Supramolecular Zwitterions Based on a Novel Boronic Acid-Squarate Dianion Synthon

Reaction of squaric acid (H2SQ) with the three pyridine-appended boronic acid derivatives (BA), viz 4-pyridinylboronic acid (1BA), 3-pyridinylboronic acid (2BA), and (4-(pyridin-4-yl)phenyl)boronic acid (3BA), leads to formation of supramolecular zwitterions of general formula [SQ(BAH)2]•xH2O generated by proton transfer from the squaric acid to the pyridine sites. The zwitterion SQ(1BAH)2]•2H2O can further react with the neutral molecule bipyridine (bpy) leading thus to ternary system of formula [SQ(1BAH)2]•bpy.