Synthon robustness in saccharinate salts of some substituted pyridines

Synthon robustness or lack of structural interference is a sought after goal in crystal engineering. The crystal structures of saccharinate salts 1-6 show the robustness of the newly identified hydrogen bonded synthons I and III

Isostructurality in the Guest Free Forms and in the Clathrates of 1,3,5-Triethyl-2,4,6-tris(4-halophenoxy)methylbenzenes

Crystal structures of the guest free forms and some solvates of 1,3,5-triethyl-2,4,6-tris­(4-halophenoxy)­methylbenzenes (1X, X = I, Br, Cl, F) have been studied. The guest free forms of 1I, 1Br, and 1Cl are isostructural, but the crystal structure of 1F is different from the heavier halogen analogues. An entirely different crystal structure of the Me analogue, which is known to be isosteric to the corresponding bromo compound, shows the importance of the electronic factors of the halogens in this series of structures. 1I and 1Br form four types of architectures in their solvates depending upon the inter-halogen interaction geometries. All these solvates are two dimensionally isostructural to the guest free form. 1Cl forms three different types of frameworks in its solvates, and the ethylacetate solvates of the 1I, 1Br, and 1Cl are isostructural. 1F forms only one type of solvate which is isostructural to the corresponding 1Cl solvate

Uniaxial Negative Thermal Expansion in an Organic Complex Caused by Sliding of Layers

Generally, materials undergo thermal expansion along all directions upon heating. The very few materials that show the opposite trend along one or more of their crystallographic axes have plenty of applications. Herein we report a negative thermal expansion along one axis in the crystal structure of a 1:1:1 organic complex of 1,3,5-benzenetricarboxylic acid (BTA), 2,6-dimethylaniline (DMA), and water molecules. The unusual thermal expansion in this structure is caused by sliding of layers, which is unprecedented

Using halogen···halogen interactions to direct noncentrosymmetric crystal packing in dipolar organic molecules

Halogen atoms Cl, Br, and I steer crystallization of 2-halo-3-hydroxypyridine 1, pyridine-N-oxides 2, and 2-halo-3-aminopyridine 3 in noncentrosymmetric space groups efficient for nonlinear optical materials. Whereas the strong hydrogen-bond chains are aligned antiparallel, the L- or V-geometry of weak interhalogen interaction steers polar alignment in the solid state, even for high dipole moment (μ) halogenated N-oxides 2 (μ > 5.0 D). Six out of seven structures evaluated crystallize in polar/chiral space groups due to interhalogen interactions compared to the one in six probability of noncentrosymmetric packing for achiral molecules

Polymorphism through Desolvation of the Solvates of a van der Waals Host

2,4,6-Triethyl-1,3,5-tris­(phenoxymethyl)­benzene (<b>1H</b>), a van der Waals host molecule, forms 10 solvates with 1,4-dioxane (DXN), <i>p</i>-xylene (PXL), pyridine (PYD), chloroform (CLF), tetrachloromethane (TCM), tetrahydrofuran (THF), benzene (BEN), and ethyl acetate (EAC), which exhibit conversion to three different phases upon desolvation. Crystal structures of two of the guest-free phases were identified by producing single crystals of <b>1H</b> from acetonitrile and ethyl acetate solutions. These two forms are converted to the third form upon heating. The third phase is also obtained after desolvation of the 1,4-dioxane solvate, but no single crystals corresponding to this phase could be isolated. Crystallization from THF and TCM produced two different solvates concomitantly in each case, whereas the EAC solution of <b>1H</b> concomitantly produced the guest-free form II as well as minor quantities of a solvate. One of the THF solvates is isostructural to the CLF solvate, and the other THF solvate is isostructural to one of the TCM solvates

Uniaxial Negative Thermal Expansion in an Organic Complex Caused by Sliding of Layers

Generally, materials undergo thermal expansion along all directions upon heating. The very few materials that show the opposite trend along one or more of their crystallographic axes have plenty of applications. Herein we report a negative thermal expansion along one axis in the crystal structure of a 1:1:1 organic complex of 1,3,5-benzenetricarboxylic acid (BTA), 2,6-dimethylaniline (DMA), and water molecules. The unusual thermal expansion in this structure is caused by sliding of layers, which is unprecedented

Isostructurality in the Guest Free Forms and in the Clathrates of 1,3,5-Triethyl-2,4,6-tris(4-halophenoxy)methylbenzenes

Crystal structures of the guest free forms and some solvates of 1,3,5-triethyl-2,4,6-tris­(4-halophenoxy)­methylbenzenes (1X, X = I, Br, Cl, F) have been studied. The guest free forms of 1I, 1Br, and 1Cl are isostructural, but the crystal structure of 1F is different from the heavier halogen analogues. An entirely different crystal structure of the Me analogue, which is known to be isosteric to the corresponding bromo compound, shows the importance of the electronic factors of the halogens in this series of structures. 1I and 1Br form four types of architectures in their solvates depending upon the inter-halogen interaction geometries. All these solvates are two dimensionally isostructural to the guest free form. 1Cl forms three different types of frameworks in its solvates, and the ethylacetate solvates of the 1I, 1Br, and 1Cl are isostructural. 1F forms only one type of solvate which is isostructural to the corresponding 1Cl solvate

Shape and Geometry Corrected Statistical Analysis on Halogen···Halogen Interactions

Two new corrections, namely, area and shape corrections, have been introduced in the statistical analysis of halogen···halogen interactions. Before geometrical corrections, all the halogens show a clear preference for type 1 contact, but after the geometrical corrections the type 2 interaction has taken over type 1 contact for Cl, Br, and I for the Δθ ≠ 0 contacts. In the case of iodine, the population with type 1 contact becomes negligible and the directionality of the contacts increases dramatically after the area along with shape corrections. Without geometrical corrections, F shows a very high preference for lower Δθ, but after the correction it does not show much preference for any angle. Therefore, we anticipate that these corrections would bring a significant change in the concept about the halogen···halogen interactions

Interhalogen Interactions in the Light of Geometrical Correction

Geometrical correction, used in statistical analysis on interhalogen interactions, provides a new insight into the nature of halogens. Statistical analysis without geometrical correction shows preference for Type 1 interactions over Type 2 interactions, but the trend is reversed after geometrical correction. It is known that polarizability in F is very small and hence should not show much preference for any particular angle in C–F···F–C interactions. Statistical analysis without geometrical correction could not prove it, but it is demonstrated here after geometrical correction. It is shown here that population after geometrical corrections vs θ1 and θ2 plots provides more meaningful information than the usually practiced population vs Δθ plot. The geometrical corrections proposed here are more general and can be used in several other interactions to eliminate geometrical bias from the statistical data in the process of extracting true chemical information from statistical analysis

Thermal Expansion Study as a Tool to Understand the Bending Mechanism in a Crystal

Here for the first time thermal expansion study has been explored to understand the bending mechanism in crystals. Dimorphic 4-chlorobenzonitrile has been chosen to demonstrate it. We have postulated that some of the structural features of the concave and convex sides of the bent crystal would resemble thermally compressed and expanded crystal structures respectively in the expansion–contraction bending mechanism. In this mechanism it has been shown that the strain is proportional to the thickness of the crystal and inversely proportional to the radius of the curvature of the bent crystal. On the other hand, in the case of slip plane mechanism, the amount of sliding of a layer with respect to its neighbor at the two terminals of the crystal is proportional to the arc angle of the bent crystal and the distance between the two consecutive slip planes