Synthesis and structural investigation of brightly colored organoammonium 1,3-dimethylviolurates

Abstract Seven new organoammonium 1,3-dimethylviolurates [R 1 R 2 R 3 NH][1,3-Me 2 Vio] R 1 = R 2 = H, R 3 = t Bu ( 3 ), R 3 = Cy (cyclohexyl) ( 4 ), R 3 = Ad (adamantyl) ( 5 ), R 3 = C 6 H 2 Me 2 -4,5-NH 2 -2 ( 6 ); R 1 = H, R 2 = R 3 = Et ( 7 ), i Pr ( 8 ); R 1 = H, R 2 + R 3 = (–CH 2 –) 4 ( 9 ) have been prepared by treatment of 1,3-dimethylvioluric acid ( 2 , = HMe 2 Vio) with different primary and secondary amines. All violurate salts form bright blue or red/purple, nicely crystalline solids. The compounds have been characterized by their solid-state IR and solution NMR ( 1 H, 13 C) and UV-spectroscopic data as well as elemental analyses. Structure determinations by single-crystal X-ray diffraction of compounds 4 , 7 and 9 revealed supramolecular self-assembly into different one-dimensional substructures through cation–anion N–H⋯N and N–H⋯O hydrogen bonds. In addition, the molecular and crystal structure of anhydrous 1,3-dimethylvioluric acid ( 2 ) has also been determined.