Diastereomeric complex of (R/S)-piperidine-3-carboxylic acid with (2R,3R)-tartaric acid: Structural, spectroscopic and computational studies

2:2 Complex of (R) and (S)-piperidine-3-carboxylic acids (P3C) with (2R,3R)-tartaric acid (TA), 1, has been characterized by single-crystal X-ray analysis, FTIR and NMR spectroscopies, and by DFT calculations. The crystals of 1 are monoclinic, space group P21. The crystal structure is formed by two distinct P3CH+·TA− components, A and B, linked by an O–H⋯O hydrogen bond of 2.603(2) Å. The A and B components differ in the absolute configuration of the C(3) atom of P3CH+; (S) in A and (R) in B. The piperidinium-3-carboxylic acid and (2R,3R)-semi-tartrate anion moieties of the components A and B are linked by O–H⋯O hydrogen bonds of 2.517(1) and 2.535(1) Å, respectively. In A and B the piperidinium rings adopt the chair conformation with the carboxyl group in the equatorial position. The structures of the monomers of P3CH+·TA−, 3A and 3B, as well as of a dimer 2, have been optimized by the B3LYP/6-31G(d,p) approach. The chemical shift assignments were based on two-dimensional 1H–1H and 1H–13C experiments.

► (2R,3R)-Tartaric acid forms crystalline complex with (R) and (S)-piperidine-3-carboxylic acid.
► Theoretical IR spectrum of the complex predicts 8 bands attributed to νCO, νasCOO and δNH modes.
► Ring α and β C atoms give NMR cross-peaks with equatorial and axial protons attached to them.