Abstract
The crystal structure of the title compound, C11H13N3O2S2, has been determined previously on the basis of refinement against laboratory powder X-ray diffraction (PXRD) data, supported by comparison of measured and calculated (13)C solid-state NMR spectra [Hangan et al. (2010). Acta Cryst. B66, 615-621]. The molecule is tautomeric, and was reported as an amine tautomer [systematic name: N-(5-ethyl-1,3,4-thiadiazol-2-yl)-p-toluenesulfonamide], rather than the correct imine tautomer. The protonation site on the molecule's 1,3,4-thiadiazole ring is indicated by the intermolecular contacts in the crystal structure: N-H...O hydrogen bonds are established at the correct site, while the alternative protonation site does not establish any notable intermolecular interactions. The two tautomers provide essentially identical Rietveld fits to laboratory PXRD data, and therefore they cannot be directly distinguished in this way. However, the correct tautomer can be distinguished from the incorrect one by previously reported quantitative criteria based on the extent of structural distortion on optimization of the crystal structure using dispersion-corrected density functional theory (DFT-D) calculations. Calculation of the (13)C SS-NMR spectrum based on the correct imine tautomer also provides considerably better agreement with the measured (13)C SS-NMR spectrum.
Highlights
Determination of molecular crystal structures from powder X-ray diffraction (PXRD) data is relatively common in the chemical literature (see, for example, Sanphui et al, 2014; doi:10.1107/S2053229614015356Acta Cryst. (2014)
The crystal structure of the title compound has been reported by Hangan and co-workers [Hangan et al, 2010; Cambridge Structural Database (CSD; Allen, 2002) refcode UKIRAI] on the basis of refinement against laboratory PXRD data, supplemented by comparison of measured and calculated 13C solid-state nuclear magnetic resonance (SS-NMR) spectra
An optimization of the crystal structure is divided into three sequential steps with: (i) only H atoms allowed to move; (ii) all atoms allowed to move with unit-cell parameters fixed; (iii) all atoms allowed to shown that the imine tautomer (II) is present in the crystal structure, and that tautomers (I) and (II) can be quantitatively distinguished by the results of DFT-D geometry optimizations and the published 13C SS-NMR spectra
Summary
Determination of molecular crystal structures from powder X-ray diffraction (PXRD) data is relatively common in the chemical literature (see, for example, Sanphui et al, 2014; Figure 1 Intermolecular interactions for (a) amine tautomer (I), the N—H group points directly towards a neighbouring methyl group, and (b) imine tautomer (II), where intermolecular N—HÁ Á ÁO hydrogen bonds generate ribbons along the a axis. The experimental data were taken from Hangan et al (2010). C11H13N3O2S2 283.36 Orthorhombic, Pbca 298 8.53925 (14), 15.0207 (3), 21.3958 (3) 2744.33 (8) 8 Cu K 1, = 1.54056 A Flat sheet, 25 Â 1. Data collection Diffractometer Specimen mounting Data collection mode Scan method 2 values (). Bruker D8 Advance diffractometer Bruker sample cup Reflection Continuous 2min = 3.54, 2max = 50.03, 2step = 0.005
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