Self-recognition in a flexible bis(pyrrole) Schiff base derivative: formation of a one-dimensional hydrogen-bonded polymer

The title Schiff base compound, N,N'-bis(pyrrol-2-ylmethylene) propane-1,2-diamine, C13H16N4, forms an interesting supramolecular structure ( a one-dimensional ladder-like polymer) in the solid state that is based on the existence of complementary intermolecular N - H...N=C hydrogen bonds between the monomer units. The polymer axis is collinear with the c axis of the orthorhombic unit cell. Quantum-chemical AM1 calculations clearly indicate that self-recognition in this system by hydrogen bonding is favoured on electrostatic grounds, since the partial atomic charge on the H atom of the pyrrole NH group (0.274 e) complements the partial atomic charge of the N atom of the C=N group (-0.239 e) on a neighbouring molecule.