Amide hydrogen bonding: control of the molecular and extended structures of two symmetrical pyridine-2-carboxamide derivatives

The crystal structures of two symmetrical pyridine-2-carboxamides, namely N,N'-(propane-1,3-diyl)bis(pyridine-2-carboxamide), C(15)H(16)N(4)O(2), (I), and N,N'-(butane-1,4-diyl)bis(pyridine-2-carboxamide), C(16)H(18)N(4)O(2), (II), exhibit extended hydrogen-bonded sequences involving their amide groups. In (I), conventional bifurcated amide-carbonyl (N-H)...O hydrogen bonding favours the formation of one-dimensional chains, the axes of which run parallel to [001]. Unconventional bifurcated pyridine-carbonyl C-H...O hydrogen bonding links adjacent one-dimensional chains to form a `porous' three-dimensional lattice with interconnected, yet unfilled, voids of 60.6 (2) Å(3) which combine into channels that run parallel to, and include, [001]. 4% of the unit-cell volume of (I) is vacant. Compound (II) adopts a Z-shaped conformation with inversion symmetry, and exhibits an extended structure comprising one-dimensional hydrogen-bonded chains along [100] in which individual molecules are linked by complementary pairs of amide N-H...O hydrogen bonds. These hydrogen-bonded chains interlock via π-π interactions between pyridine rings of neighbouring molecules to form sheets parallel with (010); each sheet is one Z-shaped molecule thick and separated from the next sheet by the b-axis dimension [7.2734 (4) Å].