Search

The 1:1 complex of piperidine-4-carboxylic acid (isonipecotic acid, P4C) with 2,6-dichloro-4-nitrophenol (DCNP), has been investigated by single-crystal X-ray analysis, Raman and FTIR spectroscopy and theoretical calculations. The hydrogen-bonded-ion-pair complex is observed in the crystalline state with the O⋯H⋯OOC hydrogen bond of 2.453(16) Å. FTIR spectrum shows a broad absorption in the 1600–400 cm −1 region characteristic of very short OHO hydrogen bond, broken by the Evans holes. The complexes are joined through N H⋯O into a H-bonding network. The N H⋯O mode appears as a broad band in the range of 3100–2000 cm −1 . In the structure optimized at the B3LYP/6–311 + +G(d,p) level of theory the proton is transferred from DCNP to P4C, and molecules are joined through the O⋯HOOC hydrogen bond of 2.640 Å. The experimental and theoretical infrared spectra are discussed. Detail interpretation of the vibrational spectra has been carried out with the use of computed Potential Energy Distribution (PED). [ABSTRACT FROM AUTHOR]

( 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 C H⋯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. [ABSTRACT FROM AUTHOR]