B-11 NMR spectroscopy provided direct evidence that boric acid reacts with Azomethine H to form a 1: 1 bischelate complex. A new peak with a -17.9 ppm chemical shift is due to the chelate complex containing tetrahedral boron. It has been quantitatively confirmed that the reaction includes two chemical equilibria;, one is related to the ligand formation and the other to the complex formation. The formation constant for the ligand is small, less than 10, whereas that for the complex is relatively large, greater than 10(5). Azomethine H is hydrolyzed in aqueous solution because of its low stability, and the ligand formation is responsible for the nature of its complexation with boric acid. (C) 2004 Elsevier Ltd. All rights reserved.