Strategies towards chiral molecular conductors

Introduction of chirality into conducting systems is a topic of much current interest as it allows the preparation of multifunctional materials in which the chirality may modulate the structural disorder or expresses its influence through the electrical magneto-chiral anisotropy effect. The access to various chiral electroactive precursors for molecular conductors is therefore of paramount importance. Different families of chiral tetrathiafulvalene (TTF) derivatives are reviewed together with the corresponding synthetic strategies. Systems based on stereogenic carbon or sulfur atoms, axial and supramolecular chirality have been developed. In other systems the use of achiral TTFs with chiral anions have provided molecular conductors, although in most of them to date the anion is present in racemic form. Starting from some of these precursors several chiral conductors have been prepared and in two cases, involving either chiral TTF-oxazolines salts or BEDT-TTF salts with metal-oxalate anions and chiral solvent molecules, differences between the conductivity of the racemic and enantiopure forms have been found, as a consequence of the structural disorder in the solid state. Further developments in this field are expected to be directed especially towards helical architectures, possibly based on supramolecular chirality, and systems combining conductivity, magnetism and chirality in both organic and inorganic lattices

Substituted BEDT-TTF derivatives: synthesis, chirality, properties and potential applications

The increasing availability of functionalized BEDT-TTF derivatives in both racemic and enantiopure forms opens up great opportunities for preparing multifunctional materials and chiral conducting systems in the form of crystals, thin films and polymers. Functionalities such as amino and carboxyl will allow attachment to other molecular systems, while intermolecular interactions between substituents, e.g. hydrogen bonding and halegon- - - halegon interactions, provides additional tools for designing solid state radical cation structures. In this review the syntheses of substituted derivatives of BEDT-TTF and closely related donors are surveyed, along with the structures and properties of the radical cation salts so far prepared, as a stimulus for future application of these versatile and attractive molecules. Particular attention is paid to the preparation of single enantiomers, and to the stereochemical consequences of the synthetic procedures

A competition between N---O and C---O through space interactions in the crystal structures of 3,3'-dinitro-2,2'-bipyridine N-oxides and N,N'-dioxides

The crystal structures of a series of 3,3’-dinitro-2,2’-bipyridine N-oxides and N,N’-dioxides consistently show 1,5 interactions between nitro oxygen atoms and aromatic carbon atoms ((ON)O---C: 2.623(2)-2.839(2) Å) while there are also 1,6 interactions between N-oxide oxygen atoms and nitro nitrogen atoms in most cases (O---N(O2): 2.737(2)-2.874(3) Å). The O---C interactions appears to be a common feature in ortho-nitro-biphenyl systems, and there is some evidence that the effect is cooperative when there are ortho nitro groups on both rings. The O---N interactions are considerably longer than the corresponding 1,5 N---O interaction measured here in 8-nitroquinoline-1-oxide (O---N(O2): 2.5418(17) Å), which in turn is longer than the corresponding N---O interaction in the corresponding 8-diazonium-1-oxide analogue

1,6-Interactions between dimethylamino and aldehyde groups in two biphenyl derivatives

The title compounds, 2-(dimethylamino)biphenyl-2'-carboxaldehyde, C15H15NO, and 2-(dimethylamino)biphenyl-2',6'-dicarboxaldehyde, C16H15NO2, show similar 1,6-interactions [N...C=O 2.929 (3) to 3.029 (3) Å] between the dimethylamino and aldehyde groups located in the ortho positions of the two rings, which lie at 58.1 (1)-62.4 (1)° to each other

Structural studies of peri-interactions and bond formation between electron-rich atomic centres and N-phenylcarboxamides or nitroalkenyl groups

Structural studies of peri-interactions with dimethylamino groups in naphthalene systems indicate that the N-phenylcarboxamide group has a through-space electron attracting power closer to that of a carboxylic ester than a N,N-dialkylcarboxamide, while 2-nitroalkenyl groups have a lower through-space electron attracting power. However, addition of a benzoyl group to the 2-position of the nitroethenyl group leads to cyclisation to give a zwitterion, in which the carbanion is stabilised by full conjugation with the nitro group and partial conjugation with the carbonyl group. An interesting case where a steric interaction overrides an electrophile/nucleophile attraction is also described. The limitations to the interpretation of short contact distances from crystallographic measurements are discussed

Activation and regioselectivity of five-membered cyclic thionocarbamates to nucleophilic attack

The cyclic thionocarbamate of alaninol undergoes nucleophilic attack by sulfur nucleophiles at 5-C to give 1-thiopropyl-2-amine derivatives when derivatised on nitrogen with a Boc group. Iodide under microwave conditions causes a rearrangement to the isomeric thiazolidinone, while "hard" nucleophiles react at the thione group to yield a variety of product types by subsequent C–N or C–O cleavage. X-ray crystallography studies showed that the N-Boc group reduces delocalisation of electron density from nitrogen into the thione group, and thus promotes activation of the ring to nucleophilic attack

Sparse Image Reconstruction on the Sphere: Analysis and Synthesis

We develop techniques to solve ill-posed inverse problems on the sphere by sparse regularization, exploiting sparsity in both axisymmetric and directional scale-discretized wavelet space. Denoising, in painting, and deconvolution problems and combinations thereof, are considered as examples. Inverse problems are solved in both the analysis and synthesis settings, with a number of different sampling schemes. The most effective approach is that with the most restricted solution-space, which depends on the interplay between the adopted sampling scheme, the selection of the analysis/synthesis problem, and any weighting of the ℓ1 norm appearing in the regularization problem. More efficient sampling schemes on the sphere improve reconstruction fidelity by restricting the solution-space and also by improving sparsity in wavelet space. We apply the technique to denoise Planck 353-GHz observations, improving the ability to extract the structure of Galactic dust emission, which is important for studying Galactic magnetism

Two modes of peri-interaction between an aldehyde group and a carboxylate anion in naphthalaldehydate salts

Crystal structures of the salts of 1,8-naphthalaldehydic acid (8-formyl-1-naphthoic acid) show one of two types of interaction between the functional groups. In the more commonly observed case, a carboxylate oxygen lies close to the aldehyde carbonyl carbon atom (O⋯C: 2.445–2.630 Å) and makes an n–pi* interaction. However, in two other cases the carboxylate group has rotated so that the aldehyde now directs its hydrogen atom at the face of the carboxylate group and forms a surprisingly short contact with the carbon atom (H⋯C: 2.29 and 2.42 Å). This interaction is likely to be electrostatic in nature