Crystal structures of 6-nitro-quinazolin-4(3)-one, 6-amino-quinazolin-4(3)-one and 4-amino-quinazoline hemi-hydro-chloride dihydrate.

The title compounds, 6-nitro-quinazolin-4(3)-one (CHNO; ), 6-amino-quinazolin-4(3)-one (CHNO; ) and 4-amino-quinazolin-1-ium chloride-4-amino-quinazoline-water (1/1/2), (CHN ·Cl·CHN·2HO; ) were synthesized and their structures were determined by single-crystal X-ray analysis. In the crystals of and , the quinazoline mol-ecules form hydrogen-bonded dimers N-H⋯O inter-actions. The dimers are connected by weak inter-molecular C-H⋯N and C-H⋯O hydrogen bonds, forming a layered structure in the case of .