Figure 6
The hydrogen-bonded chains formed by the trans configuration of the formamide, vis thioamide groups in (a) (1), (b) (2), (c) (3) and (d) (4). Note the very similar hydrogen-bonded interactions in (a)-(c), compared with (d), as a result of screw-axis symmetry in the latter case compared with the glide planes in the others.  [article HTML]

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