Molecular Adducts of 2,6-Diaminopyridine with Nitro-Substituted Aromatic Carboxylic Acids and the Crystal Structure of the 1 : 1 Adduct of 2,6-Diaminopyridine with 2-Nitrobenzoic Acid

Abstract

The 1 : 1 adducts of 2,6-diaminopyridine (2,6-dap) with a series of nitro-substituted aromatic carboxylic acids have been prepared and the crystal structure of one of these, with 2-nitrobenzoic acid (2-nba), [(2,6-dap)⁺ (2-nba)^-] has been determined by X-ray crystallography and refined to a residual R 0·034 for 655 observed reflections. Crystals are monoclinic, space group P 2₁/c, with four molecules in a cell of dimensions a 7·376(2), b 22·837(3), c 7·716(2) Å, β 90·01(2)°. The structure involves proton transfer with the resulting pyridinium proton and an amine proton combining with the carboxyl oxygens of the 2-nba molecule in a primary cyclic hydrogen-bonding association. Additional interactions, involving all the remaining amine protons of 2,6-dap with both carboxyl oxygens and one nitro oxygen of 2-nba, complete a chain polymer structure. All other members of this series have been confirmed by infrared spectroscopy as proton transfer adducts.