Rediscovery of the Forgotten Middle Child: A Comprehensive Study on the Coordination Chemistry of Melam

Abstract

Melam or bis(4,6-diamino-1,3,5-triazin-2-yl)amine is a chemical compound that has already been studied by Liebig almost 200 years ago. Despite this, melam's ability to act as a bidentate ligand has hardly been explored so far. The main focus of this work was therefore to advance the knowledge about melam's coordination chemistry by the synthesis of its complexes with CuCl, CuBr, CuI, CuCN, and AgCl as well as their structural characterization by single crystal and powder X-ray diffraction. Their crystal structures were found to feature channels along the molecules’ stacking direction. It was further shown that these melam complexes have excellent hydrolytic and thermal stability, making them potentially interesting for heterogeneous catalysis in aqueous media either as promising precursors for polymeric carbon nitrides or possibly already on their own, especially since it should be possible to fine-tune properties by preparing solid solutions of these melam complexes, which was exemplarily demonstrated between the CuBr and CuI derivatives. Additionally, the crystal structure of melam's HCl salt was elucidated, which proved to be closely related to that of the coordination complex between melam and CuCl, underlining the similar chemical behavior of Cu⁺ and H⁺ toward melam.