Conformational dualism of dipyridyl-substituted formamidine

A new polymorph of the β-modification of N,N′-di(pyridin-2-yl)formamidine that is more thermodynamically stable than the known α-modification is obtained. The crystal of β-modification contains hydrogen bonded molecular dimers with a skewed geometry. Therefore, the space group is not centrosymmetric – P4₂. This geometry is a result of the molecular E-syn,syn conformation in crystals of the β-phase, which differs from the E-anti,syn conformation in the α-phase. The number of crystallographically non-equivalent molecules (8) in the β-modification is unusually large for organic compounds. The structure of the packing is analyzed, and it is shown that the centers of dimers follow the sites of a distorted body-centered cubic pseudo-lattice (А_т ≈ 10 Å, α_т = 90°) with a 16 times decreased unit cell volume. Reasons for symmetry violations causing modulations are considered.