¹⁴N NQR Study of Polymorphism and Hydrogen Bonding in Molecular Complex Isonicotinamide−Oxalic Acid (2:1)

Abstract

The complete (14)N nuclear quadrupole resonance (NQR) spectra have been measured in the two polymorphic crystalline phases of the molecular complex isonicotinamide-oxalic acid (2:1) by nuclear quadrupole double resonance. The observed NQR frequencies, quadrupole coupling constants, and asymmetry parameters (η) have been assigned to the two nitrogen positions (ring and amide) in a molecule on the basis of the intensity and multiplicity of the double resonance signals. The NQR data for the ring nitrogen in both polymorphic phases deviate from the correlation relations observed in substituted pyridines. This deviation is analyzed in a model, where it is assumed that an additional electric charge on the nitrogen atom changes the NQR parameters. The model suggests that this additional electric charge is negative so that the N···H-O hydrogen bond seem to be partially ionic, of the type N(-)···H-O.

A 14N nuclear quadrupole resonance study of phase transitions and molecular dynamics in hydrogen bonded organic antiferroelectrics 55DMBP–H2ca and 1,5-NPD–H2ca

“…A strong correlation is observed also in the case of hydrogen bonded pyridine. 17 In pyridine q ZZ is negative and equal À4.58 MHz. The principal axis Z points approximately along the bisector of the CNC angle, whereas the principal axis Y points perpendicular to the pyridine ring.…”

14 N Nuclear Quadrupole Resonance Study of Piroxicam: Confirmation of New Polymorphic Form V

“…Some promising results were obtained by applying nuclear magnetic resonance (NMR) and more recently by nuclear quadrupole resonance (NQR) . The latter turned out to be a suitable supplemental and/or alternative method to more commonly used XRD or vibrational spectroscopy in research on solid APIs …”

“…14,15 The latter turned out to be a suitable supplemental and/or alternative method to more commonly used XRD or vibrational spectroscopy in research on solid APIs. [16][17][18] Nuclear quadrupole resonance is based on the interaction of the nuclear quadrupole moment tensor (Q) and the electric field gradient tensor (EFG) at the site of the nucleus. 19,20 Induced transitions between these levels are the basis of NQR.…”

Anticooperativity of FH···Cl− hydrogen bonds in [FH)nCl]− clusters (n = 1…6)

“…In a condensed phase (crystals, amorphous systems, polymers), the value of NQC could be determined from the NQR spectra, corresponding to transitions between levels of the hyperfine structure, which are located in the radio frequency region. Therefore, NQC could be used for investigations of the electron‐nuclear structure of particles during intermolecular interaction and could be both measured experimentally and calculated.…”

“…In a condensed phase (crystals, amorphous systems, polymers), the value of NQC could be determined from the NQR spectra, corresponding to transitions between levels of the hyperfine structure, which are located in the radio frequency region. Therefore, NQC could be used for investigations of the electron-nuclear structure of particles during intermolecular interaction [104][105][106] and could be both measured experimentally and calculated. We have calculated a constant χ for all three atoms involved in FHÁÁÁCl − hydrogen bonds of [(FH) n Cl] − clusters- 35 Cl, 2 H (D) isotopes and the unstable isotope 18 F*, which have nonzero quadrupole moments.…”