1,1-diamino-2,2-dinitroethylene under high pressure-temperature

Abstract

The structural phase stability of 1,1-diamino-2,2-dinitroethylene (FOX-7) has been studied up to 10 GPa through isothermal compression at 100 °C and 200 °C using synchrotron mid- and far-infrared spectroscopy. During isothermal compression at 100 °C changes are observed in vibrational spectra with increase in pressure that are indicative of significant distortion to monoclinic α phase or a possible structural transformation to a high pressure α(') phase at 2.2 GPa and α(") phase at 6.1 GPa. At 200 °C, for the far- and mid-IR regimes, the similar changes were observed at 2.1 (2.0) GPa and 5.3 (5.5) GPa, respectively. The observed change is nearly isobaric, consistent with previously reported high pressure and room temperature values, up to the highest temperature of 200 °C reached in our experiments. Over the total P-T range investigated, up to ∼10 GPa and 200 °C, we observed no evidence of sample decomposition. The observed changes are partially reversible with only slight evidence of the high pressure distortion remaining upon complete decompression. Additional isobaric heating at 1.07 GPa was performed in the mid-IR regime, which clearly revealed an onset of decomposition at 360 °C. Further x-ray or neutron diffraction, which are needed to fully resolve the cause of observed changes above 2 and 5 GPa, are ongoing.

A study of solvent selectivity on the crystal morphology of FOX-7 via a modified attachment energy model

“…Due to these attractive characteristics, many studies have been performed on its synthesis, 1,2 polymorphism, [3][4][5][6][7] thermal analysis, [8][9][10][11] and crystallization. Due to these attractive characteristics, many studies have been performed on its synthesis, 1,2 polymorphism, [3][4][5][6][7] thermal analysis, [8][9][10][11] and crystallization.…”

Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations

“…However, they found that no lattice transformations could be observed up to 8 GPa under hydrostatic conditions. Recent experiments at different temperatures and pressures found three possible phase transitions (at 2 GPa, 5 GPa and above 10 GPa) in mid and far IR regions 11,12 . Pravica et al 11 reported the strengthening of the hydrogen bond and softening of NH 2 stretching frequencies at high pressure by using IR experiments.…”

“…Starting from the synthesis of this compound in 1998 3 , several studies were carried out to investigate its structural properties from ambient 4 to extreme conditions [5][6][7][8] , its thermal behavior with decomposition mechanism 9,10 and vibrational spectroscopy (IR and Raman) at different pressures and temperatures 5,11,12 . Beeman and Ostrak 4 determined the crystal structure of FOX-7 to be monoclinic with the space group P2 1 /n, which contains four molecules (56 atoms) per unit cell.…”

High‐Temperature Structural Transformations of 1,1‐Diamino‐2,2‐dinitroethene (FOX‐7)

“…Recent data indicate possiblee xistence of the fourth modification of this compound, d-FOX-7, which is stable above 453 Ku ntil the compound decomposes above 524 K [5,8,[11][12][13].I nt he cited papers, the conclusion on the existence of d-FOX-7 wasm ade based on IR spectroscopic data and on the enhancement of thermals tability of FOX-7 after heating at temperatures above 488 K. The heat effect of the g!d transformation was not reported since this process proceeds after the onset of thermal decomposition of FOX-7.…”

“…At normal pressure the a-phase is stable below 373 K [ 1] and the stability range of the b-phase is 373-418 K [ 1,2]. The g-phase has been considered to exist from 435 Ku ntil rapid thermal decomposition at 504 K[ 2],b ut lateri tw as shown [1,3,4] that at ambient pressure the boundary between the areas of thermodynamics tability of b-a nd g-FOX-7 lies in the range of 418-423 K.High-temperature conversions of FOX-7, includingi ts thermal decomposition, have been investigated intensely [5][6][7][8][9][10].Recent data indicate possiblee xistence of the fourth modification of this compound, d-FOX-7, which is stable above 453 Ku ntil the compound decomposes above 524 K [5,8,[11][12][13].I nt he cited papers, the conclusion on the existence of d-FOX-7 wasm ade based on IR spectroscopic data and on the enhancement of thermals tability of FOX-7 after heating at temperatures above 488 K. The heat effect of the g!d transformation was not reported since this process proceeds after the onset of thermal decomposition of FOX-7.According to Refs. [8,9],d ecompositiono fF OX-7 in the temperature range 463-488Kis accompanied bym ass loss of 30-40 %a nd polymorphous transition of g-phase into hypothetical d-polymorph.The pressure-temperature (P-T)p hase diagram of FOX-7 was determined basedo nt he data obtained by means of in situ synchrotron infrared radiations pectroscopya nd available literature values [11].A ccording to this diagram, at room temperature a-FOX-7 transforms in high-pressure modifications Ia nd II above 2and 4.5 GPa, respectively.The phased iagrams uggests the existence of two potential triple points at high P and T values: b + g + d and a + b + d.[a] V.Abstract:S tucturalt ransformations of 1,1-diamino-2,2-dinitroethene( FOX-7) were investigated in the temperature range 298-513 Kbymeans of DSC,TG, isothermal calorimetry,P XRD, IR spectroscopy, and electron microscopy.T he data obtained confirmt he existenceo ft he high-temperature d-FOX-7 polymorph stable above 480 K. The heat effect of the g!d transformation is À 4.6 Jg À1 (À680 Jmol À1 ).…”