Crystal engineering of primary cubanecarboxamides.: Repetitive formation of an unexpected N-H•••O hydrogen-bonded network

The unusual N-H . . .O hydrogen bond pattern in a family of primary cubanecarboxamides is described. 4-Chloro-1-cubanecarboxamide, 1, and the corresponding bromo and iodo derivatives, 2 and 3, form the shallow-glide hydrogen-bonded motif instead of the usual 5.1 Angstrom translated ribbon pattern, more characteristic of primary amides. This behavior is also seen, somewhat unexpectedly, for cubanecarboxamide, 4, but more pr less unsurprisingly for 1,4-cubanedicarboxamide, 5. This repetitive occurrence of the same hydrogen 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 Angstrom translation pattern for two reasons: (1) steric-it is too large to fit-in a 5.1 A translated structure and (2) electronic-its carbon acidity is sufficient to result in the appearance of C-H . . .O hydrogen bonds to the C=O group, disrupting any putative 5.1 Angstrom translated structure. Such a molecule supermolecule relationship is of value in crystal engineering strategies.