Crystal Engineering of Primary Cubanecarboxamides. Repetitive Formation of an Unexpected N-H...O Hydrogen-Bonded Network.
The unusual N-H...O H bond pattern in a family of primary cubanecarboxamides is described. 4-Chloro-1-cubanecarboxamide, 1, and the corresponding bromo and iodo derivs., 2 and 3, form the shallow-glide H-bonded motif instead of the usual 5.1 .ANG. translated ribbon pattern, more characteristic of primary amides. This behavior is also seen, somewhat unexpectedly, for cubanecarboxamide, 4, but more or less unsurprisingly for 1,4-cubanedicarboxamide, 5. This repetitive occurrence of the same H bond pattern is of significance in crystal engineering wherein synthon robustness is measured in terms of such repetitivity. The cubyl group is directly responsible for the appearance of the shallow-glide motif in this family in preference to the 5.1 .ANG. translation pattern for two reasons: (1) steric-it is too large to fit in a 5.1 .ANG. translated structure and (2) electronic-its C acidity is sufficient to result in the appearance of C-H...O H bonds to the C:O group, disrupting any putative 5.1 .ANG. translated structure. Such a mol. -> supermol. relation is of value in crystal engineering strategies.
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