Mechanical Properties and Temperature and Pressure Effects on the Crystal Structure of (2S,3S,4R)-2,3,4-(Trinitratomethyl)-1-nitroazetidine (TMNA) by Single-Crystal X-ray Diffractometry and Density Functional Theory

Abstract

Knowledge of how crystalline materials react to external stimuli such as temperature, pressure, and stress is crucial for their screening, modification, and potential use. Here, we reveal and discuss the crystal structure of recently synthesized (2S,3S,4R)-2,3,4-(trinitratomethyl)-1-nitroazetidine [C 6 H 9 N 5 O 11 , (TMNA)] obtained by single-crystal X-ray diffractometry and calculated by solid-phase density functional theory (DFT) with the CASTEP code using Perdew−Burke− Ernzerhof functional optimized with the Grimme dispersion correction. We report the effects of temperature and pressure on the structure and unit cell lattice parameters in the range between 0 and 325 K and ambient pressure and 10 GPa. TMNA presents a nitroazetidine moiety with three ethyl nitric ester groups, each bonded to one of the three carbon ring atoms, and belongs to the monoclinic crystal system, space group P2 1 /c. The ambient temperature and pressure structure remain stable in the temperature and pressure ranges studied and exhibit both anisotropic thermal expansion and pressure contraction. Thermal isobaric expansion results in a soft expansion along the c-crystallographic axis and a hard expansion along the b-axis (c > a > b), with a measured volume thermal expansion coefficient of 174 (8) MK −1 , compared to our DFT estimated value of 236 MK −1 . Pressure compression calculations under isotropic and isothermal conditions reveal a volume contraction of approximately 25% with the unit cell c lattice shortening by approximately 50% less than the a and b lattices (c < b ≅ a). A Birch−Murnaghan equation-ofstate fit of the data yields bulk modulus and pressure derivative values of 10.5 (1) GPa and 7.0 (1), respectively. Finite strain DFT calculations yield the elastic constants of TMNA, which we employ to derive its bulk and shear modulus values of 9.96 and 4.94 GPa, respectively. TMNA presents linear compressibility values of approximately 37, 40, and 23TPa −1 along the [100], [010], and [001] directions, respectively. The compressibility values obtained from the elastic constants agree with those derived by fitting the high−pressure data, ensuring model consistency. We compare our TMNA results to those reported for nitrotoluene and other azetidines.