Hydrogen bonding in two tetracyclic indole alkaloids

3-Acetyl-1,6,7,12b-tetrahydroindolo[2,3-a]quinolizin-2(12H)-one, C17H16N2O2 , consists of two symmetry-independent molecules and each forms a layered s tructure stabilized by N-H . . .O and C-H . . .O hydrogen bonds. In 3-acety l-6,7-dihydroindolo[2,3-a]quinolizin-4(12H)-one monohydrate, C17H14N2O2.H2O , the structure is stabilized by O-H . . .O, N-H . . .O and C-H . . .O hydr ogen bonds, with the ordered water molecule playing a crucial role in the s elf-assembly. Contribution from the weak interactions to the strong hydroge n-bonded network is a common feature in both structures.