X-ray crystallographic studies were carried out for seven conglomerates, seventeen racemic compounds, and four enantiomerically pure salts of chiral primary amines with achiral monocarboxylic acids. The crystal structures of the conglomerate salts revealed that these crystals can be regarded as being an assembly of a characteristic columnar hydrogen-bond network in which the ammonium cations and the carboxylate anions are aligned around a 2-fold screw axis (21-column). On the other hand, the crystal structures of the racemic-compound salts could be broadly classified into two types. One type is a crystal consisting of 21-columns; the other type is a crystal consisting of a different type of columnar hydrogen-bond network in which the ammonium cations and the carboxylate anions are related by inversion centers (i-column). Our results suggest that both the formation and the assembly of 21-columns are essential in the formation of conglomerates from these salts, and that the difference in the packing of 21-columns between conglomerate salts and racemic-compound salts is governed by van der Waals interaction between the 21-columns.

The crystal structures of the diastereomeric salts of 1-arylethylamines with mandelic acid or p-methoxymandelic acid have been studied. This revealed that there was correlation between the efficiencies of the optical resolutions of the amines with the resolving reagents and the crystal structures of the salts. A characteristic hydrogen-bond layer, consisting of stable columnar structures and having a planar boundary surface, was found to be common to the less-soluble salt crystals; these crystals were considered to be stabilised from the viewpoint of both their hydrogen-bonding and van der Waals interactions. In contrast, in the corresponding more-soluble salts and in those diastereomeric salts which could not be separated by crystallisation, no such particularly stabilised crystal structure was formed; there only existed either columnar structures or planar boundary surfaces in these crystals. These results strongly suggest that for successful resolution it is necessary to realise a hydrogen-bond layer, consisting of stable columns and having planar boundary surfaces, in the crystals of one of the pair of diastereomeric salts. In order to achieve such a crystal structure, complementarity in molecular length between a target racemate and a resolving reagent must be considered the most important and fundamental factor.

Here we show the first observation of an unusual intermolecular magnetic interaction in the liquid-crystalline (LC) state of an all-organic radical compound at 73 C on water; the magnetic interaction actually allows the LC droplet on water to be attracted by a weak permanent magnet, whereas the crystalline phase did not respond to the magnet.

Paramagnetic, calamitic, chiral liquid crystals (LCs) have attracted great interest due to their following characteristics: i) unwinding of the helical superstructure of chiral smectic C (SmC*) and cholesteric (N*) phases upon the application of weak magnetic fields; [1] ii) expected orientation control of ferroelectric liquid crystals (FLCs) by the application of weak magnetic fields, making use of the magnetoelectric effect, i.e., the influence of the internal electric field on the magnetic properties and vice versa; [2][3][4] and iii) the direct observation and characterization of microscopic molecular movement in FLCs (and SmC* phases), as well as in N* phases, by electron paramagnetic resonance (EPR) spectroscopy. We have been particularly interested in the observation of magnetoelectric interactions in paramagnetic FLCs, which may lead to an increase in the molecular paramagnetic susceptibility anisotropy (Dv para ), and thereby may enable the orientation control of FLCs by weak magnetic fields. [2][3][4] Thus far, several ferroelectric and paramagnetic chiral metallomesogens (SmC*) have been prepared. However, the intrinsic high viscosity of these molecules, brought about by the ligand-coordinated metal-complex structure, results in a slow response or no response to applied electric fields, and seems to render their orientation control by weak magnetic fields difficult, even in bulk mesophases. [5,6] With a view to obtaining a series of paramagnetic, all-organic, calamitic chiral mesogens that exhibit stable LC phases with low viscosity, we have successfully prepared prototype LC materials 1a-d containing a chiral five-membered cyclic nitroxide unit within the rigid core (Scheme 1). These molecules show a N or N* phase over a wide temperature range between 60 and 100°C. [7] It is noteworthy that the orientation of the N phases of 1a-d can be affected by a very weak magnetic field of 0.05 T or less during both the heating and cooling processes. Here, we report that enantiomerically enriched compounds 2a-e with longer side chains show desired SmC* (and N*) phases which are thermally stable over a wide temperature range between 50 and 90°C (Scheme 1). The spontaneous polarization and the optical response time of bistable switching upon the application of an electric field have been measured and evaluated for these chiral LC materials, along with their tilt angle. The C 1 -symmetric (2S,5S)-2,5-dimethyl-2-alkoxyphenyl-5-[4-(4-alkoxybenzenecarbonyloxy)phenyl]pyrrolidine-1-oxy derivatives 2a-e exhibit LC phases; (2S,5S)-2a shows the monotropic SmC* phase upon cooling from the isotropic (I) phase, (2S,5S)-2b,c show enantiotropic SmC* and N* phases, and (2S,5S)-2d,e only show an enantiotropic SmC* phase ( Fig. 1 and Table 1). Upon observation by hot-stage polarizing microscopy, the SmC* phases typically show a Schlieren texture with fourfold brushes under homeotropic boundary conditions, and a broken fan-shaped texture in a thin sandwich cell (4 lm thickness) under homogeneous planar boundary conditions (Figs...