ca. 2.7–2.8A, in the cluster and ca. 2.9A, between clusters. The chains of clusters run along the a-axis. Unit cell dimensions and structure of ReS, differ from the one reported recently by Murray et al.Inorg. Chem., 33 (1994) 4418) where only one sandwich is present and the centers of symmetry are in the Re layer. The structure of ReSe2 differs from that reported by Alcock and Kjekshus (Acta Chem. Scand., 19 (1965) 79), in the sense that these authors interchanged inversion-centers and pseudo-centers.

(Cyclopentadienylamine)scandium(2,3-dimethyl-1,3-butadiene): A 1,3-Diene Complex of Scandium with Sc(I)- and Sc(III)-like Reactivity

The scandium 2,3-dimethyl-1,3-butadiene complex [η5,η1-C5H4(CH2)2NMe2]Sc(C6H10) (2) reacts with PhCN via initial nitrile insertion into the Sc−diene bond to give a dimeric μ2-imido species, but with a 2,2‘-bipyridine via the elimination of the free diene. The latter shows that 2 can be used to generate the reactive fragment [η5,η1-C5H4(CH2)2NMe2]ScI.

Novel synthesis of 4(5)-monosubstituted imidazoles via cycloaddition of tosylmethyl isocyanide to aldimines

4(5)-Monosubstituted imidazoles (9) have been prepared via base-induced cycloaddition of tosylmethyl isocyanide (TosMIC) to N-(dimethylsulfamoyl)aldimines (2) or N-tosylaldimines (3). In the first case, N-(dimethylsulfamoyl)imidazoles 8 are the initial reaction products, from which the dimethylsulfamoyl group is readily removed with aqueous HBr. In the second case, the tosyl group of 1-tosylimidazoles 10 is lost spontaneously to give 4(5)-monosubstituted imidazoles 9 in one operation

Refinement of the crystal structure of tetragonal Al2Cu

Abstract New single-crystal X-ray diffraction data have been obtained for the θ-phase of aluminum-copper (Al2Cu). Results of the refinement are presented. The structure is found to be in accordance with the one determined by J. B. Friauf (J. Amer. Chem. Soc. 49, 3107–3114 (1927)) . The compound crystallizes in the tetragonal space group I4 mcm (No. 140) with a unit cell of dimensions a = 6.067(1) and c = 4.877(1) A. There are four formula-units per unit cell. A full-matrix least-squares refinement with 237 observed reflections and 8 parameters converged to RF = 0.032 (wR = 0.037). In addition to more accurate values for the lattice parameters and the atomic coordinates, anisotropic temperature factors are obtained.