Accessing the rich carbon nitride materials chemistry by heat treatments of ammonium thiocyanate, NH4SCN

Abstract

Carbon nitride materials include functional materials, and their chemical diversity and complexity are becoming increasingly appreciated. Heating of NH4SCN leads to a range of new carbon nitride compounds, which have been structurally characterized by single-crystal X-ray diffraction. Heating at ambient pressure to 175°C leads to guanidinium thiocyanate, H6CN3SCN (1), and when maintaining that temperature for about 12 h a water-insoluble carbon nitride product is formed, which is a co-crystal between melamine and melamium thiocyanate, [H6C3N6]·[H10C6N11]+·[SCN]− (2). In situ powder X-ray diffraction measurements of this material reveal a gradual transformation from (2), via two intermediate products, to a final melon-like end product. The first of these forms between 350 and 400°C, and is an adduct of melam and melamium thiocyanate, [H9C6N11]·2[H10C6N11]+·2[SCN]− (3). The second forms between 400 and 480°C, and is identified as melem, 2,5,8-triamino-tri-s-triazine, H6C6N10 (4). On heating of (2) in a sealed ampoule to 600°C, various crystals were obtained and six crystal structures were determined from the batch: 1,3,5-triazine-2,4,6-triamino, H6C3N6 (5), 1,3,5-triazine-2,4-diamino, H5C3N5 (6), 1,1′,3,3′,5,5′-triazine-2,2′,4,4′-tetraamino, H8C6N10 (7), 2[H6C3N6]·[H10C6N11]+·[SCN]− (8) and 2[H6C3N6]·[H7C3N6]+·[SCN]− (9). Finally, a recrystallized decomposition product was found to be [H6C3N6]·[H7C3N6]+·[SCN]−·[H2O] (10).