Molecular tiltation and supramolecular interactions induced uniaxial NTE and biaxial PTE in bis-imidazole-based co-crystals

Order−disorder phase transition and anisotropic thermal expansion phenomena are commonly reported for inorganic and multicomponent organic materials but rarely in single-component molecular crystals. Research in this domain leads to numerous practical applications and development in fundamental research. Herein, we report variable-temperature X-ray diffraction studies on an imidazole-based novel single-component material, 2-(3,5-bis(trifluoromethyl)phenyl)-4,5-dihydro-1H-imidazole. Our study demonstrates that the lightweight material undergoes isosymmetric dynamic order−disorder reversible phase transition after 150 K with a hysteresis loop of ∼15 K and displays diverse thermal expansions along the crystallographic axes before and after the phase transition. The material exhibits positive (PTE), near zero (ZTE), and negative (NTE) thermal expansions along a-, b-, and c-axes, respectively, leading to uniaxial NTE and biaxial PTE characteristics. The phase transition at low temperatures was supported via differential scanning calorimetry and variable-temperature powder X-ray diffraction studies. The mechanism of the disorder−order phase transition and the anisotropic thermal expansions were understood by analyzing eight sets of single-crystal X-ray diffraction data collected in the range of 298−100 K. While this study provides new insights into the unusual thermal behavior of single-component organic crystals, the eco-friendly pure organic material could be a promising candidate for device applications.

Section: Introductionmentioning

confidence: 99%

Dynamic Order–Disorder Reversible Phase Transition and Anisotropic Thermal Expansions in a Single-Component Organic Molecular Crystal

Vikas,

Negi,

Munshi

2024

“…Stronger intermolecular interactions, such as halogen and hydrogen bonds, are typically less affected by temperature than weaker interactions, such as π stacking. Several studies have demonstrated the correlation between intermolecular interaction type and TE, and the type of interaction can be used as a way to control TE in solid materials. − This concept has been referred to as interaction dependence. , …”

Section: Introductionmentioning

confidence: 99%

Polymorphism and π Stacking Affect Thermal Expansion Behavior in Halogen-Bonded Cocrystals Based on 1,4-Diiodoperchlorobenzene

George III,

Karimi,

Juneja

et al. 2024

The thermal expansion behavior of a series of halogen-bonded cocrystals containing 1,4-diiodoperchlorobenzene as the donor is described. Two of the solids are polymorphs and contain 4-stilbazole as the acceptor, while the third solid contains 4-(phenylethynyl)pyridine as the acceptor, and this solid is isostructural with one of the polymorphs. All solids are sustained by I•••N halogen bonds, and the least thermal expansion occurs along this direction in all solids. The polymorphs exhibit significant differences in π stacking, and we show that electronically similar face-to-face stacked rings undergo more expansion compared to electronically different stacked rings. Moreover, in the two polymorphs, the directions of moderate expansion and most expansion are reversed, demonstrating how cocrystal polymorphism can affect material properties.

“…The imidazole moiety is an important component for the synthesis of porous materials such as ZIFs , and MOFs. , Imidazole is also used for the synthesis of organic co-crystals and salts. , Several compounds containing an imidazole moiety have shown unusual thermal expansion properties. − Tao and co-workers described the giant anisotropic thermal expansion induced by the rotation of imidazolium ions in a single crystal of a copper complex . Recently, Negi and others reported the unusual thermal expansion properties of bisimidazolium terephthalate salt ( IMD-TPH ) .…”

Section: Introductionmentioning

confidence: 99%

“…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. − …”

Section: Introductionmentioning

confidence: 99%

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

Chuskit

Sethi

Harsha

et al. 2023

Self Cite

The thermal expansion of an organic salt, 4-methylimidazolum-4-hydroxybenzoate (4-MIMD-HBC) has been studied by variable temperature single-crystal X-ray diffraction (VT-SCXRD). The salt exhibits unusual biaxial negative thermal expansion (NTE) and uniaxial large positive thermal expansion (PTE), whereas imidazolium-4-hydroxybenzoate (IMD-HBC) shows uniaxial NTE and biaxial PTE. Although the crystal structures of IMD-HBC and 4-MIMD-HBC are almost similar, there is a significant difference of the thermal expansion property between these two salts. The scissor-like motion of the hydrogen bonded networks is responsible for uniaxial NTE and PTE in both IMD-HBC and 4-MIMD-HBC salts along two principal axes, X1 and X3. IMD-HBC shows PTE along the other principal axis X2, where 4-MIMD-HBC exhibits NTE. The difference in thermal expansion between the two salts along X2 arises due to the methyl substituent, which induces HBC moieties in 4-MIMD-HBC to come closer to each other as the temperature increases, resulting contraction along X2.