Anionic complexes having vapochromic behavior are investigated: [K­(H2O)]­[M­(ppy)­(CN)2], [K­(H2O)]­[M­(bzq)­(CN)2], and [Li­(H2O) n ]­[Pt­(bzq)­(CN)2], where ppy = 2-phenylpyridinate, bzq = 7,8-benzoquinolate, and M = Pt­(II) or Pd­(II). These hydrated potassium/lithium salts exhibit a change in color upon being heated to 380 K, and they transform back into the original color upon absorption of water molecules from the environment. The challenging characterization of their structure in the vapochromic transition has been carried out by combining several experimental techniques, despite the availability of partially ordered and/or impure crystalline material. Room-temperature single-crystal and powder X-ray diffraction investigation revealed that [K­(H2O)]­[Pt­(ppy)­(CN)2] crystallizes in the Pbca space group and is isostructural to [K­(H2O)]­[Pd­(ppy)­(CN)2]. Variable-temperature powder X-ray diffraction allowed the color transition to be related to changes in the diffraction pattern and the decrease in sample crystallinity. Water loss, monitored by thermogravimetric analysis, occurs in two stages, well separated for potassium Pt compounds and strongly overlapped for potassium Pd compounds. The local structure of potassium compounds was monitored by in situ pair distribution function (PDF) measurements, which highlighted changes in the intermolecular distances due to a rearrangement of the crystal packing upon vapochromic transition. A reaction coordinate describing the structural changes was extracted for each compound by multivariate analysis applied to PDF data. It contributed to the study of the kinetics of the structural changes related to the vapochromic transition, revealing its dependence on the transition metal ion. Instead, the ligand influences the critical temperature, higher for ppy than for bzq, and the inclination of the molecular planes with respect to the unit cell planes, higher for bzq than for ppy. The first stage of water loss triggers a unit cell contraction, determined by the increase in the b axis length and the decrease in the a (for ppy) or c (for bzq) axis lengths. Consequent interplane distance variations and in-plane roto-translations weaken the π-stacking of the room-temperature structure and modify the distances and angles of Pt­(II)/Pd­(II) chains. The curve describing the intermolecular Pt­(II)/Pd­(II) distances as a function of temperature, validated by X-ray absorption spectroscopy, was found to reproduce the coordinate reaction determined by the model-free analysis.

Understanding of polymorphism of organic semiconducting materials is the key to structural control of their electrical and mechanical properties. Motivated by the ambipolar n-type charge transport and electroluminescence of thienopyrrolyldione end-capped oligothiophenes, here we studied the propensity of one representative to crystallize as different polymorphs which display distinctly different mechanically properties. The crystal structures of the two polymorphs (denoted “α” and “β”) of the material, 2,2′-(2,2′-thiophene-5,5′-diyl)­bis­(5-butyl-5H-thieno­[2,3-c]­pyrrole-4,6)-dione (C4-NT3N), were determined. In the α phase, the molecules interact strongly by π-stacking, forming columns which are bonded via C–HO and chalcogen bonds, and this packing is consistent with the elastic behavior observed with the crystals. Instead, the β phase has the molecules aligned along their core forming layers. While the molecules interact strongly within the layers, they are practically unbound between the layers. The presence of slip planes in this form explains the plastic deformation induced by applying a force perpendicular to the (001). The thermal behavior and the enantiotropic relationship of the polymorphs are reported.

A productive deracemization process based on a quaternary phase diagram study of a naphthamide derivative is reported. New racemic compounds of an atropisomeric naphthamide derivative have been discovered, and a quaternary phase diagram has been constructed that indicated that four solids are stable in a methanol/H2O solution. Based on the results of a heterogeneous equilibria study showing the stable domain of the conglomerate, a second‐order asymmetric transformation was achieved with up to 97 % ee. Furthermore, this methodology showcases the chiral separation of a stable racemic compound forming system and does not suffer from any of the typical limitations of deracemization, although application is still limited to conglomerate‐forming systems. We anticipate that this present study will serve as a fundamental model for the design of sophisticated chiral separation processes.

N,N’-dipentyl-3,4,9,10-perylendiimide (PDI-C5) is an organic semiconducting material which has been extensively investigated as model compound for its optoelectronic properties. It is known to be highly thermally stable, that it exhibits...

The efficient classification or prediction of crystal structures into a small number of families of related structures can be extremely important in the design of materials with specific packing and properties.

Here we report the full thermal characterization of an n-type NDI derivative semiconductor, NDI-C6. It has five polymorphs, Form ε is only obtained in thin films.

Invited for the cover of this issue is the group of Gérard Coquerel at Université de Rouen Normandie. The image depicts a pyramid‐like tetrahedron of the quaternary phase diagram showing where symmetry breaking can take place. Read the full text of the article at 10.1002/chem.201903338.

Phase diagrams play a critical role for tuning crystallization. This study explains the basics of phase diagrams starting from the ternary system to a quaternary system with and without fast racemization in the liquid phase. Experimentally, an atropisomeric naphthamide derivative in MeOH/H2O serves as an example. Deracemization is ensured by a second‐order asymmetric transformation up to 97% ee. Readers are encouraged to look at the animation (in the Supporting Information) detailing the construction of the degenerated quaternary system in a step‐by‐step manner. More information can be found in the Full Paper by G. Coquerel et al. on page 13890.