Hirshfeld Surface Investigation of Structure-Directing Interactions within Dipicolinic Acid Derivatives

Abstract

Six compounds based on dipicolinic acid esters have been synthesized and Hirshfeld surfaces used to investigate the structure-directing effects of functional groups in controlling their solid-state behavior. Compounds <b>1</b>-<b>4</b> are 4-bromo dipicolinic acid esters substituted with methyl, ethyl, propyl, and benzyl groups, respectively. The main structure-directing motif within <b>1</b>-<b>3</b> is a pairwise O···H interaction involving two carbonyl oxygen atoms and two aromatic H atoms. The introduction of bulky benzyl groups in <b>4</b> forces a significant change in the position of this interaction. Compounds <b>2</b> and <b>4</b> were used in Suzuki coupling reactions to prepare extended analogues <b>5</b> and <b>6</b>, respectively, and their solid-state behavior was also studied using Hirshfeld surfaces. Extension of these dipicolinic acid esters results in the complete loss of the pairwise O···H interaction in <b>5</b>, where the dominant structure-directing motifs are π-based interactions. However, the pairwise O···H interaction reappears for the more flexible <b>6</b>, demonstrating control of the solid-state structure of these dipicolinic acid derivatives through the choice of functional groups.