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![[Figure 4]](ky3231fig4mag.jpg)
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Figure 4
The crystal structure of 2-amino-4,6-dinitrotoluene was initially determined from PXRD data at 293 K (Graham et al., 2004  ). The fit to the data improved significantly upon modelling disorder in the C6-nitro group, but the limited quality and resolution of the PXRD data precluded accurate refinement of the site-occupancy factors (SOFs). To address this, each O atom was modelled over two positions, with SOFs constrained to sum to 1.0 (atom numbers correspond with Table 5). The structure was solved with fixed SOF values and the solution yielding the best agreement with the data was selected as most probable. Subsequent single-crystal determination at the same temperature (structure shown above) confirmed the disorder model. In both determinations, each O atom of the 6-nitro group is disordered between a high-occupancy site (O23: 80% single crystal, 70% PXRD) and a low-occupancy site, with excellent agreement in the positions of the high-occupancy sites. The observed structural differences can be attributed to the disparity in available diffraction data – the single-crystal analysis utilized 1111 observed reflections extending to ∼0.8 Å resolution, while the PXRD dataset contained just 146 unique reflections with a maximum resolution of ∼1.8 Å. This represents an early application of DASH for crystal structure determination, predating the now-standard incorporation of Rietveld refinement and periodic DFT-D geometry optimization into the workflow. |
![[Figure 4]](ky3231fig4.jpg)
 | STRUCTURAL CHEMISTRY |
ISSN: 2053-2296
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