Impact of Torsional and Conformational Flexibility on Pedal Motion and Thermal Expansion in Pyridyl Bisimine Cocrystals

Abstract

The impact of intermolecular interactions and molecular motion on solid-state properties is an active field of interest for chemists and materials scientists. For example, cocrystallization has been shown to modify and/or enhance the solid-state behaviors of a molecule when compared to the single-component solid. Here, we describe a series of cocrystals containing bis(pyridin-4-ylmethylene)benzene-1,4-diamine (BPDI) and ditopic or tritopic hydrogen-bond-donor molecules that are conformationally flexible. The components in all the cocrystals self-assemble through hydroxyl-pyridine heterosynthons to afford one-dimensional chains due to the conformations of the donor molecules. BPDI is torsionally flexible, and in cocrystals with ditopic hydrogen-bond donors, the molecule is almost planar, whereas in cocrystals with tritopic hydrogen-bond donors, BPDI is significantly twisted. This twisting in BPDI affects crystal packing and affords higher thermal expansion coefficients. Cocrystallization of BPDI with resveratrol, another torsionally flexible molecule, induces molecular pedal motion in BPDI and results in larger expansion behavior in the cocrystal.

Salt Cocrystal and Salt of Marbofloxacin with Butenedioic Acid: Impact of cis–trans Isomerism of Coformer on the Conformation and Properties of Marbofloxacin

“…However, the regulation of API physical and chemical properties by pharmaceutical cocrystals/salts is not always better, and there are some cocrystals for which the solubility, dissolution, or permeability is reduced or remains unchanged. − The same is true for salt cocrystals, a pharmaceutical cocrystalline form that differs from pharmaceutical cocrystals (nonionic supramolecules) and salts (anion and cation) by having a salt structure with a neutral molecule. − As often happens, it is hard to predict the changes in the arrangement and physicochemical properties of pharmaceutical molecules in cocrystals/salt produced by coformers. This is because coformers with different configurations change intermolecular interactions during the cocrystallization process, which may result in the twisting of the flexible groups from the pharmaceutical molecules affecting the arrangement of the molecules in the crystals, which in turn leads to differences in their physicochemical properties after cocrystallization. − Changes in conformation have been shown to affect the optical properties of solid materials. , Regrettably, in the pharmaceutical industry, it is not clear how coformers affect the conformation, assembly, and physicochemical properties of molecules in pharmaceutical cocrystals/salts. Therefore, rational modulation of the conformation, crystal structure, and physicochemical properties of API molecules based on different configurational coformers has been an arduous challenge.…”

Biaxial Negative Thermal Expansion in an Organic Imidazolium Salt: Modulation of the Thermal Expansion Property by Methyl Substitution

“…Study of thermal expansion properties of some materials is absolutely necessary for their application in certain fields such as civil engineering, spacecraft, cookware, etc. − Although positive thermal expansion (PTE) is a common phenomenon observed in most materials, negative thermal expansion (NTE) in a certain class of materials, including a few organic compounds, has added an interesting topic of research in materials science. − A large number of materials have been explored to understand the mechanism of NTE. − The unusual thermal expansion phenomena have been observed in several classes of materials, viz., metal oxides, − zeolites, , metal–organic frameworks, − metal cyanides, − organic salts, − cocrystals, − and inclusion compounds. − …”

Fundamentally Intertwined: Anharmonic Intermolecular Interactions Dictate Both Thermal Expansion and Terahertz Lattice Dynamics in Molecular Crystals

“…Instead, structural studies often attempt to deduce the role of dynamic effects indirectly, and recently there are numerous studies that have attributed thermal expansion phenomena to molecular dynamics. [14][15][16][17][18] However, increasing dynamics with rising temperature alone does not necessarily correlate with thermal expansion. Structural changes require asymmetric (anharmonic) interactions, as harmonic interactions will not produce any thermal expansion effects, nor change in vibrational frequency as a function of temperature.…”