Deformation of the four-membered supramolecular ring in a series of dialkylammonium hydrogen 2,2′-biphenyldicarboxylates

Abstract

Cocrystallizations of 2,2′-biphenyldicarboxylic acid (bpdcH2) with dialkylamine (daa) such as dimethylamine, diethylamine, dipropylamine, and diisopropylamine afford four organic ionic compounds with a general formula of [(bpdcH)(daaH)]. Structural analysis reveals that they all feature a centrosymmetric [(bpdcH)-(daaH)2-(bpdcH)] ion-pair dimer as a hydrogen-bonded synthon in the crystal structure, and the stacking of these ion-pair dimers is mainly directed by the C–H···π interactions between the phenyl groups of adjacent (bpdcH)– anions. Notably, the R44(12) ring motif of these ion-pair dimers can show a flexible and deformable conformation to cater for a lower energetic arrangement of the overall crystal structure.