First published as an Advance Article on the web 15th June 2004 2,4-Diamino-1,3,5-triazines have been prepared by reaction of dicyandiamide with nitriles under microwave irradiation, a method that can be considered as a green procedure due to the reduction in the use of solvents during synthesis and purification, the short reaction time and the simplicity of the procedure. The structures have been confirmed in solution by NMR spectroscopy. Variable temperature experiments have been used to calculate the free energy of activation for rotation about the amino–triazine bond. The crystal structures of three 2,4-diamino-6-R-1,3,5-triazine derivatives (3a: R ¼ phenyl, 3i: R ¼ 1-piperidino and 3g: R ¼ 1-phenylpyrazol-3-yl) have been determined by X-ray analysis. The N–HÁ Á ÁN interactions change from structure to structure, resulting in a variation from pseudo-honeycomb networks to corrugated rosette layers.