Two Achiral Isomers of Chloronitropyridine Crystallize as Polar Materials with Different Molecular Packing Motifs Based on Similar Intermolecular Interactions

Abstract

The molecular structures of two of the ten possible isomers of chloronitropyridine have been studied by spectroscopic techniques and single crystal X-ray diffraction. The structures of 2-chloro-4-nitropyridine (1) [monoclinic, Pc, a = 3.7711(14) A, b = 8.919(3) A, c = 9.324(3) A, β = 99.506(5)°] and 5-chloro-2-nitropyridine (2) [triclinic, P1, a = 3.7559(13) A, b = 6.071(2) A, c = 6.939(2) A, α = 85.703(5)°, β = 89.619(5)°, γ = 75.189(5)°] reveal that the isomers crystallize in non-centrosymmetric space groups with different molecular packing motifs based on similar intermolecular interactions. Each compound packs into molecular sheets via short chlorine–oxygen contacts and C–H⋯X (X = O, N) interactions of the nitro oxygen atoms and the pyridine nitrogen atom. The sheets further pack with an offset face-to-face π-stacking geometrical arrangement of the aromatic rings to form the three-dimensional structures. Achiral 2-chloro-4-nitropyridine (1) crystallizes as a polar material in the non-centrosymmetric and non-enantiomorphous space group Pc while the isomeric achiral compound 5-chloro-2-nitropyridine (2) forms a polar material that approximates inversion symmetry in the non-centrosymmetric enantiomorphous space group P1. The molecular structures of achiral 2-chloro-4-nitropyridine and 5-chloro-2-nitropyridine have been studied by X-ray diffraction revealing that they crystallize as polar materials. The structures have different packing motifs based on similar intermolecular interactions consisting of π-stacked molecular sheets formed by chlorine–oxygen contacts and C–H⋯X (X = O, N) interactions.