Solid-state photochemistry of the mixed crystals between benzoquinones and polymethylbenzenes

Nine mixed crystals combined 1,4-benzoquinone (1), 2,5-xyloquinone (2) and duroquinone (3) with durene (a), pentamethylbenzene (b) and hexamethylbezene (c) were prepared by a melting-resolidifying process and characterized by powder X-ray diffractometry, DSC and IR. Only the mixed crystal of 3 and a formed a 2:1 novel molecular crystal (4); other eight mixed crystals were simple polycrystalline mixtures of the two components. Irradiation of the molecular crystal 4 (3/a) and the mixed crystals 1/a, 1/b and 3/b caused intermolecular hydrogen abstraction to give hydroquinones and in some cases adducts. Product selectivities in the solid state were different from those in solution. Correlation between the crystal structure and the reactivity of 4 is discussed.     

Dutch resolution of racemic 4-hydroxy- and 4-fluorophenylglycine with mixtures of phenylglycine and (+)-10-camphorsulfonic acid

4-Hydroxyphenylglycine and 4-fluorophenylglycine can be resolved with (+)-10-camphorsulfonic acid only if dl- or d-(−)-phenylglycine is added. When using dl-phenylglycine this is co-resolved in this process. In this resolution process mixed crystals are formed of the (+)-10-camphorsulfonic acid salts of the d-(−)-enantiomers of phenylglycine and the para substituted phenylglycines. In the crystal lattice of the mixed salts approximately 25–30% of the d-(−)-phenylglycine molecules can be randomly replaced by d-(−)-para substituted phenylglycines, resulting in the desired resolution. The overall non-stoichiometric composition of the mixed crystals reflects to some extent the composition in solution. This behaviour is typical for solid solutions. The solid solution behaviour in this so called ‘Dutch resolution’ is proven by differential scanning calorimetry (DSC), X-ray crystal structure determination and powder diffraction.     

Discovery of a solid solution of enantiomers in a racemate-forming system by seeding

A racemic liquid of opposite enantiomers usually crystallizes as a racemic compound (racemate), rarely as a conglomerate, and even more rarely as a solid solution. We discovered a Type II solid solution (mixed crystal) of the enantiomers of the chiral drug tazofelone (TZF) by seeding its racemic liquid with enantiomerically pure crystals (enantiomorphs). Without seeding, the racemic liquid crystallized as a racemic compound. The crystal structure of this solid solution resembles that of the enantiomorph but has static disorder arising from the random substitution of enantiomers. This solid solution is a kinetic product of crystallization made possible by its faster growth rate compared to that of the competing racemate (by 4- to 40-fold between 80 and 146 degrees C). The free energy of the solid solution continuously varies with the enantiomeric composition between those of the conglomerate and the racemates. The existence of the TZF solid solution explains the absence of eutectic melting between crystals of different enantiomeric compositions. The ability of TZF to simultaneously form racemate and solid solution originates from its conformational flexibility. Similar solid solutions of enantiomers may exist in other systems and may be discovered in similar ways. The study demonstrates the use of cross-nucleation for discovering and engineering crystalline materials to optimize physical properties.     

Probing the Crystal Structure Landscape by Doping: 4‐Bromo, 4‐Chloro,and 4‐Methylcinnamic Acids

Accessing the data points in the crystal structure landscape of a molecule is a challenging task, either experimentally or computationally. We have charted the crystal structure landscape of 4‐bromocinnamic acid (4BCA) experimentally and computationally: experimental doping is achieved with 4‐methylcinnamic acid (4MCA) to obtain new crystal structures; computational doping is performed with 4‐chlorocinnamic acid (4CCA) as a model system, because of the difficulties associated in parameterizing the Br atom. The landscape of 4CCA is explored experimentally in turn, also by doping it with 4MCA, and is found to bear a close resemblance to the landscape of 4BCA, justifying the ready miscibility of these two halogenated cinnamic acids to form solid solutions without any change in crystal structure. In effect, 4MCA, 4CCA and 4BCA form a commutable group of crystal structures, which may be realized experimentally or computationally, and constitute the landscape. Unlike the results obtained by Kitaigorodskii, all but two of the multiple solid solutions obtained in the methyl‐doping experiments take structures that are different from the hitherto observed crystal forms of the parent compounds. Even granted that the latter might be inherently polymorphic, this unusual observation provokes the suggestion that solid solution formation may be used to probe the crystal structure landscape. The influence of π⋅⋅⋅π interactions, weak hydrogen bonds and halogen bonds in directing the formation of these new structures is also seen.     

Probing the Crystal Structure Landscape by Doping: 4‐Bromo, 4‐Chloro,and 4‐Methylcinnamic Acids

Accessing the data points in the crystal structure landscape of a molecule is a challenging task, either experimentally or computationally. We have charted the crystal structure landscape of 4‐bromocinnamic acid (4BCA) experimentally and computationally: experimental doping is achieved with 4‐methylcinnamic acid (4MCA) to obtain new crystal structures; computational doping is performed with 4‐chlorocinnamic acid (4CCA) as a model system, because of the difficulties associated in parameterizing the Br atom. The landscape of 4CCA is explored experimentally in turn, also by doping it with 4MCA, and is found to bear a close resemblance to the landscape of 4BCA, justifying the ready miscibility of these two halogenated cinnamic acids to form solid solutions without any change in crystal structure. In effect, 4MCA, 4CCA and 4BCA form a commutable group of crystal structures, which may be realized experimentally or computationally, and constitute the landscape. Unlike the results obtained by Kitaigorodskii, all but two of the multiple solid solutions obtained in the methyl‐doping experiments take structures that are different from the hitherto observed crystal forms of the parent compounds. Even granted that the latter might be inherently polymorphic, this unusual observation provokes the suggestion that solid solution formation may be used to probe the crystal structure landscape. The influence of π???π interactions, weak hydrogen bonds and halogen bonds in directing the formation of these new structures is also seen.     

碘酸盐的晶体结构与热力学性质——(Ⅰ)碘酸盐的晶体结构特点

本文根据作者等人的实验结果并结合文献报导的数据,综述了碘酸盐及其复盐的晶体结构特点和分类。对α-LiIO_3,Li_2H(IO_3)3,Mg(IO_3)_2,Mg(IO_3)_2-LiIO_3固溶体,Zn(IO_3)_2等晶体结构变迁的情况进行了分析。阐述了由于空位数量和分布的不同,以及阳离子性质(电价、离子极化能力和离子半径等)的不同,晶格场发生变化,引起了IO_3~-在不同方向和不同程度的移动或转动,因而有可能在不同方向上形成不同程度的各种畸变型结构和超结构。     

What is syncrystallization? States of the pH indicator methyl red in crystals of phthalic acid

The concept of syncrystallization was reinvestigated by focusing on phthalic acid (PA) grown with methyl red (MR). Crystals are alternately red and yellow in adjacent growth sectors. X-ray structures of MR and its cocrystals, revealing MR in the neutral, zwitterionic, and protonated states, as well as measurements of linear birefringence and linear dichroism of mixed crystals, were used to investigate mechanisms of PA coloring. These experiments were complemented by force field calculations of the lowest energy stable surfaces of expressed facets and energies of MR on and in crystals, as well as molecular orbital calculations of MR. Two MR species were detected in PA having distinct energies, polarizations, and face selectivities. Assignments of structures to these MRs, previously thought to be neutral and protonated, required a nuanced analysis of hydrogen bonds. The essential difference between yellow and red species is whether the MR carboxylic acid proton is inter- or intramolecularly hydrogen bound. Inferences about mixed crystal structure drawn from an examination of cocrystals of PA and MR are inconsistent with polarization spectroscopy signaling caution when using stoichiometric compounds as models of dilute solid solutions. Upon heating mixed crystals, linear dichroism diminishes and oriented, elongated pools of MR separate and pass through the bulk in directions perpendicular to the direction of elongation. These batonnets subsequently crystallize leaving macroscopic oriented crystals of a MR-rich phase within PA. No evidence was found for the simultaneous crystallization of MR and PA; however, the MR reorientation on heating as well as the separation and recrystallization of a MR-rich phase are distinct processes that could be embraced by the literal meaning of syncrystallization.     

A novel quartz crystal microbalance gas sensor based on porous film coatings. A high sensitivity porous poly(methylmethacrylate) water vapor sensor

We describe a novel and generally applicable approach for creating voids in films deposited on the surface of solid substrates. Such films are advantageous when a quartz crystal microbalance (QCM) is the basis of a sensor. We show that films with large void volumes produce more sensitive sensors than with the original film. Poly(methylmethacrylate) (PMMA) was used as the polymer layer deposited on a quartz crystal microbalance (QCM) to demonstrate our technique for the model system of water vapor analysis in flowing nitrogen gas. A film of pure PMMA on a QCM is a sensor for water vapor in a gas phase. A more sensitive sensor was created by dip coating QCM crystals into solutions containing mixtures of PMMA and poly(d,l-lactide) (PDLL) and then evaporating the solution films on the QCM crystals to form mixed polymer films of varying PDLL content. The PDLL was then removed from the mixed polymer films by exposure to a NaOH solution to form pure PMMA films having various void volumes. A leached PMMA film that originally contained 50% by weight PDLL had a 3.7 times larger QCM sensitivity for water vapor than a pure PMMA film.     

Physical vapor transport and crystal growth of GeSexTe1−x solid solutions

Physical vapor transport studies of GeSe_xTe_1–x (x = 0.1, 0.2, 0.3, and 0.4) solid solutions demonstrated, that individual, large single crystals of these materials can be grown in closed ampoules. A compositional analysis of the grown crystals revealed, that the mass transport (crystal growth) process under steady-state conditions is pseudo-congruent and controlled by diffusion processes in the source material. From these experiments, the degree of nonstoichiometry (Ge-vacancy concentrations) of GeSe_xTe_1–x single crystals could be estimated. The effects of the cubic to rhombohedral phase transformation during cooling on the microstructure and morphology of the grown mixed crystals are observed. This work provides the basis for subsequent defect studies and electrical measurements on these crystals.     

Crystal engineering on industrial diaryl pigments using lattice energy minimizations and X-ray powder diffraction

Diaryl azo pigments play an important role as yellow pigments for printing inks, with an annual pigment production of more than 50,000 t. The crystal structures of Pigment Yellow 12 (PY12), Pigment Yellow 13 (PY13), Pigment Yellow 14 (PY14), and Pigment Yellow 83 (PY83) were determined from X-ray powder data using lattice energy minimizations and subsequent Rietveld refinements. Details of the lattice energy minimization procedure and of the development of a torsion potential for the biphenyl fragment are given. The Rietveld refinements were carried out using rigid bodies, or constraints. It was also possible to refine all atomic positions individually without any constraint or restraint, even for PY12 having 44 independent non-hydrogen atoms per asymmetric unit. For PY14 (23 independent non-hydrogen atoms), additionally all atomic isotropic temperature factors could be refined individually. PY12 crystallized in a herringbone arrangement with twisted biaryl fragments. PY13 and PY14 formed a layer structure of planar molecules. PY83 showed a herringbone structure with planar molecules. According to quantum mechanical calculations, the twisting of the biaryl fragment results in a lower color strength of the pigments, whereas changes in the substitution pattern have almost no influence on the color strength of a single molecule. Hence, the experimentally observed lower color strength of PY12 in comparison with that of PY13 and PY83 can be explained as a pure packing effect. Further lattice energy calculations explained that the four investigated pigments crystallize in three different structures because these structures are the energetically most favorable ones for each compound. For example, for PY13, PY14, or PY83, a PY12-analogous crystal structure would lead to considerably poorer lattice energies and lower densities. In contrast, lattice energy calculations revealed that PY12 could adopt a PY13-type structure with only slightly poorer energy. This structure was found experimentally as a metastable gamma phase of PY12. Calculations on mixed crystals (solid solutions) showed that mixed crystals of PY12 and PY13 should adopt the PY13 structure with planar molecules, resulting in high color strengths; this was proven experimentally (Pigment Yellow 188). Similarly, the high color strength of mixed crystals consisting of PY13 and PY14 (Pigment Yellow 174), and PY13/PY83 (Pigment Yellow 176) is explained by the crystal structures.     

Contribution à l'étude du système quaternaire KCl?RbCl?CsCl?H2O: II. L'isotherme de 25°C

The experimental study at 25°C of the system KCl? RbCl? CsCl? H₂O has shown the existence of a new type of quaternary system with formation of mixed crystals. — The solubility diagram is characterized by the presence of one univariant line and one binary miscibility gap. Two types of solid solutions are present: ( K, Rb , Cs) Cl and (K, Rb, Cs ) Cl; the incorporation in the latter is small.     

Influence of solid solution formation on polarity: molecular modeling investigation of the system 4-chloro-4'-nitrostilbene/4,4'-dinitrostilbene

Growth-induced polarity formation in solid solutions composed of dipolar 4-chloro-4'-nitrostilbene molecules and nonpolar 4,4'-dinitrostilbene molecules was investigated by means of two molecular modeling procedures. Calculation of the mixing energy in the bulk structures predicted solid solution formation within the whole composition range. Computation of the interaction energies present at growing surfaces allowed the distribution coefficient as well as the fraction of dipoles in either the up or down orientation to be calculated by a mean-field model. Miscibility and polarity were found to vary for the faces (hkl) investigated, leading to crystals composed of sectors with different compositions and polarities. The present study highlights the fact that a solid solution crystal may not be a homogeneous entity and that surface effects arising during slow growth can have an impact on solid state properties.     

Photochromism of mixed crystals containing bisthienyl-, bisthiazolyl-, and bisoxazolylethene derivatives

Single crystals composed of two or three different kinds of diarylethenes, having similar geometrical structures but different colors in the closed-ring isomers, 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a), 1,2-bis(5-methyl-2-phenyl- 4-thiazolyl)perfluorocyclopentene (2a), and 1,2-bis(5-methyl-2-phenyl-4-oxazolyl)perfluorocyclopentene (3a) have been prepared in an attempt to form single crystals which exhibit different colors, depending on illumination wavelengths. When 1a and 2a are mixed in ethanol and the content of 2a in the feed is higher than that of 1a, only a needle-shaped crystal is obtained. The crystal shape is similar to that of 2a. On the other hand, high content of 1a in the feed leads to formation of a block-shaped crystal, of which the shape is similar to that of 1a. At a feed ratio of 1:1 for 1a and 2a, two types of crystals such as needle- and block-shapes are obtained from the same batch. Mixed crystals composed of three kinds of derivatives 1a/2a/3a have also been prepared. A crystal composed of the three derivatives in the molar ratio of 32 (1a):53 (2a):15 (3a) was obtained. X-ray analysis proved that 1a and 3a are packed in the crystal lattice of 2a. The mixed crystal 1a/2a/3a changed color from colorless to yellow, red, and blue upon irradiation with light of appropriate wavelengths.     

Asymmetric intramolecular cyclobutane formation via photochemical reaction of N,N-diallyl-2-quinolone-3-carboxamide using a chiral crystalline environment

Crystal structures and photochemical reactions of three N,N-diallyl-2-quinolone-3-carboxamides were investigated. One quinolonecarboxamide afforded chiral crystals of a P2(1) crystal system by spontaneous crystallization, and the molecular chirality in the crystal was effectively transferred to cyclobutane in 96% ee by an intramolecular 2 + 2 photocycloaddition reaction in the solid state.     

H2Pc-VOPc二元体系的制备和表征

八十年代,国外Canon,IBM,HP,Ricoh,Xerox等公司开发出由计算机控制、数字扫描、激光成像的高分辨激光打印机,并逐渐占领市场。这种激光打印机具有印刷质量高、寿命长、印刷速度快、版面可任意调制、噪音小等特点。     

Synthesis and Comparative Analysis of Molecular and Supramolecular Structures of 4,8-Disubstituted 1,5-Dichloro-2,6-dioxotricyclo[5.1.0.0 3,5]octanes

A series of 4,8-disubstituted 1,5-dichloro-2,6-dioxotricyclo-[5.1.0.0^3,5]octanes, synthesized by various methods, were studied by X-ray single crystal diffraction. The conformation (syn/anti) of the molecules does not depend on the method of preparation and nature of substituents. All the compounds crystallize in centrosymmetric space groups with half of the molecules in the asymmetric part of the unit cell. The main influence which the substituents render is on the packing of molecules in crystals and on the types of intermolecular interactions and supramolecular structures.     

I NQR and spectroscopic investigation of impurity-doped and mixed lithium iodate Li1−xHxIO3 crystals

The ¹²⁷I NQR, IR absorption and Raman spectra of impurity-doped and mixed lithium iodate Li_1−xH_xIO₃ crystals grown from water solutions with different LiIO₃/HIO₃ ratios were investigated depending on the content of the impurity hydrogen x. The NQR results suggested that, at small concentration of doping iodic acid x<0.22, the lattice dynamics of the crystal grown from water solution changes significantly though the crystal retains hexagonal symmetry. Spectroscopic studies are compatible with average hexagonal symmetry of the grown doped crystals. From the results of Raman studies at room temperature and 100 K, the concentration range of hydrogen dopant 0.22<x<0.36 was found where disordered solid solution crystals Li_1−xH_xIO₃ are formed.     

Identification of Molecular Crystals Capable of Undergoing an Acyl‐Transfer Reaction Based on Intermolecular Interactions in the Crystal Lattice

Investigation of the intermolecular acyl‐transfer reactivity in molecular crystals of myo‐inositol orthoester derivatives and its correlation with crystal structures enabled us to identify the essential parameters to support efficient acyl‐transfer reactions in crystals: 1) the favorable geometry of the nucleophile (? OH) and the electrophile (C?O) and 2) the molecular assembly, reinforced by C? H???π interactions, which supports a domino‐type reaction in crystals. These parameters were used to identify another reactive crystal through a data‐mining study of the Cambridge Structural Database. A 2:1 co‐crystal of 2,3‐naphthalene diol and its di‐p‐methylbenzoate was selected as a potentially reactive crystal and its reactivity was tested by heating the co‐crystals in the presence of solid sodium carbonate. A facile intermolecular p‐toluoyl group transfer was observed as predicted. The successful identification of reactive crystals opens up a new method for the detection of molecular crystals capable of exhibiting acyl‐transfer reactivity.