Synthesis, spectroscopic and theoretical studies of (R/S)-piperidinium-3-carboxylic acid 2,6-dichloro-4-nitrophenolate

Abstract

(R/S)-Piperidine-3-carboxylic acid (P3C, nipecotic acid) forms a stable 1:1 hydrogen-bonded complex with 2,6-dichloro-4-nitrophenol (DCNP). Both, in crystal and in the optimized theoretically structure by the B3LYP/6-311++G(d,p) approach the proton is transferred from DCNP to P3C. The (R) and (S)-stereoisomersic complexes of piperidinium-3-carboxylic acid 2,6-dichloro-4-nitrophenolate, P3C+H·DCNP−, aggregate into centrosymmetric cyclic dimers through the COOH⋯O− and N+H⋯ONO hydrogen bonds of 2.57(1) and 3.06(1) Å, respectively, which in turn are linked into a ladder-type cyclamer through the CH⋯Cl hydrogen bonds of 3.71(1) Å. The title compound is characterized by single-crystal X-ray analysis, Raman and FTIR spectroscopies. The structures of the complexes of the ratio 1:1 (monomer), 2:2 (dimer) and 4:4 (cyclamer) of P3C+H·DCNP− units are optimized by the B3LYP/6-311++G(d,p) approach and compared with the solid-state experimental structure. Detail interpretation of the vibrational spectra has been carried out by computing Potential Energy Distribution (PED). Charge delocalization has been analyzed using the Natural Bond Orbital (NBO) method.