Interactions of water molecule in 2-(quinuclidinium)-propionic acid bromide hydrate

Hydrogen bonds in the crystal structure of hydrophobic and hydrophilic COOH-functionalized imidazolium ionic liquids

Hydrogen bonds such as the classic O–H⋯X (halide ion) hydrogen bond and the carboxyl group dimer were observed in the crystal structures of hydrophilic and hydrophobic COOH-functionalized imidazolium ionic liquids, respectively.

Stable Molecular Complex of Squaric Acid with 2-(Quinuclidinium)propionate

Squaric acid (3,4-dihydroxy-3-cyclobuten-1,2-dione, H2SQ) forms a complex with 2-(quinuclidinium)propionate (QNPr). In crystals, the molecules of H2SQ and zwitterions of QNPr are bridged by two strong non-equivalent O–H⋯O hydrogen bonds of 2.476(2) and 2.482(1) Å. The complex is investigated by X-ray diffraction, FTIR, and NMR techniques, and the results are supported by density functional theory calculations. The solid-state aggregation is consistent with the NMR results, recorded for an aqueous solution, and is also reproduced for the structure optimized at the B3LYP/6-311++G(d,p) level of theory. The calculated IR frequencies for the optimized structure have been used for the assignment of the experimental FTIR spectrum, where the broad absorption at ~2400 cm–1 corresponds to the short asymmetric OH⋯O bonds.