Hydrogen Bonding Selectivity in Molecular Assembly: A Novel 2:1 Molecular Complex of Caffeine and 4-Hydroxybenzoic Acid via C– H···O/O– H···O/O– H···N Hydrogen Bond Coupling

Abstract

Caffeine (1) and 4-hydroxybenzoic acid (2) form a novel 2:1 molecular complex via C—H---O hydrogen bonding. Selectivity in the formation of hydrogen bonds in the X-ray structure of the complex is predicted by the relative acidity and basicity of the participating atoms in the groups. This is first time reported that caffeine is complexed with an aromatic hydroxy acid through two C—H---O hydrogen bonds involving N-CH₃ hydrogen and ring hydrogen of caffeine.