Wilhelm Seichter

A new organic nanoporous architecture: Dumb-bell-shaped molecules with guests in parallel channels

A new type of dumb-bell-shaped host molecule (6-8) has been synthesised, of which 1,8-bis((1)-adamantyl)-1,3,5,7-octatetrayne (8 = BAOT) forms an open porous architecture when cocrystallised with a number of typical solvent molecules. Adamantyl substituents attached to a tetraalkyne spacer build up the walls of parallel channels wherein guest molecules are aligned. Surprisingly, the tetraalkyne unit is significantly bent. Desolvation experiments provide evidence for a reversible inclusion of guests. In the case of the inclusion of 2-butanone, a partial substitution by symmetrical and asymmetrical long-chain chromophores during crystallisation was possible. Stained crystals showed optical frequency doubling. The crystal structure analysis revealed a centric space group, although considerable translational and orientational disorder was present. Application of scanning pyroelectric microscopy revealed that the growth of inclusion compounds with 2-butanone produced polar ordering of guest molecules, which were aligned in two macro-domains of opposing polarity. The resulting orientation of the carbonyl dipoles is in agreement with the theoretical prediction of a Markov model of spontaneous polarity formation based on molecular recognition processes on growing crystal faces. The present case represents a new example of a property-driven supramolecular synthesis.

Interaction of an extended series of N-substituted di(2-picolyl)amine derivatives with copper(II). Synthetic, structural, magnetic and solution studies

The interaction of Cu(II) with the following secondary N-substituted derivatives of di(2-picolyl)amine () are reported: N-cyclohexylmethyl-di(2-picolyl)amine (), N-benzyl-di(2-picolyl)amine (), N-(4-pyridylmethyl)-di(2-picolyl)amine (), N-(4-carboxymethylbenzyl)-di(2-picolyl)amine (), N-(9-anthracen-8-ylmethyl)-di(2-picolyl)amine (), 1,3-bis[di(2-picolyl)aminomethyl]benzene (), 1,4-bis[di(2-picolyl)aminomethyl]benzene () and 2,4,6-tris[di(2-picolyl)amino]triazine (). The solid complexes [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2), Cu()(ClO(4))(2), Cu()(2)(ClO(4))(2), [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O, Cu(2)()(ClO(4))(4), [Cu(2)()(Cl)(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were isolated and X-ray structures of [Cu()(micro-Cl)](2)(PF(6))(2), [Cu()(micro-Cl)](2)(PF(6))(2).0.5CH(2)Cl(2,) [Cu()(2)(ClO(4))(2)(H(2)O)].0.5H(2)O, [Cu(2)()Cl(4)] and [Cu(2)(+H)(micro-OCH(3))(2)(H(2)O)](ClO(4))(3).C(4)H(10)O were obtained. The series is characterised by a varied range of coordination geometries and lattice architectures which in the case of [Cu()(ClO(4))(2)(H(2)O)].0.5H(2)O includes a chain-like structure formed by unusual intermolecular pi-interactions between metal bound perchlorate anions and the aromatic rings of adjacent anthracenyl groups. Variable temperature magnetic susceptibility measurements have been performed for [Cu()(micro-Cl)](2)(PF(6))(2) and [Cu()(micro-Cl)](2)(PF(6))(2).0.5H(2)O over the range 2-300 K. Both compounds show Curie-Weiss behaviour, with the data indicating weak antiferromagnetic interaction between the pairs of copper ions in each complex. Liquid-liquid (H(2)O/CHCl(3)) extraction experiments involving and as extractants showed that, relative to the parent (unsubstituted) dipic ligand , substitution at the secondary amine site in each case resulted in an increase in extraction efficiency towards Cu(II) (as its perchlorate salt); at least in part, this increase may be attributed to the enhanced lipophilicities of the N-substituted derivatives.

Supramolecular control of fluorinated benzophenones in the crystalline state

Crystal structures of three fluorinated benzophenones were determined via single crystal X-ray diffraction. The occurrence of the C–F⋯H, F⋯F, C–F⋯πF interactions in these crystal structures indicates that a base limit of fluorine atoms in the molecule seems to be necessary for successful competition with the hydrogen type of interactions.

Conformational behaviour and first crystal structures of a calix[4]arene featuring a laterally positioned carboxylic acid function in unsolvated and solvent-complexed forms

A detailed conformational analysis of a rarely investigated type of compound, a laterally monosubstituted calix[4]arene (1, which has a carboxylic acid function in the lateral position), is reported. 2D solution NMR techniques at various temperatures and in different solvents have been used, showing interesting aggregation behaviour for the different conformers. The first illustrations of crystal structures of this compound type are given, including the unsolvated carboxylic calix[4]arene and two mixed solvent complexes containing EtOH–H2O and EtOH–THF, respectively. Isostructurality calculations have been carried out, allowing detailed comparison of the investigated structures, and an unusual conformational chirality isomerism of the calixarene molecule is demonstrated.

Macrocyclic and open-chain ligands with the redox switchable trithiadiazapentalene unit: synthesis, structures and complexation phenomena

Abstract This review focuses on synthesis, structure and binding properties of crown compounds and their open-chain analogues containing a trithiadiazapentalene building block. This heterocyclic unit favours in particular the complexation and solvent extraction of the soft transition metal ions Ag(I), Pd(II), Hg(II) and Au(III). The redox active system trithiadiazapentalene/trithiotriuret introduced into a crown ring allows the control of Ag(I) and Hg(II) phase transfer in solvent extraction experiments. Crystal structures of metal complexes with these pentaleno crown compounds show significant differences of both SS bond lengths of the trithiadiazapentalene unit and package arrangements in the cell.

Trimethoxybenzene- and trimethylbenzene-based compounds bearing imidazole, indole and pyrrole groups as recognition units: synthesis and evaluation of the binding properties towards carbohydrates

The aim of the study was to evaluate the potential of trimethoxybenzene- and trimethylbenzene-based compounds bearing imidazole or indole groups as recognition sites in the complexation of carbohydrates. Representatives of these compounds were prepared and their binding properties toward selected carbohydrates evaluated. The results of the binding studies were compared with those obtained for the prepared pyrrole bearing analogues and for the previously described triethylbenzene-based receptors.

Syntheses and crystal structures of cobalt and nickel complexes of 2,6-bis(hydroxymethyl)pyridine

2 : 1 (L : M) Complexes of 2,6-bis(hydroxymethyl)pyridine (dhmp) with different Co(II) salts [CoCl2·6H2O, Co(SCN)2, Co(NO3)2·6H2O, CoSO4·7H2O and Co(OTos)2·6H2O] and Ni(II) salts [NiCl2·6H2O, Ni(NO3)2·6H2O, NiSO4·7H2O and Ni(OTos)2·6H2O] have been prepared (1–9) and studied by infrared spectroscopy and X-ray crystallography. Influences on the distortion of the coordination polyhedron, the arrangement of the donor atoms and the packing structure of the complexes were investigated in terms of the different kinds of anions and cations. In the metal chloride Complexes 1 and 2, water of hydration was found, while in Complex 3 the counterion (SCN–) acts as a ligand. The crystal structures of all complexes, except 3, show N2O4 hexacoordinated metal ions; in 3 the coordination environment is N4O2. Complex 1 is another exception in containing cobalt(III) instead of cobalt(II) as for the other complexes with cobalt salts. Logically, in Complex 1, one of the dhmp ligands is mono-deprotonated. In the neutral Complexes 2 and 4–9, the basal planes of the octahedra are made up of O donors and N atoms occupy the axial positions. In 1 as well as in 3, two N and two O atoms form the base, but in 1 O, and in 3 N atoms are on the axis of the coordination sphere. Moreover, the nickel Complexes 2, 5, 7 and 9 are more symmetrical in structure than the cobalt Complexes 1, 4, 6 and 8, in accordance with the Jahn–Teller effect. Packing structures of the complexes show specific interactions based on strong and weak H-bonds that involve the counterions, hydroxy groups and aromatic units, leading to extended network structures.

Crystalline packings of diketoarylhydrazones controlled by a methyl for trifluoromethyl structural change

Three new hydrazone compounds having a p-iodoaryl and diketohydrazone molecular skeleton in common but feature a gradual replacement of the two methyl groups for trifluoromethyl terminal ones were prepared and comparatively studied with regard to their crystal structures. A quantum chemical calculation of the single trifluoromethyl modified compound was undertaken to decide on the hydrogen bonded ring site. While the molecular structures of the compounds remain rather unimpaired by the fluorine substitution, their crystalline packings are markedly affected, showing a distinct supramolecular control in the crystal lattices.

Synthesis and properties of new 9,10-anthraquinone derived compounds for molecular electronics

Fourteen new derivatives of 9,10-anthraquinone or 9,10-dimethoxyanthracene were designed, synthesised and characterised. Regarding the structure, the compounds are π-conjugated (cross and linear, respectively) and feature thiophene terminated side arms attached to five different positions of the anthraquinone or anthracene core. The synthesis of the compounds involves a cross-coupling procedure in the key reaction steps. Crystal structures of compounds 5 and 19 have been studied. The thiophene containing title compounds 1–5 can be reduced and oxidised by a two step redox process. The electrochemical parameters have been analysed by cyclic voltammetry (CV). Theoretical calculations in the framework of all-electron density functional theory (DFT) were used to investigate the electronic structure of the individual free molecules. Furthermore, calculations of the transport properties of model devices containing compounds 1–3 and respective reduced hydroquinone derivatives assembled at Au(111) electrodes were carried out to evaluate their potential for the application as redox-active switches.

Versatile Inclusion Behaviour of a Dinitrocalix[4]arene Having Two Ester Pendants – Preparation and X-ray Crystal Structures of Complexes

An upper-rim dinitro-substituted calix[4]arene possessing two lower-rim ethyl ester pendant groups (1) has been shown to form solid inclusion compounds with acetone (1:1) (1a), DMF (1:1) (1b), DMSO (1:1) (1c) and n-BuOH (2:1) (1d). X-ray crystal structures of the four complexes 1a–d are reported and comparatively discussed, including isostructurality calculations. Although the solid-state conformation of the dinitrocalix[4]arene moiety, stabilized by two intramolecular O–H…O bonds, is maintained in the four inclusion compounds, and all four co-crystals have similar unit cell dimensions and identical space group symmetries, only three of them (1a–c) are homostructural. Depending on the nature of the guest molecule, either the upper or the lower rim site of the calixarene is involved in the complexation, demonstrating either cavitate- or clathrate-type of supramolecular interactions, respectively. Moreover, due to the different guest recognition modes, the calixarene host in 1d is rotated through a non-crystallographic virtual rotation of 180° within the unit cell, in relation to the host molecules in each of the other three homostructural compounds 1a–c, thus giving rise to supramolecular morphotropism – to our knowledge the first case ever described.