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

The title compounds, 6-nitro-quinazolin-4(3 )-one (C H N O ; ), 6-amino-quinazolin-4(3 )-one (C H N O; ) and 4-amino-quinazolin-1-ium chloride-4-amino-quinazoline-water (1/1/2), (C H N ·Cl ·C H N ·2H O; ) 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 . In the crystal of , N-H⋯N and C-H⋯O inter-actions link the dimers into a three-dimensional network structure. The asymmetric unit of consists of two quinazoline mol-ecules, one of which is protonated, a chloride ion, and two water mol-ecules. The chloride anion and the water mol-ecules form hydrogen-bonded chains consisting of fused five-membered rings. The protonated and unprotonated quinazolin mol-ecules are linked to the chloride ions and water mol-ecules of the chain by their amino groups.