Crystal and Molecular Structures of Quinolin-8-ol and its Salts with Acetylenedicarboxylic Acid, and Butane-1,2,3,4-tetracarboxylic Acid

Abstract

The crystalline compounds quinolin-8-ol (1) and its two salts 2, and 3 have been prepared and structurally characterized. Compound 1 crystallizes in the triclinic, space group P-1, with a = 6.5775(5) A, b = 7.8285(6) A, c = 14.4617(13) A, α = 96.099(2), β = 92.4700(10)°, γ = 106.171(3), V = 709.09(10) A3, Z = 4. Compound 1 is a new polymorph of quinolin-8-ol, and displays as dimer. Compound 2 crystallizes in the monoclinic, space group P2(1)/n, with a = 7.4815(11) A, b = 18.844(3) A, c = 8.0396(8) A, β = 94.069(10), V = 1130.5(3) A3, Z = 4. Compound 3 crystallizes in the triclinic, space group P-1, with a = 7.0968(6) A, b = 8.6854(7) A, c = 11.0494(11) A, α = 105.169(2), β = 90.3700(10)°, γ = 106.031(2), V = 629.50(10) A3, Z = 1. In the compound 3, the middle two COOH groups were ionized. In the compounds 2 and 3, as predicted on the basis of pKa differences, proton transfer from the COOH group to the hetero-nitrogen of the quinolin-8-ol molecule occurs, resulting in the formation of the hydrogen or dihydrogen salts. In neither of the compounds (2 and 3) the primary cyclic hydrogen-bonded R 2 2 (8) A–B heterodimer was formed, involving the second oxygen of the anion and the 8-hydroxy substituent of quinolin-8-ol. Instead, this molecule acts in a bridging mode to link the associated molecular units into chain polymers via combination of hydrogen bonds and other nonbonding interactions. The role of these non-covalent interactions in the crystal packing is analyzed. Under these weak interactions, compounds 2 and 3 displayed 3D framework structures. The crystal structures of quinolin-8-ol and its two salts from acetylenedicarboxylic acid, and butane-1,2,3,4-tetracarboxylic acid display extensive classical hydrogen bonding as well as other non-covalent CH–O, CH2–O, O–Cπ, CH–Cπ, and π···π interactions, giving 0/3D framework structures.