Small structural modifications can result in completely different intermolecular interactions: a case of the ferrocenyl N-acyl pyrazolines

Abstract

The series of new ferrocenyl pyrazolines have been synthesized by the reaction of ferrocenyl chalcones and their analogues with hydrazine hydrate in the presence of corresponding carboxylic acid. Single-crystal X-ray crystallographic analysis of N-formyl, N-acetyl [1] and N-propanoyl pyrazoline derivatives revealed interesting ability of these compounds to form very different intermolecular interactions, despite their pronounced structural similarity. Amongst 28 dimers formed in four crystal structures with the stabilization energy Etot < - 15 kJ/mol [2], not a single dimer is the same for any pair of structures. These findings demonstrate the exceptional flexibility of ferrocenyl N-acyl pyrazolines in formation of intermolecular interactions. The compounds show similar antioxidant activity, comparable to quercetin. The similar activity of these pyrazolines can be explained by their flexibility for different intermolecular interactions.