Characterization of self-assembled supramolecular [Ga4L6] host-guest complexes by electrospray ionization mass spectrometry

Self-assembled supramolecular host-guest complexes have been characterized by electrospray ionization mass spectrometry. The spectra obtained by use of a Q-TOF instrument equipped with a Z-spray ion source show primarily the 3- and 4- charge states of the assemblies. The assemblies have the general formula [guest subset Ga4L6]11- where L represents the chelating bidentate catechol ligand 1,5-bis(2',3'-dihydroxy-benzamido)naphthalene and guests are tetramethyl ammonium (Me4N+), tetraethyl ammonium (Et4N+), tetra-n-propyl ammonium (Pr4N+) and decamethylcobaltocenium (Cp*2Co+) cations. For the first time, the mass spectrum of the empty assembly [Ga4L6]12- is reported. This article also reports that provided the electrospray ion source is capable of preserving noncovalent interactions, it is possible to observe host-guest complexes containing both weak binding guests as well as sterically demanding guests in the mass spectra. The present data suggest that electrospray mass spectrometry is a powerful tool for characterization of supramolecular host-guest complexes.     

Improvement of ITO-free inverted polymer-based solar cells by using colloidal zinc oxide nanocrystals as electron-selective buffer layer

In this study, we report on the improvement of ITO-free inverted polymer/fullerene solar cells by introducing a zinc oxide (ZnO) layer between the active layer and the cathode. The ZnO layers are deposited from solution, using colloidal ZnO nanocrystals with a rodlike shape, which are obtained using a wet-chemical synthesis route at low temperature. The nanocrystals are widely characterized with respect to their structural, optical, and electronic properties. In particular, simulations of powder X-ray diffraction data based on Rietveld refinement are shown to be a suitable method to characterize the average crystallite shape and particle size. Cyclic voltammetry reveals that nanocrystalline ZnO is an appropriate choice as electron-selective buffer layer in organic solar cells based on a bulk heterojunction of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). Using ITO-free inverted solar cells in substrate configuration with an opaque Cr/Al/Cr bottom electrode, we demonstrate that introducing a cathodic interlayer of ZnO nanocrystals leads to a notable enhancement in photovoltaic performance. The magnitude of the effect is found to depend on the solvents used to process the active layer. In case of absorber blends processed from o-dichlorobenzene, we show an almost threefold increase in efficiency from 0.8 to 2.2% at an active area of 1 cm².     

Synthese und Eigenschaften von Triphenylzinnmolybdaten mit kettenförmigen Anionen des Typs 1∞[(Ph3Sn)MoO4]–. Die Kristallstrukturen von (nPr4N)[(Ph3Sn)MoO4]·CH3CN, (nBu4N)[(Ph3Sn)MoO4], [Zn(en)2(Ph3Sn)2(MoO4)2]·2DMF·EtOH und [Cu(en)2(Ph3Sn)2(MoO4)2]·2DMF·EtOH

The reaction of Ph₃SnCl, (R₄N)₂[Mo₆O₁₉] and (R₄N)OH in a molar ratio of 6:1:10 leads to the formation of (R₄N)[(Ph₃Sn)MoO₄] (R = ⁿPr ( 1 ), ⁿBu ( 2 )). Compounds 1· CH₃CN and 2 have been charactarized by IR spectroscopy and single crystal X‐ray diffraction. 1· CH₃CN forms orthorhombic crystals, space group P2₁2₁2₁ with a = 1339.9(2), b = 1508.9(2), c = 1733.2(3) pm. 2 crystallizes in the monoclinic space group P2₁ with a = 1342.6(2), b = 2280.3(4), c = 1344.0(2) pm, β = 118.34(1). Both compounds 1 and 2 consist of isolated R₄N⁺ cations and polymeric $\rm^{1}_{\infty}$ [(Ph₃Sn)MoO₄]^– chains with an alternating arrangement of Ph₃Sn⁺ and MoO₄^2– groups. Treatment of (Ph₃Sn)₂MoO₄ with bis(ethylenediamine)copper(II) succinate yields [Cu(en)₂(Ph₃Sn)₂(MoO₄)₂] ( 3 ). The zinc derivative [Zn(en)₂(Ph₃Sn)₂(MoO₄)₂] ( 4 ) is obtained similarly by reaction of (Ph₃Sn)₂MoO₄ with bis(ethylenediamine)zinc(II) formiate. Compounds 3· 2DMF · EtOH and 4· 2DMF · EtOH crystallize in the monoclinic space group P2₁/n with a = 1998.0(2), b = 1313.3(1), c = 2181.6(2) pm, β = 90.97(1)° for 3 and a = 2015.4(1), b = 1316.7(1), c = 2157.0(1) pm, β = 90.40(1)° for 4 . Like in the cases of 1 and 2, polymeric $\rm^{1}_{\infty}$ [(Ph₃Sn)MoO₄]^– chains are observed. The [M(en)₂]²⁺ units (M = Cu, Zn) act as linkers between the $\rm^{1}_{\infty}$ [(Ph₃Sn)MoO₄]^– chains to give 2D layer structures with (6, 3) net topology.     

Aldehydselektivität von alkylhafnium-komplexen in aldehyd-keton-konkurrenzversuchen; vergleich zu zirkonium- und titan-analogen komplexen sowie theoretische deutung

Cl₃Hf-Me, in contrast to MeLi is not able to attack an ester or a nitrile group and fails to discriminate in competition experiments between heptanal and diethylketone. To the contrary, Cl ₃Hf-Bu and (EtO)₃Hf-Me are highly aldehyde-selective. An explanation of these findings in comparison with alkylzirconium and alkyltitanium complexes is given.     

A linear-time algorithm for edge-disjoint paths in planar graphs

In this paper we discuss the problem of finding edge-disjoint paths in a planar, undirected graph such that each path connects two specified vertices on the boundary of the graph. We will focus on the “classical” case where an instance additionally fulfills the so-calledevenness-condition. The fastest algorithm for this problem known from the literature requiresO (n ^5/3(loglogn)^1/3) time, wheren denotes the number of vertices. In this paper now, we introduce a new approach to this problem, which results in anO(n) algorithm. The proof of correctness immediately yields an alternative proof of the Theorem of Okamura and Seymour, which states a necessary and sufficient condition for solvability.     

Molecular thermodynamics of fluid mixtures containing molecules differing in size and potential energy

Recent computer-simulation work by Shing and Gubbins (1983) for binary mixtures has shown that common semiempirical models (van der Waals n-fluid models) are in error when the molecules of the two components differ appreciably in size; the error is most severe in the dilute region. While perturbation theories are much better, they (like computer simulations) are not as yet useful for engineering work because of prohibitive computer requirements.This work proposes an algebraic expression for the Helmholtz energy of a mixture which gives results in very good agreement with those reported by Shing and Gubbins. This expression, using the local-composition concept, is based on a simplified but realistic picture of a fluid mixture: short-range order and long-range disorder. The proposed expression uses the Mansoori-Carnahan-Starling-Leland equation for the contribution of repulsive forces. For the contribution of attractive forces, it uses a new expression based on not one but several radii for the first-neighbor shell, one radius for each component.With reasonable simplifications, the resulting equation for the Helmholtz energy indicates that the van der Waals “constant” a is a strict quadratic function of mole fraction only at very low densities; at advanced densities, there are small deviations from the quadratic mixing rule. For practical calculations, the computer requirements are nearly the same as those for conventional engineering models.