Discotic liquid crystals at the air water interface

The monolayer properties of two types of discotic liquid crystals, hexasubstituted triphenylenes 1 and azo derivatives of phloroglucinol 5, were examined. First investigations show that these discotic liquid crystals form stable monolayers. It could be shown that electron acceptors insert into the monolayer of 1. Azo discs display a packing behaviour at the monolayer that is ascribed to a side-on packing of the molecules.     

New Steroidal Glycosides from Balanites aegyptiaca

Five new steroidal glycosides were isolated from the roots of Balanites aegyptiaca, a widely used African medicinal plant. On the basis of spectroscopic and chemical evidence, their structures were determined as (3β,12α,14β,16β)‐12‐hydroxycholest‐5‐ene‐3,16‐diyl bis(β‐D ‐glucopyranoside) ( 1 ), (3β,20S,22R,25R)‐ and (3β,20S,22R,25S)‐26‐(β‐D ‐glucopyranosyloxy)‐22‐methoxyfurost‐5‐en‐3‐yl β‐D ‐xylopyranosyl‐(1→3)‐β‐D ‐glucopyranosyl‐(1→4)[α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐glucopyranoside ( 2 and 3 , resp.), and (3β,20S,22R,25R)‐ and (3β,20S,22R,25S)‐spirost‐5‐en‐3‐yl β‐D ‐xylopyranosyl‐(1→3)‐β‐D ‐glucopyranosyl‐(1→4)[α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐glucopyranoside ( 4 and 5 , resp.)     

Ag8Ca19N7 – Nitrogen Bridged Ca19N7 Superoctahedra surrounded by Silver Tetrahedra

By reacting Ca₃N₂ and silver powder at a temperature of 1300 K the subnitride Ag₈Ca₁₉N₇ was obtained. The title compound crystallizes in the space group Fm3m (No. 225) and has the lattice constant a = 1472.0(2) pm at T = 210 K and a = 1474.43(3) pm at T = 295 K. Ag₈Ca₁₉N₇ combines two very interesting, but rather different structural features, Ag₄ tetrahedra and Ca₁₉N₇ superoctahedra. An analysis of the bonding situation has been performed by means of Extended‐Hückel calculations.     

Solid State Structure of [Na4(μ‐dioxane)8/2(μ‐dioxane)(PPh2)4]∞: Unprecedented Supramolecular Arrangement of Na and P Atoms in Eight‐membered Na4P4 Rings

NaPPh₂, prepared from sodium and PClPh₂ in refluxing dioxane, crystallises from dioxane as [Na₄(μ‐dioxane)_8/2(μ‐dioxane)(PPh₂)₄]_∞ ( 1 ), in which the basic structural features are eight‐membered Na₄P₄ rings, linked by intermolecularly bridging dioxane molecules to give a three‐dimensional network, and inclusion of one dioxane molecule inside the eight‐membered ring. 1 crystallises in the orthorhombic space group Cmc2₁ (no. 36), T = 203(2) K, a = 27.377(1) Å, b = 10.579(1) Å, c = 23.608(1) Å, V = 6837.3(6) ų, Z = 4, and the absolute structure parameter 0.3(2). The refinement converged to R1 = 0.0632, wR2 = 0.1701 (for reflections with I > 2σ(I)), R1 = 0.0707, wR2 = 0.1781 (all data).     

Zwitterionic Spirocyclic λ5Si‐Silicates with Two Bidentate Acetohydroximato(2–) or Benzohydroximato(2–) Ligands: Synthesis,Structure, and Dynamic Stereochemistry

The syntheses of the zwitterionic spirocyclic λ⁵Si‐silicates 7–14 are described. The chiral zwitterions contain a pentacoordinate (formally negatively charged) silicon atom and a tetracoordinate (formally positively charged) nitrogen atom, the ate and onium center being connected by an alkylene group. The zwitterions each contain two identical bidentate diolato(2–) ligands that formally derive from acetohydroximic acid or benzohydroximic acid. The stereochemistry and dynamic behavior of these compounds were investigated by experimental and theoretical methods. For this purpose, the zwitterionic λ⁵Si‐silicates 7–14 were studied by solution (¹H, ¹³C, ²⁹Si) and solid‐state (¹³C, ¹⁵N, and ²⁹Si CP/MAS) NMR experiments. In addition, compounds 7 , 8 , 10 , 11 , and 13 were structurally characterized by single‐crystal X‐ray diffraction. The dynamic behavior (intramolecular enantiomerization) of 7 and 13 in solution was studied by VT ¹H NMR experiments. These experimental studies were completed by ab initio investigations of the related anionic model species 15 . The chiral compounds 7–14 exist as (λ)‐ and (δ)‐enantiomers in the solid state and in solution. The trigonal‐bipyramidal structure of the respective Si‐coordination polyhedra, with the two carbon‐linked oxygen atoms in the axial sites, is the energetically most favorable one. The (λ)‐ and (δ)‐enantiomers of 7–14 are configurationally stable in solution on the NMR time scale ([D₆]DMSO, room temperature). They undergo an intramolecular (λ)/(δ)‐enantiomerization (twist‐type mechanism), with an activation free enthalpy of δG^{ = 72–73 kJ mol^–1 (experimentally established for 7 and 13 ; calculated energy barrier for the model species 15 : 66.0 kJ mol^–1).     

Synthese und Strukturaufklärung von neuen (Eisencarbonyl)zinkund ‐cadmiumchlorid‐Derivaten

Syntheses and Structure Elucidations of Novel (Ironcarbonyl)zinc and ‐cadmium Chloride Derivatives Reactions of zinc/cadmium chloride with Na₂[Fe(CO)₄] lead to a number of new (iron carbonyl)zinc/cadmium chlorides, wherein the reaction course depends on the used solvent used. In the reaction of ZnCl₂ with Na₂[Fe(CO)₄], three new substances can be prepared. The compound [Zn₂Cl₂Fe(CO)₄(THF)₂] ( 1 ), which consists of neutral polymeres, is formed in THF, the ionic compound [Na(DME)₃][Zn₂Cl₃Fe(CO)₄] ( 2 ) forms in DME, and from a mixture of THF and TMEDA the compound [Zn₂Cl₂Fe(CO)₄(TMEDA)₂] ( 3 ) is obtained as a monomere. Also by using CdCl₂, the reaction with Na₂[Fe(CO)₄] in THF leads to the polymeric compound ([(Cd₄Cl₆)Fe(CO)₄(THF)₅] ( 4 )). Carrying out the reaction in a mixture of toluene and DME leads to the formation of the ionic compound [Na(DME)₃]₂[Cd₆{Fe(CO)₄}₆Cl₂(DME)₂] ( 5 ) in which an annular dianion consisting of twelve metal atoms is found. From an aqueous solution and subsequent work‐up in THF, the compound [Fe(THF)₄(H₂O)₂][Cd₈{Fe(CO)₄}₄Cl₉(THF)₆]₂ ( 6 ) can be prepared which contains an cluster anion that is built of anellated six membered rings.     

Importance of the Anchor Group Position (Para versus Meta) in Tetraphenylmethane Tripods: Synthesis and Self‐Assembly Features

The efficient synthesis of tripodal platforms based on tetraphenylmethane with three acetyl‐protected thiol groups in either meta or para positions relative to the central sp³ carbon for deposition on Au (111) surfaces is reported. These platforms are intended to provide a vertical arrangement of the substituent in position 4 of the perpendicular phenyl ring and an electronic coupling to the gold substrate. The self‐assembly features of both derivatives are analyzed on Au (111) surfaces by low‐temperature ultra‐high‐vacuum STM, high‐resolution X‐ray photoelectron spectroscopy, near‐edge X‐ray absorption fine structure spectroscopy, and reductive voltammetric desorption studies. These experiments indicated that the meta derivative forms a well‐ordered monolayer, with most of the anchoring groups bound to the surface, whereas the para derivative forms a multilayer film with physically adsorbed adlayers on the chemisorbed para monolayer. Single‐molecule conductance values for both tripodal platforms are obtained through an STM break junction experiment.