Crystal structures of 6-nitro­quinazolin-4(3H)-one, 6-amino­quinazolin-4(3H)-one and 4-amino­quinazoline hemi­hydro­chloride dihydrate

The title compounds, 6-nitro­quinazolin-4(3H)-one (C(8)H(5)N(3)O(3); I), 6-amino­quinazolin-4(3H)-one (C(8)H(7)N(3)O; II) and 4-amino­quinazolin-1-ium chloride–4-amino­quinazoline–water (1/1/2), (C(8)H(8)N(3) (+)·Cl(−)·C(8)H(7)N(3)·2H(2)O; III) were synthesized and their structures were determined by single-crystal X-ray analysis. In the crystals of I and II, the quinazoline mol­ecules form hydrogen-bonded dimers via N—H⋯O inter­actions. The dimers are connected by weak inter­molecular C—H⋯N and C—H⋯O hydrogen bonds, forming a layered structure in the case of I. In the crystal of II, N—H⋯N and C—H⋯O inter­actions link the dimers into a three-dimensional network structure. The asymmetric unit of III consists of two quinazoline mol­ecules, one of which is protonated, a chloride ion, and two water mol­ecules. The chloride anion and the water mol­ecules form hydrogen-bonded chains consisting of fused five-membered rings. The protonated and unprotonated quinazolin mol­ecules are linked to the chloride ions and water mol­ecules of the chain by their amino groups.