Syntheses and Structures of Protonated Acetylenedicarboxylic Acid

Abstract

Acetylenedicarboxylic acid (C 4 H 2 O 4 ) was protonated in the binary superacidic systems HF/MF 5 (M = As, Sb). Depending on the stoichiometric ratio of Lewis acid and acetylenedicarboxylic acid mono-and diprotonated acetylenedicarboxylic acid was obtained. The salts of diprotonated acetylenedicarboxylic acid were characterized by vibrational spectroscopy and in case of [C 4 H 4 O 4 ][SbF 6 ] 2 by a single-crystal X-ray structure analysis. The salt crystallizes in the monoclinic space group C2/c with four formula units per unit cell. Furthermore, salts of monoprotonated acetylenedicarboxylic acid were synthesized and characterized by single-crystal X-ray structure analysis. The salts [C 4 H 3 O 4 ][AsF 6 ] and [C 4 H 3 O 4 ][SbF 6 ] crystallize in the monoclinic space group C2/c with four formula units per unit cell. The monoprotonation is better described as a twofold hemiprotonation of acetylenedicarboxylic acid. The experimental results are discussed together with quantum chemical calculations.

Synthesis and Structure of Protonated Propiolic Acid

“…The Sb−F bond lengths of the [SbF 6 ] − anion are typical for distorted [SbF 6 ] − anions. The bond lengths are between 1.859(2) and 1.904(2) Å and are comparable to literature data. , …”

“…The bond lengths are between 1.859(2) and 1.904(2) Å and are comparable to literature data. 18,19 Crystal Structure of [C 3 HD 2 O 2 ][Sb 2 F 11 ] (3). The deuterated monoprotonated propiolic acid 3 crystallizes in the monoclinic space group P21/n with four formula units per unit cell.…”