Experimental Study of Structure–Energy Changes in Molecules and Crystals of 2,2-Dinitropropane-1,3-diol Caused by Temperature Variations

Crystals of 2,2-dinitropropane-1,3-diol were prepared and grown at different temperatures. An X-ray analysis was used to study the structure of three phases (1, 2 and 3) of the 2,2-dinitropropane-1,3-diol crystals. The calorimetric study of the crystals temperature behavior (1) showed the presence of two phase transitions in the regions of T=309 K and T=340 K, as well as crystals (2) with a phase transition at T=340 K. Observations in a hot stage with the optical microscope phase transitions for separate crystals were made. X-ray diffraction studies of polycrystalline samples (1) for temperatures increasing up to the temperatures of phase transitions I and II demonstrated that phase transition I is followed by conversion of crystals 1 into 2, and transition II is connected with conversion of crystals 2 into a disordered body-centered structure. The temperature behavior of the bands of symmetric N–O stretching vibrations of nitro groups and stretching vibrations of O–H groups was studied by IR spectroscopy. The temperature dependence of hydrogen bonds redistribution and nitro group reorientational dynamics was examined. Data on the structure–dynamic rearrangement in the crystal lattice of the examined compound were obtained by the NMR pulse method in the solid phase using relaxational free induction decay of protons. The kinetic parameters of the process were obtained.