Aromatic Dicarboxylic Acids as Building Blocks of Extended Hydrogen-bonded Architectures

Abstract

An examination of the crystal structures of four compounds, 5-amino iso-phthalic acid hemihydrate (monoclinic, P2₁/n, a = 8.142 (2), b = 17.444 (3), c = 11.140 (2) Å, β=94.19 (3)°, D_c =1.601 g cm⁻³, Z=8, R_w ² = 0.106 for 1401 unique reflections), piperazinium(2+) 5-amino iso-phthalate (monoclinic, P2₁/c, a = 11.820 (2), b = 9.516 (2), c = 12.618 (3) Å, β = 116.70 (3)°, D_c = 1.400 g cm⁻³, Z = 4, R_w ², = 0.104 for 2222 unique reflections), 2-chloro-benzylammonium 2-carboxylate-6-carboxylic pyridine (monoclinic, P2₁/c, a = 22.391 (2), b = 9.322 (3), c=13.274 (2) Å, β=92.567 (11), D_c =1.482 g cm⁻³, Z=8, R_w 2 = 0.113 for 3610 unique reflections), and 3-fluoro-benzylammonium 2-carboxylate-6-carboxylic pyridine hydrate (monoclinic, P2₁/c, a = 9.862 (2), b = 13.246 (3), c = 21.153 (4) Å, β = 98.00 (3), D_c =1.463 g cm⁻³, Z = 8, R_w 2 = 0.154 for 2552 unique reflections), has identified a robust hydrogen-bonded, ribbon-like motif, generated by the geometric fit and hydrogenbond complementarity of the [— COO]⁻ and the [— COOH] functionalities. This preferred interaction between neighbouring anions results in infinite 1-D anionic architectures that are held together by short and near-linear O—H…O hydrogen bonds. In 1 and 2, the amino functionality acts as a crosslink (through N—H…O interactions) between adjacent sheets, thereby generating extended 2-D architectures. 5-Amino iso-phthalic acid exists as a zwitterion in the solid state, an observation which was also indicated by vibrational spectroscopic data. The crystal packing in both 3 and 4 consists of 2-D domains of anions and cations, stacked in an ⋅⋅AABBAABB⋅⋅ manner where the anionic sheets are constructed around the carboxylic-carboxylate supramolecular connector.

Key Words:

• Crystal engineering
• hydrogen bonding
• carboxylic acids