Experimental and Theoretical Charge Density Study of the Chemical Bonding in Chlorokojic Acid Crystal Structure

The experimental charge density in the chlorokojic acid
crystal structure was investigated on the basis of high-resolution
X-ray diffraction data collected at 80(2) K. The nature of chemical
bonding and halogen interactions has been studied by means of deformation
densities and by topological analysis using the Bader’s quantum
theory of atoms in molecules (QTAIM). A comparison between the experimental
and theoretical results, from calculations concerning gas phase and
periodic DFT/B3LYP, was performed. For the intermolecular hydrogen
bonds of O–H···O, C–H···O,
and C–H···Cl types, full characteristics of
bond critical points (BCP’s) were provided indicating closed-shell
interactions. The topological analysis of charge density distribution
revealed the presence of intermolecular C–Cl···O
halogen bridge and halogen–halogen interactions of C–Cl···Cl–C
type forming supramolecular Cl3 synthons, crucial for three-dimensional
structure formation of chlorokojic acid. The pronounced anisotropy
of electrostatic potential at the Cl atom clarifies both electrophilic
and nucleophilic properties of the substituent.