Conformers and hydrogen bond transformations in N-methylpiperidine betaine 2,4-dinitrophenolate crystals

Abstract

The molecular structure of a complex of N-methylpiperidine betaine with 2,4-dinitrophenol has been determined by X-ray diffraction. The crystals are orthorhombic, space group Fdd2 with a=41.854(8), b=44.000(9), c=6.9270(10) A ̊ , Z=32, V=12757(4) A ̊ 3. Such an exceptionally large cell is due to high symmetry of the crystal and to the presence of two crystallographically non-equivalent complexes, denoted as (a) and (b). The symmetry-independent dinitrophenolate molecules clearly differ in conformation, which modify their electronic structure and affects the hydrogen bonds. The OHO intermolecular hydrogen bonds are very short, with O⋯O distances of 2.419(6) and 2.441(6) Å. We have established that the hydrogen atom is closer to the phenol molecule in complex (a), while it is shared between the oxygen atoms of the carboxylate group of betaine and phenolate ion in complex (b), which is consistent with the conformations of the molecules. FTIR spectrum shows a broad absorption in the 2000–400 cm −1 region characteristic of such short hydrogen bonds.