Crystal and molecular structure of the quinuclidine betaine with p-hydroxybenzoic acid complex studied by X-ray diffraction, DFT, FTIR, and NMR methods

Quinuclidine betaine (1-carboxymethyl-1-azabicyclo[2.2.2]octane inner salt, QNB) forms a complex with p-hydroxybenzoic acid (HBA) at the 1:1 ratio. The crystals are triclinic, space group P1¯, with two symmetry non-equivalent QNB·HBA complexes linked by a sequence of four O-H···O hydrogen bonds into a zigzag chain. Both oxygen atoms of the carboxylate groups of two QNB are linked with two HBA molecules through the COO···HOOC hydrogen bonds of 2.561(2), and 2.556(2) Å, and the COO···HO hydrogen bonds of 2.609(2) and 2.687(2) Å. A trio ABC band at ca. 2800, 2550, 1910 cm−1 observed in the FTIR spectrum is characteristic of a medium-strong hydrogen bond in carboxylic acids. The second-derivative IR spectrum confirms the presence of two non-equivalent CO and two COO groups. The molecular structures of the 1:1 and 2:2 complexes have been optimized by the B3LYP/6-31G(d,p) approach. The experimental and predicted, by GIAO/B3LYP/6-31G(d,p), 1H and 13C chemical shifts correlate linearly.