The molecular structure of 4-substituted pyridine N-oxides–boron trifluoride triel bonded complexes: Peculiarities and regularities

Abstract

Pyridine N-oxides are widely used in medicine, organic synthesis and design of functional coordination compounds and supramolecular systems. However, at present, issues related to the complex formation and stereochemistry of pyridine N-oxide molecular complexes as well as the nature of the complexing bond and the substituent effect remain relevant. In this paper the substituent effect on geometric, electronic, thermodynamic and spectral properties was established by quantum chemical calculations (DFT/M062-X/aug-cc-pvTZ) for the series of 4-substituted pyridine N-oxides with boron trifluoride as model complexes. Theoretical insights into the nature of OB triel bond was considered in terms of QTAIM and NBO analysis. A conformational analysis has been performed to resolve the contradictions in the literature data concerning the stereochemistry of such complexes. The calculated structural parameters, as well as complex formation energy, binding energy, thermodynamic characteristics, vibrational frequencies and chemical shifts reveal high correlation with the empirical Hammett substituent constants.