Influence of dicarboxylic acid structure on tape networks in co-crystals of 2-pyridone

We report here on the formation of co-crystals of 2-pyridone and several long chain dicarboxylic acids HO₂C(CH₂)_nCO₂H with n an odd number. Supramolecular tapes, illustrating several hydrogen bond motifs, were observed. Co-crystals with malonic acid (n=1) crystallise in the space group P2/n, with a=19.213, b=4.031, c=19.508, β=114.67°; glutaric acid (n=3) in P-1, with a=5.437, b=9.592, c=11.797, α=66.50°, β=81.64°, γ=83.00°; pimelic acid (n=5) in C2/c, with a=19.828, b=5.135, c=17.401, β=102.98°; and azelaic acid (n=7) in P2₁/c, with a=16.644, b=5.036, c=18.213, β=103.09°. Tape compositions of both 1:1 acid:base and 1:2 acid:base were obtained suggesting that tape stochiometry is independent of the number of constituent carbon atoms in the acid backbone. The results also suggest that the 2-pyridone dimer may in certain cases act as a supramolecular analogue of phenazine.